The prevalence and risk factors of Mycobcaterium bovis infections in domestic animals and man in Eritrea

Abstract

The aim of this thesis was to explore the prevalence of Mycobacterium bovis (M. bovis) infection (bovine tuberculosis; BTB) and its potential risk factors for animals and humans in Eritrea. To that end, BTB prevalence in the intensive livestock production system (dairy cattle) in three major milk producing regions (Maekel, Debub & Anseba), and in the extensive livestock (mixed crop-livestock, and pastoral) system in cattle, goats, and camels in four regions (Debub, Anseba, Gash Barka, and Southern Red Sea) of Eritrea was investigated. The investigation in the intensive system was conducted by subjecting more than halve of Eritrea’s dairy cattle population (around 15,000), to the single intradermal comparative tuberculin test (SICTT). The individual animal and herd BTB prevalence in the dairy sector were variable across the country with Maekel having the highest (21.5% & 40.9%), followed by Debub, 7.3% and 10%, and Anseba, 0.2% and 1.6%, respectively. The overall individual animal and herd prevalence within the dairy sector was 11% and 17.3%, respectively, and pregnant-lactating cattle were more at risk for being SICTT positive, as compared to the other categories. This study was followed by an investigation that attempted to associate the potential herd-level risk factors with the herd prevalence reported. The result of this study showed that herds with higher numbers of cows, and those at farms with concrete floors, were more at risk for being SICTT positive, compared with their references in the dairy sector. The BTB prevalence study in the extensive livestock production system examined cattle (n = 1077), goats (n = 876), and camels (n = 195) using SICTT, and studied its potential risk factors in animals (migration, multispecies mixing at water points and pasture, introduction of new animals into existing herds) and in humans (lack of awareness of the consequences of drinking raw contaminated milk, close contact with their animals, sharing of the same dwelling with their animals). The overall prevalence of BTB in the livestock within this system was low, but was spread throughout most of the sampled regions. In addition, consumption of unpasteurized milk was common. To determine if M. bovis was circulating in the dairy cattle in Eritrea, and to gain insight into its spatial and temporal distribution, a molecular study was conducted on tissues with tuberculosis-like lesions (TBL) collected at the Asmara municipal slaughterhouse, the largest in Eritrea. The results revealed the most important strains of M. bovis in Eritrea and their (dis)similarities with the strains generally present in East Africa and Europe, as well as potential routes of introduction of M. bovis in the country. To gain insight into the role of M. bovis in human tuberculosis in the country, sputum samples from multidrug resistant tuberculosis (MDR-TB) suspected patients were investigated using molecular detection techniques. This study was not able to identify M. bovis in the collected samples, but it did identify M. tuberculosis strains and four NTM species [M. sherrisii, M. yongonense, M. intracellulare, and M. avium].