HOST-PATHOGEN ASSOCIATION AND TRANSMISSION DYNAMICS OF BRUCELLA SPECIES IN KENYA AND TANZANIA

Abstract

Bacterial pathogen of the genus Brucella is a gram-negative organism with several species. It causes a disease called ―brucellosis‖ in humans, and animals worldwide. Association between animal and human Brucella sero-positive cases have been documented within Kenya and Tanzania. But data on the species of Brucella circulating in various susceptible hosts, including the zoonotic species B. abortus and B. melitensis is insufficient, thus limiting adoption of species or host-targeted control strategies. The primary objective of this study was to assess hostpathogen association and transmission dynamics of Brucella species among animal and human populations. While the specific objectives were 1) To identify Brucella species circulating in livestock and wildlife in Marsabit, Narok in Kenya and Northern Tanzania 2) To identify Brucella species responsible for human infections in Marsabit, Narok in Kenya and Northern Tanzania 3) To assess molecular diversity and transmission dynamics of Brucella species in different hosts within Kenya and Tanzania. Therefore, a cross-sectional study was undertaken at the wildlife, livestock, and human areas in Marsabit and Narok, Kenya as well as Northern Tanzania. A total of 1384 samples from cattle (709), goats (274), sheep (191), pigs (79), camels (61), buffaloes (70), and humans (257) were collected from Narok, Marsabit in Kenya and Northern Tanzania. Information on history of retained placenta or abortion, location, and age of sampled livestock were recorded. Information such as gender, location of residence, and age were obtained and recorded from the study participants. Real-time PCR assays were run on all the samples with primers that are specific for IS711 and bcsp31 targets to detect the genus Brucella. Another real-time PCR assay with AlkB and BMEI1162 targets was run to detect B. abortus and B. melitensis species, respectively in all the samples that had amplifications with both genus targets to answer objectives one and two. Mixed effects logistic regression models and descriptive analysis were done using lme4, sjstats, and gmodels packages in R-statistical software. Overall, 199 (33.3%) livestock samples and 99 (38.5%) human samples were found to be positive for the genus Brucella for the third objective. This study found B. abortus to be associated with camels (OR=2.9, 95% CI: 1.3–6.3), and cattle (OR=2.3, 95% CI: 1.1–4.6), while B. melitensis had significant association with both goats (OR=1.7, 95% CI: 1.0 – 3.1) and sheep (OR=3.6, 95% CI: 2.0 – 6.7). The DNA belonging to both B. melitensis and abortus were found in multiple livestock species, buffaloes, and humans, suggesting occurrence of crosstransmission of the two Brucella species among the different hosts. Occurrence of crosstransmission of Brucella spp. beyond their known preferential host was further strengthened by detection of B. abortus in Pigs, that has always been associated with B. suis. Animals with either retained placenta or abortion history were associated with presence of B. melitensis, and B. abortus, respectively. Therefore, retained placenta and aborted materials could be facilitating the transmission of B. melitensis and B. abortus. Persons within 21 to 40 years of age were more likely to have a PCR positive results for Brucella (OR=2.8, 95% CI: 1.2-6.6) than other age categories. Multiple livestock species are responsible for transmitting Brucella to humans. Therefore, brucellosis control in humans should target cattle, sheep, goats, pigs, and camels, while using One Health multidisciplinary approach.