School of Biodiversity, One Health, and Veterinary Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom.
University of Global Health Equity, Kigali, Rwanda.
PLoS Negl Trop Dis. 2022 Oct 28;16(10):e0010871. doi: 10.1371/journal.pntd.0010871. eCollection 2022 Oct.
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.
裂谷热病毒（RVFV）是一种经蚊子传播的病原体，曾在非洲和阿拉伯半岛引发过涉及人和动物的疫情。许多研究已经发现，在这些疫情之间，牲畜中存在 RVFV 的循环，但很少有报告描述这一疫情间（IEP）的感染人群发病率。本研究应用一般感染力（FOI）模型，对年龄调整的横断血清学数据进行分析，以重建 2009 年至 2015 年期间坦桑尼亚北部牛、山羊和绵羊的年度 FOI 和 RVFV 感染人群发病率，该期间无报告的人间或动物间裂谷热（RVF）病例。为了评估该期间可能发生的 RVFV 人间溢出，我们使用多水平逻辑回归来量化村一级牲畜 RVFV FOI 与人类 RVFV 血清阳性之间的关系。预测平均年发病率为每 10000 只动物 72 例（95%可信区间[CrI] 63，81），每 10000 头牛、绵羊和山羊分别为 96 例（95% CrI 81，113）、79 例（95% CrI 62，98）和 39 例（95% CrI 28，52）。研究村庄之间的传播强度存在差异，最高估计的村庄级 FOI 为 2.49%（95% CrI 1.89，3.23），最低为 0.12%（95% CrI 0.02，0.43）。人类 RVFV 血清阳性率为 8.2%（95%置信区间 6.2，10.9）。人类 RVFV 血清阳性与牲畜的村一级 FOI 密切相关，个体血清阳性的几率每增加 1000 只动物每年 1 例 RVFV 血清转换，就会增加约 1.2 倍（95% CrI 1.1，1.3）。饮用生奶的历史也与人类 RVFV 血清阳性呈正相关。自上一次报告的疫情以来，坦桑尼亚北部牲畜中的 RVFV 一直以低水平循环。尽管我们的数据不能确定 IEP 期间是否有人间 RVFV 感染，但人类血清阳性与牛、山羊和绵羊的 FOI 之间的强烈关联支持这样一种假设，即在 IEP 期间牲畜中的 RVFV 循环对坦桑尼亚北部未被发现的人畜共患病溢出构成风险。我们进一步证明了饮用生奶可能在 RVFV 从动物传播到人类方面发挥了作用。
