Infection of dogs with Echinococcus granulosus: causes and consequences in an hyperendemic area

Background: Tunisia is a hyper endemic country for human echinococcosis. The infection is transmitted via the eggs of Echinococcus granulosus which are passed in the faeces of the definitive canid host. Methods: This study evaluated the contamination rate of the dog faeces in different climatic conditions at eight different geographic regions throughout Tunisia. Dog faecal samples were collected from the soil and the Echinococcus eggs were identified using microscopic and molecular (Eg1121/1122 PCR, Egss1 PCR and Nad1 PCR-RFLP) tools. Results: The contamination index of dog faeces by E. granulosus eggs ranged from 8.3% to 41.3% depending on the region. Comparisons of the dog faecal contamination rate against human incidence found them to be independent. Neither human prevalence nor dog contamination index appeared to be related to climatic conditions or geographic characteristics. The genetic variability of E. granulosus samples was different within each region but was not related to geographic distance which is indicative of local divergent evolutions rather than isolation by distance. Conclusions: A high environmental dog contamination index does not necessarily correspond to high prevalence in humans as transmission is strongly linked to human behavior and hygiene.