Abstract:
Background: Brucellosis is a disease of worldwide public health and economic importance. Successful control is
based on knowledge of epidemiology and strains present in an area. In developing countries, most investigations
are based on serological assays. This study aimed at investigating a dairy herd experiencing abortions in order to
establish within-herd seroprevalence to Brucella spp., identify, characterize Brucella strains by Multiple Loci Variable
Number of Tandem Repeats Analysis (MLVA-VNTR) and investigate possible spillover to other species.
Results: The within-herd seroprevalence in cattle (n = 200) was 48 % (95 % CI 41–55), using an indirect ELISA,
while the Rose Bengal Test (RBT) yielded lower prevalence (21.5 %; 95 % CI 16–27). Two sheep (n = 35) and one
goat (n = 50) were seropositive using ELISA while none of the dogs (n = 6) was positive with the RBT. Three
Brucella were isolated from an aborted fetus and associated membranes. Real time PCR (IS711), Bruce-ladder and
classical biotyping classified the isolates as B. abortus biovar 3. MLVA-VNTR revealed two different but closely
related genotypes. The isolates showed unique profiles, providing the first genotypic data from Tanzania. These
genotypes were not related to B. abortus biovar 3 reference strain Tulya originally isolated from a human patient in
Uganda in 1958, unlike the genotypes isolated and characterized recently in Kenya. High within-herd prevalence,
isolation of the pathogen and abortion confirm that B. abortus is circulating in this herd with cattle as reservoir hosts.
A low seroprevalence in sheep and goats suggests a spillover of B. abortus from cattle to small ruminants in the herd.
Conclusions: This is the first isolation and characterization of B. abortus biovar 3 from a dairy cow with abortion in
Tanzania. The origin of the Tanzanian genotypes remain elusive, although they seem to be related to genotypes found
in Europe, Turkey and China but not related to B. abortus biovar 3 reference strain or genotypes from Kenya.
Importantly, replacement heifers are commonly sourced from large farms like this to smallholder farmers, which
poses risk of spread of bacteria to other herds. B. abortus is a significant zoonotic risk and animal health problem
in this production system, therefore further studies on humans is recommended.
