R. A. GRIESEMER AND R. L. FARRELL 
953 
Figure 3. — Peribronchiolar dust pneumonoconiosis in 
a dog housed outdoors. The crystals of illite appear 
white in polarized light x 125. 
may be enlarged and affected with the same type 
I of lesion. Granulomatous hilar masses may com- 
'i press the main bronchus or bronchi producing a 
chronic, dry, non-productive cough in an other- 
wise clinically healthy dog. 
Dirofilariasis 
Personal communications with personnel in 
laboratory animal facilities indicate that the 
I majority of dogs in the southern states and 
many of those in the eastern coastal states are 
infected with Dirofilaria immitis, the dog heart- 
worm. Although there is a low prevalence in 
northern and western states, the increasing mo- 
bility of the dog population makes it mandatory 
that all random-source dogs be screened for evi- 
dence of infection. 
Present knowledge of the disease is reviewed 
by Pacheco.® Subclinical infections are asso- 
ciated with chronic pulmonary arteritis (Figure 
6) characterized by villous intimal proliferation, 
medial hypertrophy, and arteriosclerosis.'^'^ Fre- 
quently pulmonary endarteritis and obstructive 
fibrosis develops around live adult worms. The 
severity of the disease is related in part to the 
number of parasites, but much variation occurs 
so that extensive pulmonary arteritis may occur 
with minimal numbers of circulating micro- 
filariae and without congestive heart failure. 
Infrequently massive microfilariasis of the lung 
is associated with tiny granulomas, presumably 
an inflammatory response to dead microfilariae. 
Other Infectious Diseases 
Young dogs or dogs that are immunosup- 
pressed or severely stressed may develop lesions 
of infectious diseases during the experiment. 
They include the interalveolar proliferative 
pneumonia of canine distemper,^ the focal fibri- 
nonecrosis of toxoplasmosis,^*' and the trachei- 
tis and bronchitis associated with herpesvirus, 
adenovirus, or parainfluenza virus.^^ Space 
limitations prevent discussion of visceral larva 
migrans (Toxocara canis) , blastomycosis, cocci- 
dioidomycosis, tuberculosis, paragonamiasis, 
verminous tracheitis (Oslerus osleri), and lym- 
phoma of the lung. 
Figure 4. — Multiple granulomas caused by Histo- 
plasma capsulatum in the lung of a dog that had a 
chronic cough. 
