The genus Baylisascaris contains 9 relatively host-specific species. The eggs embryonate and become infective in the environment 2–4 weeks after elimination in feces. B procyonis, found in raccoons, is the most pathogenic for intermediate hosts, including humans. Dogs are susceptible to B procyonis and can shed its eggs. One female B procyonis worm can produce >100,000 eggs per day, suggesting that heavily infected raccoons can shed >1,000,000 eggs daily, which can remain infective for years and withstand freezing temperatures of -15oC. Infections in humans have 4 different presentations: neural larval migrans, ocular larval migrans, visceral larval migrans, and subclinical infections. Clinical neural larval migrans has been diagnosed in the United States, mostly in toddlers or young children; some cases were fatal, and the remaining patients had neurologic impairment. Ocular larval migrans generally affects only 1 eye and is considered the most common cause of diffuse unilateral subacute neuroretinitis syndrome. Visceral larval migrans has been described in young children as being associated with nonspecific clinical signs (eg, fever, lethargy, nausea, macular rash, pneumonia, hepatomegaly). The disease can also be asymptomatic. Prevention and control are focused on avoiding contact with raccoons and their feces.

This comprehensive Baylisascaris spp review discussed the highly pathogenic B procyonis, which has global distribution and poses significant public health implications. Infection in humans ranges from neural and/or ocular and/or visceral larval migrans to subclinical disease. The potential for a heavily infected raccoon definitive host to shed >1,000,000 environmentally hardy eggs per day is startling; any location with potential raccoon-to-human interactions yields a high risk for infection. Raccoons are commonly seen in urban and suburban locations; prevention (by minimizing human [and canine/feline] interaction with raccoons and the areas that they frequent) is the key to control.—Indu Mani, DVM, DSc

Related Article: Baylisascaris procyonis & Raccoon Feces Ingestion

Baylisascariosis—Infections of animals and humans with ‘unusual’ roundworms. Bauer C. VET PARASITOL 193:404-412, 2013.

This capsule is part of the WSAVA Global Edition of Clinician's Brief.