Association of Wolbachia with heartworm disease in cats and dogs

• Published in: Veterinary parasitology Vol. 170; no. 1; pp. 50 - 60
• Main Authors: Dingman, Patricia, Levy, Julie K., Kramer, Laura H., Johnson, Calvin M., Lappin, Michael R., Greiner, Ellis C., Courtney, Charles H., Tucker, Sylvia J., Morchon, Rodrigo
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 28-05-2010; Amsterdam; New York: Elsevier
• Subjects: Animals; Anti-Bacterial Agents; antibodies; Antibodies, Bacterial - blood; Antibodies, Helminth - blood; bacterial infections; cat diseases; Cat Diseases - drug therapy; Cat Diseases - immunology; Cat Diseases - microbiology; Cat Diseases - parasitology; Cats; Dirofilaria immitis; Dirofilaria immitis - immunology; Dirofilaria immitis - microbiology; dirofilariasis; Dirofilariasis - immunology; Dirofilariasis - parasitology; DNA, Bacterial - chemistry; DNA, Bacterial - genetics; dog diseases; Dog Diseases - drug therapy; Dog Diseases - immunology; Dog Diseases - microbiology; Dog Diseases - parasitology; Dogs; etiology; Heartworm disease; heartworm-associated respiratory disease; immunohistochemistry; Immunohistochemistry - veterinary; lesions (animal); Lung Diseases, Parasitic - drug therapy; Lung Diseases, Parasitic - immunology; Lung Diseases, Parasitic - microbiology; Lung Diseases, Parasitic - parasitology; Lung Diseases, Parasitic - veterinary; mixed infection; polymerase chain reaction; Polymerase Chain Reaction - veterinary; pulmonary artery; Pulmonary lesions; respiratory tract diseases; Statistics, Nonparametric; Wolbachia; Wolbachia - immunology; Wolbachia pipientis; Cats; Wolbachia; Heartworm disease; Pulmonary lesions; Dirofilaria immitis; Dogs
• ISSN: 0304-4017; 1873-2550
• DOI: 10.1016/j.vetpar.2010.01.037

Although the presence of adult
Dirofilaria immitis in the pulmonary arteries and its associated arteritis and thromboembolic disease can explain some of the manifestations of canine and feline heartworm disease, the cause of other findings remains unclear. Cats with
D. immitis antibodies but lacking adult parasites in the pulmonary arteries frequently develop histological lesions of the airways, resulting in a condition termed Heartworm-Associated Respiratory Disease. All
D. immitis parasites harbor
Wolbachia pipientis bacteria and
D. immitis-infected animals can have circulating
Wolbachia antibodies and pro-inflammatory
Wolbachia antigens (WSP) deposited in tissues. Little is known about the role that
Wolbachia plays in lung disease of animals naturally infected with
D. immitis. The purpose of this study was to determine the contribution of
Wolbachia to the pathogenesis of natural heartworm disease in cats and dogs. We hypothesized that animals having sufficient
Wolbachia burden to be detected in lung tissue by immunohistochemistry and/or polymerase chain reaction (PCR) would have more severe pulmonary disease than those with bacteria below the limits of detection. We further hypothesized that animals that were immunoreactive to pro-inflammatory WSP would have more severe pulmonary lesions than those that were seronegative for WSP antibodies. Blood and lung tissue samples were collected from cats and dogs representing three different
D. immitis infection statuses: heartworm-free, heartworm-exposed, heartworm-infected. There was a positive but weak correlation between the magnitude of
D. immitis antibody titers and WSP titers in cats (
r
=
0.57,
p
<
0.001) and in dogs (
r
=
0.39,
p
<
0.001). Pulmonary lesions were more common in HW-infected animals than in HW-free animals. Pulmonary arteriolar occlusion was more common in HW-infected cats (57%;
p
=
0.003) than in HW-infected dogs (17%). Although pulmonary lesions were most common in HW-infected animals, there was no clear additive effect when either
Wolbachia DNA/WSP was detected in lung tissue or when circulating
Wolbachia antibodies were detected. There were no significant differences in the magnitude of pulmonary lesion scores within each HW-infection status group regardless of whether
Wolbachia DNA/WSP or antibodies were detected. The relationship between
Wolbachia and lung pathology in heartworm-infected animals remains to be determined. The lack of clear evidence for a role of
Wolbachia in heartworm disease creates a dilemma for veterinarians treating animals in
D. immitis-endemic areas. Although the indiscriminant use of antibiotics should be avoided, many clinicians prescribe doxycycline based on the favorable responses observed in human filarial diseases and promising results from the first published studies of doxycycline use in
D. immitis-infected dogs.