Objective—To determine the prevalence and severity
of pulmonary arterial lesions in cats seropositive for
heartworms (Dirofilaria immitis) but lacking adult
heartworms in the heart and lungs during necropsy.
Animals—630 adult cats from an animal control shelter
Procedure—Cats were tested for adult heartworms
in the heart and pulmonary arteries and antibody
against heartworms in the serum. Histologic examination
was conducted on the right caudal lung lobe of
24 heartworm- and antibody-positive cats; 24 heartworm-negative and antibody-positive cats; and 24
heartworm-, antibody-, and antigen-negative cats.
Wall areas of 10 small to medium-sized pulmonary
arteries of each cat were measured and expressed as
a proportion of total cross-sectional area.
Results—Heartworm infection or seropositive status
was significantly and strongly associated with severity
of medial hypertrophy of pulmonary arterial walls.
Heartworm- and antibody-positive cats and heartworm-negative and antibody-positive cats had a significant
increase in wall thickness, compared with
wall thickness for heartworm- and antibody-negative
cats. Heartworm- and antibody-positive cats had the
most severe hypertrophy. The proportion with occlusive
medial hypertrophy was significantly higher in
heartworm- and antibody-positive cats (19/24 [79%])
and heartworm-negative and antibody-positive cats
(12/24 [50%]), compared with heartworm- and antibody-negative cats (3/24 [13%]).
Conclusions and Clinical Relevance—Cats with
serologic evidence of exposure to heartworms,
including those without adult heartworms in the lungs
and heart, have a greater prevalence of pulmonary
arterial lesions than heartworm-negative cats without
serologic evidence of exposure. Additional studies are
needed to define the pathogenesis, specificity, and
clinical importance of these lesions. (Am J Vet Res
Objective—To compare heartworm serum antibody
(Ab) and antigen (Ag) test results, using commercial
laboratories and in-house heartworm test kits, with
necropsy findings in a population of shelter cats.
Animals—330 cats at an animal shelter.
Procedure—Between March and June 1998, 30 ml
of blood was collected from the cranial and caudal
venae cavae of 330 cats that were euthanatized at a
local animal shelter. Results of heartworm Ab and
Ag serologic tests for heartworm infection were
compared with necropsy findings in this population
of cats, using commercial laboratories and in-house
test kits to measure serum Ab and Ag concentrations.
Results—On necropsy, adult Dirofilaria immitis were
found in 19 of 330 (5.8%) cats. Combining results
from serum Ab and Ag tests achieved higher sensitivities
than using serum Ab and Ag test results alone
(ie, maximum sensitivities of 100% vs 89.5%, respectively),
whereas use of serum Ag and Ab test results
alone achieved higher specificities compared with the
use of a combination of serum Ab and Ag results (ie,
maximum specificities of 99.4% vs 92.9%, respectively).
Conclusions and Clinical Relevance—On the basis
of our findings, if a cat has clinical signs that suggest
heartworm disease despite a negative heartworm
serum Ab test result, an alternative heartworm Ab
test, a heartworm Ag test, thoracic radiography, or
two-dimensional echocardiography should be performed.
(J Am Vet Med Assoc 2000;216:693–700)