Ecological and biological factors involved in the transmission ofEchinococcus multilocularisin the French Ardennes

In order to identify the respective importance of the ecological and biological factors involved in the transmission ofEchinococcus multilocularis, we estimated grassland vole intermediate host (Microtussp. andArvicola terrestris) population densities, in relation to the diet of the definitive host (red fox,Vulpes vulpes) and with the prevalence ofE. multilocularisin the fox population. The study was conducted in the Ardennes, north-eastern France, which is an area with a high incidence of alveolar echinococcosis. Surface index methods showed thatMicrotuswas the most abundant intermediate host in the area. Furthermore,Microtuswas present in one-third of the 144 faeces and 98 stomach content samples examined and represented more than two-thirds of the rodent occurrences. Red fox predation onMicrotuswas significantly correlated withMicrotusrelative abundance. In contrast, the relative abundance ofA. terrestriswas very low. This species, as well asClethrionomys glareolusandApodemussp., was little consumed.E. multilocularisprevalence in foxes was determined from carcasses and reached 53% (95% confidence interval 45–61%). Intensity of infection varied from 2 to 73,380 worms per fox, with 72% of the sampled worm burden harboured by 8% of the sampled foxes. The selected explanatory variables (sex, year, age class, health and nutritional condition, and season) failed to predict prevalence rate and worm burden. The high prevalence rate in foxes indicates the possibility of intenseE. multilocularistransmission, apart from periods, or in landscapes, favourable to large population outbreaks of grassland rodents.