Department of Life Science, National Taiwan Normal University, Taipei, Taiwan.
Center for Diagnostics and Vaccine Development, Centers for Disease Control, Ministry of Health and Welfare, Taipei, Taiwan.
PLoS Negl Trop Dis. 2020 Jan 21;14(1):e0007519. doi: 10.1371/journal.pntd.0007519. eCollection 2020 Jan.
Ecological determinants of most emerging vector-borne diseases are understudied, particularly for neglected tropical disease. Moreover, although socioeconomic impacts can have significant downstream effects on human risks to vector-borne diseases via a change in land cover, particularly facilitating the invasion of exotic plants, related studies remains very scarce. Scrub typhus and spotted fever are neglected diseases emerging around the globe and are transmitted by chigger mites and ticks infective of Orientia tsutsugamushi and Rickettsia spp., respectively, with small mammals as the primary hosts of both vectors.
METHODOLOGY/PRINCIPAL FINDINGS: We investigated how invasions of the plant Leucaena leucocephala caused by widespread abandonment of farmlands driven by industrialization affected abundance of chiggers and ticks in Penghu Island, Taiwan. We determined ectoparasite abundance by trapping small mammals in three types of habitats (invasion site, agricultural field, human residential) every two months for a year. Based on ectoparasite burdens, invasion sites harbored more chiggers and ticks than the other two habitats. Furthermore, hosts maintained higher burdens of both vectors in early winter and burdens of chiggers were more stable across seasons in invasion sites, suggesting that sites with invasive plants could be a temporary refuge for both vectors and might help mitigate the negative influence of unfavorable climate. Infective rates of O. tsutsugamushi in chiggers and Rickettsia in ticks were also consistently not lower in invasion sites. Top soil temperature and relative humidity were similar across the three habitats, but invasion sites contained more of the rat Rattus losea, on which chiggers and ticks were more engorged than those from the most commonly trapped species (Suncus murinus shrew), indicating that abundance of the host R. losea instead of microclimate might better determine the abundance of both vectors.
CONCLUSIONS/SIGNIFICANCE: This study highlights an important but largely neglected issue that socioeconomic change can have unexpected consequences for human health induced particularly by invasive plants, which could become a hotspot for emerging infectious diseases but usually are very hard to be eradicated. In the future, a more comprehensive approach that integrates socio-economics, land use, exotic species, and human health should be considered to fully understand potential emergence of vector-borne diseases.
大多数新发的虫媒传染病的生态决定因素研究不足，尤其是被忽视的热带病。此外，尽管社会经济影响可能通过改变土地覆盖，特别是促进外来植物的入侵，对人类感染虫媒传染病的风险产生重大的下游影响，但相关研究仍然非常稀缺。恙虫病和斑疹热是全球新出现的被忽视的疾病，分别由恙螨和蜱虫传播，这些虫媒可感染东方立克次体和立克次体属，小型哺乳动物是两种虫媒的主要宿主。
方法/主要发现：我们研究了由于工业化导致的农田广泛废弃，进而引起植物银叶相思入侵，对台湾澎湖列岛恙螨和蜱虫丰度的影响。我们通过在三种生境（入侵地、农田、人类居住点）中每两个月用诱捕器捕获小型哺乳动物，每年进行两次，来确定外寄生虫的丰度。根据外寄生虫的负担，入侵地的恙螨和蜱虫数量多于其他两种生境。此外，在初冬，宿主身上的两种虫媒的负担更高，而且在入侵地，恙螨的负担在整个季节都更稳定，这表明有入侵植物的地方可能是两种虫媒的临时避难所，并可能有助于减轻不利气候的负面影响。在入侵地，恙螨感染的东方立克次体和蜱虫感染的立克次体的感染率也没有更低。三种生境的表土温度和相对湿度相似，但入侵地的老鼠数量更多，即褐家鼠，它们的恙螨和蜱虫比最常捕获的物种（臭鼩鼱）的恙螨和蜱虫更饱食，这表明宿主褐家鼠的数量而不是小气候可能更好地决定了两种虫媒的数量。
结论/意义：本研究强调了一个重要但在很大程度上被忽视的问题，即社会经济变化可能通过外来植物对人类健康产生意想不到的后果，特别是在入侵植物可能成为新发传染病热点但通常很难根除的情况下。在未来，应该考虑一种更全面的方法，将社会经济学、土地利用、外来物种和人类健康结合起来，以充分了解虫媒传染病的潜在发生。
