Seroprevalence and characterization of Brucella SPP. isolated from humans and cattle in Southern and Western provinces of Zambia..
Mfune, Lindizyani, Ruth
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Brucellosis is one of the top seven neglected zoonoses endemic in livestock and humans in developing countries including Zambia. A cross-sectional study was conducted between May 2017 and August 2021 in Zambia in the Southern province in Choma, Monze and Namwala and in the Western province in Mongu and Senanga. The study aimed to investigate exposure to and characterise the circulating Brucella spp. in cattle and humans to gain insight into their public health importance. A total of 1,815 sera from 175 cattle herds were collected and screened against brucellosis. The Rose Bengal Test (RBT) and competitive Enzyme-Linked Immuno Assay (c-ELISA) were used in serial testing to detect antibodies against Brucella species. A total of 1,047 variable biological samples including ten hygroma fluid, 210 vaginal swabs, four foetal materials, 666 milk samples from cattle and 157 whole human blood samples, were cultured and analysed. Molecular analysis (16S rRNA PCR, Real-Time PCR, Multiplex Bruce Ladder PCR) was conducted to isolate, identify and characterize Brucella spp. The Brucella isolates were evaluated for susceptibility to six antimicrobials using the disk diffusion method, namely; rifampicin (5μg per disk), trimethoprim-sulfamethoxazole (23.75 μg), doxycycline (30 μg), tetracycline (30 μg) ciprofloxacin (5 μg), streptomycin (10 μg), gentamicin (10 μg) and chloramphenicol (30 μg). The breakpoints used have been established according to the 2020 Clinical Laboratory Standards Institute guidelines for slow-growing bacteria (Haemophilus spp.). The herd-level and individual animal anti-Brucella antibody seroprevalences were 32 per cent (CI 95%: 25.0-38.9) and 9.92 per cent (CI 95%: 8.5-11.2). The Western province had a higher herd-level seroprevalence (32.3%, CI 95%: 20.7-43.8). Five isolates (3 human blood and 2 cattle milk isolates) were identified to Brucella genus level using 16S rRNA PCR and characterised by 16S rRNA sequencing. A similarity search by blastn of the sequences (identity of 99%) identified them as Brucella spp and confirmed by Real-time PCR performed using IS711 and bcsp31 gene targets. On Bruce ladder Multiplex PCR, the Brucella strain had similar phenotypic characteristics as the Brucella vaccine strain S19. All isolates (3, 8 and 12) were resistant to trimethoprim-sulfamethoxazole, doxycycline, tetracycline and chloramphenicol but sensitive to rifampicin. All three isolates showed intermediate resistance to ciprofloxacin. The overall brucellosis seroprevalence rates at the individual animal and herd levels were 9.92 per cent and 32 per cent respectively. Brucella species are circulating in human and bovine milk in the Southern province of Zambia. Molecular typing of the isolated Brucella spp. DNA indicates that they belong to the Brucella abortus S19 vaccine strain. While vaccination is the traditional and recommended method for controlling brucellosis, the current study findings show that the S19 vaccine that we are using continues to be detected not only in animals and animal products but also in humans long after it has been used in animals underscores it is zoonotic transmission potential from cattle to humans which seems to be a public health problem.
The University of Zambia
- Veterinary Medicine