Taxonomy:

Phylum Nematoda                                                                                                                           Class Secernentea                                                                                                                       Order Strongylida                                                                                                                         Superfamily Trichostrongyloidea                                                                                                      Family Molineidae

This trichostrongyle nematode is in the same family as the genus Nematodirus, the small intestinal nematode of ruminants.  It has a unique life cycle, with viviparous females, and no shed fecal stage  Ollulanus tricuspis infects predominantly cats and wild felids, and occasionally pigs, foxes and dogs, in Europe, North and South America, Australia and the Middle East.It occurs most commonly in cat colonies or in stray cats and occasionally in stray dogs. It has been reported in Canada once in a pig and a few times in cats. Adult O. tricuspis are very small with males measuring only 0.7-0.8 mm and females 0.8-1 mm in length. The adults can be identified microscopically by the spiral coil of their head and the tricuspid posterior end of the female nematode. 

Ollulanus tricuspis adults live in the stomach and can burrow into the gastric mucosa. The larva develops to third-stage larva in the uterus of the adult female. Once released from the female, the larva is immediately infective and can either stay in the stomach and develop into an adult in 4-5 weeks (autoinfection), or can leave the animal in the vomitus and infect another animal when they ingest the vomit.

Most cats infected with O. tricuspis are asymptomatic, although occasionally vomiting, anorexia, emaciation or catarrhal gastritis can be seen with heavy infestations. Ollulanus tricuspis infections in pigs can result in chronic gastritis. Diagnosis is difficult due to the small size of the parasite and the lack of eggs or larva in the feces. Diagnosis can be made through discovery of larva or adults in vomitus, through endoscopic biopsy, or scrapings collected by gastric lavage. Often diagnosis is only made at necropsy. Ollulanus tricuspis infections can be treated with extra-label use of ivermectin or fenbendazole.