World Library  
Flag as Inappropriate
Email this Article

Epidemiology of snakebites

Article Id: WHEBN0034397403
Reproduction Date:

Title: Epidemiology of snakebites  
Author: World Heritage Encyclopedia
Language: English
Subject: Epidemiology of asthma, Epidemiology of child psychiatric disorders, Epidemiology of bed bugs, Epidemiology of breast cancer, Epidemiology of childhood obesity
Publisher: World Heritage Encyclopedia

Epidemiology of snakebites

Most snakebites are caused by non-venomous snakes. Of the roughly 3,000 known species of snake found worldwide, only 15% are considered dangerous to humans.[1][2][3] Snakes are found on every continent except Antarctica.[1] The most diverse and widely distributed snake family, the colubrids, has approximately 700 venomous species,[4] but only five generaboomslangs, twig snakes, keelback snakes, green snakes, and slender snakes—have caused human fatalities.[4]

Since reporting is not mandatory in many regions of the world,[1] snakebites often go unreported. Consequently, no accurate study has ever been conducted to determine the frequency of snakebites on the international level. However, some estimates put the number at 5.4 million snakebites, 2.5 million envenomings, resulting in perhaps 125,000 deaths.[1]

Others estimate 1.2 to 5.5 million snakebites, 421,000 to 1.8 million envenomings, and 20,000 to 94,000 deaths.[1] Many people who survive bites nevertheless suffer from permanent tissue damage caused by venom, leading to disability.[5] Most snake envenomings and fatalities occur in South Asia, Southeast Asia, and sub-Saharan Africa, with India reporting the most snakebite deaths of any country.[1]

Worldwide, snakebites occur most frequently in the summer season when snakes are active and humans are outdoors.[1][6] Agricultural and tropical regions report more snakebites than anywhere else.[1][7] Victims are typically male and between 17 and 27 years of age.[2][6][8] Children and the elderly are the most likely to die.[2][9]


Number of Snakebite Envenomings per Year
Region Low Estimate High Estimate
Asia 237,379 1,184,550
Australasia 1,099 1,260
Caribbean 1,098 8,039
Europe 3,961 9,902
Latin America 80,329 129,084
North Africa / Middle East 3,017 80,191
North America 2,683 3,858
Oceania 361 4,635
Sub-Saharan Africa 90,622 419,639
Total: 420,549 1,841,158
Number of Deaths from Envenoming per Year
Region Low Estimate High Estimate
Asia 15,385 57,636
Australasia 2 4
Caribbean 107 1,161
Europe 48 128
Latin America 540 2,298
North Africa / Middle East 43 78
North America 5 7
Oceania 227 516
Sub-Saharan Africa 3,529 32,117
Total: 19,886 93,945

Although Africa is home to four venomous snake families—Atractaspididae, Colubridae, Elapidae, and Viperidae—approximately 60% of all bites are caused by vipers alone. In drier regions of the continent, such as sahels and savannas, the saw-scaled vipers inflict up to 90% of all bites.[10] The puff adder is responsible for the most fatalities overall,[11] although saw-scaled vipers inflict more bites in North African countries, where the puff adder is typically not found.[7] The black mamba, although responsible for far less snakebite incidents, is the species which has the highest mortality rate in Africa and in the world.[12]

Most bites occur in industrial plantations, which attract many types of snake prey. Banana plantations are associated with vipers such as night adders, while rubber and palm tree plantations attract elapids, including cobras and black mambas.[13] Important cobra species include the forest cobra and the black-necked spitting cobra.[14] In forested areas of Guinea, cobras may inflict more than 30% of all venomous bites.[15]

Mambas, cobras, and some larger puff adder species may claim territories of up to 1 to 2 square kilometres (0.4 to 0.8 sq mi), which are used by the snakes for hunting and reproduction. These snakes are large enough to defend their territory from intruders, including humans.[10] The black mamba, in particular, is among the most venomous snakes in the world and one of the most aggressive. It is the longest snake on the continent and is able to move at 11 kilometres per hour (6.8 mph), making it unusually dangerous.[16] Although black mambas cause only 0.5-1% of snakebites in South Africa, they produce the highest mortality rate and the species is responsible for many snake bite fatalities. The black mamba is the species with the highest mortality rate in every single nation in which it occurs in, despite not being responsible for the most numerous number of snakebites. It is also the species which has the highest mortality rate worldwide.[12]

