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((Short description|Highly modified saliva containing zootoxins))
((Use dmy dates|date=October 2020))
[[File:Vipera berus - Venom delivery apparatus.JPG|thumb|''[[Vipera berus]]'' - Venom delivery apparatus]]
'''Snake venom''' is a highly toxic [[saliva]]<ref>((cite web|title=Reptile Venom Research|url=http://www.reptilepark.com.au/venom_snake.asp|publisher=Australian Reptile Park|access-date=21 December 2010|url-status=dead|archive-url=https://web.archive.org/web/20100202234912/http://www.reptilepark.com.au/venom_snake.asp|archive-date=2 February 2010))</ref> containing [[zootoxin]]s that facilitates in the immobilization and digestion of [[prey]].  This also provides defense against threats. Snake venom is injected by unique [[fang]]s during a [[Snakebite|bite]], whereas some species are also able to spit [[venom]].<ref name=Bauchot/>

The glands that secrete zootoxins are a modification of the [[parotid gland|parotid salivary gland]]s found in other [[vertebrates]] and are usually located on each side of the head, below and behind the eye, and enclosed in a muscular sheath. The venom is stored in large glands called [[Alveolus|alveoli]] before being conveyed by a duct to the base of channeled or tubular fangs through which it's ejected.<ref name=Firefly>((cite book | veditors = Halliday A, Kraig T | title = Firefly Encyclopedia of Reptiles and Amphibians| url = https://archive.org/details/fireflyencyclope0000unse_p6l7 | url-access = registration |year=2002|publisher=Firefly Books Ltd.|location=Toronto, Canada|isbn=978-1-55297-613-5|pages=[https://archive.org/details/fireflyencyclope0000unse_p6l7/page/202 202–203]))</ref><ref name=JVenom/>

Venom contains more than 20 different compounds, which are mostly proteins and [[peptides|polypeptides]].<ref name=Firefly/><ref name=":0">((Cite journal |last1=Oliveira |first1=Ana L. |last2=Viegas |first2=Matilde F. |last3=da Silva |first3=Saulo L. |last4=Soares |first4=Andreimar M. |last5=Ramos |first5=Maria J. |last6=Fernandes |first6=Pedro A. |date=July 2022 |title=The chemistry of snake venom and its medicinal potential |journal=Nature Reviews Chemistry |language=en |volume=6 |issue=7 |pages=451–469 |doi=10.1038/s41570-022-00393-7 |issn=2397-3358 |pmc=9185726 |pmid=35702592))</ref> The complex mixture of proteins, enzymes, and various other substances has toxic and lethal properties.<ref name=Bauchot/> Venom serves to immobilize prey.<ref name=Mattison>((cite book| vauthors = Mattison C |title=The New Encyclopedia of Snakes|year=2007 |publisher=Princeton University Press (Princeton and Oxford) first published in Blandford|location=New Jersey, USA (first published in the UK)|isbn=978-0-691-13295-2|page=117))</ref> [[Enzyme]]s in venom play an important role in the digestion of prey,<ref name=JVenom>((cite journal | vauthors = Bottrall JL, Madaras F, Biven CD, Venning MG, Mirtschin PJ | title = Proteolytic activity of Elapid and Viperid Snake venoms and its implication to digestion | journal = Journal of Venom Research | volume = 1 | issue = 3 | pages = 18–28 | date = September 2010 | pmid = 21544178 | pmc = 3086185 ))</ref> and various other substances are responsible for important but non-lethal biological effects.<ref name=Bauchot>((cite book| vauthors = Bauchot R |title=Snakes: A Natural History|url=https://archive.org/details/snakesnaturalhis0000bauc |url-access=registration |year=1994|publisher=Sterling Publishing Co., Inc.|location=New York City, NY, USA|isbn=978-1-4027-3181-5|pages=[https://archive.org/details/snakesnaturalhis0000bauc/page/194 194–209]))</ref> Some of the proteins in snake venom have very specific effects on various biological functions, including blood coagulation, blood pressure regulation, and transmission of nerve or muscle impulses. These venoms have been studied and developed for use as pharmacological or diagnostic tools, and even drugs.<ref name=Bauchot/><ref name=":0" />

== Chemistry ==
[[Proteins]] constitute 90-95% of venom's dry weight and are responsible for almost all of its biological effects.<ref name=":0" /><ref>((cite journal | vauthors = Cardoso KC, Da Silva MJ, Costa GG, Torres TT, Del Bem LE, Vidal RO, Menossi M, Hyslop S | display-authors = 6 | title = A transcriptomic analysis of gene expression in the venom gland of the snake Bothrops alternatus (urutu) | journal = BMC Genomics | volume = 11 | issue = 1 | pages = 605 | date = October 2010 | pmid = 20977763 | pmc = 3017861 | doi = 10.1186/1471-2164-11-605 | doi-access = free ))</ref> The hundreds, even thousands, of proteins found in venom include toxins, [[neurotoxin]]s in particular, as well as nontoxic proteins (which also have pharmacological properties), and many enzymes, especially [[hydrolysis|hydrolytic]] ones.<ref name=Bauchot/> Enzymes ([[Molecular mass|molecular weight]] 13-150 KDa) make up 80-90% of [[Viperidae|viperid]] and 25-70% of [[elapid]] venoms, including digestive [[hydrolase]]s, [[L-amino-acid oxidase]], [[phospholipase]]s, [[thrombin]]-like pro-coagulant, and [[kallikreins|kallikrein]]-like [[serine proteases]] and [[metalloproteinases]] (hemorrhagins), which damage vascular [[endothelium]]. Polypeptide toxins (molecular weight 5-10 KDa) include [[cytotoxin]]s, [[cardiotoxin]]s, and [[:wikt:postsynaptic|postsynaptic]] neurotoxins (such as [[Alpha-Bungarotoxin|α-bungarotoxin]] and [[Cobratoxin|α-Cobratoxin]]), which bind to [[acetylcholine receptor]]s at neuromuscular junctions. Compounds with low molecular weight (up to 1.5 KDa) include metals, peptides, lipids, [[nucleosides]], carbohydrates, amines, and [[oligopeptides]], which inhibit [[angiotensin-converting enzyme]] (ACE) and potentiate bradykinin (BPP). Inter- and intra-species variation in venom chemical composition is geographical and ontogenic.<ref name=Firefly/> [[Phosphodiesterase]]s interfere with the prey's cardiac system, mainly to lower the [[blood pressure]]. [[Phospholipase A2]] causes [[hemolysis]] by lysing the [[phospholipid]] [[cell membranes]] of [[red blood cells]].<ref>((cite journal | vauthors = Condrea E, Devries A, Mager J | title = Hemolysis and splitting of human erythrocyte phospholipids by snake venoms | journal = Biochimica et Biophysica Acta (BBA) - Specialized Section on Lipids and Related Subjects | volume = 84 | issue = 1 | pages = 60–73 | date = February 1964 | pmid = 14124757 | doi = 10.1016/0926-6542(64)90101-5 )) ((closed access))</ref> Amino acid [[oxidase]]s and [[protease]]s are used for digestion. Amino acid oxidase also triggers some other enzymes and is responsible for the yellow colour of the venom of some species. [[Hyaluronidase]] increases tissue permeability to accelerate the absorption of other enzymes into tissues. Some snake venoms carry [[fasciculin]]s, like the [[mamba]]s (''Dendroaspis''), which inhibit [[cholinesterase]] to make the prey lose muscle control.<ref name=Fasciculins>((cite journal | vauthors = Rodríguez-Ithurralde D, Silveira R, Barbeito L, Dajas F | title = Fasciculin, a powerful anticholinesterase polypeptide from Dendroaspis angusticeps venom | journal = Neurochemistry International | volume = 5 | issue = 3 | pages = 267–74 | year = 1983 | pmid = 20487949 | doi = 10.1016/0197-0186(83)90028-1 | s2cid = 8952817 )) ((closed access))</ref>

