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Green mamba (Dendroaspis angusticeps), a beautiful yet potentially deadly arboreal snake, widely-distributed in sub-Saharan Africa, which produces a neurotoxic venom.
One and a half million people fall victim to venomous snake bites in sub-Saharan Africa every year. Up until very recently, no large-scale study of the scale of the problem had been conducted and public health authorities had underestimated the issue.
Aiming to make up for the lack of reliable data, the organization L'Institut de Recherche pour le Développement (IRD) performed a meta-analysis, which is a critical review of existing scientific works. This involved the detailed study of over 100 scientific articles, conference proceedings and clinical reports published between 1970 and 2010. The result has been much more reliable figures for the number of snake bite victims in this part of the world.
The number of people who die annually in the area to the south of the Sahara as a result of snake bites is at least 7,000, although this is almost certainly an underestimate. The number of limb amputations carried out for the same reason may range from 6,000 to 14,000 or more every year.
Working in the fields: a high-risk activity
The IRD study also highlighted the situations most likely to result in bites, with 95% occurring in rural areas, particularly in plantations. The people most at risk are therefore agricultural workers.
Urban areas are not exempt from such incidents either, even if the incidence of bites is between ten and twenty times lower than in rural settings. There are also seasonal factors. In some regions during the rainy season, snake bites account for over 10% of hospital admissions.
In the case of the most dangerous African snake species, two types of venom can be distinguished. There is the neurotoxic venom of the cobras and mambas, which causes respiratory paralysis, potentially killing the victim by asphyxia within one to six hours following a bite.
The hemorrhagic and necrotic form of venom produced by vipers - including the ocellated carpet viper, which is a common species on the African savannah - induces tissue swelling (edema) and tissue death (necrosis) in the limbs as well as hemorrhaging. If untreated, this can prove fatal in just a few days.
A vicious circle
The effective treatment remains intravenous injection of an appropriate antivenom as swiftly as possible after the bite, in order to neutralize the toxic substance. Unfortunately, the availability of these antidotes is currently restricted and only 10% of venomous snake bites are treated.
Shortage of data has meant that up to now, the scale of problem had not been appreciated by the health authorities. Moreover, such remedies are costly and their shelf-life is short - typically just 3-5 years - discouraging their purchase. Furthermore, without proper training for medical personnel in the use of antivenoms, such treatment can give disappointing results, subsequently deterring their usage.
These various factors reduce demand and manufacturers then hesitate before producing antivenoms they cannot be sure of selling. What has now happened is that accessibility to antivenoms in Africa has fallen tenfold since the 1980s, down from 200,000 doses per year to less than 20,000 in the early 2000s.
Only one in 10 victims are being treated, owing to a shortage of suitable anti-venom and lack of awareness among health care practitioners. The tragedy of this situation is that the level of mortality caused by snake bites in Africa is currently correspondingly higher now than it was thirty years ago.
Reference: Jean-Philippe Chippaux. Estimate of the burden of snakebites in sub-Saharan Africa: A meta-analytic approach. Toxicon, 2011; 57 (4): 586 DOI: 10.1016/j.toxicon.2010.12.022