Crotalus (Rattlesnakes)

Clinical effects - The over-all spread of effects of this genus covers a broader spectrum than any other. The typical effect of a bite from a Crotalus species is similar to most viper bites with massive edema and tissue destruction. With the exception of C. scutulatus and durrissus, the effects are more or less similar, ranging from lethal (C. vergrandis) to dangerous (C. viridis) with effects all quite similar. Bites from all species of Crotalus should be considered to be a medical emergency, even from small, relatively mild species such as C. cerastes (sidewinder).

C. scutulatus (Mojave rattlesnake) and C. durrissus (Neotropical rattlesnake) bites of which are almost devoid of localized symptoms and instead follow the pattern more expected from the bite of an elapid with potential blindness, paralysis and inhibition of respiration. The mojave rattlesnake occupies an overlapping range with the western diamondback and very similar so great care must be taken if a bite occurs within the range of this snake since the effects are so different. The bite may appear to be a dry bite from a western diamondback since little, if any, local effects are observed and appropriate treatment may be delayed or held off until to late. The powerful neurotoxins of this specie cause death due from respiratory arrest. In the northern part of its range, the Neotropical rattlesnake venom is overwhelmingly neurotoxic and the bite pathology is representative of this. However, by the southern part of the range the venom has gradually changed composition so that it is now almost entirely hemotoxic.

This provides the perfect example of the danger of generalizing about the properties of a particular venom. Just because a venom is, for example, primarily hemotoxic that does not mean that neurotoxicological effects should be discounted or ignored entirely. This is particularly dangerous in a specie such as the Neotropical rattlesnake which has dramatic variation of the composition of the venom (as a parenthetical aside, this also raises taxonomic questions as to whether venom composition should play a role in the classification of the snake and perhaps that the difference is so great that the snake should be separated into different species rather than subspecies). All snake bites should be treated as a poisoning that is attacking on many fronts, as well as a soft tissue trauma of the crushing sort in the case of the vipers.

Crotalus adamanteus (Eastern diamondback rattlesnake)

C. adamanteus (eastern diamondback) is easily one of the most dangerous snakes in the world, attaining lengths of over nine feet and being the heaviest snake in the world at over thirty four pounds. The venom of the Eastern diamondback is not particularly toxic, being over ten times less so than the Indian cobra, but the huge quantities delivered along with the aggressive nature of the snake makes it extremely deadly with many deaths having been recorded. Characteristic of bites are localised and systemic muscle damage, as evidenced by a 20 fold increase in serum creatanine kinase levels. In addition, the blood becomes virtually incoagulable but the pathology is distinguised from classic disseminated intravascular coagulation by platelet counts and plasma levels of antithrombin III and factors II and VIII were not being drastically altered. Fibrinogen levels become markedly decreased and plasminogen and alpha-2-plasminogen inhibitor are five times below normal while plasminogen activator is twenty times above normal. These blood effects are caused by partial proteolysis of fibrinogen followed by activation of plasminogen by released plasminogen activator.

Adamalysin II is a 24 kDa zinc that is a member of a large family of metalloproteinases isolated as small proteinases or proteolytic domains of mosaic hemorrhagic proteins from various snake venoms.

CAM toxin is a myotoxin that shows a surprisingly close relationship to those of peptide c (C. v. helleri), myotoxin a (C. v. viridis), crotamine (C. d. terrificus), myotoxin I and II (C. v. concolor).

Crotalase is a thrombin-like enzymes, crotalase from the eastern diamondback rattlesnake (Crotalus adamanteus) similar to gyroxin (C. durrissus terrificus), ancrod from the Malayan pit viper (Callesoma rhodostoma) and a thrombin-like enzyme from the Central American rattlesnake (Crotalus durissus durissus)

Phospholipase A2 from this species are similar in structure and function to PLA2s Trimeresurus flavoviridis, T. okinavensis, and Crotalus atrox and to the basic subunit of crotoxin (C. durrissus).