{| class="wikitable" style="float:center; margin:0 1em 0.5em;"
|+ Main enzymes of snake venom<ref name=Bauchot/><ref name=":0" /><ref>((Cite book |last=Mackessy |first=Stephen P. |url=https://www.taylorfrancis.com/books/9780429623622 |title=Handbook of Venoms and Toxins of Reptiles |date=2021-05-01 |publisher=CRC Press |isbn=978-0-429-05420-4 |editor-last=Mackessy |editor-first=Stephen P. |edition=2 |location=Second edition. ((!)) Boca Raton : CRC Press, 2021. |language=en |doi=10.1201/9780429054204))</ref>
|-
!Type
!Name
!Origin
|-
| [[Oxidoreductase]]s || [[Lactate dehydrogenase|lactate dehydrogenase]] || Elapidae
|-
|                 || [[L-amino-acid oxidase]]  || All species
|-
|                 || [[Catalase]]              || All species
|-
| [[Transferase]]s    || [[Alanine amino transferase]] ||
|-
| [[Hydrolase]]s      || [[Phospholipase A2]]  || All species
|-
|                 || [[Lysophospholipase]]            || Elapidae, Viperidae
|-
|                 || [[Acetylcholinesterase]]         || Elapidae
|-
|                 || [[Alkaline phosphatase]]        || ''[[Bothrops atrox]]''
|-
|                 || [[Acid phosphatase]]            || ''[[Deinagkistrodon acutus]]''
|-
|                 || [[5'-nucleotidase]]              || All species
|-
|                 || [[Phosphodiesterase]]           || All species
|-
|                 || [[Deoxyribonuclease]]            || All species
|-
|                 || Ribonuclease 1               || All species
|-
|                 || [[ATPase|Adenosine triphosphatase]]     || All species
|-
|                 || [[Amylase]]                      || All species
|-
|                 || [[Hyaluronidase]]                || All species
|-
|                 || NAD-Nucleotidase             || All species
|-
|                 || Kininogenase                 || Viperidae
|-
|                 || [[Factor X]] activator           || Viperidae, Crotalinae
|-
|                 || [[:wikt:Heparinase|Heparinase]]                || Crotalinae
|-
|                 || α-Fibrinogenase              || Viperidae, Crotalinae
|-
|                 || β-Fibrinogenase              || Viperidae, Crotalinae
|-
|                 || α-β-Fibrinogenase            || ''[[Gabon viper|Bitis gabonica]]''
|-
|                 || [[Fibrinolysis|Fibrinolytic enzyme]]         || [[Pit viper|Crotalinae]]
|-
|                 || [[Prothrombin activator]]       || Crotalinae
|-
|                 || [[Collagenase]]                  || Viperidae
|-
|                 || [[Elastase]]                     || Viperidae
|-
| Lyases          || [[Glucosaminate ammonia-lyase]]   ||
|}

Snake toxins vary greatly in their functions. The two broad classes of toxins found in snake venoms are [[neurotoxin]]s (mostly found in elapids) and [[hemotoxin]]s (mostly found in viperids). However, exceptions occur – the venom of the [[black-necked spitting cobra]] (''[[Naja nigricollis]]''), an elapid, consists mainly of [[cytotoxin]]s, while that of the [[Crotalus scutulatus|Mojave rattlesnake]] (''Crotalus scutulatus''), a viperid, is primarily neurotoxic. Both elapids and viperids may carry numerous other types of toxins.

{| class="wikitable"
|- valign="top"
! scope="row"| α-neurotoxins
| [[Alpha-Bungarotoxin|α-Bungarotoxin]], α-toxin, [[:wikt:erabutoxin|erabutoxin]], [[cobratoxin]] 
|- valign="top"
! scope="row" | β-neurotoxins ([[Phospholipase A2|PLA2]])
| [[Beta-bungarotoxin|β-Bungarotoxin]], Notexin, [[:wikt:ammodytocin|ammodytoxin]], [[crotoxin]], [[taipoxin]] 
 |- ="top"
! scope="row" | κ-neurotoxins
| [[Kappa-bungarotoxin]]
|- valign="top"
! scope="row" | Dendrotoxins ([[Kunitz domain|Kunitz]])
| [[Dendrotoxin]], toxins I and K; possibly [[beta-bungarotoxin|β-Bungarotoxin]] chain B
|- valign="top"
! scope="row" | Cardiotoxins
| ''Naja nigricollis'' y-toxin, [[cardiotoxin III]] (aka cytotoxins)
|- valign="top"
! scope="row" | Myotoxins
| [[Myotoxin]]-a, [[crotamine]]
|- valign="top"
! scope="row" | Sarafotoxins
| [[Sarafotoxin]]s a, b, and c
|- valign="top"
! scope="row" | Hemorrhagins (metalloprotease)
| [[Mucrolysin]], [[Atrolysin A|Atrolysin]]s, [[Acutolysin A|Acutolysin]]s, etc.<ref name=KW-1200>((cite web |title=Keyword: Hemorrhagic toxin KW-1200 |url=https://www.uniprot.org/keywords/KW-1200 |website=UniProt |access-date=1 June 2019))</ref>
|- valign="top"
! scope=row | Hemotoxins (serine protease)
| [[Venombin A]]
|}

== Toxins ==
((missing information|section|how evolutionary/structural classifications correspond to functional classifications|date=August 2021))

===Neurotoxins===
((Synapse map))

The beginning of a new neural impulse goes as follows:

# An exchange of ions (charged atoms) across the nerve cell membrane sends a depolarizing current towards the end of the nerve cell (cell terminus).
# When the depolarizing current arrives at the nerve cell terminus, the neurotransmitter [[acetylcholine]] (ACh), which is held in [[vesicle (biology and chemistry)|vesicles]], is released into the space between the two nerves (synapse). It moves across the synapse to the postsynaptic receptors.
# ACh binds to the receptors and transfers the signal to the target cell, and after a short time, it's destroyed by acetylcholinesterase.

====Fasciculins====
:These toxins attack [[cholinergic]] neurons (those that use ACh as a transmitter) by destroying acetylcholinesterase (AChE). ACh, therefore, cannot be broken down and stays in the receptor. This causes [[tetany]] (involuntary muscle contraction), which can lead to death. The toxins have been called fasciculins since after injection into [[mice]], they cause severe, generalized and long-lasting (5-7 h) [[fasciculation]]s (rapid muscle contractions).
:Snake example: found mostly in the venom of [[mamba]]s (''Dendroaspis'' spp.) and some [[rattlesnake]]s (''Crotalus'' spp.)<!--
-->
====Dendrotoxins====
:[[Dendrotoxin]]s inhibit neurotransmissions by blocking the exchange of positive and negative ions across the neuronal membrane lead to no nerve impulse, thereby paralyzing the nerves.
:Snake example: [[mamba]]s<!--
-->
====α-neurotoxins====
:[[Alpha-neurotoxin]]s are a large group; over 100 postsynaptic neurotoxins having been identified and sequenced.<ref>((cite journal | vauthors = Hodgson WC, Wickramaratna JC | title = In vitro neuromuscular activity of snake venoms | journal = Clinical and Experimental Pharmacology & Physiology | volume = 29 | issue = 9 | pages = 807–14 | date = September 2002 | pmid = 12165047 | doi = 10.1046/j.1440-1681.2002.03740.x | s2cid = 20158638 | url = https://www.researchgate.net/publication/11221875 | doi-access = free )) ((closed access))</ref> α-neurotoxins attack the [[Nicotinic acetylcholine receptor]]s of cholinergic neurons. They mimic the shape of the acetylcholine molecule, and so fit into the receptors, where they block the ACh flow, leading to a feeling of numbness and paralysis.
:Snake examples: [[king cobra]] (''Ophiophagus hannah'') (known as hannahtoxin containing α-neurotoxins),<ref>((cite journal | vauthors = He YY, Lee WH, Zhang Y | title = Cloning and purification of alpha-neurotoxins from king cobra (Ophiophagus hannah) | journal = Toxicon | volume = 44 | issue = 3 | pages = 295–303 | date = September 2004 | pmid = 15302536 | doi = 10.1016/j.toxicon.2004.06.003 )) ((closed access))</ref> [[sea snakes]] (Hydrophiinae) (known as erabutoxin), [[many-banded krait]] (''Bungarus multicinctu''s) (known as [[α-bungarotoxin]]), and [[cobras]] (''Naja'' spp.) (known as [[cobratoxin]])

=== Cytotoxins ===
[[File:Fully functional membrane.jpg|300px|thumb|right|Fully functional membrane]]
[[File:Destroyed membrane.JPG|300px|thumb|right|Destroyed membrane]]