There are also venomous colubrids in Africa, although of these only two arboreal genera, the boomslang and the twig snakes, are likely to inflict life-threatening bites. Of the Atractaspididae, Atractaspis is the species involved in the majority of bites. Since these snakes are nocturnal and fossorial, living in burrows underground, bites remain rare, peaking at 1 to 3% in certain areas of the Sudanian savanna. However, there is no anti-venom or other effective therapy for Atractaspis envenomation, and the case fatality rate remains approximately 10%, with death typically occurring quickly.[17]

Snakebites in Africa are most common in the sub-Saharan countries (scorpion stings are more common in Northern Africa), and typically occur during the rainy season when snakes are more active.[18] Agricultural plantations and pastoral areas are involved in approximately 50 to 60% of reported snakebites,[15] while outdoor activities such as collecting firewood and water account for another 20% of bites.[10] Approximately 1 million snakebites occur in sub-Saharan Africa each year,[19] resulting in up to 500,000 envenomations, 25,000 deaths and another 25,000 permanent disabilities.[20]

Because there is no reliable reporting system in place and because most victims never report their injury to health care facilities, these numbers are uncertain.[19] One comprehensive study estimates that 91,000 to 420,000 snake envenomings occur in sub-Saharan Africa annually, resulting in anywhere from 4,000 to 30,000 deaths.[1] The same study estimates that 3,000 to 80,000 envenomations occur in North Africa, although far fewer people, less than 100, die each year.[1] The variability of these estimates is indicative of the difficulty in accurately assessing snakebite morbidity and mortality.

In sub-Saharan Africa, over 50% of snakebite injuries are not appropriately treated.[19] Between 40 and 80% of victims, depending on the country, exclusively rely on traditional medicine for treatment.[19] Most victims who receive treatment by health care professionals have nevertheless delayed seeking medical attention for over 24 hours, and often up to 1 to 2 weeks.[19] In many sub-Saharan countries, poor availability of expensive antivenom contributes to morbidity, and snakebites continue to remain a neglected health problem.[19]


On the Indian subcontinent, almost all snakebite deaths have traditionally been attributed to the Big Four, consisting of the Russell's viper, Indian cobra, saw-scaled viper, and the common krait. However, studies have shown that the hump-nosed viper, previously considered essentially harmless and misidentified as the saw-scaled viper, is capable of delivering a fatal bite.[21][22] In regions of Kerala, India, it may be responsible for nearly 10% of venomous bites.[22] Commonly used antivenoms in India do not appear to be effective against hump-nosed viper bites.[21][22] According to the most conservative estimates, at least 81,000 snake envenomings and 11,000 fatalities occur in India each year, making it the most heavily affected country in the world.[1] The Malayan pit viper and banded krait are two other species involved in a significant number of venomous bites.

In Myanmar (Burma), approximately 70 to 80% of bites are inflicted by the Russell's viper, which is frequently found in rice fields.[23] In Japan, the majority of venomous bites are inflicted by the Asian pit vipers.[23] In Sri Lanka, approximately 40% of bites are caused by the Russell's viper, while 35% are caused by the Indian cobra.[23] In Thailand, the monocled cobra is responsible for the majority of snakebite fatalities.[24] Tea plantations are sometimes associated with elapids such as the common cobras and the king cobra.

Reports of large man-eating pythons are common in Southeast Asia, although the threat is typically exaggerated. However, in the Philippines, more than a quarter of Aeta men (a modern forest-dwelling hunter-gatherer group) have reported surviving a reticulated python attack.[25] Pythons are nonvenomous ambush predators, and both the Aeta and pythons hunt deer, wild pigs, and monkeys, making them competitors and prey.[25]

Throughout Western Asia, the species responsible for the majority of bites tend to be more venomous than European snakes, but deaths are infrequent. Studies estimate that perhaps 100 fatal bites occur each year.[1][13] The Palestine viper and Lebetine viper are the most important species.[13] While larger and more venomous elapids, such as the Egyptian cobra, are also found throughout the Middle East, these species inflict fewer bites.


