238 
PULMONARY MODELS 
monary tissues as part of their life cycle may 
induce MHPA as A. abstrusus. 
MATERIALS AND METHODS 
Young cats were used to help insure against 
having the natural lesion and were either ob- 
tained as kittens or were raised in the labora- 
tory. They were caged on wire to prevent inges- 
tion of parasites and were 10 to 12 weeks of age 
at the start of the experiment. They were di- 
vided into 6 groups and were infected and se- 
quentially killed to study the development of 
MHPA. 
Group L Fifty-nine cats were infected with 
1,000 infective A. abstrusus larvae and were in- 
fected for 1 to 137 weeks. 
Group II. Thirty-three cats were infected 
with 2,000 T. cati infective eggs/week. They 
were killed after 2 to 74 weeks of infection. 
Group III. Fourteen cats were infected with 
4,000 infective T. canis eggs/week. They were 
killed after 3 to 18 weeks of infection. 
Group IV. Twelve cats were infected with 
4,000 Ascaris suum infective eggs/week and 
were killed after 3 to 32 weeks of infection. 
Group V. Nine cats were infected with 4,000 
Toxascaris leonina infective eggs/week and 
were killed after 9 weeks of infection. 
Group VI. Thirty-one cats were raised the 
same as the experimental groups but were not 
exposed to parasites. 
Lungs were fixed in 10% buffered formalin. 
Tissues were embedded in paraffin, cut at 6 mi- 
crons and stained with hematoxylin and eosin. 
The following special stains were performed on 
lung sections : VerhoefF's elastic stain, Gomori's 
trichrome, oil-red-0, and periodic acid-schiff- 
reaction. 
RESULTS 
Group I, Aelurostrongylus abstrusus. The 
first arterial lesions appeared at 6 weeks post- 
infection (PI). Endothelial swelling, suben- 
dothelial vacuolation and mild myocyte hyper- 
plasia were the first changes observed. The 
tunica media increased in thickness by 8 weeks 
PI and was very thick by 12 to 14 weeks and ap- 
peared to reach a maximum thickness at 40 
weeks PI (Figures 1 and 2). Occasionally, mi- 
totic cells were present and many myocytes con- 
tained vacuoles with droplets that stained pink 
with H & E and were negative with the PAS re- 
action and oil-red-0 stain. Medial myocytes 
were commonly orientated irregularly and some 
occurred in fascicles. The affected arteries were 
very tortuous. The lumens of the vessels ap- 
peared almost occluded in some arteries. 
Endarteritis was mild in most cases and was 
characterized by endothelial proliferation, sub- 
endothelial vacuolation along with a scattering 
of eosinophil leukocytes. The internal elastic 
membrane was fragmented in some vessels. 
1 
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w-k? 
^ .t^'T 
Figure 1.— Lung section from a cat infected with 
Aelurostrongylus abstrusus for 118 weeks. A pul- 
monary artery with a thickened media and mild per- 
iarteritis. H. and E stain; x 160. 