====Phospholipases====
:[[Phospholipase]] is an enzyme that transforms the phospholipid molecule into a lysophospholipid (soap) → the new molecule attracts and binds fat and ruptures cell membranes. [[Phospholipase A2]] is one specific type of phospholipases found in snake venom.
:Snake example: [[Okinawan habu]] (''Trimeresurus flavoviridis'')<!--
-->
====Cardiotoxins / Cytotoxins====
:[[Cardiotoxin]]s are components that are specifically toxic to the heart. They bind to particular sites on the surface of muscle cells and cause depolarisation → the toxin prevents muscle contraction. These toxins may cause the heart to beat irregularly or stop beating, causing death. An example is the [[three-finger toxin|three-fingered]] [[cardiotoxin III]] from [[Chinese cobra]], an example of the short three-fingered family (((InterPro|IPR003572))).
: Snake example: [[mamba]]s, and some ''[[Naja]]'' species<!--
-->
====Hemotoxins====
:[[Hemotoxin]]s cause hemolysis, the destruction of red blood cells (erythrocytes), or induce blood coagulation (clotting, e.g. [[mucrocetin]]). A common family of hemotoxins includes snake venom metalloproteinases such as [[mucrolysin]].<ref name=KW-1200/><ref>((cite journal | vauthors = Bernardoni JL, Sousa LF, Wermelinger LS, Lopes AS, Prezoto BC, Serrano SM, Zingali RB, Moura-da-Silva AM | title = Functional variability of snake venom metalloproteinases: adaptive advantages in targeting different prey and implications for human envenomation | journal = PLOS ONE | volume = 9 | issue = 10 | pages = e109651 | date = 2014-10-14 | pmid = 25313513 | pmc = 4196926 | doi = 10.1371/journal.pone.0109651 | bibcode = 2014PLoSO...9j9651B | doi-access = free ))</ref>
:Snake examples: most [[Viperidae|vipers]] and many [[Naja|cobra]] species: The tropical rattlesnake ''[[Crotalus durissus]]'' produces [[convulxin]], a coagulant.<ref name="pmid_19552682"/>

===Myotoxins===
[[image:Crotamin 1H5O.png|thumb|The [[tertiary structure]] of crotamine (((PDB|1H5O)))]]
[[Myotoxin]]s are small, basic [[peptide]]s found in [[rattlesnake]]<ref name="PUB00001595">((cite journal | vauthors = Griffin PR, Aird SD | title = A new small myotoxin from the venom of the prairie rattlesnake (Crotalus viridis viridis) | journal = FEBS Letters | volume = 274 | issue = 1–2 | pages = 43–47 | date = November 1990 | pmid = 2253781 | doi = 10.1016/0014-5793(90)81325-I | s2cid = 45019479 | doi-access = free ))</ref><ref name="PUB00005315">((cite journal | vauthors = Samejima Y, Aoki Y, Mebs D | title = Amino acid sequence of a myotoxin from venom of the eastern diamondback rattlesnake (Crotalus adamanteus) | journal = Toxicon | volume = 29 | issue = 4–5 | pages = 461–468 | year = 1991 | pmid = 1862521 | doi = 10.1016/0041-0101(91)90020-r ))</ref> and [[lizard]] (e.g. [[Mexican beaded lizard]])<ref>((cite journal | vauthors = Whittington CM, Papenfuss AT, Bansal P, Torres AM, Wong ES, Deakin JE, Graves T, Alsop A, Schatzkamer K, Kremitzki C, Ponting CP, Temple-Smith P, Warren WC, Kuchel PW, Belov K | display-authors = 6 | title = Defensins and the convergent evolution of platypus and reptile venom genes | journal = Genome Research | volume = 18 | issue = 6 | pages = 986–994 | date = June 2008 | pmid = 18463304 | pmc = 2413166 | doi = 10.1101/gr.7149808 ))</ref> venoms. This involves a non-enzymatic mechanism that leads to severe [[skeletal muscle]] [[necrosis]]. These peptides act very quickly, causing instantaneous [[paralysis]] to prevent [[prey]] from escaping and eventually death due to [[diaphragm (anatomy)|diaphragmatic]] paralysis.

The first myotoxin to be identified and isolated was [[crotamine]], discovered in the 1950s by [[Brazil]]ian [[scientist]] [[José Moura Gonçalves]] from the venom of tropical South American rattlesnake ''[[Crotalus durissus terrificus]]''. Its biological actions, [[molecular structure]] and [[gene]] responsible for its synthesis were all elucidated in the last two decades.

==Determining venom toxicity (LD<sub>50</sub>)==
((missing information|section|why albumin dilution works better|date=August 2021))
Snake venom toxicity is assessed by a toxicological test called the [[median lethal dose]], lethal dose 50% (abbreviated as LD<sub>50</sub>), which determines the concentration of a toxin required to kill half the members of a tested population. The potency of wild snake venom varies considerably because of assorted influences such as [[Environment (biophysical)|biophysical environment]], physiological status, [[ecological systems|ecological variables]], genetic variation (either [[adaptation|adaptive]] or incidental), and other molecular and ecological evolutionary factors.((Citation needed|date=September 2021)) This is true even for members of one species. Such variation is smaller in captive populations in laboratory settings, though it cannot be eliminated. However, studies to determine snake venom potency must be designed to minimize variability.

Several techniques have been designed to this end. One approach is to use 0.1% bovine serum albumin (also known as "fraction V" in [[Cohn process]]) as a diluent in determining LD<sub>50</sub> values. It results in more accurate and consistent LD<sub>50</sub> determinations than using 0.1% saline as a diluent. For example, fraction V produces about 95% purified albumin (dried crude venom). Saline as a diluent consistently produces widely varying LD<sub>50</sub> results for nearly all venomous snakes. It produces unpredictable variation in precipitate purity (35-60%).<ref name="BSC">((cite journal | vauthors = Broad AJ, Sutherland SK, Coulter AR | title = The lethality in mice of dangerous Australian and other snake venom | journal = Toxicon | volume = 17 | issue = 6 | pages = 661–4 | date = 17 May 1979 | pmid = 524395 | doi = 10.1016/0041-0101(79)90245-9 | url = http://www.kingsnake.com/aho/pdf/menu5/broad1979b.pdf ))</ref> Fraction V is structurally stable because it has seventeen [[disulfide bonds]]; it's unique in that it has the highest solubility and lowest [[isoelectric point]] of major plasma proteins. This makes it the final fraction to be precipitated from its solution. [[Bovine serum albumin]] is located in fraction V. The precipitation of albumin is done by reducing the pH to 4.8, near the pH of the proteins, and maintaining the ethanol concentration at 40%, with a protein concentration of 1%. Thus, only 1% of the original plasma remains in the fifth fraction.<ref name="factorv">((cite journal | title=Edwin J. Cohn and the Development of Protein Chemistry | date=31 July 2003 | vauthors= Rosen FS | journal=The New England Journal of Medicine | volume=349 | issue=5 | pages=511–512 | doi=10.1056/NEJM200307313490522))</ref>

When the ultimate goal of plasma processing is a purified plasma component for [[Injection (medicine)|injection]] or [[Blood transfusion|transfusion]], the plasma component must be highly pure. The first practical large-scale method of blood plasma fractionation was developed by [[Edwin J. Cohn]] during [[World War II]]. it's known as the [[Cohn process]] (or Cohn method). This process is also known as cold ethanol fractionation, as it involves gradually increasing the [[concentration]] of [[ethanol]] in the [[Solution (chemistry)|solution]] at 5&nbsp;°C and 3&nbsp;°C.<ref name="Mate">((cite journal | vauthors = Matejtschuk P, Dash CH, Gascoigne EW | title = Production of human albumin solution: a continually developing colloid | journal = British Journal of Anaesthesia | volume = 85 | issue = 6 | pages = 887–95 | date = December 2000 | pmid = 11732525 | doi = 10.1093/bja/85.6.887 | doi-access = free ))</ref> The Cohn Process exploits differences in plasma proteins properties, specifically, the high [[solubility]] and low [[isoelectric point|pI]] of albumin. As the ethanol concentration is increased in stages from 0 to 40%, the pH declines from neutral (pH ~ 7) to about 4.8, which is near the pI of albumin.<ref name="Mate" /> At each stage, proteins are [[precipitation (chemistry)|precipitated out]] of the solution and removed. The final [[precipitate]] is purified albumin. Several variations to this process exist, including an adapted method by Nitschmann and Kistler that uses fewer steps, and replaces [[centrifugation]] and bulk freezing with [[filtration]] and diafiltration.<ref name="Mate" /><ref name="Brod">((cite journal | vauthors = Brodniewicz-Proba T | title = Human plasma fractionation and the impact of new technologies on the use and quality of plasma-derived products | journal = Blood Reviews | volume = 5 | issue = 4 | pages = 245–57 | date = December 1991 | pmid = 1782484 | doi = 10.1016/0268-960x(91)90016-6 ))</ref> Some newer methods of albumin purification add additional purification steps to the Cohn process and its variations. Chromatographic albumin processing emerged in the 1980s, however, it was not widely adopted until later due to the scarity of large-scale [[chromatography]] equipment. Methods incorporating chromatography generally begin with cryo-depleted plasma undergoing buffer exchange via either [[diafiltration]] or buffer exchange chromatography, to prepare the plasma for following [[ion exchange chromatography]] steps. After ion exchange, generally purification steps and buffer exchange occur.<ref name="Mate" />