The yellow-lipped sea krait is a timid but highly venomous sea snake common throughout tropical Indo-Pacific waters.

The vast majority of venomous snakebites in Australasia occur in the Australasian ecozone. At least 300 evenomations occur each year in Papua New Guinea, 30 in the Solomon Islands, and 10 Vanuatu.[1] The majority of bites in New Guinea are caused by the death adders, and a smaller number by the endemic small-eyed snake and other local species.[26] Most of the Pacific Islands are free of terrestrial snakes, although sea snakes are common in coral reefs. In the Oceania ecozone, only Micronesia and Tonga, where at least 10 envenomations occur annually, face an appreciable burden of snakebite.

In Australia, there are many more annual cases of spiderbite and jellyfish envenomation than snakebite; however, when considering the number of fatal cases, snakebite is the most serious type of envenoming.[27] Australia is unique in that it is the only continent where venomous snakes constitute the majority of species.[28] Nearly all venomous species in Australia are elapids, as vipers are absent from the continent.[27]

The brown snakes, death adders, mulga snakes, taipans, and tiger snakes are the five groups that inflict virtually all reported snakebites, although copperheads, rough-scaled snakes, and members of the genus Hoplocephalus are also occasionally involved in bites. Of the five dangerous groups, the highly venomous eastern brown snake, which is widespread and common in both rural and urban environments, is the most important—it is estimated to be responsible for up to 60% of all deaths caused by snakebite.[28]

In Northern Australia, sea snakes are common and occasionally inflict bites, although far less frequently than terrestrial snakes.[27] Several venomous colubrids exist in Australia as well, such as the brown tree snake, although they have geographically limited distributions and only very rarely deliver a medically significant bite.[29] In Tasmania and Kangaroo Island, which have a cooler, moister habitat than mainland Australia, the tiger snakes and copperhead snakes inflict the majority of bites. The brown snakes are not present on these islands.[30]

Despite the fact that many Australian snakes have unusually potent venom, wide access to antivenom, which is available for all dangerous species,[27] has made deaths exceedingly rare. It is believed that up to 1,500 definite or suspected snakebites occur in Australia each year, of which about 200 are serious enough to warrant antivenom therapy.[1][27] Approximately 2 to 4 fatalities occur annually.[27]


In Europe, nearly all of the snakes responsible for venomous bites belong to the viper family, and of these, the coastal viper, nose-horned viper, asp viper, and Lataste's viper inflict the majority of bites.[13] Although Europe has a population of some 731 million people, snake bites are only responsible for about 30 fatalities each year, largely due to wide access to health care services and antivenom, as well as the relatively mild potency of many native species' venom.[13]

North America

Of the 120 known indigenous snake species in North America, only 20 are venomous to human beings, all belonging to the families Viperidae and Elapidae.[2] However, in the United States, every state except Maine, Alaska, and Hawaii is home to at least one of 20 venomous snake species.[2] Up to 95% of all snakebite-related deaths in the United States are attributed to the western and eastern diamondback rattlesnakes.[2][31] Further, the majority of bites in the United States occur in the southwestern part of the country, in part because rattlesnake populations in the eastern states are much lower.[32]

The state of North Carolina has the highest frequency of reported snakebites, averaging approximately 19 bites per 100,000 persons.[33] The national average is roughly 4 bites per 100,000 persons.[33] Fewer than 1% of venomous snakebites in the United States are caused by coral snakes,[34] the rest being caused by the pit vipers (rattlesnakes, copperheads, and cottonmouths).

Mexico is estimated to have at least 28,000 snake envenomings annually, although only a small number of these lead to death.[1] Central America is home to 23 species of pit vipers, and they inflict the vast majority of reported bites. Of these, Bothrops asper is the most important species, partly because it is abundant in lowland areas and partly because it is frequently found in agricultural and pastoral areas where humans work. Of the elapids, the yellow-bellied sea snake has, very rarely, caused venomous bites, while the coral snakes, although common, inflict only 1 to 2% of all reported snake bites.[35] Of the coral snakes, Micrurus nigrocinctus is responsible for the most bites.[36]

Colubrid species found in Central America only cause mild to moderate envenomation in healthy adults, and most of these bites have occurred in humans handling the snakes.[36] Panama may have the greatest incidence of snakebites in Latin America, while El Salvador has the lowest (mostly because B. asper is not found in this country).[37] The total number of snakebites in Central America is estimated to be 4,000 to 5,000, although as in other regions of the world, snakebites are probably underreported.[37]

South America

In the Neotropics, the lance-headed vipers inflict the majority of fatal bites, although of the many known species, only two, the common lancehead and terciopelo, are responsible for most fatalities.[5][7] The tropical rattlesnake is another important species.


