Prevalence of Onchocerca lupi in shelter dogs from an endemic region of the Southwestern USA.

BACKGROUND

Onchocerca lupi is a zoonotic, vector-borne filarioid nematode that mainly infects wild and domestic canids in the Southwestern USA, Europe, Asia, and Africa. Clinical canine infections are associated with ocular disease, characterized by the presence of nodules and conjunctivitis. Subclinical cases can be challenging to diagnose, even with evaluation of cutaneous tissues for microfilariae. Current diagnostic tests include conventional polymerase chain reaction (cPCR) to detect O. lupi DNA, and, alternatively, real-time PCR (qPCR), which provides more rapid results and higher throughput. The objectives of this study were to: I) optimize a novel qPCR assay that detects O. lupi and II) to assess the prevalence of O. lupi in shelter dogs from Albuquerque, NM, USA.

METHODS

This probe-based qPCR was optimized with a detection threshold of 0.33 pg for DNA of an adult female O. lupi. We further optimized the assay by performing a dynamic range test to determine the ideal dilution factor and inclusion of an internal positive control. We collected skin snips from the interscapular region of 404 dogs between January and September 2023. Demographics were recorded, including age, sex, American Kennel Club breed groups, and coat color. Dogs were separated into age groups, including juveniles ≤ 1 year old (n = 120; 29.7%), adults > 1-7 years old (n = 260; 64.3%), and seniors > 7 years old (n = 24; 5.9%). Of those, 194 were female, and 210 were male. We also had nine different American Kennel Club breed groups represented, as well as two coat colors: single (33.0%) and mixed (67.0%). Genomic DNA was subjected to cPCR followed by Sanger sequencing and our probe-based qPCR. Both PCRs targeted a fragment of the cytochrome oxidase c subunit 1 (cox1) of the mitochondrial DNA. We performed statistical analysis to assess any association between exposure factors, such as age, sex, breed, and coat color and the outcome, whether O. lupi was present.

RESULTS

Overall, eight (1.9%; 95% confidence interval (CI) 0.8-3.8%) dogs tested O. lupi-positive via qPCR and five (1.2%; 95% CI 0.4-2.8%) via cPCR. Of the qPCR-positive dogs, six were adults and two were juveniles. Age (P = 0.704), sex (P = 0.910), breed groups (P = 0.217), and coat color (P = 0.781) were not statistically associated with a qPCR-positive result with a cutoff of P < 0.2. In addition, 20 dogs tested positive for Cercopithifilaria bainae via cPCR and sequencing, but these did not cross-react with our qPCR.

CONCLUSIONS

This is the first epidemiological study on O. lupi in a canine population from an urban center within an endemic area in North America. Active surveillance using reliable diagnostic tools can better elucidate the epidemiology of this zoonotic parasite and enable the implementation of strategies for control and prevention.