C. atrox (Western diamondback)

The slightly less large C. atrox (western diamondback) reaches sizes over six feet, aggressive, and is quite capable of delivering lethal doses with deaths on record for this specie. The bite pathology is very similar to that of the eastern diamondback with extensive edema, necrosis and blood destruction. This, and the eastern diamondback, both lack the small myotoxin seen in C. viridis subspecies and also in C. exsul.

Crotalus atrox venom contains a variety of proteases which render fibrinogen incoagulable and solubilize fibrin. Atroxase is an example of this class, being an A alpha, B beta fibrinogenase. The protease consists of a single nonglycosylated polypeptide chain with a molecular weight of 23,500 and an isoelectric point of pH 9.6. Amino acid analysis indicates atroxase to contain 206 residues with no sulfhydryl groups. Metal analysis found zinc and potassium at 1 mol/mol of protein, and calcium at 0.3 mol/mol of protein. Proteolytic activity is inhibited by ethylenediaminetetraacetate and alpha 2-macroglobulin. Proteolytic specificity is similar to that of several hemorrhagic toxins found within the same venom, yet atroxase shows no hemorrhagic activity and exhibits low lethality. Atroxase cleaves the A alpha chain of fibrinogen first followed by the B beta chain and shows no effect on the gamma chain. The nonspecific action of the enzyme results in the extensive hydrolysis of fibrinogen which releases a variety of fibrinopeptides. Fibrin solubilization appears to occur primarily from the hydrolysis of alpha-polymer and unpolymerized alpha and beta chains. Although crude venom induces platelet aggregation, atroxase demonstrated no ability to induce or inhibit aggregation.

Catrocollastatin is an example of of a different class of metalloprotease from this venom, this 50 kDa component inhibits collagen induced platelet aggregation by binding to collagen via its disintegrin like domain. The amino acid sequence is highly similar to that of haemorrhagic metalloproteinase jararhagin from Bothrops jararaca venom, HR1B from Trimeresurus flavoviridis, Ht-e from C. atrox and trigramin from T. gramineus. Like jararhagin and HR1B, catrocollastatin is a multidomain molecule composed of an N- terminal domain, a metalloproteinase domain, a disintegrin-like domain and a cysteine-rich C-terminal domain. In the disintegrin-like domain, the frequently seen RGD (Arg-Gly-Asp) sequence is replaced by SECD (Ser-Glu-Cys-Asp).

The catroxobins are thrombin-like coagulant enzymesthat have sequences highly homologous to other thrombin-like venom enzymes, and to pancreatic kallikrein and trypsin, but less so to the B chain of thrombin. Catroxobin clotts human fibrinogen very slowly, releasing fibrinopeptide A and a small amount of fibrinopeptide B.

The venom also contains numerous other fibrinolytic hemorrhagic toxins.

C. basiliscus (Mexican west coast rattlesnake)

Clinical effects - Very similar to that of the western diamondback in both size of the animal, venom yield and bite pathology. The venom is slightly more toxic than that of the western diamondback with the yield similar.

Distinct fibrinolytic enzymes have been purified from the venom of Crotalus basiliscus that are similar other other metalloproteases fround in the venoms of other Crotalus as well as Agkistrodon venoms. An example of these enzymes is basilase, a fibrinolytic enzyme that hydrolyzes fibrin directly without activation of plasminogen.

C. cerastes (Sidewinder)

Clinical effects - The venom is about twice as strong as that of the eastern diamondback, however this specie is not believed capable of delivering a lethal dose due to small venom yield. The venom contains mytoxins similar to those found in other species of rattlesnake.

C. durissus

Unlike all other species of rattlesnake, except C. scutulatus (Mojave green rattlesnake), C. durrissus subspecies venoms are unique in the venom containing powerful presynaptic neurotoxins. Thrombin like toxins and mytoxins are still present but localised effects are greatly lessened.

Crotalus durissus cascavella (cascavell)

Convulxin from the venom of Crotalus durissus terrificus is the same platelet-activating agent as the presently described platelet- activating glycoprotein (PAG) from the venom of Crotalus durissus cascavella.

