DIROFILARIA-IMMITIS - EXPERIMENTAL-INFECTION OF RABBITS WITH IMMATURE5TH-STAGE WORMS

To establish an animal model for human pulmonary dirofilariasis, we ex perimentally infected nine rabbits with immature fifth-stage worms of Dirofilaria immitis. The rabbits were infected by subcutaneous transpl antation with various numbers of immature worms collected from 110- an d 120-day-old infections of dogs. Four of seven rabbits infected with up to four larvae possessed encapsulated worms in the lungs at 196 or 308 days posttransplantation. Two rabbits transplanted with eight worm s died of pulmonary hemorrhagic infarction 18 and 28 days post-transpl antation. Marked histopathologic changes were observed in the lungs at the site of degenerating worms, which were encapsulated by a fibrous wall. Severe to mild infiltrations with eosinophils, heterophils, lymp hocytes, plasma cells, and histiocytes were found in granulomas and th eir surrounding areas, The findings in these rabbits resemble those re ported for human cases of pulmonary dirofilariasis.