Clinicopathologic observation in prepatent period of canine dirofilariasis

An experiment was carried out to clarify changes in dogs in the early stage of infection with Dirofilaria immitis. Eleven dogs free from this parasite were inoculated with mature larvae of the parasite. Clinical and pathological examinations were performed in them at regular intervals for 7 months after inoculation. The main pathological condition of dirofilariasis is located in the pulmonary artery. Changes in this artery were found to have been induced in those dogs by the parasitism of immature worm. Histopathologically, they began to be observed as endarteritis 5 months after inoculation. The endarterium was clearly coarsened and thickened one month later. The endarteritis was presumed to be one of the important factors to cause pulmonary hypertension which would lead to congestive heart failure. Furthermore, angiocardiography (ACG) revealed the presence of worms 5 months after inoculation. When changes in the intima of the pulmonary artery were observed 6 months and more after inoculation, they consisted of derangement of the dendritic structure, suspension of the blood circulation, and abnormal winding of blood vessels in the area supplied by the peripheral portion of the pulmonary artery. These results suggest that ACG may be of very high diagnostic significance in detecting pathological changes of dirofilariasis in the initial stage of infection early and exactly.