T. W. SWERCZEK 
239 
Figure 2. — Higher magnification of a pulmonary ar- 
tery showing hyperplasia of the media, vacuolation 
of the myocytes, chronic endarteritis and periarteri- 
tis. H and E stain ; X 400. 
MHPA was found in all cats infected with A. 
abstrusus for 6 weeks or more. 
Group II, T. cati. Medial hyperplasia of the 
pulmonary arteries was a consistent finding in 
cats infected 8 weeks or more. At 3 weeks PI 
mild endothelial swelling and proliferation, sub- 
endothelial vacuolation, medial myocyte hyper- 
plasia, perivascular edema and periarteritis 
were observed. By 5 weeks PI, the tunica intima 
and media were thickened. The endothelial cells 
were hyperplastic and very irregular and the 
subendothelium contained fibroblasts, many eo- 
sinophil leukocytes and vacuoles. The internal 
elastic membrane was occasionally fragmented. 
Periarteritis was common and characterized by 
the presence of edema, plasma cells, lympho- 
cytes and many eosinophil leukocytes. The tun- 
ica media was very hyperplastic by 10 weeks PI 
and gradually increased to a maximum thick- 
ness at approximately 34 weeks PI, reaching a 
pronounced thickness of 45 to 50 cell layers (Fig- 
ures 3 and 4) . 
Endarteritis and periarteritis were less fre- 
quently observed in cats exposed for more than 
16 weeks. The lumens of the affected vessels ap- 
peared obliterated in some cases and the arter- 
ies were very tortuous. 
MHPA was found in all cats infected for 3 
weeks or more with T. cati. 
Figure 3. — Pulmonary artery from a cat infected with 
Toxocara cati for 52 weeks. Endarteritis and marked 
hyperplasia of the tunica media. H and E stain ; X 64. 
