Pharmaco-epidemiological and toxicological studies of snake envenomations in selected areas of Kenya
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Venomous stakes are snakes which have venom glands and specialized teeth for the injection of the venom into the victims. Snake envenomation is a global problem with annual figures of 5 million envenomations, 40,000 or more deaths and about 100,000 people ending up with severe sequelae. However, these figures are approximate as most countries do not possess reliable epidemiological reporting systems. This also applies to Kenya where envenomations occur but the precise data on frequencies, mortalities and factors associated with snake envenomations are not well documented. This study was carried out to determine the frequencies of envenomations, mortalities and factors responsible for snake envenomations. Snake envenomation is treated using antivenoms. Antivenoms are made by milking venom from the selected snakes and injecting it to an animal that will undergo an immune response to the venom, producing antibodies against the active venom antigens. The antivenoms are manufactured from venoms obtained from snakes specific to certain regions. Due to regional 'venom specificity, these antivenoms may not be effective when used in other countries. The purpose of the study was also to test the efficacy of two of the most commonly used antivenoms in Kenya namely polyvalent antivenom I and polyvalent antivenom II. Epidemiological studies were carried out on snake envenomations 111 areas where envenomations have been reported in Kenya, namely Kakamega, Kabarnet, Kapenguria and Makueni over a 3 year period (January 2007 to December 2009). Secondary data from hospital records were used to compile" frequencies of snake envenomations, mortalities and antivenom administration. Semi structured questionnaires were administered to respondents who included: doctors, clinical officers, nurses, hospital pharmacists and private pharmacists. Information obtained on victims of envenomations were: age, gender, time of day, and season of the year when envenomations happen, occupation, part of the body bitten, access to hospitals and the role of traditional healers. Data on availability, effectiveness of anti venoms and challenges to antivenom use in the hospitals were also gathered using the questionnaire. Acute toxicity studies were performed in mice using the venom of one of the most common venomous snakes in Kenya, the black mamba (Dendroaspis polylepsis). These studies included: the determination of the median lethal dose (LDso) of black mamba venom in mice by the moving average method of Weil (1952). Other parameters studied in the toxicity study were: symptoms of poisoning and the effects of the venom on hematological parameters. Postmortem of dead and sacrificed animals was done to determine the gross pathological effects of the venom. The LDso value of Black mamba venom (0.340mg/kg) was used to determine the antidotal effectiveness of two polyvalent antivenoms labeled I and II currently being used in Kenyan hospitals. This was done by administering high LDso values of the venom followed by the antivenom to determine the effect of treatment on lethality of the venom. The results obtained from hospital records for envenomations showed that out of 176 envenomations there were only 4 mortalities (2.3%). Antivenoms although available were administered to only a few patients i.e. 49/176 (27.8%). The survival rates were observed to be high i.e. 125/127 (98%) even without antivenom administration. The antivenoms in use were generally effective in treating snake envenomations. In relation to factors influencing envenomations, findings in this study demonstrated that there were no major differences in envenornations between either gender (males 90, females 86). The age groups 1-15 years and 16-30 years were mostly envenomated with the former contributing 41.4% and the latter contributing 31.8% of all the envenomations. These age groups could also be more physically active than the other age groups. Envenornations OCCUlTedmainly in the bush and farms and affected mostly manual and agricultural workers. This could be due to presence of many snakes in these areas and also failure to wear protective clothing. Envenomations occurred mostly during dry seasons compared to rainy seasons. The lower limbs were more envenomated than other parts of the body i.e. 75% compared to 25% for other parts of the body. This could be due to easy accessibility of lower limbs by the offending snake and failure to wear protective clothing (like shoes) by the victims. The two polyvalent antivenoms labelled I and II were found effective in protecting mice against Black mamba venom. Antivenom I protected rmce at 3xLDso and antivenom II protected mice at 3xLDso and 4xLDso. The black mamba venom exhibited neurotoxic symptoms with no significant hemotoxicity. The neurotoxic symptoms exhibited during acute toxicity included: analgesia, weakness and incordination, increased or decreased respiration. Postmortem results indicated that black mamba venom mainly caused paralysis of smooth muscles of the blood vessels 'in the liver, lungs, kidneys, gastrointestinal tract and the spleen leading to congestion and the affected organs appearing darker than normal ones. In conclusion, the results showed that mortalities as a result of envenomations were relatively low, 4/l76 (2.3%) possibly because of the non-poisonous nature of the snakes involved. Envenomations were influenced by various external factors and antivenoms 111 use were effective but antivenom administration was restricted to a few patients.