Oxyspirura petrowi is a heteroxenous nematode found in northern bobwhite (Colinus virginianus) of the Rolling Plains ecoregion of Texas. Despite its impact on this popular gamebird, genetic level studies on O. petrowi remain relatively unexplored. To accomplish this, we chose the previously studied nuclear rDNA 18S region as well as the mitochondrial COX1 gene region of O. petrowi to investigate phylogenetic relations between O. petrowi and other nematode species. In this study, we generate primers using multiple alignment and universal nematode primers to obtain a near-complete 18S and partial COX1 sequence of O. petrowi, respectively. Phylogenetic trees for O. petrowi’s 18S and COX1 gene regions were constructed using the Maximum Likelihood and Maximum Parsimony method. A comparative analysis was done based on the nuclear and mitochondrial region similarities between O. petrowi and other nematode species that infect both humans and animals. Results revealed a close relation to the zoonotic eyeworm Thelazia callipaeda as well as a close relation with filarial super family (Filarioidea) such as the human eyeworm Loa loa and Dirofilaria repens eyeworm of dog and carnivores.

Thelazia callipaeda (Spirurida, Thelaziidae) eyeworm causes ocular infection in carnivores and humans in the Far East; this infection has been recently reported also in Europe – northern and southern Italy – in dogs, cats and foxes. The natural vector/s of T. callipaeda is/are unknown and the development of the nematode in its definitive hosts is limited to an experimental trial on dogs. To contribute new insights into the development of T. callipaeda in the definitive host in field conditions, eyeworms were collected from naturally infected dogs from an area with a high prevalence of infection (up to 60·14%) in the Basilicata region of southern Italy, from January 2002 to December 2003. Conjunctival secretions were also collected and examined for the presence of immature stages. The presence of blastomerized eggs throughout the period – except for the months from May to November – indicates a seasonality in the reproductive activity of T. callipaeda, coinciding with the presence/absence of the vector. In fact, 1st-stage larvae were found in the lachrymal secretions of dogs in summer (June–July 2002 and 2003), ready to be ingested by flies feeding about the eyes. The evidence of 4th-stage larvae in March 2002 and April, July and October 2003 may be accounted for by the presence of flies that act as intermediate hosts of T. callipaeda from early spring to early autumn. The presence of immature stages in October indicates an overlapping generation of nematodes and a 2nd cycle of vector infection. This basic knowledge of the development of T. callipaeda will hopefully help future epidemiological studies to identify the intermediate hosts and define the likely risk for vectors in field conditions.