952 
ANIMAL DISEASES 
Histoplasmosis 
Histoplasmosis in dogs^ is endemic in the 
same regions of the United States as in man. The 
respiratory tract is the principal portal of entry 
for the disease in the dog as well as in man. In 
many instances, the pulmonary disease is sub- 
clinical. Healed or healing pulmonary lesions 
are found at necropsy as multifocal firm nod- 
ules from one to ten millimeters in diameter 
(Figure 4). The granulomatous foci, elicited by 
the fungus Histoplasma capsulatum, are sur- 
rounded and replaced by fibrous connective tis- 
sue. Often the centers of the lesions are caseous 
and partially mineralized (Figure 5) . (It should 
be noted that tuberculous lesions in dogs, 
rarely, if ever, calcify) . The final nodular lesion 
can be detected clinically only by radiography 
(Figure 1). The hilar bronchial lymph nodes 
Figure 1. — Postmortem radiograph of an old dog's 
lungs. The dense areas (arrow) are irregular foci of 
fibrosis. The tiny white discrete flecks are foci of min- 
eralization that are representative of the density and 
distribution of healed lesions of histoplasmosis. 
pleural and subjacent parenchymal fibrosis can 
be found in dogs over 6 to 8 years of age (Fig- 
ures 1 and 2). 
Pneumoconiosis 
Dust pneumoconiosis in dogs has received lit- 
tle attention although the lesions are found reg- 
ularly in dogs housed outdoors. Dust macules 
were reported in the lungs of experimental dogs 
by Goyal and Gupta.^ The macules contained 
mainly silicates which were common air pollu- 
tants originating from a nearby desert area. 
In central Ohio, a form of pneumoconiosis 
caused by dust from clay soils occurs in dogs, 
especially in the larger working breeds that live 
in a rural environment. The lesions are dust 
macules containing illite, a silica-containing 
compound common to clay soils in Ohio. The 
gray macules range in size from 1 mm in diame- 
ter to microscopic clusters of a few dust-laden 
macrophages. Thin, needlelike, biref ringent spic- 
ules in the macules (Figure 3) are composed 
primarily of illite. 
Figure 2. — Photomicrograph of the lung from the 
same dog as Figure 1 illustrating interstitial fibrosis. 
Masson's trichrome stain x 155. 
