Woolsey Ian David, Webster P, Thamsborg S, Schnyder Manuela, Monrad Jesper, Kapel C M O
Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark.
Parasitology and Aquatic Diseases, Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark.
Int J Parasitol Parasites Wildl. 2017 Jun 24;6(3):139-145. doi: 10.1016/j.ijppaw.2017.06.005. eCollection 2017 Dec.
The French heartworm is found in European red fox () and dog populations, where it appears to be spreading geographically. Once introduced into new areas, it establishes in local fox populations, typically to over 50% prevalence in a few years. High susceptibility and constant excretion of first stage larvae (L1) by the definitive hosts are prerequisites for sustaining high parasite biomass in a particular habitat. The present study explores the hypothesis that repeated ingestion of gastropods in nature will result in accumulation of adult worms and elevated excretion of L1 in feces. Experimentally infected foxes were subsequently inoculated via stomach tube once (9 weeks post initial inoculation) or twice (9 and 13 weeks post inoculation (wpi)) with 100 third stage larvae (L3) previously isolated from aquatic snails infected with L1 from a naturally infected dog. Despite large variation in fecal larval excretion for the individual animals within the groups, excretion of L1 was significantly higher in foxes twice inoculated as compared to foxes inoculated only once. With an outlier in the once inoculated group removed, excretion became significantly higher in the three times inoculated group. Establishment of adult worms varied and only a trend to higher worm burdens was found in the group of foxes inoculated three times. However, this became significant with the same single outlier removed. Overall, it appears that protective immunity to does not appear to occur in with animals exhibiting high infection intensities without obvious clinical signs. The increasing larval excretion in foxes being repeatedly exposed to L3 support the hypothesis that foxes under natural conditions may repeatedly ingest infected gastropods and remain a source of environmental contamination for several months, potentially contributing to the establishment of endemic foci through increasing L1 excretion.
法国心丝虫存在于欧洲赤狐（）和犬类种群中，且似乎正在地理上扩散。一旦引入新区域，它会在当地狐类种群中定殖，通常在几年内患病率超过50%。终末宿主的高易感性和持续排泄第一期幼虫（L1）是在特定栖息地维持高寄生虫生物量的先决条件。本研究探讨了这样一个假设，即自然界中狐反复摄食腹足纲动物会导致成虫积累以及粪便中L1排泄量增加。随后，对实验感染的狐狸通过胃管接种一次（初次接种后9周）或两次（接种后9周和13周（wpi）），接种100条先前从感染了来自自然感染犬的L1的水生蜗牛中分离出的第三期幼虫（L3）。尽管各组内个体动物的粪便幼虫排泄量差异很大，但与仅接种一次的狐狸相比，接种两次的狐狸L1排泄量显著更高。去除单次接种组中的一个异常值后，三次接种组的排泄量变得显著更高。成虫的定殖情况各不相同，在三次接种的狐狸组中仅发现有虫负荷增加的趋势。然而，去除同一个单一异常值后，这一趋势变得显著。总体而言，似乎在狐狸中未出现针对法国心丝虫的保护性免疫，动物表现出高感染强度却无明显临床症状。反复接触法国心丝虫L3的狐狸幼虫排泄量增加，支持了这样一个假设，即自然条件下的狐狸可能反复摄食受感染的腹足纲动物，并在数月内一直是环境污染源，可能通过增加L1排泄促成地方病疫源地的形成。
