Epidemiological status of brucellosis and its impact on abortions in humans and domestic ruminants in Kagera ecosystem of Tanzania.

Abstract

Brucellosis is a zoonotic disease of both public health and economic importance. Little is known about the local understanding of brucellosis by pastoralists as well as its status and impact in the Kagera region of Tanzania. Extended study was carried out to determine the epidemiological status of brucellosis and estimate its impact on pregnancy outcome in Kagera region, which is a part of the Kagera river basin ecosystem shared by Burundi, Rwanda, Uganda and Tanzania. Specifically, this study aimed to assess the knowledge, perception and practices related to brucellosis among pastoralists in Kagera region; to estimate the prevalence of brucellosis in humans, domestic ruminants in Kagera region; to determine the contribution of brucellosis to abortions in humans and domestic ruminants in Kagera region and to characterize the different Brucella species prevalent in humans and domestic ruminants in Kagera region. Firstly, a cross-sectional study was conducted in June 2017 to assess the knowledge, perception and practices on brucellosis among pastoralists of Kagera ecosystem, Tanzania, using qualitative methods. Focus group discussions were conducted with livestock farmers, administration leaders, religious representatives and youth and discussions with key informants were conducted, involving officials of livestock. wildlife and public health departments in each district. Using a content analysis with inductive and deductive methods, this study revealed low knowledge on causes, symptoms and mode of transmission of brucellosis by interviewees. Pastoralists perceived the interactions between humans, livestock and wildlife; also the movement of people and animals crossing borders, to be potential risks for introduction of brucellosis in their communities. Moreover, habits of drinking raw milk, assisting parturitions in animals without protective gears and absence of vaccination programs are practices which could increase the transmission of brucellosis in this area. Secondly, the magnitude of brucellosis and its associated risks factors in humans and domestic ruminants in this region wereestimated. The estimation of brucellosis seroprevalence was important for any action plan regarding the reduction of the socio-economic impact of the disease in the study area. Human sera were analyzed using Rapid Slide agglutination and Fluorescence Polarization Assay (FPA) tests, while animal sera were screened using Rose Bengal Plate (RBPT) and confirmed by the c-ELlSA test. Out of 156 patients with malaria-like symptoms screened for brucellosis, 7.7% (95% CI: 3.8-12.2%) had antibodies consisting 1.9 % (95% CI: 0.0-4.5%) and 5.8 % (95% Cl: 2.6-12.6%) for B. abortus and B. melitensis, respectively. At individual animal level, brucellosis was prevalent at 5.9% (95% CI: 4.0-8.6%), 2.5% (95% CI: 0.8-5.7%) and 0.5% (95% CI: 0.01-2.8%) in cattle (n=426), goats (n=206) and sheep (n=197), respectively. At herd level, brucellosis seroprevalence was 18.2% (95% CI: 12.0-25.8%) in cattle and 6.9% (95% Cl=2.2-15.3%) in small ruminants. In humans, brucellosis was associated with the assisting in parturition without wearing protective gears (OR= 5.6: p= 0.02). Seropositivity to Brucella was associated with bovine species (OR=3.5; p=0.01), specifically in herds of medium size with 50-200 animals (OR= 4.2, protective factor. Thirdly, a prospective cohort study involving pregnant women and gravid ruminants was conducted to understand the association of brucellosis with pregnancy outcome. The abortion rate was 11.8% and 12.3% in humans and in ruminants, respectively. (n=76) and 5% (95% CI: 3.1-8) in gravid ruminants (121 cattle, 125 goats and 111 sheep). Among abortive cases, 4 women (out of 9), 2 cows (out of 7), 2 goats (out of 26) and zero sheep (out of 11) were positive to brucellosis. Seropositivity for anti-BruceZ/a antibodies was likely similar in aborted and non-aborted cases in humans (p=0.08) and in ruminants (p=0.2). Seropositivity to Brucella was associated with a risk of exposure to brucellosis in Positivity to both RBPT and FPA tests was 21% (95% CI: 12.5-32) in pregnant women p= 0.01). The knowledge of brucellosis among pastoralists (OR=0.1; p=0.007) was a pregnant women (OR=19; 95% Cl: 1.8-203, p=0.01) also in gravid cow (OR=11; 95% Cl: 1.3-18, p=0.02). However, absence of malaria-like symptoms in pregnant women (OR=0.12; 95% CI: 0.0-1.2, p=0.07) and the good disposal of aborted materials in gravid ruminants (OR=0.2; 95% Cl: 0.0-1.1, p=0.06) were protective for Brucella infections. At population level, brucellosis was associated with abortions (Population attributable risk: PAR) at 3.5% in pregnant women and at 0.5% in gravid ruminants in the study area. Lastly, Brucella species were characterized using genomic DNA which was obtained from samples (of humans and domestic ruminants) positive to serology tests. Molecular-based methods including real-time PCR, PCR amplification of 16S rRNA genes and Sanger sequencing were used. Brucella spp. was detected in 47 out of 125 sera and milk samples using real-time PCR. Brucella species were detected in raw milk of cows and goats, which could be a possible route of transmission to humans. In addition, presence of Brucella in reproductive failures in the study area; despite the limited sample size. Twenty out of 47 samples showed amplification of 16S rRNA gene to PCR. Sequence analysis and blasting confirmed the presence of Brucella spp. in pastoral areas of Kagera region. Despite the lack of proof for an epidemiological relationship, in this study, all the clades with Tanzanian sequences connected from clade with sequences of B. melitensis, B. abortus and B. suis from USA, Sudan and Iran. However, the Brucella from Kagera were phylogenetically distinct from other species isolated in USA, New Zealand, Germany and Egypt. This was expected based on the distance between the geographical regions from which the data for the phylogeny reconstruction were obtained. This is the first study to report 16S rRNA gene sequencing of Brucella species in East and Central Africa. A livestock vaccination program re-inforced with a high index of Brucella diagnosis is needed to eradicate brucellosis in animals and minimize exposure to Brucella infections in humans in Kagera river basin sera from abortive woman supports the suspected contribution of brucellosis to ecosystem. A coordinated One Health approach is recommended and further studies are suggested to reveal further the status of brucellosis in Kagera ecosystem that will guide its control and prevention. The results from this study have a potential of contributing to the reduction of economic and reproductive burden of brucellosis among pastoral communities, the planning of joint cross-border collaboration in controlling brucellosis in East Africa Community and this promoting safety in animal trade and transactions.