In Australia there are about 3,000 snake bites per year, of which 200 to 500 receive antivenom; on average one or two will prove fatal. About half the deaths are due to bites from the brown snake; the rest mostly from tiger snake, taipan and death adder. Some deaths are sudden however, in fact it is uncommon to die within four hours of a snake bite.
Between 1979 and 1998 there were 53 deaths from snakes, according to data obtained from the Australian Bureau of Statistics.
In 1906, the untreated death rates were as high as 40% to 50% for death adder and tiger snake bites! Improved supportive treatment and the availability of effective antivenom has reduced this considerably.
Antivenom are prepared from horse serum. The risk of anaphylaxis is very low (less than 1% even for polyvalent antivenom), but is increased in people who have had prior exposure to horses, equine tetanus vaccines, and a general allergic history. This increased risk is much more common in people aged 50 years or more. About 4% of all administrations are associated with minor reactions.
Pre-treatment with a non-sedating anti-histamine, subcutaneous adrenaline, and iv steroids is still recommended, although severe reactions are rare. In general the risk from the snake toxins is much greater than the risk of administering the antivenom.
Each State in Australia has a specifically formulated polyvalent antivenom to suit local snake species however, it is preferable to use a snake-specific antivenom whenever possible to reduce the chance of reactions. Details of which antivenom to use varies from state to state, and are found with the packs and test kits.
If an antivenom is administered, ALWAYS advise the patient of the possibility of delayed serum sickness (up to 14 days later). This is characterised by fever, rash, generalised lymphadenopathy, aching joints and renal impairment. The likelihood of developing this depends on the volume of antivenom required. It occurs in about 10% of patients who are given polyvalent antivenom. Treatment with steroids is usually all that is needed.
Shelf life of antivenom is 3 years when stored in a refrigerator. Antivenom should not be frozen.
Bites of snake handlers comprise 10% of snakebites in Australia, and implicated snakes include several uncommon snakes kept in captivity that rarely cause bites in the wild. Snake handlers are often reluctant to receive antivenom because of a belief that they are at greater risk of systemic hypersensitivity reactions to antivenom, but there is little evidence to suggest this is true. However, they may develop hypersensitivity reactions to venom, which must be considered in the differential diagnosis.
The forked tongue is not poisonous but is actually a chemical brush used to transfer molecules to the Jacobson’s organ in the roof of the mouth, where the snakes sense of taste and smell is located. A widely forked tongue increases the ability of a snake to track its prey.
Snakes do not have ears and cannot hear sound. Instead they detect sound by sensing vibrations passing through the ground.
Snakes’ skin is not slimy and normally it is dry.
Snakes are not attracted to milk beyond the fact that it is wet and easy to find by smell.
The venom toxicity of a juvenile snake is the same as that of an adult although they usually produce less venom.
Less than 10% of newborn snakes survive to adulthood. Most are eaten by predators, such as birds or feral cats, or are killed by humans.
In reality the danger presented by snakes is not nearly as great as perceived. Sporting accidents, dog attacks, lightning strikes and even peanuts cause more human deaths in Australia than snakebite.
The presence of the blue-tongued skink (lizard) is no indication that snakes are absent.
Australia’s most venomous (yield) snake is the King Brown (Pseudechis australis). Believed involved in very few fatalities.
The most toxic snake venom on mice (of the species tested) is the Inland Taipan (Oxyuranus microlepidotus).
Australia’s deadliest snakes are the brown snakes (Pseudonaja spp.). Believed involved in 22 of the past 38 deaths attributed to snakebite.
The world’s deadliest snake, based on documented deaths, is probably the Saw-scaled Viper (Echis carinatus) especially in Sri Lanka. The deaths of nearly fifty people per million from snakebite occur there each year. Today in Australia we have 0.13/million deaths each year.
The toxicity of snake venom is tested in mice. Mice aren’t people.