Most of the Pacific Islands are free of terrestrial snakes;[13] however, sea snakes are common in the Indian Ocean and tropical Pacific Ocean, but are not found in the Atlantic Ocean or the Caribbean, Mediterranean or Red Seas.[38] While the majority of species live close to shorelines or coral reefs, the fully pelagic yellow-bellied sea snake can be found in the open ocean.[38] Over 50% of bites inflicted by sea snakes, which are generally not aggressive, occur when fishermen attempt to remove snakes which have become tangled in fishing nets.[38][39]

Symptoms may appear in as little as 5 minutes or take 8 hours to develop, depending on the species and region of the body bitten.[38] Although sea snakes are known for extremely potent venom, about 80% of reported bites end up being dry.[38][40] It is estimated that each year 15,000 to 75,000 fisherman are bitten by sea snakes.[41] The advent of antivenom and advances in emergency medicine have reduced fatalities to about 3% of snakebite cases.[38] The highly venomous beaked sea snake is responsible for more than 50% of all sea snake bites, as well as the majority of envenomings and fatalities.[41]



  1. ^ a b c d e f g h i j k l m n o Kasturiratne, A.; Wickremasinghe A. R., de Silva N., Gunawardena N. K., Pathmeswaran A., et al. (2008). Winkel, Ken, ed. "The Global Burden of Snakebite: A Literature Analysis and Modelling Based on Regional Estimates of Envenoming and Deaths". PLOS Medicine 5 (11): e218.  
  2. ^ a b c d e f g Gold, Barry S.; Richard C. Dart; Robert A. Barish (1 April 2002). "Bites of venomous snakes". The New England Journal of Medicine 347 (5): 347–56.  
  3. ^ Russell, F. E. (1990). "When a snake strikes". Emerg Med 22 (12): 33–4, 37–40, 43. 
  4. ^ a b Mackessy, Stephen P. (2002). "Biochemistry and pharmacology of colubrid snake venoms". Journal of Toxicology: Toxin Reviews 21 (1–2): 43–83.  
  5. ^ a b Gutiérrez, José María; Bruno Lomonte; Guillermo León; Alexandra Rucavado; Fernando Chaves; Yamileth Angulo (2007). "Trends in Snakebite Envenomation Therapy: Scientific, Technological and Public Health Considerations". Current Pharmaceutical Design 13 (28): 2935–50.  
  6. ^ a b Wingert W, Chan L (1 January 1988). "Rattlesnake Bites in Southern California and Rationale for Recommended Treatment". West J Med 148 (1): 37–44.  
  7. ^ a b c Gutiérrez, José María; R. David G. Theakston; David A. Warrell (6 June 2006). "Confronting the Neglected Problem of Snake Bite Envenoming: The Need for a Global Partnership". PLOS Medicine 3 (6): e150.  
  8. ^ Parrish H (1966). "Incidence of treated snakebites in the United States". Public Health Rep 81 (3): 269–76.  
  9. ^ Gold BS, Wingert WA (1994). "Snake venom poisoning in the United States: a review of therapeutic practice". South. Med. J. 87 (6): 579–89.  
  10. ^ a b c Mackessy 2010, p. 456
  11. ^ Mallow, David; David Ludwig; Goran Nilson (2004). True Vipers: Natural History and Toxinology of Old World Vipers. Malabar, FL: Krieger Publishing Company.  
  12. ^ a b c Van Der Vlies, C. (2010). Southern Africa Wildlife and Adventure. British Columbia, Canada/Indiana, United States: Trafford Publishing. pp. 180–181.  