However, chromatographic methods began to be adopted in the 1980s.((Citation needed|date=September 2021)) Developments were ongoing between when Cohn fractionation started emerge in 1946, and when [[chromatography]] emerged, in 1983. In 1962, the Kistler and Nistchmann process was created as a spin-off of the Cohn process. In the 1990s, the Zenalb and the CSL Albumex processes were created, which incorporated chromatography with variations. The general approach to using chromatography for plasma fractionation for albumin is: recovery of supernatant I, delipidation, [[anion exchange chromatography]], cation exchange chromatography, and gel filtration chromatography. The recovered purified material is formulated with combinations of sodium octanoate and sodium N-acetyl tryptophanate and then subjected to viral inactivation procedures, including pasteurization at 60&nbsp;°C. This is a more efficient alternative than the Cohn process because:

* smooth automation and a relatively inexpensive plant was needed,
* easier to sterilize equipment and maintain a good manufacturing environment
* chromatographic processes are less damaging to the albumin protein
* a more successful albumin result can be achieved.((citation needed|date=July 2022))

Compared with the Cohn process, albumin purity increased from about 95% to 98% using chromatography, and the yield increased from about 65% to 85%. Small percentage increases make a difference in regard to sensitive measurements such as purity. The big drawback has to do with the economics. Although the method offered efficient, acquiring the necessary equipment was difficult. Large machinery is necessary, and for a long time, the lack of equipment availability limited its widespread use.((Citation needed|date=September 2021))

== Evolution ==
((Main|Evolution of snake venom))
Venom evolved just once among all [[Toxicofera]] about 170 million years ago, and then diversified into the huge venom diversity seen today.<ref name="Fry 2012">((cite journal | vauthors = Fry BG, Casewell NR, Wüster W, Vidal N, Young B, Jackson TN | title = The structural and functional diversification of the Toxicofera reptile venom system | journal = Toxicon | volume = 60 | issue = 4 | pages = 434–48 | date = September 2012 | pmid = 22446061 | doi = 10.1016/j.toxicon.2012.02.013 ))</ref> The original toxicoferan venom was a very simple set of proteins that were assembled in a pair of glands. Subsequently, this set of proteins evolved independently in the various lineages of toxicoferans, including [[Snake|Serpentes]], [[Anguimorpha]], and [[Iguania]].<ref name="Casewell et al.">((cite journal | vauthors = Casewell NR, Wüster W, Vonk FJ, Harrison RA, Fry BG | title = Complex cocktails: the evolutionary novelty of venoms | journal = Trends in Ecology & Evolution | volume = 28 | issue = 4 | pages = 219–29 | date = April 2013 | pmid = 23219381 | doi = 10.1016/j.tree.2012.10.020 ))</ref> Several snake lineages have since lost the ability to produce venom, often due to a change in diet or a change in predatory tactics.<ref name="Fry 2012"/> In addition to this, venom strength and composition has changed due to changes in the prey of certain snake species. For example, the venom of the marbled sea snake (''Aipysurus eydouxii'') became significantly less toxic after the diet of this species changed from fish to strictly fish eggs.<ref name="Fry 2012" /> The evolution of venom is thought to be responsible for the enormous expansion of snakes across the globe.<ref name="Fry 2012"/><ref name="Lomonte et al.">((cite journal | vauthors = Lomonte B, Fernández J, Sanz L, Angulo Y, Sasa M, Gutiérrez JM, Calvete JJ | title = Venomous snakes of Costa Rica: biological and medical implications of their venom proteomic profiles analyzed through the strategy of snake venomics | journal = Journal of Proteomics | volume = 105 | pages = 323–39 | date = June 2014 | pmid = 24576642 | doi = 10.1016/j.jprot.2014.02.020 ))</ref>

The mechanism of evolution in most cases has been [[gene duplication]] in tissues unrelated to the venom.<ref name="Casewell et al." /> Pre-existing salivary proteins are the likely ancestors of most venom toxin genes.<ref>((Cite journal |last1=Hargreaves |first1=Adam D. |last2=Swain |first2=Martin T. |last3=Hegarty |first3=Matthew J. |last4=Logan |first4=Darren W. |last5=Mulley |first5=John F. |date=August 2014 |title=Restriction and Recruitment—Gene Duplication and the Origin and Evolution of Snake Venom Toxins |journal=Genome Biology and Evolution |volume=6 |issue=8 |pages=2088–2095 |doi=10.1093/gbe/evu166 |issn=1759-6653 |pmc=4231632 |pmid=25079342))</ref> Expression of the new protein in the venom gland followed duplication.<ref name="Casewell et al."/> Then proceeded [[natural selection]] for [[Adaptation|adaptive traits]] following the birth-and-death model, where duplication is followed by functional diversification, resulting in the creation of structurally related proteins that have slightly different functions.<ref name="Fry 2012"/><ref name="Casewell et al."/><ref name="pmid_17233905"/> The study of venom evolution has been a high priority for scientists in terms of scientific research, due to the medical relevance of snake venom, in terms of making antivenom and cancer research. Knowing more about the composition of venom and the ways it can potentially evolve is very beneficial. Three main factors that affect venom evolution have been closely studied: predators of the snake that are resistant to snake venom, prey that are in an [[evolutionary arms race]] with snakes, and the specific diets that affect the intraspecific evolution of venom.<ref name="Fry 2012" /><ref>((cite journal | vauthors = Barlow A, Pook CE, Harrison RA, Wüster W | title = Coevolution of diet and prey-specific venom activity supports the role of selection in snake venom evolution | journal = Proceedings. Biological Sciences | volume = 276 | issue = 1666 | pages = 2443–2449 | date = July 2009 | pmid = 19364745 | pmc = 2690460 | doi = 10.1098/rspb.2009.0048 ))</ref> Venoms continue to evolve as specific toxins and are modified to target a specific prey, and toxins are found to vary according to diet in some species.<ref name="pmid_17900344"/><ref name="pmc_2690460"/>

Rapid venom evolution can also be explained by the arms race between venom-targeted molecules in resistant predators, such as the [[opossum]], and the snake venom that targets the molecules. Scientists performed experiments on the opossums and found that multiple trials showed replacement to silent substitutions in the von Willebrand factor (''vWf'') gene that encodes for a venom-targeted hemostatic blood protein. These substitutions are thought to weaken the connection between vWf and a toxic snake venom ligand (botrocetin), which changes the net charge and hydrophobicity. These results are significant to the venom evolution because it's the first citation of rapid evolution in a venom-targeted molecule. This shows that an evolutionary arms race may be occurring in terms of defensive purposes. Alternative hypotheses suggest that venom evolution is due to trophic adaption, whereas these scientists believe, in this case, that selection would occur on traits that help with prey survival in terms of venom evolution instead of predation success. Several other predators of the pit viper (mongooses and hedgehogs) show the same type of relationship between snakes, which helps to support the hypothesis that venom has a very strong defensive role along with a trophic role. Which in turn supports the idea that predation on the snakes can be the arms race that produces snake venom evolution.<ref>((cite journal | vauthors = Jansa SA, Voss RS | title = Adaptive evolution of the venom-targeted vWF protein in opossums that eat pitvipers | journal = PLOS ONE | volume = 6 | issue = 6 | pages = e20997 | date = 22 June 2011 | pmid = 21731638 | pmc = 3120824 | doi = 10.1371/journal.pone.0020997 | bibcode = 2011PLoSO...620997J | doi-access = free ))</ref>

