Epidemological investigations of rift valley fever in livestock in three ecological zones of Malawi.
Due to uncertainty on the status of Rift Valley fever (RVF) in Malawi, limited knowledge about its epidemiology, and debates on whether it is a real or perceived threat for the livestock and human population in the country, a study was formulated to investigate the epidemiology of RVF. The study was carried out between January, 2020 and July, 2020 in 8 districts of Malawi, namely Chitipa (CP), Karonga (KA), Salima (SA), Mangochi (MH), Chiradzulu (CZ), Thyolo (TO), Chikwawa (CK) and Nsanje (NE). These districts were purposively selected from three ecological zones (EZ). Across-section survey using semi-structured questionnaire (n=400), was conducted to capture knowledge, attitude and management practices (KAP) information towards RVF. Average KAP score was calculated from total scores for knowledge, attitude and practices and assessed. In addition, 1,523 whole blood samples of cattle, goat and sheep were collected and 361 livestock farmers participated in questionnaire administration to capture information on potential risk factors. Indirect competition ELISA (cELISA) and IgM Antibody Capture Enzyme-Linked Immunoassay (MAC-ELISA) were used to detect presence of Rift Valley fever virus (RVFV) antibodies in serum. Questionnaire survey and the sero-positivity data, were analyzed for quantitative results using descriptive statistics. Bivariate analysis for association was conducted using Pearson chi-square and univariate linear regression, followed by multivariate analysis using stepwise binary logistic regression to determine the predictors of knowledge and risk factors for RVFV sero-positivity. Further, molecular techniques were used to isolate and identify RVFV genome from serum that tested positive to IgM ELISA test. Participants had overall poor knowledge (score= 17.94%), negative attitude (score= 9.40%), and poor management practices (score= 41.23%) towards RVF. Only 8.25% participants had sufficient knowledge on RVF. The crude seroprevalence was 17.14%, (95% CI= 15.33-19.11) at individual livestock level. The seroprevalence across the ecological zones (EZ) were 20.34%, 11.78% and 14.55% for EZ1, EZ2 and EZ3, respectively, while seroprevalence for species were 21.35%, 7.72% and 25.68% for cattle, goat and sheep, respectively. The overall herd seroprevalence was 33.24%, (95% CI= 28.18-38.11). Sheep herd registered seroprevalence of 100% (95% CI= 73.23– 1.00) higher than cattle and goat (p=0.019), consisted of 64.29% for IgG seroprevalence and 35.71% for IgM seroprevalence herds. Further, the herd seroprevalence for EZ2 was comparatively higher at 36.36%, (95% CI= 28.6-44.55) than EZ1 34.12%, (95% CI= 24.40-45.88) and EZ3 29.32%, (95% CI= 21.92–37.95), at (p=0.047). Risk factors for RVFV seropositivity at individual livestock was sex of livestock and risk factors at herd level were areas receiving rainfall amount of <1,000mm and mixed species herds. The study demonstrated the presence of RVFV through detection of RVFV genome from three samples of livestock. Results of this study provided epidemiological information of RVF in livestock in Malawi and the available gaps in control and prevention of the disease. Therefore, the study recommends community sensitization on RVF and investigation of RVFV seroprevalence in humans working in the risky areas for better clarification of impact of predisposing factors and risky management practices observed in the study area. Further, recommends study on molecular epidemiology of RVFV in livestock, humans and mosquitoes to effectively describe the RVFV in circulation.
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