CIRAD, UMR TETIS, Sainte-Clotilde, Reunion Island, France.
TETIS, Univ Montpellier, AgroParisTech, CIRAD, CNRS, INRAE, Montpellier, France.
PLoS Negl Trop Dis. 2021 Feb 18;15(2):e0009029. doi: 10.1371/journal.pntd.0009029. eCollection 2021 Feb.
Murine typhus is a flea-borne zoonotic disease that has been recently reported on Reunion Island, an oceanic volcanic island located in the Indian Ocean. Five years of survey implemented by the regional public health services have highlighted a strong temporal and spatial structure of the disease in humans, with cases mainly reported during the humid season and restricted to the dry southern and western portions of the island. We explored the environmental component of this zoonosis in an attempt to decipher the drivers of disease transmission. To do so, we used data from a previously published study (599 small mammals and 175 Xenopsylla fleas from 29 sampling sites) in order to model the spatial distribution of rat fleas throughout the island. In addition, we carried out a longitudinal sampling of rats and their ectoparasites over a 12 months period in six study sites (564 rats and 496 Xenopsylla fleas) in order to model the temporal dynamics of flea infestation of rats. Generalized Linear Models and Support Vector Machine classifiers were developed to model the Xenopsylla Genus Flea Index (GFI) from climatic and environmental variables. Results showed that the spatial distribution and the temporal dynamics of fleas, estimated through the GFI variations, are both strongly controlled by abiotic factors: rainfall, temperature and land cover. The models allowed linking flea abundance trends with murine typhus incidence rates. Flea infestation in rats peaked at the end of the dry season, corresponding to hot and dry conditions, before dropping sharply. This peak of maximal flea abundance preceded the annual peak of human murine typhus cases by a few weeks. Altogether, presented data raise novel questions regarding the ecology of rat fleas while developed models contribute to the design of control measures adapted to each micro region of the island with the aim of lowering the incidence of flea-borne diseases.
鼠型斑疹伤寒是一种由跳蚤传播的人畜共患疾病，最近在留尼汪岛（位于印度洋的一个大洋火山岛）报告了这种疾病。地区公共卫生部门开展了五年的调查，突出了人类疾病的强烈时空结构，病例主要报告在雨季，并限于该岛干燥的南部和西部。我们探讨了这种动物传染病的环境因素，试图破译疾病传播的驱动因素。为此，我们使用了之前发表的一项研究（来自 29 个采样点的 599 只小型哺乳动物和 175 只印鼠客蚤）的数据，以模拟整个岛屿上的鼠蚤空间分布。此外，我们在六个研究地点（564 只老鼠和 496 只印鼠客蚤）进行了长达 12 个月的老鼠及其外寄生虫的纵向采样，以模拟老鼠的蚤寄生时间动态。我们开发了广义线性模型和支持向量机分类器，以从气候和环境变量中模拟印鼠客蚤属蚤指数（GFI）。结果表明，通过 GFI 变化估计的蚤的空间分布和时间动态都受到非生物因素的强烈控制：降雨量、温度和土地覆盖。这些模型允许将蚤丰度趋势与鼠型斑疹伤寒的发病率联系起来。老鼠身上的蚤寄生在旱季末期达到高峰，对应于炎热干燥的条件，然后急剧下降。这种最大蚤丰度的高峰比每年人类鼠型斑疹伤寒病例的高峰早几周。总之，所提出的数据提出了关于鼠蚤生态学的新问题，而开发的模型有助于为该岛的每个微区域设计适应的控制措施，以降低跳蚤传播疾病的发病率。
