Fig. 21

a (left) and b (right). . Histopathology of feline lung with H & E stain or alpha-smooth muscle actin stain after L3 D. immitis infection. The cats in Group A were generally normal. a (left), b (right)] with occasional isolated area of infiltration of smooth muscle [Fig. 22 a (left), B (right)], especially in small arterioles. Cats in Group B had severe inflammation around airways [Fig. 23 a (left), b (right)] and interstitial and pulmonary arterial proliferation of smooth muscle (Figs. 22–24) not directly associated with bronchioles or arterioles. The pulmonary arterial smooth muscle proliferation was consistent with heartworm disease. Although all cats in Group A did not consistently have lung pathology (Fig. 25 a, left), in some lobes isolated areas of myofibrocyte proliferation were observed (Fig. 25 b, right). Cats in Group C had disease similar to Group B cats except that the endothelial proliferation in pulmonary arteries (Figs. 26, 27) was noted in isolated major vessels and the airway and interstitial disease was more consistent that observed in Group B cats