Akani et al. J Venom Anim Toxins incl Trop Dis. 2013, 19:2 http://www.jvat.org/content/19/1/2 RESEARCH Open Access Correlation between annual activity patterns of venomous snakes and rural people in the Niger Delta, southern Nigeria Godfrey C Akani1, Nwabueze Ebere1, Daniel Franco2, Edem A Eniang3, Fabio Petrozzi4, Edoardo Politano4 and Luca Luiselli4* Abstract Background: Venomous snakes are among the most serious health hazards for rural people in tropical regions of the world. Herein we compare the monthly activity patterns of eight venomous snake species (Elapidae and Viperidae) with those of rural people in the Niger Delta area of southern Nigeria, in order to identify the periods of highest potential risk for persons, and the human group actually at greater risk of snakebite. Results: We documented that above-ground activity of all venomous snakes peaked in the wet season, and that high snake activity and high human activity were most highly correlated between April and August. In addition, we documented that women and teenagers were at relatively higher risk of encountering a venomous snake than adult males, despite they are less often in the field than men. Conclusions: Our results suggest that future programs devoted to mitigate the social and health effects of snakebites in the Niger Delta region should involve especially women and teenagers, with ad-hoc education projects if appropriate. We urge that international organizations working on social and health problems in the developing world, such as IRD, DFID, UNDP, should provide advice through specific programs targeted at especially these categories which have been highlighted in comparatively potential higher threat from snakebites than adult men. Keywords: Monthly activity, Venomous snakes, Rural people, Nigeria Background ecologies (but not habitat selection) and venom composi- Venomous snakes certainly are among the main health tions and potency, the former is more likely to kill people hazards for rural people in tropical regions of the world, than the latter [2,3]. Secondly, in geographic areas where while it is calculated that many thousands of people die there is a higher diversity of venomous snakes, the prob- yearly on account of snakebite, especially in India, but ability of being killed by snakebite is greater than in areas also in Africa and South America [1,2]. where there are fewer dangerous snakes. So, for instance, Several independent factors may increase the probability the probability of experiencing a fatal bite is certainly higher of being bitten and eventually killed by a snake in a tropical in India or in several regions of tropical Africa (where many area. Firstly, the antipredatory behavior of a snake species sympatric highly venomous snake species do exist) than in certainly influences the likelihood of a bite: for instance, the South America. Thirdly, geographic areas with a greater puff adder (Bitis arietans) is more inclined to bite than a density of people working in rural activities are more prone Gaboon viper (Bitis gabonica); thus, despite similar to be affected by high rates of fatal bites than areas where the rural human density is low. Fourthly, the probability of beingbitteninagiventropical area cannot be constant * Correspondence: [email protected] 4Environmental Studies Centre Demetra, Rome and Fano, Italy across the year, but should depend on the monthly activity Full list of author information is available at the end of the article patterns of snakes and on correlating the activity patterns © 2013 Akani et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Akani et al. J Venom Anim Toxins incl Trop Dis. 2013, 19:2 Page 2 of 8 http://www.jvat.org/content/19/1/2 between snakes and humans [2]. Indeed, it has been bushland-secondary-forest mosaic region of the Niger demonstrated that in tropical areas three quarters of the Delta, in southern Nigeria. We conducted our surveys in bites happen during agricultural tasks, hunting or while eight states of the Federal Republic of Nigeria, from walking to or from work, and are hence linked to occupa- West to East: Delta, Bayelsa, Anambra, Imo, Rivers, tional activities [2]. Abia, Akwa-Ibom, and Cross-River. Thus, we surveyed In the present paper, by taking advantage of the most an irregular surface of approximately 400 × 250 km. The prolonged longitudinal field study (16 years) on the ecology study area, which is heavily populated with hundreds of of tropical snake communities available in the world [4,5], villages interspersed by patches of forests and cultivated we analyze the correlation between the monthly activity lands, is especially important for the economy of Nigeria patterns of eight species of venomous snakes (belonging to because of its large-scale oil extraction and liquefied nat- the families Elapidae and Viperidae) and people in