Some of the various adaptations produced by this process include venom more toxic to specific prey in several lineages,<ref name="pmc_2690460"/><ref name="Calvete et al.">((cite journal | vauthors = Calvete JJ, Ghezellou P, Paiva O, Matainaho T, Ghassempour A, Goudarzi H, Kraus F, Sanz L, Williams DJ | title = Snake venomics of two poorly known Hydrophiinae: Comparative proteomics of the venoms of terrestrial Toxicocalamus longissimus and marine Hydrophis cyanocinctus | journal = Journal of Proteomics | volume = 75 | issue = 13 | pages = 4091–101 | date = July 2012 | pmid = 22643073 | doi = 10.1016/j.jprot.2012.05.026 ))</ref><ref name="Li et al.">((cite journal | vauthors = Li M, Fry BG, Kini RM | title = Eggs-only diet: its implications for the toxin profile changes and ecology of the marbled sea snake (Aipysurus eydouxii) | journal = Journal of Molecular Evolution | volume = 60 | issue = 1 | pages = 81–9 | date = January 2005 | pmid = 15696370 | doi = 10.1007/s00239-004-0138-0 | bibcode = 2005JMolE..60...81L | s2cid = 17572816 ))</ref> proteins that pre-digest prey,<ref name="Mackessy 2010">((cite journal | vauthors = Mackessy SP | title = Evolutionary trends in venom composition in the western rattlesnakes (Crotalus viridis sensu lato): toxicity vs. tenderizers | journal = Toxicon | volume = 55 | issue = 8 | pages = 1463–74 | date = July 2010 | pmid = 20227433 | doi = 10.1016/j.toxicon.2010.02.028 ))</ref> as well as a method to track down prey after a bite.<ref name="Saviola et al.">((cite journal | vauthors = Saviola AJ, Chiszar D, Busch C, Mackessy SP | title = Molecular basis for prey relocation in viperid snakes | journal = BMC Biology | volume = 11 | issue = 1 | pages = 20 | date = March 2013 | pmid = 23452837 | pmc = 3635877 | doi = 10.1186/1741-7007-11-20 | doi-access = free ))</ref> Though venom function has evolved to be specific to prey class (e.g. particular coagulatory effects),<ref>((Cite journal |last1=Youngman |first1=Nicholas J |last2=Llinas |first2=Joshua |last3=Haworth |first3=Mark |last4=Gillett |first4=Amber |last5=Jones |first5=Lee |last6=Walker |first6=Andrew A |last7=Fry |first7=Bryan G |date=June 2022 |title=Untangling interactions between Bitis vipers and their prey using coagulotoxicity against diverse vertebrate plasmas |url=https://doi.org/10.1016/j.toxicon.2022.06.012 |journal=Toxicon |volume=216 |pages=37–44 |doi=10.1016/j.toxicon.2022.06.012 |issn=1879-3150 |pmid=35780972|s2cid=250188352 ))</ref> the evolution of broad toxicological effects (e.g. [[neurotoxicity]] or coagulotoxicity) does not appear to be broadly affected by prey type.<ref>((Cite journal |last1=Davies |first1=Emma-Louise |last2=Arbuckle |first2=Kevin |date=December 2019 |title=Coevolution of Snake Venom Toxic Activities and Diet: Evidence that Ecological Generalism Favours Toxicological Diversity |journal=Toxins |language=en |volume=11 |issue=12 |pages=711 |doi=10.3390/toxins11120711 |pmid=31817769 |pmc=6950196 |issn=2072-6651|doi-access=free ))</ref> The presence of [[digestive enzymes]] in snake venom was once believed to be an adaptation to assist digestion. However, studies of the [[western diamondback rattlesnake]] (''Crotalus atrox''), a snake with highly [[proteolytic]] venom, show that venom has no impact on the time required for food to pass through the [[Gut (zoology)|gut]].<ref name="pmid_17671964"/> These various adaptations of venom have also led to considerable debate about the definition of venom and venomous snakes.<ref name="Fry 2012"/>

==Injection==

===Vipers===
In [[Viperidae|viper]]s, which have the most highly developed venom-delivery apparatus, the venom gland is very large and is surrounded by the [[masseter]] or [[temporal muscle]], which consists of two bands, the superior arising from behind the eye, the inferior extending from the gland to the mandible. A duct carries venom from the gland to the fang. In vipers and elapids, this groove is completely closed, forming a hypodermic needle-like tube. In other species, the grooves are not covered, or only partially covered. From the anterior extremity of the gland, the duct passes below the eye and above the [[maxillary bone]], to the basal orifice of the venom fang, which is ensheathed in a thick fold of [[mucous membrane]]. By means of the movable maxillary bone hinged to the prefrontal bone and connected with the transverse bone, which is pushed forward by muscles set in action by the opening of the mouth, the fang is erected and the venom discharged through the distal orifice. When the snake bites, the jaws close and the muscles surrounding the gland contract, causing venom to be ejected via the fangs.

===Elapids===
In the [[proteroglypha|proteroglyphous]] [[elapid]]s, the fangs are tubular, but are short and do not possess the mobility seen in vipers.

===Colubrids===
[[opisthoglypha|Opisthoglyphous]] [[colubrid]]s have enlarged, grooved teeth situated at the posterior extremity of the [[maxilla]], where a small posterior portion of the upper labial or salivary gland produces venom.

===Mechanics of biting===
[[Image:ViperaBerusFang.JPG|thumb|250px|right| [[Vipera berus|European adder]] (''Vipera berus''), one fang with a small venom stain in glove, the other still in place]]

Several genera, including [[Calliophis|Asian coral snakes]] (''Calliophis''), [[Atractaspis|burrowing asps]] (''Atractaspis''), and [[Causus|night adders]] (''Causus''), are remarkable for having exceptionally long venom glands, extending along each side of the body, in some cases extending posterially as far as the heart. Instead of the muscles of the temporal region serving to press out the venom into the duct, this action is performed by those of the side of the body.

Considerable variability in biting behavior is seen among snakes. When biting, viperid snakes often strike quickly, discharging venom as the fangs penetrate the skin, and then immediately release. Alternatively, as in the case of a feeding response, some viperids (e.g. ''Lachesis'') bite and hold. A [[proteroglyph]] or [[opisthoglyph]] may close its jaws and bite or chew firmly for a considerable time.

<!-- A study performed by Chris Broeckhoven and Anton du Plessis found that -->Differences in fang length between the various venomous snakes are likely due to the evolution of different striking strategies.<ref>((cite journal | vauthors = Broeckhoven C, du Plessis A | title = Has snake fang evolution lost its bite? New insights from a structural mechanics viewpoint | journal = Biology Letters | volume = 13 | issue = 8 | pages = 20170293 | date = August 2017 | pmid = 28768797 | pmc = 5582107 | doi = 10.1098/rsbl.2017.0293 ))</ref> Additionally, it has been shown that the fangs of different species of venomous snakes have different sizes and shapes depending on the biomechanical properties of the snake's prey.<ref>((cite journal | vauthors = Cleuren SG, Hocking DP, Evans AR | title = Fang evolution in venomous snakes: Adaptation of 3D tooth shape to the biomechanical properties of their prey | journal = Evolution; International Journal of Organic Evolution | volume = 75 | issue = 6 | pages = 1377–1394 | date = June 2021 | pmid = 33904594 | doi = 10.1111/evo.14239 | s2cid = 233411378 | url = https://research.monash.edu/en/publications/334aa3e9-42d2-4947-8bd4-f8cb8e6b75d0 ))</ref>

===Mechanics of spitting===
[[Spitting cobras]] of the genera ''[[Naja]]'' and ''[[Hemachatus]]'', when irritated or threatened, may eject streams or a spray of venom a distance of ((convert|4|ft|order=flip)) to ((convert|8|ft|order=flip)). These snakes' fangs have been modified for the purposes of spitting; inside the fangs, the channel makes a 90° bend to the lower front of the fang. Spitters may spit repeatedly and still be able to deliver a fatal bite.

Spitting is a defensive reaction only. The snakes tend to aim for the eyes of a perceived threat. A direct hit can cause temporary shock and blindness through severe [[inflammation]] of the [[cornea]] and [[conjunctiva]]. Although usually no serious symptoms result if the venom is washed away immediately with plenty of water, blindness can become permanent if left untreated. Brief contact with the skin is not immediately dangerous, but open wounds may be vectors for envenomation.

==Physiological effects==
((more citations needed|date=August 2021))
The four distinct types of venom act on the body differently:
* [[Proteolytic]] venom dismantles the molecular surroundings, including at the site of the bite.
* [[Hemotoxic]] venom acts on the cardiovascular system, including the heart and blood.
* [[Neurotoxic]] venom acts on the nervous system, including the brain.
* [[Cytotoxic]] venom has a localized action at the site of the bite.

===Proteroglyphous snakes===
The effect of the venom of [[proteroglyphous]] snakes ([[Hydrophiinae|sea snakes]], [[Bungarus|kraits]], [[mamba]]s, [[Pseudechis|black snakes]], [[Notechis|tiger snakes]], and [[Acanthophis|death adders]]) is mainly on the [[nervous system]], respiratory [[paralysis]] being quickly produced by bringing the venom into contact with the central nervous mechanism that controls respiration; the pain and local swelling that follow a bite are not usually severe. The bite of all the proteroglyphous elapids, even of the smallest and gentlest, such as the [[coral snakes]], is, so far as known, deadly to humans. However, some mildly venomous elapids remain, such as the hooded snakes (''[[Parasuta]]''), bandy-bandies (''[[Vermicella]]''), etc.

