Micrognome

Snake bite. Prof D Warrell, University of Oxford

[notes on a plenary talk given at the Centenary of Tropical Medicine conference in Townsville, QLD, on 12-13th June, 2010)

Snake bite is one of the most neglected of tropical diseases. Its victims often die before admission to hospital and are thus lost from statistical analyses. A study from Bangladesh reported an estimate 700,000 bites per year causing 6000 fatalities. In India where the offical figure is 14,000 deaths from snake bite over many years, the estimated annual fatality figure has been estimated at over 45,000. Recent methods of analysis have applied a verbal autopsy to obtain more accurate data. Current figures are therefore likely to underestimate the global impact.

The burden of disease caused by snake bite is being reduced by a combination of approaches:

1. minimising contact with snakes through behaviour modification & appropriate clothing
2. improved first aid measures
3. better medical management

There has been a substantial  Australian contribution in several areas:

1        description of the Australian herpetofauna. Some are amongst the most venomous known. A new species of Taipan was recently discovered and named Oxyuranus frontalis, distinguished by a subtle difference in the arrangement of head scales, requiring examination at close quarters.

2        antivenom development. First use of antivenom was by Albert Calmette of the Institut Pasteur in Saigon, in 1894. He successfully used a specific antivenom raised against the monacled cobra venom to treat a laboratory worker who had been accidentally exposed. However, subsequent experience showed that this antivenom was too specific to use for all snake bites. In 1902 Tidswell described a tiger snake antivenom. Tiger snake bite has a fatality rate of up to 85%.

3        understanding the action & evolution of snake venom. Snake venoms are highly specialised in their action and have considerable specificity. They include a muscle damaging phospholipase, group C and D prothombin activators and naturietic peptides. The ACE inhibitor captopril was developed from the venom of the Brazilian jararaca snake.

4        development of effective first aid methods. Hamilton-Fairley recognised that snake venoms were rapidly absorbed via the lymphatics and that ligatures worked only as long as they were applied. However, some venoms are partly inactivated during this period. The pressure immobilisation method was described by Sutherland in 1979 and is now widely used. There are anecdotal descriptions of deterioration after release of the pressure bandage, but there has been no prospective RCT or other formal trials of clinical efficacy. The PIM approach is difficult to teach well, apply consistently and maintain, especially during transport to hospital. Alterntive methods e.g. the Monash foam rubber pad, may be more widely applicable at lower cost and with less prior expertise.

Before the colonial era Australia’s indigenous peoples had learned to live with some of the most dangerous snakes in the world. Data are hard to come by and suggest a currently variable experience of snake bite in indigenous communities from never recorded to a leading cause of death. Locally, the Banjan people introduce their children to the issue through dramatic instruction by wise people, or gubi murrays. They are taught to respect snakes, to walk in single file, to know places and times where snakes will be, and to burn off the area around a campsite. Snake bite is seen as a punishment for breaking the adult code. There have been no cases of snake bite or subsequent death in recent times (oral account, Russell Butler).