  13. ^ a b c d e f Chippaux, J.P. (1998). "Snake-bites: appraisal of the global situation". Bulletin of the World Health Organization 76 (5): 515–24.  
  14. ^ Valenta 2010, p. 20
  15. ^ a b Mackessy 2010, p. 459
  16. ^ Greene 1997, p. 40
  17. ^ Mackessy 2010, p. 455
  18. ^ Mackessy 2010, p. 468
  19. ^ a b c d e f Mackessy 2010, p. 454
  20. ^ Mackessy 2010, p. 465
  21. ^ a b Simpson, I. D.; Norris, R. L. (2007). "Snakes of Medical Importance in India: Is the Concept of the "Big 4" Still Relevant and Useful?". Wilderness and Environmental Medicine (Wilderness Medical Society) 18 (1): 2–9.  
  22. ^ a b c Joseph, J. K.; Simpson, I. D.; Menon, N. C. S.; Jose, M. P.; Kulkarni, K. J.; Raghavendra, G. B.; Warrell, D. A. (2007). "First authenticated cases of life-threatening envenoming by the hump-nosed pit viper (Hypnale hypnale) in India". Transactions of the Royal Society of Tropical Medicine and Hygiene 101 (1): 85–90.  
  23. ^ a b c Valenta 2010, p. 21
  24. ^ Pratanaphon, Ronachai; Surasak Akesowan; Orawan Khow; Supod Sriprapat; Kavi Ratanabanangkoon (October 1997). )"Naja kaouthia"Production of highly potent horse antivenom against the Thai cobra (. Vaccine 15 (14): 1523–1528.  
  25. ^ a b c Headland, T. N.; Greene, H. W. (2011). "Hunter–gatherers and other primates as prey, predators, and competitors of snakes". Proceedings of the National Academy of Sciences 108 (52): E1470–E1474.  
  26. ^ Mackessy 2010, p. 449
  27. ^ a b c d e f Mackessy 2010, p. 424
  28. ^ a b c Mirtschin, P.J.; R. Shineb, T.J. Niasa, N.L. Dunstana, B.J. Hougha, M. Mirtschina (2002). "Influences on venom yield in Australian tigersnakes (Notechis scutatus) and brownsnakes (Pseudonaja textilis: Elapidae, Serpentes)". Toxicon 40 (11): 1581–92.  
  29. ^ Mackessy 2010, p. 425
  30. ^ Mackessy 2010, p. 441
  31. ^ a b Valenta 2010, p. 221
  32. ^ Russell, Findlay E (1983). Snake Venom Poisoning. Great Neck, NY: Scholium International. p. 163.  
  33. ^ a b Russell, Findlay E. (1980). "Snake Venom Poisoning in the United States". Annual Review of Medicine 31: 247–59.  
  34. ^ Mackessy 2010, p. 484
  35. ^ Mackessy 2010, p. 491
  36. ^ a b Mackessy 2010, p. 492
  37. ^ a b Mackessy 2010, p. 494
  38. ^ a b c d e f Phillips, Charles M. (2002). "Sea snake envenomation". Dermatologic Therapy 15 (1): 58–61(4).  
  39. ^ Thomas, Craig; Susan Scott (1997). All Stings Considered: First Aid and Medical Treatment of Hawaii's Marine Injuries. Honolulu, HI: University of Hawaii Press. pp. 72–76.  
  40. ^ Tu, AG; Fulde GE (1987). "Sea snake bites". Clinics in Dermatology 5 (3): 118–26.  
  41. ^ a b Valenta 2010, p. 153
  42. ^ O'Shea 2008, p. 78
  43. ^  
  44. ^ O'Shea 2008, p. 115
  45. ^ Halassy, Beata; Brgles, Marija; Habjanec, Lidija; Balija, Maja Lang; Kurtović, Tihana; Marchetti-Deschmann, Martina; Križaj, Günter; Allmaier, Igor (2010). "Intraspecies variability in Vipera ammodytes ammodytes venom related to its toxicity and immunogenic potential". Comparative Biochemistry and Physiology - Part C: Toxicology & Pharmacology (Elsevier) 153 (2): 223–230.  
  46. ^ Valenta 2010, p. 186
  47. ^ O'Shea 2008, p. 57
  48. ^ O'Shea 2008, p. 46
  49. ^ O'Shea 2008, p. 40
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.