Epidemiological Study of Lumpy Skin Disease and Its Economic Impact in Ethiopia

Abstract

Lumpy skin disease (LSD) is one of economically important viral diseases of cattle in Ethiopia caused by Lumpy skin disease virus in the member of the genus Capripox viruses. The objective of this thesis is to better understand the epidemiological features of the disease in order to propose practical and applicable control and prevention options. The thesis is classified in five chapters. The first chapter describes the general agricultural production system in Ethiopia and relates the current knowledge on the virus and the disease as given by the literature.The second chapter deals with the performance of indirect fluorescence antibody test (IFAT) as a serological diagnostic and screening tool that was evaluated using methods without gold standard. Virus neutralization test (VNT) was used as the second test for comparison. The analysis of conditional dependent Bayesian model showed that the IFAT had good accuracy both in sensitivity (92%) and specificity (88%) parameters indicating that it could be used for LSD diagnosis and screening (epidemiological studies, epidemiosurveillance) with less misclassification. Its capacity to run large number of samples per plate just like ELISA could be also taken as an advantage for large epidemiological studies. The sensitivity and specificity of VNT was 78%, 97% respectively. The two tests IFAT and VNT were found conditionally independent on the disease status of the animal. Thus, higher sensitivity and throughput for IFAT would render the test being selected for screening purposes and higher specificity performance of VNT would qualify it to be used as a confirmation test. A cross sectional study was then conducted to estimate the prevalence of LSD at herd and animal-levels and to analyze the risk factors associated with the disease occurrence in Ethiopia. It is presented in the third chapter. A total of 330 questionnaire surveys were collected from 44 peasant associations (PA) distributed in 15 districts. The average herd level LSD prevalence was 42.8% (95% CI: 37.5–48.3) and it was significantly higher in the midland agro-climate 55.2% (95% CI: 47.5–62.6) than in lowland and highland agro-climate zones (22.3% and 43.5%, respectively). The observed LSD prevalence and mortality at animal level were 8.1% and 2.12% respectively which were still higher in the midland zone (10.4% and 3.2%, respectively) than in lowland and highland zones (P< 0.05). The risk factor analysis showed that three variables: the effect of agro-climates, communal grazing/watering management and introduction of new animals were significantly associated with LSD occurrence. The temporal association between LSD occurrence and increase in the biting-fly population was also positively correlated by Spearman rank correlation coefficient (0.88, 0.79 and 0.79 for highland, midland and lowland zones, respectively) and statistically significant. The need to evaluate the financial feasibility and benefit possibly expected of vaccination led us to the fourth component of the thesis: The financial cost of clinical LSD at the farm level and the economic benefit of its control by vaccination from the farmers' perspective were analyzed in five selected districts in Oromia Regional state, Ethiopia. A pre-tested questionnaire survey addressing the period of one year production cycle was considered and 747 questionnaires were collected. Descriptive epidemiological results were obtained from the questionnaire survey data. Annual cumulative incidence, mortality and case fatality rates were calculated for each breed, sex and age groups. Annual financial cost due to clinical LSD infection was calculated as the sum of the average production losses due to morbidity and mortality. The variables that accounted for financial cost estimation were milk loss, beef loss, traction power loss, and treatment and vaccination costs. Annual financial costs per head were estimated of 6.43 USD in local zebu and of 58 USD in Holstein Friesian (HF)/ crossbred cattle in infected herds. The financial benefit of controlling LSD through a one year planned vaccination was calculated using partial budget analysis and the changes in the enterprise outputs from the control intervention were measured from the variables milk production, beef production and draft work-output. The marginal rate of return (MRR) gained from the control intervention was estimated at 76 (7600%) and the net benefit per head was 3 USD and 33 USD in local zebu and HF/crossbreds cattle respectively. This implied that annual vaccination had enabled to reduce the financial costs due to LSD by 40% and 58% per head in local zebu and HF/crossbreds respectively. The analysis of the planned vaccination as compared to a non vaccination scenario for a one year time horizon have shown that the livestock producers would get substantial benefit not only from financial gain perspective but also to secure and maintain sustainable enterprise business. Finally in the fifth chapter, general discussion on the epidemiological study and control options were presented along with persistent knowledge gaps that requires further research efforts to finetune the proposed control and prevention options. The result from the risk factor analysis could also shed light on the epidemiology of LSD in other African countries suffering from the disease