C. durissus terrificus (Neotropical rattlesnake)

Clinical effects - In most of the range, much more like that of a cobra bite than a typical viper bite with little or no localized effects. In the Northern portion of the range, venom contains powerful neurotoxins with death resulting from respiratory failure. By the end of the Southern portion, however, the venom composition is overwhelmingly hemotoxic but the snake is no less deadly. This has dire implications for medical treatment, not only in the treatment protocol, but also the dilemma that the antivenom may not properly represent the composition of the particular region. This is symptomatic of a much more fundamental problem, in that C. durrissus venom is inefficient in stimulating antibody production in horses.

Convulxin in an example of platelet-activating agents found in C. durissus venoms.

Crotoxin, the main toxic component isolated from the venom of the South American rattlesnake Crotalus durissus terrificus, is a reversible protein complex composed of a non- toxic non-enzymatic acidic polypeptide (crotapotin) and a toxic basic phospholipase A2 (PLA2). The myotoxic phospholipase A2 is similar to notexin (Notechis scutatus, mainland tiger snake), taipoxin (Oxyuransus scutellatus scutellatus, coastal taipan), and Bothrops asper myotoxin. These components induce muscle necrosis by first affecting the integrity of the plasma membrane, thereby inducing a calcium influx that culminates in cell death

Crotamine a basic neurotoxic protein acting on voltage-sensitive sodium channels of skeletal muscle sarcolemma

C.enyo (Orange rattlesnake)

This venom contains less proteases than most of the other venoms. The toxicity is very high but the venom yield low. The venom contains a component or components similar to mojave toxin.

C. exsul

The venom from this species is similar , C. viridis oreganus and C. v. viridis in containing high amounts of myotoxins.

C. horridus (Timber rattlesnake)

This is a large, short tempered snake capable of delivering lethal bites in the case of large specimens. The disorder of coagulation observed after a timber rattlesnake (Crotalus horridus) bite is total absence of fibrinogen. Localised effects include massive swelling and ecchymoses of the involved extremity, generalized petechiae and a large hematomas. The venom has thrombin-like activity, clotting fibrinogen or plasma and aggregating platelets. Muscle destruction is systemic, the degree and extent of rhabdomyolysis is independent of the site of muscle sampling, being no more advanced at the site of envenomation.

Crotalocytin activates factors V, VIII, XIII, and platelets without affecting prothrombin (factor II) and antithrombin III.

The hemorrhagic proteinase IV quickly induces hemorrhage, platelet aggregation and rapidly causes fibrin deposition

C. lepidus (Banded-Rock rattlesnake)

The venom of this species contains toxins, including mytoxins, expected in a rattlesnake venom. Not typically considered capable of delivering a lethal bite.

C. mitchelli (Speckled rattlesnake)

Clinical effects, in addition to the usual edema and tissue destruction also causes extensive blistering around the bite site. Not typically capable of delivering a lethal bite.

C. m. molossus (Black-tailed rattlesnake)

Clinical effects are marked swelling and ecchymosis of the bitten extremity and thrombocytopenia and, in one case, hypofibrinogenemia. Similar effects to that seen in C. adamanteus and C. atrox. The venom had fibrinolytic and platelet aggregating properties, a coagulant effect, although present, is much less marked.

M4 is an example of fibrinolytic protease from this venom It has a pI of 9.6 and a molecular weight of 27,000. The protease hydrolyzes the A alpha and B beta chains of fibrinogen, and the alpha and beta chains of fibrin. This activity was inhibited by EDTA and restored by Ca2+ or Zn2+, but not Mg2+. The protease hydrolyzed hide power azure and casein, but it had no effect on collagen, hyaluronic acid, complement or synthetic substrates for thrombin, plasmin or kallikrein. Subcutaneous injections into mice with doses as high as 100 micrograms did not cause hemorrhage. This protease may have therapeutic use as a thrombolytic agent.

