Toxocariasis is a neglected tropical disease of humans caused by Toxocara nematodes. Two main species of Toxocara affect humans are Toxocara canis and T. cati. Human toxocariasis primarily impacts children populations of lower socioeconomic class in tropical and subtropical regions around the world. Toxocara species are prevalent worldwide and their concentration is in areas with large populations of domestic dogs and cats.
The definite hosts of Toxocara species include cats, dogs, foxes, coyotes, and wolves. T. canis primarily infects canids (dogs, foxes, and wolves), whereas T. cati primarily infects felids (cats). These hosts harbor the nematodes in their gut, shedding eggs in their feces. The embryonated eggs remain infectious for years outside the definitive host. In the wild, intermediate hosts such as other cats, dogs, rabbits, and fowl ingest the cysts, which hatch and migrate to various muscles and organs to encyst. Humans are accidental hosts who become infected by ingesting infective eggs in contaminated soil or infected paratenic hosts. Clinical disease in humans results from the migration of the parasite through extra-intestinal tissues.
The dominant clinical manifestations associated with toxocariasis are classified according to the organs affected. There are two main syndromes: visceral larva migrans (VLM), which encompasses diseases primarily associated with abdominal organs, and ocular larva migrans (OLM), in which toxocariasis pathological effects on the host are restricted to the eye and the optic nerve. Diagnosis of toxocariasis is challenging. The enzyme-linked immunoabsorbent assay (ELISA) assays are available and recommended. Additionally, given that humans are not definitive hosts for Toxocara, stool microscopy is ineffective. Other nonspecific indicators of infection include eosinophilia and hypergammaglobulinemia. Treatment choices of VLM are albendazole and mebendazole. Depending on other endemic infections, ivermectin and diethylcarbamazine (DEC) may be useful as well. Treatment of OLM is more difficult and revolves around decreasing inflammation. Prednisone is often an addition to antihelminthic agents and surgery is reserved for only the most severe cases.
Given that toxocariasis spreads via the fecal-oral route, patient education in hand-hygiene is vital in risk factor modification. Also, patients should receive instruction on other risk factors such as exposure to pets and places where animal feces are present such as sandboxes.
References:
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Fakhri Y, Gasser RB, Rostami A, Fan CK, Ghasemi SM, Javanian M, et al. Toxocara eggs in public places worldwide – A systematic review and meta-analysis. Environ Pollut. 2018;242(Pt B):1467-75
Winders WT, MenkinSmith L. Toxocara Canis (Visceral Larva Migrans, Toxocariasis) [Updated 27 February 2019]. Treasure Island, FL, StatPearls Publishing. Available from: https://www.ncbi.nlm.nih.gov/books/NBK538524/.
Woodhall DM, Fiore AE. Toxocariasis: A Review for Pediatricians. J Pediatric Infect Dis Soc. 2014;3(2):154-9.
