Brucellosis in Ethiopia: epidemiology and public health significance.

ABSTRACT Brucellosis is a common bacterial zoonotic disease that has important veterinary and public health concerns and economic impact in Sub-Saharan Africa including Ethiopia. A cross-sectional study was conducted in Addis Ababa Dairy farms and four selected districts of Borena Pastoral setting in Southern Ethiopia from November 2016 to February 2018 to estimate the prevalence of brucellosis and associated risk factors in cattle, sheep and goats and occupationally associated humans. A total of 2300 cattle, 882 small ruminants and 341 humans were serum sampled and serially tested for antibody against Brucella infection using Rose Bengal Test for screening and further confirmed by Competitive-Enzyme Linked Immunosorbent Assay. The overall individual animal level seroprevalence was 0.06 % (95% CI: 0.002 -0.4) in commercial dairy cattle in Addis Ababa, 2.4 % (CI: 1.4-3.7) in cattle, and 3.2 % (CI: 2.1-4.6) in small ruminants; both in Borena pastoral region, Southern Ethiopia. The seroprevalence recorded in humans occupationally linked to livestock production systems in Borena was 2.6 % (CI: 1.2-5). Herd size, parity, and history of abortion were risk factors associated with Brucella seropositivity (p<0.05) in cattle whereas in small ruminants the results show that district, age group, flock size, and history of abortion were found to be significantly associated risk factors with Brucella infection (P<0.05). The risk factors for Brucella infection in humans were assisting in calving and presence of seropositive animals at household (p<0.05). Existence of more than one seroreactor animal species in some villages in Borena indicates more credence to the possibility of cross-species transmission of Brucella infections. Human seropositivity in the households with seropositive animals provides evidence of a public health hazard. In addition, an outbreak investigation of abortion at Adami Tullu Agricultural Research centre, central Ethiopia, was made to isolate and characterise the causative agents using cultural and molecular tools. Fifteen Brucella abortus were isolated from various tissue samples and vaginal swabs collected during postmortem examination of seropositive animals in the centre. The B. abortus isolates and two B. melitensis previously isolated from vaginal swab of goats with history of abortion were whole genome sequenced (WGS). Subsequent phylogenetic analysis involved whole genome SNPs,core-genome SNPs, and in silico analysis of Multilocus Sequence Typing and Multiple Loci Variable Number of Tandem Repeats to characterise and determine global clustering of Ethiopian isolates. The result indicated that the B. abortus isolates from the outbreak were distinct and there were eight genotypes comprising single, double and triple locus variants circulating in the centre. Panel 1 and Panel 2A markers in MLVA-16 typing displayed no diversity among the neotypes suggesting that these are an early branching genotypes of the same strain. The core-genome phylogeny revealed that Ethiopian B. abortus form a distinct African clade branching basally with isolates previously described from Mozambique and Kenya. This clade was previously represented by only a small number of isolates, and thus the placement of Ethiopian B. abortus from the current study within this group substantially increases the representation of these basal B. abortus strains in genomic databases. On the other hand, B. melitensis isolates fall into a distinct African cluster with most isolates from Eastern African countries such as Somalia, Kenya, Eritrea, and Tanzania. The first isolation and molecular characterisation of circulating Brucella species in Ethiopia is a crucial step in planning and designing intervention strategies in the country. A coordinated One Health approach involving active involvement of human and animal health efforts to enhance public health and improve livestock productivity is recommended.