C. ruber (Red diamondback rattlesnake)

Clinical effects - The venom of this specie is perhaps the mildest of all the rattlesnakes, however this specie can reach over four feet in length and must be given respect. Exceptionally large specimens are capable of delivering a lethal dose. Crotalus ruber venom contains several different proteases, and the proteolytic activity of the crude venom is 6-15 times greater in adult than in juvenile venom.

A kallikrein-like enzyme has been isolated and characterised. This enzyme is active upon kallikrein substrates. Unlike thrombin, this kallikrein-like enzyme does not cause formation of a fibrin clot when fibrinogen is mixed with the enzyme. The B beta chain of fibrinogen is split first and A alpha chain was later cleaved. Porcine pancreatic kallikrein, on the other hand, hydrolyzes only the A alpha chain without affecting the B beta chain.

Two arginine ester hydrolases, E-I and E-II, have also been isolated and characterized. E-I and E-II have molecular weights of 32,000 and 33,000, and isoelectric points of 5.2 and 4.6, respectively. Both are active upon the glandular kallikrein substrate, but neither enzyme has been shown to have plasma kallikrein substrate hydrolytic activity. E-I has minimal fibrinogen-clotting activity. It was found to induce clotting by catalyzing the hydrolysis of only the A fibrinopeptide from the A alpha-chain of fibrinogen.

Three hemorrhagic toxins (Ht-1, -2, and -3) have also been isolated from this species. These hemorrhagic toxins are metalloproteases that degrade the A alpha chain of fibrinogen, while HT-1 also degrades the B beta chain. The proteolytic specificities of these toxins is different than that of thrombi, as evidenced by the fibrinogen being degraded but no clots being formed. Further, these toxins increased creatine kinase activity in mice serum, indicating muscle damage.

C. scutulatus (Mojave green rattlesnake)

Rattlesnake envenomation commonly produce defects in the hemostatic mechanism. However, Mojave rattlesnake (Crotalus scutulatus) envenomation has been reported not to cause a systemic bleeding diathesis. The Mojave venom causes no fibrinogen clotting and it displayed very weak ability to cause platelet aggregation and fibrinolytic activity. This is an unique species of Crotalus from North America, bites of which are almost devoid of localized symptoms and instead follow the pattern more expected from the bite of an elapid with potential blindness, paralysis and inhibition of respiration. The mojave rattlesnake occupies an overlapping range with the western diamondback and very similar in appearance so great care must be taken if a bite occurs within the range of this snake since the effects are so different. The bite may appear to be a dry bite from a western diamondback since little, if any, local effects are observed and appropriate treatment may be delayed or held off until to late. The powerful neurotoxin (mojave toxin) of this specie cause death due from respiratory arrest. The venom yield is rather large considering the small size, usually no more than three feet, yet the lethal dose being very low. This makes this snake capable of delivering enough venom in one bite to kill nine men as compared to them much larger eastern diamondback which average four to five lethal doses.

Two arginine ester hydrolases, designated AAEI and AAEII, are related to several other arginine esterases possessing kallikrein-like activities which have been isolated from snake venoms.

A hemorrhagic toxin has been isolated from the venom that is fibrinogenolytic and hydrolyzed hide powder azure, casein and collagen. The toxin also partially inactivated complement. It has no activity against elastin, fibrin, and the chromogenic substrates S-2805, S-2302 and S-2238. The enzymatic and hemorrhagic activities were inhibited by EDTA. Interestingly, hemorrhagic toxin is absent or in low quantities in Mojave rattlesnake venoms containing Mojave toxin. Chromatography by HPLC easily distinguishes Mojave rattlesnake venoms into two types by the presence or absence of the hemorrhagic toxin.

The principal toxins from the venoms of Crotalus durissus terrificus, Crotalus s. scutulatus C. vergrandis and Crotalus viridis concolor are homologous. Mojave toxin is a heterodimeric, neurotoxic phospholipase A2 (PLA2) characteristic of all rattlesnake presynaptic neurotoxins. The toxin is composed of a non-neurotoxic, non-enzymatic acidic subunit (Mtx-a) and the toxic, PLA2-active basic subunit (Mtx- b). It has great similarity to the basic subunits of related toxins from the venoms of the South American and midget faded rattlesnakes. High concentrations of homologous toxins are found in C. durissus samples, C. viridis concolor and C. tigris.