===Vipers===
Viper venom ([[Daboia|Russell's viper]], [[Echis|saw-scaled vipers]], [[Lachesis (genus)|bushmasters]], and [[Crotalus|rattlesnakes]]) acts more on the vascular system, bringing about coagulation of the blood and clotting of the pulmonary arteries; its action on the nervous system is not great, no individual group of [[nerve-cell]]s appears to be picked out, and the effect upon respiration is not so direct; the influence upon the circulation explains the great depression, which is a symptom of viperine envenomation. The pain of the wound is severe and is rapidly followed by swelling and discoloration. The symptoms produced by the bite of the European vipers are thus described by Martin and Lamb:<ref>((cite book | vauthors = Martin CJ, Lamb G | veditors = Allbutt TC, Rolleston ND |title=A System of Medicine |year=1907 |publisher=MacMillan |location=London |pages=783–821 |chapter=Snake-poison and Snake-bite))</ref>

((blockquote|The bite is immediately followed by the local pain of a burning character; the limb soon swells and becomes discolored, and within one to three hours great prostration, accompanied by [[vomiting]], and often [[diarrhea]], sets in. Cold, clammy perspiration is usual. The pulse becomes extremely feeble, and slight [[dyspnoea]] and restlessness may be seen. In severe cases, which occur mostly in children, the pulse may become imperceptible and the extremities cold; the patient may pass into [[coma]]. In from twelve to twenty-four hours these severe constitutional symptoms usually pass off; but in the meantime, the swelling and discoloration have spread enormously. The limb becomes phlegmonous and occasionally suppurates. Within a few days recovery usually occurs somewhat suddenly, but [[death]] may result from the severe depression or from the secondary effects of [[suppuration]]. That cases of death, in adults as well as in children, are not infrequent in some parts of the Continent is mentioned in the last chapter of this Introduction.))

The Viperidae differ much among themselves in the toxicity of their venoms. Some, such as the Indian Russell's viper (''Daboia russelli'') and saw-scaled viper (''E. carinatus''); the American rattlesnakes (''Crotalus'' spp.), bushmasters (''Lachesis'' spp.), and [[Bothrops|lanceheads]] (''Bothrops'' spp.); and the [[Bitis|African adders]] (''Bitis'' spp.), [[Causus|night adders]] (''Causus'' spp.), and [[Cerastes (genus)|horned vipers]] (''Cerastes'' spp.), cause fatal results unless a remedy is speedily applied. The bite of the larger European vipers may be very dangerous, and followed by fatal results, especially in children, at least in the hotter parts of the Continent; whilst the small [[Vipera ursinii|meadow viper]] (''Vipera ursinii''), which hardly ever bites unless roughly handled, does not seem to be possessed of a very virulent venom, and although very common in some parts of [[Austria]] and [[Hungary]], is not known to have ever caused a serious accident.

===Opisthoglyphous colubrids===
Biologists had long known that some snakes had rear fangs, 'inferior' venom injection mechanisms that might immobilize prey; although a few fatalities were on record, until 1957, the possibility that such snakes were deadly to humans seemed at most remote. The deaths of two prominent herpetologists, [[Robert Mertens]] and [[Karl Patterson Schmidt|Karl Schmidt]], from African colubrid bites, changed that assessment, and recent events reveal that several other species of rear-fanged snakes have venoms that are potentially lethal to large vertebrates.

[[Boomslang]] (''Dispholidus typus'') and [[twig snake]] (''Thelotornis'' spp.) venoms are toxic to blood cells and thin the blood (hemotoxic, hemorrhagic). Early symptoms include headaches, nausea, diarrhea, lethargy, mental disorientation, bruising, and bleeding at the site and all body openings. [[Exsanguination]] is the main cause of death from such a bite.

The boomslang's venom is the most potent of all rear-fanged snakes in the world based on LD<sub>50</sub>. Although its venom may be more potent than some vipers and elapids, it causes fewer fatalities owing to various factors (for example, the fangs' effectiveness is not high compared with many other snakes, the venom dose delivered is low, and boomslangs are generally less aggressive in comparison to other venomous snakes such as cobras and mambas). Symptoms of a bite from these snakes include nausea and internal bleeding, and one could die from a [[brain hemorrhage]] and [[respiratory failure|respiratory collapse]].

===Aglyphous snakes===
Experiments made with the secretion of the [[parotid gland]] of ''[[Rhabdophis]]'' and ''[[Zamenis]]'' have shown that even [[Aglypha|aglyphous]] snakes are not entirely devoid of venom, and point to the conclusion that the physiological difference between so-called harmless and venomous snakes is only one of degree, just as various steps exist in the transformation of an ordinary parotid gland into a venom gland or of a solid tooth into a tubular or grooved fang.

== Use of snake venoms to treat disease ==
Given that snake venom contains many biologically active ingredients, some may be useful to treat disease.<ref name="McCleary2013">((cite journal | vauthors = McCleary RJ, Kini RM | title = Non-enzymatic proteins from snake venoms: a gold mine of pharmacological tools and drug leads | journal = Toxicon | volume = 62 | pages = 56–74 | date = February 2013 | pmid = 23058997 | doi = 10.1016/j.toxicon.2012.09.008 ))</ref>

For instance, [[Phospholipase A2|phospholipases type A2]] (PLA2s) from the Tunisian vipers ''[[Cerastes cerastes]]'' and ''[[Macrovipera lebetina]]'' have been found to have antitumor activity.<ref name="Zouari2013">((cite journal | vauthors = Zouari-Kessentini R, Srairi-Abid N, Bazaa A, El Ayeb M, Luis J, Marrakchi N | title = Antitumoral potential of Tunisian snake venoms secreted phospholipases A2 | journal = BioMed Research International | volume = 2013 | pages = 1–9 | year = 2013 | pmid = 23509718 | pmc = 3581298 | doi = 10.1155/2013/391389 | doi-access = free ))</ref> Anticancer activity has been also reported for other compounds in snake venom.<ref name="Vyas2013">((cite journal | vauthors = Vyas VK, Brahmbhatt K, Bhatt H, Parmar U | title = Therapeutic potential of snake venom in cancer therapy: current perspectives | journal = Asian Pacific Journal of Tropical Biomedicine | volume = 3 | issue = 2 | pages = 156–62 | date = February 2013 | pmid = 23593597 | pmc = 3627178 | doi = 10.1016/S2221-1691(13)60042-8 ))</ref><ref name="Jain2012">((cite journal | vauthors = Jain D, Kumar S | title = Snake venom: a potent anticancer agent | journal = Asian Pacific Journal of Cancer Prevention | volume = 13 | issue = 10 | pages = 4855–60 | year = 2012 | pmid = 23244070 | doi = 10.7314/apjcp.2012.13.10.4855 | doi-access = free ))</ref> PLA2s hydrolyze phospholipids, thus could act on bacterial cell surfaces, providing novel antimicrobial (antibiotic) activities.<ref name="Junior2013">((cite journal | vauthors = de Oliveira Junior NG, e Silva Cardoso MH, Franco OL | title = Snake venoms: attractive antimicrobial proteinaceous compounds for therapeutic purposes | journal = Cellular and Molecular Life Sciences | volume = 70 | issue = 24 | pages = 4645–58 | date = December 2013 | pmid = 23657358 | doi = 10.1007/s00018-013-1345-x | s2cid = 15127065 ))</ref>

The [[analgesic]] (pain-killing) activity of many snake venom proteins has been long known.<ref name="Woolf2013">((cite journal | vauthors = Woolf CJ | title = Pain: morphine, metabolites, mambas, and mutations | journal = The Lancet. Neurology | volume = 12 | issue = 1 | pages = 18–20 | date = January 2013 | pmid = 23237896 | doi = 10.1016/S1474-4422(12)70287-9 | s2cid = 8697382 ))</ref><ref name="Osipov2012">((cite journal | vauthors = Osipov A, Utkin Y | title = Effects of snake venom polypeptides on central nervous system | journal = Central Nervous System Agents in Medicinal Chemistry | volume = 12 | issue = 4 | pages = 315–28 | date = December 2012 | pmid = 23270323 | doi = 10.2174/187152412803760618 | s2cid = 36274766 ))</ref> The main challenge, however, is how to deliver protein to the nerve cells: proteins usually are not applicable as pills.

