Medically important snakes and their bites in Nigeria
Associate Professor Abdulrazaq G. Habib
May we escape danger in the farm – the bites of a snake or the sting of the scorpion ... May children put their fathers into the earth and not fathers their children...
Chinua Achebe, Arrow of God
Introduction
A recent global reappraisal estimated a snake bite incidence of 8.9–93.3/100,000 persons with 10001–100000 envenoming per year and resulting mortality rate of 0.5–5.9/100,000 persons with 1001–10000 deaths per year in West Africa. It is a major medical problem in Nigeria, Africa’s most populous country with over 140million people. This brief report describes the problems and potential solutions to the snake bite menace in the country.
Snakes of medical importance in Nigeria
Three main families of snakes of medical importance are found in Nigeria: Viperidae (Vipers and Adders), Elapidae (Cobras and Mambas) and Colubridae (Boomslang) [Figure 1]. The vipers are relatively shorter, thicker snakes with long hinged front fangs. The main example in Nigeria is the saw-scaled or carpet viper (Echis spp) of which there are two main species in West Africa – Echis ocellatus and Echis leucogaster. Its world distribution stretches from Senegal to Bengal, a range perhaps second only to that of the European Viper, Vipera berus. Echis ocellatus has an average length of 35–40cm and resides in semi–arid rocky terrain [Figure 1]. It is the most prevalent cause of bites in the middle belt and the northern states of Nigeria [Figure 2]. Roman’s carpet viper (E. leucogaster) lives in the sahel belt of Nigeria and is probably under recognized as cause of human bites. Echis ocellatus has also been seen as far south, as the Shaki/Kishi area of Oyo state and in Enugu and Udi hills. The snake is mainly nocturnal entering human dwellings only rarely unlike the spitting cobra. Echis ocellatus may be confused with at least four other snakes in West Africa – Dasypeltis scabra, Telescopus variegatus, Bitis arietans (juvenile specimens) and Causus maculatus – the former two lack fangs while the latter two are also venomous.
The puff adder, B. arietans, is another viper which is bigger, thicker but less common than E. ocellatus in some areas. Additionally, it has the characteristic V or U pattern along its dorsal aspect that helps in differentiation. The night adder Causus maculatus is very similar to the carpet viper but has smooth scales and therefore does not produce a rasping sound and has large symmetrical scales on top of the head, but differentiation between the two could be fraught with difficulties. The Atractaspis spp (borrowing asps or stiletto snakes) together with C. maculatus are small vipers which are only mildly venomous. Both are present in Nigeria and the former are now regarded as a separate family the Atractaspididae.
The Elapid snakes are longer with short hinged front fangs. The spitting cobra, Naja nigricollis, is the commonest and most widely distributed African cobra and is indeed a familiar snake in Nigerian states within the savannah terrain, where it is usually coloured black, dark brown or steel grey with pink or reddish throat bars. The average length was found to be 117cm. It is the most important snake at Malumfashi district of Katsina state, though another cobra Naja Katiensis which has a shorter length and brown colour along its back is also found. Naja nigricollis, unlike N. katiensis, may inhabit the savannah bordering the forest zones. The forest cobra N. melanoleuca inhabits the southern forests of Nigeria and is usually black in colour. The Egyptian cobra, N. haje, is seen mostly in the northern states with snake charmers. Most cobra species are also nocturnal. Cobra spit in the eyes may lead to acute snake venom ophthalmia with permanent blindness.
The mambas (Dendroaspis spp) occasionally cause bites in northern Nigeria and to a lesser extent other parts of the country. The boomslang, Dispholidus typus, is a member of Colubridae which possess short non-hinged fangs situated far back in the mouth. Fourteen (14) venomous species have been found in Nigeria (see Table 1 for names of common snakes in major Nigerian languages and English and Figure 1 for their pictures).
To be continued ...
