Prevalence of Dirofilaria immitis infection among shelter cats

Objective-To determine prevalence of Dirofilaria immitis infection among sh elter cats. Design-Cross-sectional study. Animals-239 cats euthanatized at an animal sh elter in southeastern Michigan. Procedure-A gross necropsy focusing on the thoracic cavity, heart, lungs, a nd pulmonary vessels was performed within 5 hours after cats were euthanati zed. Blood was collected directly from the heart of cats found to be infect ed and tested, using a filter test for microfilariae. Serum was tested for D immitis antigens by use of 2 antigen detection kits and for D immitis-spe cific antibodies by use of 2 antibody detection kits. Results-Cats ranged from approximately 4 months to 15 years old. Adult D im mitis were found in 6 (2.5%) cats. Blood could not be recovered from 1 of t he cats with heartworm infection. For the 5 other cats, results of the filt er test were negative, and results of both antigen and both antibody tests were positive. Conclusions and Clinical Relevance-Results suggest that cats living in an u rban area in the northern part of the United States have a low prevalence o f adult D immitis infection. However, this is likely to be an underestimate of the true prevalence of infection, because no attempts were made to iden tify cats infected with larval or juvenile stages of D immitis.