== Immunity ==

===Among snakes===
The question whether individual snakes are immune to their own venom has not yet been definitively settled, though an example is known of a cobra that self-envenomated, resulting in a large [[abscess]] requiring surgical intervention, but showing none of the other effects that would have proven rapidly lethal in prey species or humans.<ref name="cobra">((cite web|title=Sterile tail abscess in Naja annulifera - self-envenomation case|url=http://www.snakegetters.com/demo/haje/index.html|archive-url=https://web.archive.org/web/20041027040201/http://www.snakegetters.com/demo/haje/index.html|url-status=dead|archive-date=27 October 2004|access-date=2 April 2009))</ref> Furthermore, certain harmless species, such as the [[North America]]n [[Lampropeltis getula|common kingsnake]] (''Lampropeltis getula'') and the [[Central America|Central]] and [[South America]]n [[mussurana]] (''Clelia'' spp.), are proof against the venom of the [[crotalines]], which frequent the same districts, and which they are able to overpower and feed upon. The [[Spilotes pullatus|chicken snake]] (''Spilotes pullatus'') is the enemy of the [[Saint Lucia lancehead|fer-de-lance]] (''Bothrops caribbaeus'') in St. Lucia, and in their encounters, the chicken snake is invariably the victor. Repeated experiments have shown the European [[grass snake]] (''Natrix natrix'') not to be affected by the bite of the [[Vipera berus|European adder]] (''Vipera berus'') and the [[Vipera aspis|European asp]] (''Vipera aspis''), this being due to the presence, in the blood of the harmless snake, of toxic principles secreted by the parotid and labial glands, and analogous to those of the venom of these vipers. Several North American species of rat snakes, as well as king snakes, have proven to be immune or highly resistant to the venom of rattlesnake species. The king cobra, which does prey on cobras, is said to be immune to their venom.

===Among other animals===
The [[hedgehog]] (Erinaceidae), the [[mongoose]] (Herpestidae), the [[honey badger]] (''Mellivora capensis'') and the [[opossum]] are known to be immune to a dose of snake venom.((citation needed|date=November 2016)) Recently, the honey badger and domestic pig were found to have convergently evolved amino-acid replacements in their nicotinic acetylcholine receptor, which are known to confer resistance to alpha-neurotoxins in hedgehogs.<ref>((cite journal | vauthors = Drabeck D, Jansa S | title = Why the Honey Badger Doesn't Care: Independent Evolution of Resistance to Three Finger Toxins in the Nicotinic Acetylcholine Receptor. | year = 2015 | journal = Toxicon | volume = 99 | pages = 68–72| doi = 10.1016/j.toxicon.2015.03.007 | pmid = 25796346 ))</ref> Whether the [[pig]] may be considered immune is still uncertain, though early studies show endogenous resistance in pigs tested against neurotoxins.<ref>((cite journal | vauthors = Grasset E, Zoutendykanda A, Schaafsma A | date = 1935 | title = Studies on the toxic and antigenic properties of Southern African snake venoms with specialreference to the polyvalency of South African antivenene. | journal = Trans. R. Soc. Trop. Med. Hygiene | volume = 28 | issue = 6 | pages = 601–612 | doi = 10.1016/S0035-9203(35)90031-1 ))</ref> Though the pig's [[Subcutaneous tissue|subcutaneous]] layer of fat may protect it against snake venom, most venoms pass easily through vascular fat layers, making this unlikely to contribute to its ability to resist venoms. The [[garden dormouse]] (''Eliomys quercinus'') has recently been added to the list of animals refractory to viper venom. Some populations of [[California ground squirrel]] (''Otospermophilus beecheyi'') are at least partially immune to rattlesnake venom as adults.

===Among humans===
The acquisition of human immunity against snake venom is ancient (from around 60 CE, [[Psylli]] tribe). Research into development of vaccines that will lead to immunity is ongoing. [[Bill Haast]], owner and director of the Miami Serpentarium, injected himself with snake venom during most of his adult life, in an effort to build up an immunity to a broad array of venomous snakes, in a practice known as [[mithridatism]]. Haast lived to age 100, and survived a reported 172 snake bites. He donated his blood to be used in treating snake-bite patients when a suitable antivenom was not available. More than 20 so-treated individuals recovered.<ref>((cite news |url=http://www.floridatrend.com/article.asp?page=1&aID=56043&slug=farewell-to-these-famous-floridians |title=Farewell to these famous Floridians |access-date=2 April 2012|newspaper=Florida Trend|date=19 December 2011))</ref><ref>((cite web| vauthors = Rosenberg C |url=http://articles.latimes.com/2011/jun/21/local/la-me-bill-haast-20110621 |title=Bill Haast dies at 100; snakes were the charm for south Florida celebrity |work=[[Los Angeles Times]] |date=21 June 2011 |access-date=2012-10-16))</ref><ref>((cite news| vauthors = Schudel M |url=https://www.washingtonpost.com/local/obituaries/bill-haast-dies-at-100-florida-snake-man-provided-venom-for-snakebite-serum/2011/06/18/AGgZjfaH_story.html |title=Bill Haast dies at 100: Florida snake man provided venom for snakebite serum |newspaper=[[The Washington Post]] |date=2011-06-18 |access-date=2012-10-16))</ref> Amateur researcher Tim Friede also lets venomous snakes bite him in the hopes of a vaccine against snake venom being developed, and has survived over 160 bites from different species as of January 2016.<ref>((cite web |url=https://www.independent.co.uk/news/world/americas/man-makes-deadly-snakes-bite-him-160-times-in-hunt-for-human-antidote-a6825791.html |title=Man makes deadly snakes bite him 160 times in hunt for human antidote ((pipe)) Americas ((pipe)) News ((pipe)) The Independent |website=[[Independent.co.uk]] |date=2016-01-21 |access-date=2016-07-07))</ref>

==Traditional treatments==
((hatnote|For approaches proven effective by modern medicine, see ((section link|Snakebite#Treatment)).))
The [[World Health Organization]] estimates that 80% of the world's population depends on traditional medicine for their primary health-care needs.<ref>((cite journal|title = Traditional Phytotherapy for Snake bites by Tribes of Chitradurga District, Karnataka, India | vauthors = Hiremath VT, Taranath TC |volume = 14|issue = 2|pages = 120–125|date=February 2010|journal = Ethnobotanical Leaflets|url = http://opensiuc.lib.siu.edu/ebl/vol2010/iss2/2/ <!-- alternate: http://www.ethnoleaflets.com/leaflets/chitra.htm -->))</ref> Methods of traditional treatments of snakebites, although of questionable efficacy and perhaps even harmful, are nonetheless relevant.

Plants used to treat snakebites in Trinidad and Tobago are made into tinctures with alcohol or olive oil and kept in rum flasks called snake bottles, which contain several different plants and/or insects. The plants used include the vine called monkey ladder (''[[Bauhinia cumanensis]]'' or ''[[Bauhinia excisa]]'', Fabaceae), which is pounded and put on the bite. Alternatively, a tincture is made with a piece of the vine and kept in a snake bottle. Other plants used include mat root (''[[Aristolochia|Aristolochia rugosa]]''), cat's claw (''[[Pithecellobium|Pithecellobim unguis-cati]]''), tobacco (''[[Nicotiana tabacum]]''), snake bush (''[[Barleria lupulina]]''), obie seed (''[[Kola nut|Cola nitida]]''), and wild gri gri root (''[[Acrocomia aculeata]]''). Some snake bottles also contain the caterpillars (''[[Battus polydamas]]'', Papilionidae) that eat tree leaves (''[[Aristolochia|Aristolochia trilobata]]''). Emergency snake medicines are obtained by chewing a three-inch piece of the root of bois canôt (''[[Cecropia peltata]]'') and administering this chewed-root solution to the bitten subject (usually a hunting dog). This is a common native plant of Latin America and the Caribbean, which makes it appropriate as an emergency remedy. Another native plant used is mardi gras (''[[Renealmia|Renealmia alpinia]]'') (berries), which are crushed together with the juice of wild cane (''[[Costus|Costus scaber]]'') and given to the bitten. Quick fixes have included applying chewed tobacco from cigarettes, cigars, or pipes.<ref>((cite journal | vauthors = Zethelius M, Balick MJ | title = Modern medicine and shamanistic ritual: a case of positive synergistic response in the treatment of a snakebite | journal = Journal of Ethnopharmacology | volume = 5 | issue = 2 | pages = 181–5 | date = March 1982 | pmid = 7057657 | doi = 10.1016/0378-8741(82)90042-3 | url = http://sciweb.nybg.org/science2/pdfs/mb/Sham_ritual_snakebite_jep_1982.pdf )) ((closed access))</ref> Making cuts around the puncture or sucking out the venom had been thought helpful in the past, but this course of treatment is now strongly discouraged, due to the risk of self-envenomation through knife cuts or cuts in the mouth (suction cups from snake bite kits can be used, but suctioning seldom provides any measurable benefit).<ref>((cite web|url=http://www.ces.ncsu.edu/gaston/Pests/reptiles/snakebitetx.htm |title=Treating Snake Bites |publisher=Ces.ncsu.edu |access-date=2012-10-16))</ref><ref>((cite web |url=https://www.cdc.gov/niosh/topics/snakes/symptoms.html|title=CDC - Venomous Snakes - NIOSH Workplace Safety and Health Topic |publisher=CDC.gov |date=2016-07-01 |access-date=2016-07-07))</ref>

=== Serotherapy ===
Serotherapy using [[antivenom]] is a common current treatment and has been described back in 1913.((NoteTag|This section is based on the 1913 book ''The Snakes of Europe'', by G. A. Boulenger, which is now in the [[public domain]] in the United States (and possibly elsewhere) Because of its age, the text in this article should not necessarily be viewed as reflecting the current knowledge of snake venom)) Both adaptive immunity and serotherapy are specific to the type of snake; venom with identical physiological action do not cross-neutralize. Boulenger 1913 describes the following cases:

A European in Australia who had become immune to the venom of the deadly Australian [[tiger snake]] (''Notechis scutatus''), manipulating these snakes with impunity, and was under the impression that his immunity extended also to other species, when bitten by a [[lowland copperhead]] (''Austrelaps superbus''), an allied elapine, died the following day.

