Rattlesnake Envenomation in 12 New World Camelids

Snakebite in domestic animals: First global scoping review

Snakebite is a Neglected Tropical Disease estimated to cause more than 100,000 human deaths and disable more than 400,000 victims each year. It primarily affects poor agricultural workers, farmers, and cattle herders living in rural areas of developing countries. It is thus an occupational disease. However, the impact of snakebite on these rural communities could be even higher if a One Health approach is taken to consider the direct impact on domestic animals and indirect impact on the livelihood of affected communities. To explore this hypothesis we developed the first scoping review to identify and characterize the global literature on snakebite in domestic animals. Three bibliographic databases (PubMed, Web of Science and Agricola) were searched using terms related to snake, snakebite and domestic animals for publications up to December 31^st, 2016. Two independent reviewers screened publications applying inclusion/exclusion criteria to select relevant material. Relevant information was then extracted from the selected literature. The global literature on snakebite in domestic animals (n = 143 observational studies, reviews and letters) mainly represented North America, Europe and Australia (69%) with less information from Central and South America, Asia and Africa (31%). Observational studies (n = 119) mostly concerned pets (78%) and to a lesser extent livestock (22%). Thirty-four snake species were reported as responsible for bites in domestic animals. WHO's Medically Important Venomous Snakes were more frequently involved. The social-ecological determinants of snakebite were poorly documented but the reviewed literature suggested a strong seasonality and a diversity of habitat. Snakebite in animals caused neurotoxic, cytotoxic and hemotoxic envenomation syndromes similar to humans and death. Half of publications on envenomed livestock reported a fatality rate above 47%. There was no literature on the indirect impact of snakebite on livelihood caused by animal morbidity and mortality. The results of this scoping review suggest a high and under-reported burden in terms of mortality in animals and a potential economic impact of snakebite in terms of losses in livelihood of affected communities. However, major knowledge gaps with respect to impact of snakebite on livestock and livelihood were identified. Filling these gaps is necessary for a full understanding of the impact of snakebite and to raise scientific, political and public awareness on this neglected issue.

Snake-venom resistance as a mammalian trophic adaptation: lessons from didelphid marsupials

Mammals that prey on venomous snakes include several opossums (Didelphidae), at least two hedgehogs (Erinaceidae), several mongooses (Herpestidae), several mustelids, and some skunks (Mephitidae). As a group, these taxa do not share any distinctive morphological traits. Instead, mammalian adaptations for ophiophagy seem to consist only in the ability to resist the toxic effects of snake venom. Molecular mechanisms of venom resistance (as indicated by biochemical research on opossums, mongooses, and hedgehogs) include toxin-neutralizing serum factors and adaptive changes in venom-targeted molecules. Of these, toxin-neutralizing serum factors have received the most research attention to date. All of the toxin-neutralizing serum proteins discovered so far in both opossums and mongooses are human α1B-glycoprotein homologs that inhibit either snake-venom metalloproteinases or phospholipase A(2) myotoxins. By contrast, adaptive changes in venom-targeted molecules have received far less attention. The best-documented examples include amino-acid substitutions in mongoose nicotinic acetylcholine receptor that inhibit binding by α-neurotoxins, and amino-acid substitutions in opossum von Willebrand factor (vWF) that are hypothesized to weaken the bond between vWF and coagulopathic C-type lectins. Although multiple mechanisms of venom resistance are known from some species, the proteomic complexity of most snake venoms suggests that the evolved biochemical defences of ophiophagous mammals are likely to be far more numerous than currently recognized. Whereas most previous research in this field has been motivated by the potential for medical applications, venom resistance in ophiophagous mammals is a complex adaptation that merits attention from comparative biologists. Unfortunately, evolutionary inference is currently limited by ignorance about many relevant facts that can only be provided by future research.

Rattlesnake envenomation in horses: 58 cases (1992-2009)

OBJECTIVE

To characterize signalment, clinical and laboratory findings, treatment, and outcome in horses with rattlesnake envenomation in northern California.

DESIGN

Retrospective case series.

ANIMALS

58 client-owned horses evaluated for rattlesnake envenomation at 2 referral hospitals from 1992 to 2009.

PROCEDURES

Records of horses with rattlesnake envenomation were reviewed, and data concerning signalment, clinical and laboratory findings, treatment, and outcome were collected. In addition, a rattlesnake-bite severity score (RBSS) was assigned to each horse. Variables were compared between horses that survived and those that did not.

RESULTS

The overall mortality rate was 9%. Nine horses received antivenin; no complications were reported and none of the 9 died. The most common laboratory findings associated with severity of envenomation were thrombocytopenia, hypoproteinemia, hyperlactatemia, and a high RBSS.

CONCLUSIONS AND CLINICAL RELEVANCE

Most horses in this study had a good prognosis after being bitten by rattlesnakes. Laboratory and clinical examination findings may be useful for identifying horses with a poorer prognosis. Treatment with antivenin may be beneficial and warrants further evaluation.