C. tigris (tiger rattlesnake)

The most toxic species of rattlesnake. Little is known of the specific components in the venom. The venom does contain toxins similar to mojave toxin.

C. unicolor (Aruba Island rattlesnake)

Clinical effects - This is a small, shy, and rare snake with bites being uncommon. However, the close taxonomic relationship between this and C. durrissus results in the possession of virulent venom.

C. vegrandis (Urocoan rattlesnake)

This snake is lacking in the myotoxins found in North American rattlesnake venoms. Vegrandis toxin is a presynaptic neurotoxin strongly homologous with crotoxin from the venom of Crotalus durissus terrificus.

Crotalus viridis concolor (Midget faded rattlesnake)

Small myotoxins are the major components in this and C. v. viridis venoms, comprising an from a third to almost half the total venom protein.

Concolor toxin presynaptic neurotoxin closely related to crotoxin (Crotalus durissus terrificus), and Mojave toxin (Crotalus scutulatus)

Myotoxins I and II are homologous proteins found to other myotoxins from rattlesnake venoms, namely myotoxin a, crotamine and peptide C, and has a similar pathology.

C. viridis helleri, (Southern Pacific rattlesnake)

This species is closely related to C.v.oreganis ( Northern pacific rattlesnake) C. viridis lutosus (great basin rattlesnake).

Localized effects are lessened with more systemic effects occurring. Contains high amounts of mytoxins proteins which are responsible for the extensive muscle necrosis that is the main feature of the bite pathology. The venom also contains high amounts of metalloproteases responsible for much of the hemorrhage clinically seen.

A disintegrin has been isolated from this species and named crotavirin

C.v.viridis (Prairie rattlesnake)

This species is less toxic than the Pacific rattlesnakes, with large specimens able to deliver barely a lethal dose. Deaths from this specie are rare but local symptoms can be pronounced. The major toxins, as for C. v. concolor, are myotoxins. These components comprise from over a third to almost half the total protein in the venom.

Myotoxin-a from this subspecies is a basic protein with 42 amino acid residues and three disulfide bonds. This bonding and small size give it a very compact structure. The earliest visible, and ultimately most pronounced, damage occurs within the muscle cell, specifically in the sarcomplasmic reticulum membrane system. The myotoxin show significant homology with the myotoxins peptide c (C. v. helleri), myotoxin a (C. v. viridis), crotamine (C. d. terrificus), myotoxin I and II (C. v. concolor).

In addition, this subspecies contains in its venom several highly hemorrhagic metalloproteinases which cleave N,N- dimethylcasein and fibrinogen.

Sistrurus (Massasaugas, Pigmy rattlesnakes)

The cllinical effects of S. catenatus (Massasauga Rattlesnake) indicates that it is more toxic than the pygmy rattlesnakes and has been known to cause deaths. S. miliarius barbouri (Pigmy rattlesnake) on the other hand, has much mild venom, deaths are almost unknown. However, concern for local necrosis exists as well as disruption of blood chemistry. Bite is unusually painful and produces dramatic swelling even by the standards used in judging viper bites. A disintegrin has been isolated from the venom. Barbourin contains KGD instead of RGD. This component is highly homologous to other peptides of the viper venom GPIIb- IIIa antagonist family but was the first member which did not contain the Arg-Gly-Asp (RGD) amino acid sequence, believed to be required for inhibition of receptor function. The conservative Lys for Arg substitution appears to be the sole structural feature which imparts integrin specificity to barbourin, since venom peptide analogs with Lys substitutions were also specific for GPIIb-IIIa. Thus, barbourin represents a new structural model useful for designing potent and GPIIb- IIIa-specific compounds that may have therapeutic value as platelet aggregation inhibitors.