In [[India]], the serum prepared with the venom of [[monocled cobra]] ''Naja kaouthia'' has been found to be without effect on the venom of two species of [[kraits]] (''Bungarus''), Russell's viper (''Daboia russelli''), saw-scaled viper (''Echis carinatus''), and [[Trimeresurus popeiorum|Pope's pit viper]] (''Trimeresurus popeiorum''). Russell's viper serum is without effect on colubrine venoms, or those of ''[[Echis]]'' and ''[[Trimeresurus]]''.

In [[Brazil]], serum prepared with the venom of lanceheads (''Bothrops'' spp.) is without action on rattlesnake (''Crotalus'' spp.) venom.

Antivenom snakebite treatment must be matched as the type of envenomation that has occurred. In the Americas, polyvalent antivenoms are available that are effective against the bites of most pit vipers. [[Crofab]] is the antivenom developed to treat the bite of North American pit vipers.<ref>http://www.savagelabs.com/Products/CroFab/Home/crofab_frame.htm ((Webarchive|url=https://web.archive.org/web/20160303212825/http://www.savagelabs.com/Products/CroFab/Home/crofab_frame.htm |date=3 March 2016 )) Link to PDF for full prescribing information, retrieved 11/12/12</ref> These are not effective against [[coral snake]] envenomation, which requires a specific antivenom to their neurotoxic venom. The situation is even more complex in countries such as India, with its rich mix of vipers (Viperidae) and highly neurotoxic cobras and kraits of the Elapidae.

==Notes==
((NoteFoot))

== See also ==
*[[Antivenom]]
*[[Venomoid]]
*[[Snakebite]]
*[[Toxicofera]]

== References ==
((Reflist|32em|refs=

<ref name="pmid_19552682">((cite journal | vauthors = Hermans C, Wittevrongel C, Thys C, Smethurst PA, Van Geet C, Freson K | title = A compound heterozygous mutation in glycoprotein VI in a patient with a bleeding disorder | journal = Journal of Thrombosis and Haemostasis | volume = 7 | issue = 8 | pages = 1356–63 | date = August 2009 | pmid = 19552682 | doi = 10.1111/j.1538-7836.2009.03520.x | s2cid = 205728095 | doi-access = free )) ((open access))</ref>

<!--
<ref name="Kini2007">((cite journal | vauthors = Kini RM | title = Evolution of three-finger toxins - a versatile mini protein scaffold | journal = Acta Chimica Slovenica | volume = 58 | issue = 4 | pages = 693–701 | date = December 2011 | pmid = 24061117 | url = http://acta.chem-soc.si/58/58-4-693.pdf )) ((open access))</ref>

<ref name="pmid_18701431">((cite journal | vauthors = Juárez P, Comas I, González-Candelas F, Calvete JJ | title = Evolution of snake venom disintegrins by positive Darwinian selection | journal = Molecular Biology and Evolution | volume = 25 | issue = 11 | pages = 2391–407 | date = November 2008 | pmid = 18701431 | doi = 10.1093/molbev/msn179 )) ((open access))</ref>
-->

<ref name="pmid_17233905">((cite journal | vauthors = Lynch VJ | title = Inventing an arsenal: adaptive evolution and neofunctionalization of snake venom phospholipase A2 genes | journal = BMC Evolutionary Biology | volume = 7 | issue = 2 | pages = 2 | date = January 2007 | pmid = 17233905 | pmc = 1783844 | doi = 10.1186/1471-2148-7-2 | doi-access = free )) ((open access))</ref>

<!--
<ref name="Savitzky1980">((cite journal | vauthors = Savitzky AH | title = The Role of Venom Delivery Strategies in Snake Evolution | journal = Evolution; International Journal of Organic Evolution | volume = 34 | issue = 6 | pages = 1194–1204 | date = November 1980 | pmid = 28568463 | doi = 10.2307/2408300 | jstor = 2408300 )) ((closed access))</ref>
-->

<ref name="pmid_17900344">((cite journal | vauthors = Pahari S, Bickford D, Fry BG, Kini RM | title = Expression pattern of three-finger toxin and phospholipase A2 genes in the venom glands of two sea snakes, Lapemis curtus and Acalyptophis peronii: comparison of evolution of these toxins in land snakes, sea kraits and sea snakes | journal = BMC Evolutionary Biology | volume = 7 | pages = 175 | date = September 2007 | pmid = 17900344 | pmc = 2174459 | doi = 10.1186/1471-2148-7-175 | doi-access = free )) ((open access))</ref>

<ref name="pmc_2690460">((cite journal | vauthors = Barlow A, Pook CE, Harrison RA, Wüster W | title = Coevolution of diet and prey-specific venom activity supports the role of selection in snake venom evolution | journal = Proceedings: Biological Sciences | volume = 276 | issue = 1666 | pages = 2443–9 | date = July 2009 | pmid = 19364745 | pmc = 2690460 | doi = 10.1098/rspb.2009.0048 | jstor = 30244073 )) ((open access))</ref>

<ref name="pmid_17671964">((cite journal | vauthors = McCue MD | title = Prey envenomation does not improve digestive performance in western diamondback rattlesnakes (Crotalus atrox) | journal = Journal of Experimental Zoology Part A | volume = 307 | issue = 10 | pages = 568–77 | date = October 2007 | pmid = 17671964 | doi = 10.1002/jez.411 )) ((closed access))</ref>

))

== Further reading ==
((Refbegin))
* ((cite journal | vauthors = Jonassen I, Collins JF, Higgins DG | title = Finding flexible patterns in unaligned protein sequences | journal = Protein Science | volume = 4 | issue = 8 | pages = 1587–95 | date = August 1995 | pmid = 8520485 | pmc = 2143188 | doi = 10.1002/pro.5560040817 ))
* ((cite book | vauthors = Shaw IC  |veditors=Waring RH, Steventon GB, Mitchell SC | title = Molecules of Death | url = https://archive.org/details/moleculesdeath00wari  | url-access = registration  | edition = Second | publisher = Imperial College Press | location = River Edge, N.J | year = 2007 | pages = [https://archive.org/details/moleculesdeath00wari/page/n353 329]–344 | isbn = 978-1-86094-815-2 | chapter = Chapter 19: Snake Toxins))
((Refend))

==External links==
((Commons category))
*[http://snakesarelong.blogspot.com/2013/09/basics-of-snake-fangs.html An overview of the diversity and evolution of snake fangs.]
*[http://www.toxinology.com/fusebox.cfm?staticaction=snakes/ns-snvenom.htm Snake Venoms]((UMichOPM|families|superfamily|55)) - Calculated orientations of snake venom phospholipases A2 and myotoxins in the lipid bilayer.
*[https://web.archive.org/web/20120413182323/http://www.venomdoc.com/LD50/LD50men.html LD50's for most toxic venoms.]
*[http://www.avru.org Australian Venom Research Unit] - a general source of information for venomous creatures in Australia.
*[http://www.biomedcentral.com/1472-6882/1/10 biomedcentral.com] - Medicinal and ethnoveterinary remedies of hunters in [[Trinidad]].
*[http://reptilis.net/serpentes/venom.html reptilis.net] - How venom works.
*[https://web.archive.org/web/20101031014922/http://snakevenom.net/2010/01/drying-storage-snake-venom/ snakevenom.net] - Drying and storage of snake venom.

((Toxins))
((Authority control))

((DEFAULTSORT:Snake Venom))
[[Category:Venomous snakes|*]]
[[Category:Snake toxins]]
[[Category:Wilderness medical emergencies]]

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