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Epidémiologie moléculaire de la fièvre aphteuse en Afrique Subsaharienne : cas du Tchad

Abstract : Foot-and-mouth-disease (FMD) is a highly contagious disease that affects domestic and wild artiodactyles. It is endemic in Chad. However, there is very little research on FMD, as the prevalence and risk factors associated with the disease and all circulating serotypes are not well known. My thesis aims to contribute to a better understanding of the epidemiology of this disease, to determine areas at risk, to estimate seroprevalence in three major breeding regions (Batha, Wadi Fira and West Ennedi) and to carry out an initial molecular characterization of the serotypes of the FMDV circulating in Chad.A literature review was carried out to collect data on animal mobility and the current epidemiological situation of FMD in Chad and neighbouring countries. The objective of this work was to establish a risk map based on the occurrence of the disease in relation to animal movements. The results were used to estimate the risk of introduction and spread of FMD and to represent areas at risk using the new risk mapping approach. Thus, 12/347 Chadian communes located at the borders have a "very high" risk of introduction of the FMDV. For the risk of spread, 54 and 78 communes were characterized by a "very high" and "high" risk respectively.In addition, a cross-sectional survey was conducted between October and 2016 to determine the seroprevalence of the disease in domestic ruminants and characterize circulating viral strains. A total of 1520 sera samples (928 cattle, 216 goats, 254 sheep and 122 dromedaries) were collected for serological analysis and nine epithelial tissues from cattle showing clinical signs for virological analysis. Serological results showed an overall seroprevalence of 40% and seroprevalences of 84%, 78% and 84% in cattle over 5 years of age in East Batha, West Batha and Wadi Fira respectively. Among cattle under one year of age, seroprevalence was estimated at 67% in Wadi Fira, 64% in East Batha and 59% in West Batha. In small ruminants over 5 years of age, seroprevalence of 63%, 45%, 34% and 10% have been estimated respectively in West Batha, East Batha, Wadi Fira and West Ennedi. In small ruminants under one year of age, seroprevalence has been estimated at Wadi Fira (50%), East Batha (32%), West Batha (18%), and Ennedi West (11%). Serotyping results from sera of animals less than one year old showed that serotypes O, A, SAT1 and SAT2 circulated in 2015 in Chad. However, serotype SAT2 dominated with an overall seroprevalence of 43.3% and was present in all areas studied. It is followed by serotypes O (29.9%) present in West Batha and Wadi Fira, A (22.4%) present in East Batha and West Batha and SAT1 (4.5%) present only in Wadi Fira. Virological analyses have made it possible to characterize the serotype SAT2 of the FMDV. Phylogenetic analyses of the coding sequence for the VP1 protein made it possible to determine the SAT2 topotype VII serotype, close to the viral strains found in Cameroon in 2015 with a similarity of 98.60%.In conclusion, the serological results confirm that the disease is endemic. Furthermore, the results of molecular characterization prove the cross-border nature of the disease through uncontrolled movements of animals. All these results show that it is important for Chadian veterinary services and researchers to continue research on the molecular epidemiology of FMD throughout the country in order to characterize all serotypes circulating and then develop and implement a surveillance protocol and a risk-based control plan.
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Submitted on : Thursday, May 28, 2020 - 3:51:12 PM
Last modification on : Friday, August 5, 2022 - 2:38:11 PM


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Arada Izzedine Abdel Aziz. Epidémiologie moléculaire de la fièvre aphteuse en Afrique Subsaharienne : cas du Tchad. Médecine vétérinaire et santé animale. Institut agronomique, vétérinaire et forestier de France, 2018. Français. ⟨NNT : 2018IAVF0029⟩. ⟨tel-02640969⟩



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