rural ural gas transmission installations [7]. The forest patches areas of the Niger Delta, in southern Nigeria. This study may be dry-land or swamp rainforest type. Mangrove region is particularly interesting from the venomous-snake forests (Avicennia spp., Rhizophora racemosa) are the point of view because, having been extensively deforested dominant vegetation types in the areas of the fluvial sys- in the last 50 years, it has been invaded by the spitting tems influenced by salty or brackish water. The climate cobra (Naja nigricollis), which otherwise tends to inhabit of the study region is tropical sub-Saharan, with well the savannah, to the detriment of the once dominant cobra delineated dry and wet seasons and relatively small species (the forest cobra Naja melanoleuca), typically monthly fluctuations between maximum and minimum adapted to life in the rainforest [3,6-11]. temperatures [14]. The monthly pluviometry of the As to Nigeria, the only detailed data on the epidemi- study area is given in Figure 1. ology and occurrence of venomous snakebites came from the savannah region in the north of the country [12,13]. Measurement protocol of snake activity These studies revealed an incidence (per 100,000 inhabi- Annual snake activity patterns were assessed by visual- tants) of 48–603 bites (mean = 160), with a morbidity of encounter surveys (VES) and by counting death-on-road 100–150, a lethality in hospitals of 2.1-27, and an overall (DOR) specimens, assuming that there should be a linear mortality of 15.6 [2]. However, no such data are available relationship between intensity of above-ground activity in for the southern portion of the country, where the main snakes and their probability of being observed during VES vegetation zone is constituted by mangroves and rainforest surveys and risk of being squashed along a road [1,15-17]. [7]. Our study aims to verify, inside the rainforest vegeta- The effort time (number of days in the field) was recorded. tion zone of Nigeria, the specific period of the year in When two (or three) independent observers conducted a which the greatest activity of venomous snakes occurs in VES survey on the same day, the number of days recorded the field, and which period of the year presents the highest for the analyses was two (or three), given that there was correlation between occupational activities of people and total independence of observations and no possibility of above-ground activity of snakes. erroneously replicating the data. Survey time was typically from 7h00 to 11h00 and Methods from 16h00 to 19h00, whereas searches were generally Study area suspended during midday because of reduced snake ac- The study was conducted during field surveys between tivity at that time. Nocturnal surveys were generally September 1996 and June 2011, in the plantation- avoided due to safety reasons. Figure 1 Pluviometric patterns in the study area. Akani et al. J Venom Anim Toxins incl Trop Dis. 2013, 19:2 Page 3 of 8 http://www.jvat.org/content/19/1/2 Rural human activity number of snake observations according to species. In To compare the monthly patterns of activity between this graphical comparison, it should be emphasized that snakes and rural persons, we constructed an empirical the human index is related to a surface (hectare), con- index of the frequency of encountering of people in the trary to the ophidian index. field by month, during the snake surveys. The following human activities were considered: walking, farming, fishing, Results hunting, canoe-carving, logging, and palm-oil production. Activity patterns of venomous snakes This index was calculated during the year 2011, and was This study focuses on eight venomous ophidian species, assumed to be relatively constant over the years. four from Elapidae (the spitting cobra Naja nigricollis, the forest cobra Naja melanoleuca, the tree cobra Pseu- Statistical analyses dohaje goldii and Jameson’s green mamba Dendroaspis To evaluate whether each of the species (and the whole jamesoni) and four from Viperidae (the Gaboon viper of the species at once) was observed at a similar fre- Bitis gabonica, the nose-horned viper Bitis nasicornis, quency of occurrence throughout the various months, the green bush viper Atheris squamiger and the West the various records were grouped into monthly intervals African night adder Causus maculatus). Other venom- (from the first to the last day of each month). Then we ous snakes found in the Niger Delta include: Toxico- determined the relative sampling per monthly interval dryas blandingii, Toxicodryas pulverulenta, Thelotornis by dividing the number of days spent in the field in each kirtlandii, Dispholidus typus, Crotaphopeltis hotam- month by the total number of days in the field during boeia and Atractaspis spp. [15,16,18]. However, we the entire research period (Table 1).