The small-intestinal nematode Toxocara vitulorum infects cattle, buffalo, zebu and rarely sheep and goats, mostly in tropical and subtropical climates like those in Africa, India and Asia. It has recently been discovered in a bison herd in Manitoba, and a subsequent survey has found it in several other bison herds in the province. This is the first record of T. vitulorum in any host in Canada. Adult T. vitulorum are white and very large with males measuring up to 25 cm and females up to 30 cm. The eggs are almost colourless, subglobular with thick, finely pitted shells and measure 69-95 µm by 60-77 µm.
Toxocara vitulorum has a direct life cycle. Transmission is primarily vertical through the milk with larvae present in the milk for up to 3-4 weeks after parturition. In calves younger than 6 months of age infected through the milk, larvae undergo hepato-tracheal migration. The pre-patent period is 3-4 weeks. Calves older than 6 months of age can be infected through ingestion of larvated eggs, but this infection rarely results in patency. In these older calves the larvae undergo somatic migration which becomes arrested in the tissues, mainly the liver and lungs and also in the muscle, brain, kidney and peripheral lymph nodes. These larvae remain dormant in female calves until late in pregnancy when they resume development and migrate to the mammary gland around the time of parturition, allowing transmission through the milk.
Clinical signs in calves under 6 months of age with heavy T. vitulorum infections can include unthriftyness, catarrhal enteritis, intermittent diarrhea, intestinal obstruction and occasionally intestinal perforation leading to peritonitis and death. Migration of the parasites into the bile or pancreatic ducts can lead to biliary obstruction and cholangitis. Water buffalo are particularly susceptible to fatality due to severe anemia, diarrhea, anorexia and weight loss. Toxocara vitulorum infections often result in high mortality rates and economic losses in young buffalo calves.
Diagnosis can be made through the identification of T. vitulorum eggs in fecal examination.There is sometimes an acetone-like odour on the breath of infected animals. A wide range of anthelmintics is effective in treating T. vitulorum infections, including benzimidazoles and ivermectin. Treating calves with these drugs at 3 and 6 weeks of age can prevent the larvae from reaching patency.