Preliminary investigation of the life history of Filaroides hirthi Georgi and Anderson, 1975.

Filaroides hirthi lungworm infection increased as a function of age among 47, 9 to 32 week old Beagle pups at a commercial breeding establishment. Probit analysis of these data yielded an estimate of 50% infection was by age 17.4 +/- 3.7 weeks. This parasite and/or its associated lesions remained in at least 40% of infected Beagles at least 10 months after exposure to infection had ceased. Reinfection rendered improbable by the nature of the new environment, a laboratory animal colony. Repeated efforts have failed to demonstrate by the Baermann technique eggs or larvae of this parasite in the feces, bronchial mucus, or intact lung tissue of infected Beagles. All efforts to identify an intermediate or alternate definitive hosts have likewise proved unavailing. Piperazines, dichlorvos, thiabendazole, dithiazanine iodide, and levamisole appear to be without effect on the proportion of Beagles infected. The diet, which contained uncooked meat, was fed in a controlled experiment to 10 Beagles from an uninfected source without producing a single case of F. hirthi infection. Life cycles of other members of the superfamily Metastrongyloidea and possible explanations for the non-patency of F. hirthi infection are discussed.