Eucoleus

Eucoleus is a genus of parasitic nematodes belonging to the family Eucoleidae within the order Spirurida. Members of this genus are slender, cylindrical worms typically ranging from 15 to 30 millimetre in length, with a smooth, cuticular surface that often shows longitudinal ridges or transverse annulations. The male reproductive system is characterized by a single, long spicule and a well-developed gubernaculum, while the female has a tapered vulva located near the posterior extremity. As with many spirurid nematodes, the eggs are relatively large and are rarely shed directly from the host, instead developing within intermediate hosts such as arthropods before originating the adult stage in definitive hosts.

Life cycles of Eucoleus species are complex. The most studied species, Eucoleus aerophilus, is a respiratory tract parasite of dogs, cats, and other carnivores. After ingestion of infected arthropods or through contact with contaminated feces, the larvae migrate through the bloodstream to the lungs, where they mature into adults that reside in the trachea and bronchi. Transmission can also occur via the larvae passing through the skin of the host or through the ingestion of intermediate hosts. Mature females lay eggs in the respiratory epithelium; these eggs are coughed up and swallowed, passing through the digestive tract and being excreted in the feces, where they embryonate in the environment. The larvae become infective after a period that can range from several days to weeks, depending on ambient conditions.

Infection in domestic animals can lead to respiratory signs such as coughing, wheezing, dyspnea, and, in severe cases, bronchitis or pneumonia. Diagnosis is often made by identifying characteristic larvae in tracheal or bronchial washes or by histopathological examination of mucosal scrapings. Treatment typically involves anthelminthic drugs such as fenbendazole or pyrantel pamoate, and control measures focus on reducing exposure to arthropod intermediate hosts and improving general hygiene. Scientific literature frequently cites Eucoleus aerophilus as the primary species of veterinary importance, though other species such as Eucoleus gideoni and Eucoleus bipapillatus have been reported in wildlife and occasionally in human cases.