Prevalence and characterization of brucellosis and tuberculosis in cattle and its zoonotic risk associated factors in Rwanda

Abstract

Bovine brucellosis (BB) and bovine tuberculosis (bTB) are endemic in Rwanda; however, little is known about the diseases. Before this study, there were only three serological studies on BB, two serological studies on human brucellosis, and two studies on bTB. The aims of this study were to determine with the following objectives: to determine the prevalence and characterize Brucella in cattle from six districts which included the wildlife-livestock-human interface (5 districts) and peri-urban area together with the zoonotic associated risk factors; to characterize Brucella spp., and other abortigenic pathogens in aborted tissues from cattle from selected districts in Rwanda; to assess the awareness and occupational exposure to brucellosis, bTB, and other zoonotic diseases among abattoir workers at the six slaughterhouses in Rwanda and; to characterize BB and bTB from tissue samples collected from slaughtered animals in Rwanda using culturing and molecular characterization. The BB prevalence was determined using Rose Bengal test (RBT) and indirect enzyme-linked immunosorbent assay (i-ELISA) in series and the animal-level seroprevalence was 7.4% (141/1907) in cattle from the six districts, 8.3% (141/1691) in cattle farmed at the wildlife-livestock-human interface (5 districts), and 0.0% (0/216) in the peri-urban areas (1 district). The herd-level seroprevalence of BB was 28.9% (61/212) in herds from the six districts and 30.9% (61/198) in herds from the wildlife-livestock-human interface (5 districts). Multivariate analysis showed that old age (≥5 years), cattle from districts bordering national parks, history of abortions, and replacement animals were significantly associated with brucellosis (p < 0.05). Low awareness of zoonotic brucellosis transmission, assisting calving without biosafety protection, drinking raw milk, and manual milking were each observed in more than 21.7% of cattle keepers whose herds were seropositive. Whole blood (n=118), milk (41), and vaginal swabs (n=51) samples from brucellosis seropositive (n=183) and seronegative (n=27) cattle were cultured and Brucella cultures were identified using the 16S-23S ribosomal interspacer region (ITS) PCR assay. The culture prevalence determined by the gold standard (cultures and ITS-PCR) was 16.7% (35/210) and AMOS-PCR assay identified mixed B. melitensis and B. abortus (n=12) isolates, B. melitensis (n=3), B. abortus (n=19) while Bruce-ladder PCR assay identified B. abortus RB51 vaccine strain (n=2) amongst the B. abortus and B. melitensis cultures. Aborting livestock samples (19 aborted tissues from isolated cases for cattle and 1 aborted tissue and 3 vaginal swabs from an abortion outbreak for goats) were investigated for brucellosis using culture and PCR assays. Two aborting cattle (2/19) were infected by B. melitensis (n=1), and B. abortus (n=1) while mixed B. abortus and B. melitensis were isolated from goats. The Brucella negative samples from cattle (n=17) where further characterize using a PCR abortion panel (Anaplasma phagocytophilum, Bovine Herpes Virus Type 4, Campylobacter fetus, Chlamydophila spp., Coxiella burnetti, Leptospira spp., Listeria monocytogenes, and Salmonella spp.). Campylobacter fetus (n=7), and Leptospira spp. (n=4) were identified including co-infections (n=2) of C. fetus and Leptospira spp. BB seroprevalence using serological tests (RBT and i-ELISA) in parallel was 2.9% (8/300) from slaughtered cattle at six abattoirs in Rwanda. The culture prevalence determined by the gold standard method (culture confirmed by Brucella specific ITS-PCR) was 5.6% (11/300). AMOS-PCR assay identified mixed B. abortus and B. melitensis (n=3), B. abortus (n=3), and B. melitensis (n=5) isolated from lymph nodes while Bruce-ladder PCR assay identified B. abortus and B. melitensis. The prevalence of bTB was 1.7% (5/300) and bTB was caused by M. bovis (n=4) and M. tuberculosis (n=1). Rifampicin-resistant (RR) M. tuberculosis (n=1) was recorded. The prevalence of non-tuberculous mycobacteria (NTM) was 12.0% (36/300).