Occurrence of Dirofilaria immitis infection in shelter cats in the lower Rio Grande Valley region in South Texas, United States, using integrated diagnostic approaches.

Dirofilaria immitis is a mosquito-borne filarioid nematode that affects dogs and cats. Although heartworm infections in cats can be fatal, it is commonly neglected by cat owners and veterinarians. Moreover, diagnosing heartworm infection in cats can be challenging, requiring the integration of multiple laboratorial tests and clinical examination. The objective of this study was to estimate the occurrence of D. immitis infection in shelter cats in the Lower Rio Grande Valley (RGV) region of Texas using a combination of immunodiagnostic and molecular methods. The RGV has a large population of stray animals with limited access to veterinary care. One hundred and twenty-two paired samples of serum and DNA extracted from the blood clots of cats from 14 towns in this region were analyzed. Serum samples were used for heartworm antibody detection (Heska® Solo Step®), and heartworm antigen detection using a commercial ELISA kit (DiroCHEK®) pre- and post-immune-complex dissociation (ICD) via heat treatment. A species-specific probe-based qPCR assay targeting a fragment of the cytochrome oxidase c subunit 1 of the mitochondrial DNA was utilized to detect the presence of parasite DNA. Twenty-two cats (18%) were positive in at least one diagnostic test. Antibody testing detected most cases (19/122; 15.6%); pre- and post-ICD antigen testing detected 6 cases (6/122; 4.9%); and qPCR detected the fewest cases (4/122; 3.3%), with 2 cats positive on all three diagnostic tests. Veterinarians should encourage local cat owners to utilize year-round heartworm prevention.