Browsing by Author "Nyarobi, James"

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    Inter-epidemic Rift Valley fever virus infection incidence and risks for zoonotic spillover in northern Tanzania
    (PLOS, 2022-10-28) Ngonzi, Amos; Glanville, William; Nyarobi, James; Kibona, Tito; Halliday, Jo; Thomas, Kate; Allan, Kathryn; Johnson, Paul; Davis, Alicia; Lankester, Felix; Claxton, John; Rosta, Melinda; Carter, Ryan; Jong, Rosanne; Rubach, Matthew; Crump, John; Mmbaga, Blandina; Nyasebwa, Obed; Swai, Emanuel; Willett, Brian; Cleaveland, Sarah
    Rift Valley fever virus (RVFV) is a mosquito-borne pathogen that has caused epidemics involving people and animals across Africa and the Arabian Peninsula. A number of studies have found evidence for the circulation of RVFV among livestock between these epidemics but the population-level incidence of infection during this inter-epidemic period (IEP) is rarely reported. General force of infection (FOI) models were applied to age-adjusted cross-sectional serological data to reconstruct the annual FOI and population-level incidence of RVFV infection among cattle, goats, and sheep in northern Tanzania from 2009 through 2015, a period without reported Rift Valley fever (RVF) cases in people or animals. To evaluate the potential for zoonotic RVFV spillover during this period, the relationship between village-level livestock RVFV FOI and human RVFV seropositivity was quantified using multi-level logistic regression. The predicted average annual incidence was 72 (95% Credible Interval [CrI] 63, 81) RVFV infections per 10,000 animals and 96 (95% CrI 81, 113), 79 (95% CrI 62, 98), and 39 (95% CrI 28, 52) per 10,000 cattle, sheep, and goats, respectively. There was variation in transmission intensity between study villages, with the highest estimated village-level FOI 2.49% (95% CrI 1.89, 3.23) and the lowest 0.12% (95% CrI 0.02, 0.43). The human RVFV seroprevalence was 8.2% (95% Confidence Interval 6.2, 10.9). Human seropositivity was strongly associated with the village-level FOI in livestock, with the odds of seropositivity in an individual person increasing by around 1.2 times (95% CrI 1.1, 1.3) for each additional annual RVFV seroconversion per 1,000 animals. A history of raw milk consumption was also positively associated with human seropositivity. RVFV has circulated at apparently low levels among livestock in northern Tanzania in the period since the last reported epidemic. Although our data do not allow us to confirm human RVFV infections during the IEP, a strong association between human seropositivity and the FOI in cattle, goats, and sheep supports the hypothesis that RVFV circulation among livestock during the IEP poses a risk for undetected zoonotic spillover in northern Tanzania. We provide further evidence for the likely role of raw milk consumption in RVFV transmission from animals to people.
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    Prospective cohort study reveals unexpected aetiologies of livestock abortion in northern Tanzania
    (Springer Nature Limited, 2022-07-08) Thomas, Kate; Kibona, Tito; Claxton, John; de Glanville, William; Lankester, Felix; Amani, Nelson; Buza, Joram; Carter, Ryan; Chapman, Gail; Crump, John; Dagleish, Mark; Halliday, Jo; Hamilton, Clare; Innes, Elisabeth; Katzer, Frank; Livingstone, Morag; Longbottom, David; Millins, Caroline; Mmbaga, Blandina; Mosha, Victor; Nyarobi, James; Nyasebwa, Obed; Russell, George; Sanka, Paul; Semango, George; Wheelhouse, Nick; Willett, Brian; Cleaveland, Sarah; Allan, Kathryn
    Livestock abortion is an important cause of productivity losses worldwide and many infectious causes of abortion are zoonotic pathogens that impact on human health. Little is known about the relative importance of infectious causes of livestock abortion in Africa, including in subsistence farming communities that are critically dependent on livestock for food, income, and wellbeing. We conducted a prospective cohort study of livestock abortion, supported by cross-sectional serosurveillance, to determine aetiologies of livestock abortions in livestock in Tanzania. This approach generated several important findings including detection of a Rift Valley fever virus outbreak in cattle; high prevalence of C. burnetii infection in livestock; and the first report of Neospora caninum, Toxoplasma gondii, and pestiviruses associated with livestock abortion in Tanzania. Our approach provides a model for abortion surveillance in resource-limited settings. Our findings add substantially to current knowledge in sub-Saharan Africa, providing important evidence from which to prioritise disease interventions.