Gray foxes (Urocyon cinereoargenteus) as natural definitive hosts of Paragonimus mexicanus.

Paragonimus mexicanus is a trematode that causes pulmonary and extrapulmonary infections in humans, characterized by chest pain, dyspnea, fever, and weight loss. The detection of Paragonimus spp. is primarily achieved through the microscopic observation of eggs in feces, sputum, and pleural fluid. Paragonimus mexicanus has been found in various wild animals, including dogs, cats, raccoons, and opossums. Although the reservoirs of P. mexicanus in Costa Rica are unknown, this study analyzed fecal samples from gray foxes (Urocyon cinereoargenteus) using microscopic and molecular methods. In the morphological analysis, characteristic eggs of the genus Paragonimus were identified. DNA was extracted from fecal samples, and a fragment of the ITS2 loci of trematodes was amplified, which showed a 100 % similarity with P. mexicanus metacercariae from crabs in Ecuador. Then, a Bayesian inference phylogenetic analysis was performed with the obtained data and pre-existing sequences of P. mexicanus found in America, showing that our sequence clustered firstly with others from Colima and Veracruz (Mexico), and Ecuador, while a second cluster contained sequences from Chiapas (Mexico), Ecuador, and Guatemala. These results provide evidence of the presence of P. mexicanus in the gray fox and suggest its role as a possible new wild reservoir, which could have zoonotic implications for the infection of other animal species and humans. Additionally, our phylogenetic analysis reveals low genetic differentiation among the compared P. mexicanus populations and the possibility of additional Paragonimus species currently classified as P. mexicanus. The finding of this parasite in our country, together with comparisons with previous studies, highlights the complex evolutionary history and population dynamics of P. mexicanus.