Section for Veterinary Epidemiology, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland.
Institute of Parasitology, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland.
Parasit Vectors. 2017 Jan 11;10(1):21. doi: 10.1186/s13071-016-1951-1.
In Europe, the red fox (Vulpes vulpes) is the main definitive host of Echinococcus multilocularis, the aetiological agent of a severe disease in humans called alveolar echinococcosis. The distribution of this zoonotic parasite among the fox population is remarkably aggregated with few heavily infected animals harbouring much of the parasite burdens and being responsible for most of the environmental parasitic egg contamination. Important research questions explored were: (i) spatial differences in parasite infection pressure related to the level of urbanization; (ii) temporal differences in parasite infection pressure in relation to time of the year; (iii) is herd immunity or an age-dependent infection pressure responsible for the observed parasite abundance; (iv) assuming E. multilocularis infection is a clumped process, how many parasites results from a regular infection insult.
By developing and comparing different transmission models we characterised the spatio-temporal variation of the infection pressure, in terms of numbers of parasites that foxes acquired after exposure per unit time, in foxes in Zurich (Switzerland). These included the variations in infection pressure with age of fox and season and the possible regulating effect of herd immunity on parasite abundance.
The model fitting best to the observed data supported the existence of spatial and seasonal differences in infection pressure and the absence of parasite-induced host immunity. The periodic infection pressure had different amplitudes across urbanization zones with higher peaks during autumn and winter. In addition, the model indicated the existence of variations in infection pressure among age groups in foxes from the periurban zone.
These heterogeneities in infection exposure have strong implications for the implementation of targeted control interventions to lower the intensity of environmental contamination with parasite eggs and, ultimately, the infection risk to humans.
在欧洲，红狐（ Vulpes vulpes ）是细粒棘球绦虫（ Echinococcus multilocularis ）的主要终末宿主，细粒棘球绦虫是一种严重的人类疾病——泡型包虫病的病原体。这种人畜共患寄生虫在狐狸种群中的分布极为聚集，少数受感染严重的动物携带了大部分寄生虫，并导致了大部分环境中寄生虫卵的污染。本研究探索了以下几个重要问题：（i）与城市化程度相关的寄生虫感染压力的空间差异；（ii）与一年中时间相关的寄生虫感染压力的时间差异；（iii）是群体免疫还是年龄相关的感染压力导致了观察到的寄生虫丰度；（iv）假设细粒棘球蚴感染是一种聚集过程，那么每次常规感染会导致多少寄生虫。
通过开发和比较不同的传播模型，我们描述了感染压力的时空变化，即狐狸在单位时间内获得的寄生虫数量，这些模型包括了感染压力随狐狸年龄和季节的变化，以及群体免疫对寄生虫丰度的可能调节作用。
最符合观察数据的模型支持感染压力存在空间和季节性差异，并且不存在寄生虫诱导的宿主免疫。周期性的感染压力在不同的城市化区域具有不同的幅度，在秋季和冬季达到高峰。此外，该模型还表明，在城市周边地区的狐狸中，感染压力存在年龄组间的变化。
这些感染暴露的异质性对实施有针对性的控制干预措施具有重要意义，可以降低环境中寄生虫卵的污染强度，最终降低人类的感染风险。
