Molecular epidemiology of Brucella species in mixed livestock-human ecosystems in Kenya

Abstract

Brucellosis, caused by several species of the genus Brucella, is a zoonotic disease that affects humans and animal species worldwide. Information on the Brucella species circulating in different hosts in Kenya is largely unknown, thus limiting the adoption of targeted control strategies. This study was conducted in multi-host livestock populations in Kenya to detect the circulating Brucella species and assess evidence of host–pathogen associations. Serum samples were collected from 228 cattle, 162 goats, 158 sheep, 49 camels, and 257 humans from Narok and Marsabit counties in Kenya. Information on age, location and history of abortion or retained placenta were obtained for sampled livestock. Data on age, gender and location of residence were also collected for human participants. All samples were tested using genus level real-time PCR assays with primers specific for IS711 and bcsp31 targets for the detection of Brucella. All genus positive samples (positive for both targets) were further tested with a speciation assay for AlkB and BMEI1162 targets, specific for B. abortus and B. melitensis, respectively. Samples with adequate quantities aggregating to 577 were also tested with the Rose Bengal Test (RBT). A total of 199 (33.3%) livestock and 99 (38.5%) human samples tested positive for genus Brucella. Animal Brucella PCR positive status was positively predicted by RBT positive results (OR = 8.3, 95% CI 4.0–17.1). Humans aged 21–40 years had higher odds (OR = 2.8, 95% CI 1.2–6.6) of being Brucella PCR positive compared to the other age categories. The data on detection of different Brucella species indicates that B. abortus was detected more often in cattle (OR = 2.3, 95% CI 1.1–4.6) and camels (OR = 2.9, 95% CI 1.3–6.3), while B. melitensis was detected more in sheep (OR = 3.6, 95% CI 2.0–6.7) and goats (OR = 1.7, 95% CI 1.0–3.1). Both B. abortus and B. melitensis DNA were detected in humans and in multiple livestock host species, suggesting cross-transmission of these species among the different hosts. The detection of these two zoonotic Brucella species in humans further underpins the importance of One Health prevention strategies that target multiple host species, especially in the multi-host livestock populations.

Evidence of co-exposure with Brucella spp, Coxiella burnetii, and Rift Valley fever virus among various species of wildlife in Kenya

“…In addition, scavenging of contaminated placentas and weak offspring by predators, could be an additional risk factor for environmental transmission through mechanical dispersal for this pathogen. Other studies have shown the positivity rate of Brucella was similar for cattle (31.8%) and human (40.8%) in the same region, where there are intense wildlife and livestock interaction [ 26 , 34 ]. This highlights the interaction between wildlife, livestock, and humans in Brucella disease ecology.…”

“…burnetii differed significantly, depending on the study locations, corroborating with reports of clustering of Brucella spp , C . burnetii and cases of other infectious diseases in domesticated animals [ 26 , 34 ]. However, a statistical association between location and animal species with exposure levels to RVFV antibodies was not found, contrary to previous reports [ 36 , 37 ].…”

“…Nonetheless, the molecular findings of Brucella melitensis DNA in buffalo and giraffe further strengthen the evidence that wildlife harbors the pathogens and may have active infections that could be transmissible to susceptible hosts, especially humans, given that B . melitensis is a major cause of bloodstream infections and febrile illness in pastoral communities in eastern Africa [ 26 , 46 ].…”

“…The PCR amplifications were done using 2x Luna Universal Probe qPCR master mix (New England BioLabs, MA, USA), in a 20 μl reaction volume as previously described [ 26 ]. Amplification was performed on QuantStudio 5 Real-time PCR System (Life Technologies Inc.) with the following conditions: Initial DNA denaturation at 95°C for 1 min, followed by 42 cycles of denaturation at 95°C for 15 secs and 1 min of annealing/amplification at 57°C.…”

Prevalence of brucellosis in livestock keepers and domestic ruminants in Baringo County, Kenya

“…from one livestock host to the other, which occur PLOS GLOBAL PUBLIC HEALTH in different settings. In addition, the high prevalence noted in Marsabit County could be attributed to congregation of animals around communal watering points, keeping of mixed herds, and sharing of grazing sites that have been previously reported to increase chances of brucellosis transmission leading to the high prevalence in such regions [33]. We were also interested in establishing the sero-prevalence of brucellosis in cattle, sheep, goat and camels in the two sub-counties of Baringo County.…”