Frequency distributions of Echinococcus granulosus and other helminths in stray dogs in Tunisia

The intestinal helminths infecting stray dogs were investigated in the Testour and Bouzid regions of Tunisia. Overall, 21% of the dogs necropsied were found to be infected with Echinococcus granulosus. The prevalence among the animals from Testour (27.0%) was significantly higher than that in the dogs from Bouzid (6.9%). Although the prevalence of this species in the dog populations did give a significant fit to the age-prevalence models reported earlier, the best fit was not consistent with the known biological parameters of the parasite. The frequency distribution of E. granulosus was highly aggregated, with a mean abundance of infection of 538 parasites/host and a mean intensity in infected animals of 2534 parasites/ host. Several Taenia species were also found in the dogs, but none of these showed evidence of an aggregated distribution and the frequency distribution of each fitted a Poisson distribution, which is unusual for naturally acquired infections. All the other cestode species and the nematode species encountered had aggregated distributions in the dogs. As there was relatively little correlation between the worm burdens of the different parasite species in the dogs, individual dogs may not be generally susceptible or resistant to intestinal helminths of several species.