Baylisascaris procyonis in people

Baylisascaris procyonis is a small-intestinal nematode of raccoons in North and Central America, including Canada, and is also present in raccoons introduced into Europe and Japan.

Public health overview

Baylisascaris procyonis is a small-intestinal nematode of raccoons in North and Central America, including Canada, and is also present in raccoons introduced into Europe and Japan.  The parasite has a direct life cycle typical of ascarids: eggs are passed in the faeces and in the environment a first-stage and subsequently an infective second-stage larva develops within each egg.  Adult B. procyonis are large nematodes and females can produce very large numbers of eggs (up to 250,000 epg) which can survive for long periods in the environment.  Under ideal environmental conditions this development takes approximately two weeks.  Raccoons are infected by ingesting the larvated eggs.  In the raccoons the larvae released from the eggs undergo a mucosal migration and are mature and are patent (producing eggs) within approximately two months. Sometimes the larvated eggs are ingested by other mammals or birds, which serve as paratenic hosts.  In these hosts the larvae released from the eggs undergo a somatic migration which can involve the central nervous system and result in neurological symptoms - neural larva migrans (NLM).  If infected paratenic hosts are ingested by raccoons then the larvae released complete their development to adults in the intestinal lumen.  Young raccoons are usually infected by ingesting eggs, and older animals by ingesting infected paratenic hosts.  Young raccoons (< 1 yo) usually have higher prevalence and intensity of B. procyonis than do older animals.  Patent infections with B. procyonis can also develop in dogs, though apparently not commonly, and in some dogs the larvae undergo a somatic migration involving the central nervous system and NLM.

The major public health significance of Baylisascaris procyonis of raccoons is as a cause of larva migrans, particularly NLM, in people.  This condition has not been recognized commonly in North America (<20 cases), but there are published reports of three cases in Canada, two in children in Ontario, and one in an elderly person in British Columbia.  There was also a single case in Germany, where raccoons had been imported.  Most of the cases reported have been in children less than five years old with a history of pica and/or geophagia and exposure to raccoons and/or raccoon habitat.  Although one affected child in Louisiana made a full recovery, and a few other patients have improved following aggressive therapy, Baylisascaris NLM in people is a very serious disease, and those who survive have life-long neurological deficits. Dogs with patent B. procyonis infections are also a public health threat.  Although to date the infection in this host has been rarely reported, a lack of awareness of the possibility, and the difficulty in distinguishing the eggs of B. procyonis from those of Toxocara canis (the common ascarid of dogs), mean that the parasite might be more common in dogs than we currently believe.

Awareness of the issue of B. procyonis and larva migrans is critical to the prevention of human infections, especially in situations where there is the potential for exposure of people, particularly children, and pets to raccoons and raccoon habitats, especially the latrines.  RACCOONS SHOULD NOT BE KEPT AS PETS.

Additional information about B. procyonis is available under Dogs