Snake bite

"Which snakes are the most venomous?" This is one of the most frequently asked questions and the hardest to answer. "Most venomous", depends on the type and amount of venom injected and who is injected. As with most things, there are always those who are more sensitive to venoms than others. Also there is a risk of allergic reactions to the venom (or antivenom) . This allergic reaction can sometimes be more life threatening than the venom's toxicity itself. The toxicity of venom depends on the amount and strength of poison it produces. Most toxicity studies are preformed in mice or other laboratory animals, so may be of limited relevance to humans. For a detailed explanation on toxicity testing of venoms, and more tables of venom toxicity, go to Bryan Fry's International Venom and Toxin Database.

In Australia, around half of all deaths from snakebite involve brown snakes. However, this does not necessarily mean that brown snakes are the "most venomous". In fact, on a world scale, deaths from brown snake are negligible compared to deaths from cobras, kraits or vipers (see Published Sources: Cheng & Winkel, 2001). A large number of deaths associated with a specific species of venomous snake is often related to the snake's population size, its habitat and its nature. Those species found in large numbers in highly populated areas are more likely to cause envenomation because of the greater number of possible victims. Also a species which is aggressive and does not move away when approached is more likely to bite than a species which is shy and not aggressive.

• Brown Snakes: Eastern or common brown snake (Pseudonaja textilis), western brown snake or gwardar (P. nuchalis), the dugite (P. affinis)
• Tiger snakes: Common or mainland tiger snake (Notechis scutatus), black or island tiger snakes (N. ater)
• Taipan: Common or coastal taipan (Oxyuranus scutellatus)
• Fierce snake: also called small scaled snake, inland taipan, western taipan (Oxyuranus microlepidotus)
• Black snakes: Red-bellied black snake (Pseudechis porphyriacus), king brown snake, also called mulga snake (P. australis), spotted or blue-bellied black snake (P. guttatus), Papuan black snake (P. papuanis)
• Death Adders: Acanthophis spp.
• Copperhead: Austrelaps spp.
• Rough scaled snake: also called Clarence River snake (Tropidechis carinatus)
• Sea snakes: Family Hydrophiidae, multiple species

Snakes of lesser medical importance include the Stephen's banded snake (Hoplocephalus stephensi), pale-headed snake (H. bitorquatus), broad-headed snake (H. bungaroides), and small-eyed snake (Cryptophis nigrescens)

About Snakebite in Australia Snake venom is a complex mixture of toxic and non-toxic substances, mostly proteins. Australian snake venoms display neurotoxic (paralysing), pro-coagulant (blood clotting) or anticoagulant (blood thinning) and usually weak cytotoxic (tissue damaging) properties. Some also contain potent myotoxic (muscle damaging) activity. The composition of particular venoms influences the clinical presentation of particular snakebites. Even though not all snakes are venomous it is best, from a first aid point of view, to consider all snakes as dangerous. Sometimes only a small amount or no venom is injected, even if puncture marks are present. As venom is injected quite deeply, little is removed by incision or excision (cutting or sucking). This is a potentially dangerous practice and is to be discouraged. Appropriate first aid for venomous snake bites is the pressure-immobilisation technique.

Antivenom Antivenoms are produced from antibodies to injected venoms (see venoms and antivenoms). Antivenom is the only definitive treatment for effective bites by venomous Australian snakes. It is suggested that prior to the availability of antivenom, death ensued in approximately 45% of tiger snake envenomations and more than 90% of taipan envenomations. The decision to use antivenom should be based on the patient's history, examination and investigation findings. The type of antivenom used will depend on geographic, clinical and pathologic factors.

Epidemiology of Snakebite in Australia The true incidence of snakebite in Australia is unknown. Estimates suggest that there may be several thousand cases of snakebite in Australia each year. Of these perhaps 300 require treatment with antivenom. Surveys over recent years suggest a death rate of around 2-4 cases per year on average, although it is likely that the actual number of deaths is somewhat higher than this, due to unrecognised snakebite deaths. The most recent published survey of deaths from snakebite in Australia found a death rate of around 3.2 deaths per year, although the significance of this is not clear as yet. Prior to the development of specific antivenom therapy and improved supportive care, snakebite was associated with a high case fatality rate. Most bites occur during the warmer months, when snakes are more active and people are more likely to venture outdoors and into the bush. Australian studies of snakebite incidence demonstrate a preponderance of males among the victims, possibly related to risk taking behaviour or to occupational exposure. It is also of note that several cases of snakebite death have been associated with alcohol intoxication. Half (six) of the deaths reported in the 1992-4 survey were due to bites from brown snakes, including several sudden or unexpected deaths (within one hour). Tiger snake was the second most common cause of snakebite death, involved in four fatalities.

Most Venomous Snakes A commonly cited list, from "Australian Animal Toxins" (Sutherland and Tibballs, 1983), is included below, with additional information from the "Handbook of Clinical Toxicology of Animal Venoms and Poisons" by Meier and White (eds) 1995.

Although Australian snakes make up most of this list, the number of snake bites in Australia is relatively, small, and the number of deaths much smaller.

Prevention of Snake Bite At least 95% of snakebites occur on the limbs, with around 75% of these on lower limbs. Many cases of snake bite can be avoided by following these simple rules:

• Leave snakes alone.
• Do not attempt to catch or handle snakes.
• Wear stout shoes and adequate clothing, including long trousers, in 'snake country'. Do not wear sandals or thongs.
• Never put hands in hollow logs or thick grass or under woodpiles, building material etc without prior inspection.
• When stepping over logs, carefully inspect the ground on the other side.
• Keep barns and sheds free of mice and rats as they may attract snakes.
• Keep grass well cut - particularly in playgrounds, around houses etc.
• Take care around houses, barns etc on warm nights, as snakes may be active at this time. Use a torch and wear adequate footwear.
• Educate children in the above precautions.
• Do not handle snakes whilst intoxicated.
• Do not rely on visual identification of snakes as non-venomous, as appearances and coloration may vary considerably within species.