Molecular detection and diagnostic evaluation of Spirocerca lupi infection in dogs from Reunion Island

Spirocerca lupi is a parasitic nematode responsible for spirocercosis, a potentially severe disease in domestic dogs. Clinical manifestations are variable and nonspecific, often leading to confusion with other gastrointestinal, respiratory, or neoplastic disorders and making diagnosis challenging. Although canine spirocercosis has previously been reported on Reunion Island, the molecular epidemiology and data on its occurrence remain limited. This study aimed to investigate the circulation of S. lupi on Reunion Island, using endoscopy, coproscopy, and molecular assays. Over a 75-day period, 88 dogs were recruited on Reunion Island from a veterinary clinic (n = 54) and a municipal shelter (n = 34), regardless of their clinical status. Clinical data and fecal samples were collected from all animals. Fecal samples were processed using coproscopic flotation and preserved in ethanol-containing Eppendorf tubes and FTA cards for subsequent molecular analyses. Overall, 20 dogs (22.7%) were identified as positive for S. lupi using at least one diagnostic method. Since not all animals were subjected to every diagnostic test, results were analyzed per modality: endoscopy, performed on 31 dogs, showed a positivity rate of 48.4% (15/31). In contrast, coproscopic examination, performed on 40 dogs, yielded a lower detection rate of 15.0% (6/40), consistent with the limitations of intermittent egg shedding. Molecular analysis of all 88 dogs revealed no amplification with semi-nested PCR targeting cox1 gene, whereas ITS1 qPCR detected infection in 6.8% of dogs (6/88), including one positive sample preserved on an FTA card. Under the conditions of the present study, the ITS1 qPCR assay successfully detected S. lupi DNA, whereas no amplification was obtained with the semi-nested cox1 PCR. The present study provides evidence of the active circulation of S. lupi in Reunion Island. Substantial discordance was observed between diagnostic approaches, emphasizing that no single method is sufficient for reliable diagnosis of canine spirocercosis. The findings support the continued use of endoscopy as the reference diagnostic tool, complemented by molecular and coprological approaches in epidemiological investigations.