Seroprevalence and molecular surveillance of Dirofilaria immitis in shelter dogs from central New Mexico, US

Background Dirofilaria immitis , the causative agent of canine heartworm disease, is a mosquito-borne filarial nematode, endemic to most of North America. Clinical signs may include coughing, exercise intolerance, abnormal heart sounds, and lethargy, which can lead to heart failure and death in severe cases. For accurate diagnosis, the American Heartworm Society (AHS) recommends testing dogs annually for heartworm antigens and microfilariae detection. In this study, we assessed the prevalence and potential risk factors for D. immitis in dogs from Albuquerque, New Mexico, using antigen and microfilariae detection tests. Methods In 2023, we collected serum and whole-blood samples (n = 402) from dogs in Albuquerque, New Mexico, as part of a larger study to detect Onchocerca lupi. Serum samples were screened for D. immitis using a commercially available antigen-detection ELISA (DiroCHEK®, Zoetis) using both pre- and post-immune complex dissociation (ICD) via heat treatment. Following genomic DNA extraction, we also screened whole blood using a newly optimized probe-based real-time PCR (qPCR) assay. To assess the possible association between D. immitis presence and potential risk factors, including age, sex, breed group, and coat color, a univariate analysis was performed using either a Fisher's exact or a Chi-square test. Results Serum of 4 (0.99%) dogs tested antigen-positive pre-ICD, while 14 (3.47%) dogs tested antigen-positive post-ICD. We did not detect any positive dogs for D. immitis microfilariae by the probe-based qPCR. No risk factors were associated with the detection of the D. immitis antigen in this dog population. Conclusion Although microfilariae were not detected in this study, it is possible that infections were in the early stages of disease progression, with D. immitis detected in pre- and post-ICD via antigen testing. Low seroprevalence and no microfilariae DNA detected highlight the importance of using both pre- and post-ICD antigen detection alongside molecular-based microfilariae tests, particularly for companion animals living in low-endemic regions and for shelter populations that are less likely to be on heartworm prevention.