Pulmonary changes associated with dead filariae (Dirofilaria immitis) and concurrent antigenic exposure in dogs

Initially, a group of 5 dogs had their left pulmonary artery ligated 7 months prior to the insertion of filariae (Dirofilaria immitis). A second group of 3 dogs was used as controls for the various components of the experiment. Antigen (D. immitis) was injected subcutaneously on 3 occasions and necropsy was performed 5 weeks after insertion of filariae. These results were then compared to those from the control dogs. With exposure to antigen, severe pulmonary arterial and parenchymal disease was produced in association with the insertion of dead D. immitis filariae into the pulmonary artery. In the dogs receiving antigen, the arterial and peri-arterial pathology was generally more intense and at a more advanced stage of organization than in the control animals. Interstitial pneumonitis was also more prominent in the antigen-stimulated dogs. The advanced nature of the reaction was also reflected in the skin histology of the injection sites. The pathology was similar to that reported for natural dirofilariasis and it appears that most of the pathology of dirofilariasis is associated with reactions to dead filariae or filarial by-products and concurrent antigenic experience.