Baylisascaris procyonis

Synopsis

CAPC Recommends

• To avoid contamination with eggs of B. procyonis, raccoons should not be kept as pets and people and dogs should avoid areas frequented by raccoons.

• Dogs should be maintained on monthly intestinal parasite control products with efficacy against ascarids to treat potential newly acquired infections.

• Keeping dogs confined to a leash or in a fenced yard will limit the opportunity for dogs to acquire infection with Baylisascaris spp.

Species

Canine

• Baylisascaris procyonis is an ascarid of raccoons that is occasionally found in dogs.

• Other Baylisascaris spp. are present in wildlife hosts but have not yet been detected in dogs.

Overview of Life Cycle

• Dogs become infected with Baylisascaris procyonis via ingestion of larvated eggs from a contaminated environment or ingestion of paratenic hosts that have consumed larvated eggs and thus have larvae in their tissues.
• After ingestion of infective eggs, larvae of B. procyonis, like those of other ascarids, migrate through the abdominal organs and the musculature. However, larvae of B. procyonis can grow to a large size and if any invade the eyes or central nervous system, blindness or neurologic disease may result.

Baylisascaris procyonis egg on left, Toxocara canis on right

Stages

• Nonembryonated B. procyonis eggs may be passed in the feces of an infected dog.
• Adult ascarids in the small intestine of the infected dog are grossly similar to Toxocara and Tocascaris spp. They are large stout worms with three lips on the anterior end. Unlike the other ascarids that can infect dogs, Baylisascaris spp. do not have salient cervical alae.

Anterior end of ascarid species from dogs. Left is Baylisascaris procyonis (note lack of cervical alae). Middle is Toxocara canis. Right is Toxascaris leonina.

Disease

• Infections with adult B. procyonis have not been commonly associated with clinical disease in dogs. However, treatment is still warranted, particularly in light of the severe zoonotic disease associated with this ascarid.

• Although uncommon, there are reports of neurologic disease in dogs attributed to B. procyonis larvae migrating in the central nervous system.

Prevalence

• Baylisascaris procyonis occurs in raccoons across the United States and Canada. High prevalence rates have been reported in the midwestern, northeastern, and western states but isolated areas in Texas, Florida, and Appalachia can have localized high prevalence rates.  In some studies, up to 90% of raccoons from a given geographic region were found to be infected with B. procyonis.
• Historically this parasite was absent in the southeastern United States, but recent reports have also documented this parasite in raccoons in parts of Georgia, Florida, and North Carolina, suggesting that the range of this parasite may be expanding or that it may occur in localized populations in some areas.
• Although a large survey of dogs throughout the United States found a low percentage of dogs overall were passing B. procyonis eggs in their feces, these samples were acquired from dogs that were visiting a veterinarian so are likely an underestimate of the actual prevalence.
• Because of the serious zoonotic threat posed by this species, veterinarians and technicians should properly diagnose intestinal Baylisascaris sp. infections in dogs and make sure they receive appropriate treatment.

Host Associations and Transmission Between Hosts

• Raccoons and dogs can harbor adult B. procyonis in their intestinal tracts.
• A wide variety of vertebrates can serve as paratenic hosts that harbor larval Baylisascaris sp. infections.
  • Baylisascaris procyonis larvae have caused visceral disease and death in more than 100 species of vertebrate hosts (avian and mammalian).
  • Paratenic hosts infected with larvae, e.g., primates, rabbits, cats, and birds, can develop signs of infection similar to those seen in children with visceral or ocular larva migrans.
• This guideline is specific to B. procyonis but it is important to note that related Baylisascaris spp. can be found in other exotic pets (e.g., B. columnaris in skunks, B. potosis in kinkajous). These Baylisascaris spp. can also cause disease due to larval migrans so testing and treatment is recommended for these species if they are being kept as pets.

Prepatent Period and Environmental Factors

• Baylisascaris procyonis has a 7- to 10-week prepatent period in raccoons following ingestion of larvated eggs, but patent infections may develop in as little as 4 to 5 weeks upon ingestion of larvae in a vertebrate paratenic host.
• Experimentally dogs are not ideal hosts for this parasite, but prepatent periods for those dogs that did become infected were similar to raccoons.
• Nonembryonated eggs passed in the feces of raccoons or dogs require at least 10-14 days in the environment to larvate and develop into the infective stage. Because of the time required, fecal material has often broken down before the eggs are infective, and thus there is often no gross evidence that the environment is contaminated with infective eggs. However, once present, eggs are hardy and can survive and remain infective for years.
• Removing eggs from a contaminated environment is difficult, and common disinfectants are not effective at killing them. Strict adherence to leash laws and prompt removal of dog feces are essential aids in the prevention of ascarid infections.
• Because raccoons are the primary host, never provide outside food that attracts raccoons into areas where humans live. 
• Routinely deworming infected animals before the infections become patent will prevent environmental contamination and is another key component of achieving effective control (see Control and Prevention below).

Site of Infection and Pathogenesis

• The most severe pathology with B. procyonis is associated with migration of larvae in the eyes and central nervous system.
• Adult ascarids in the small intestine of dogs are not known to cause disease but, similar to other ascarids, could cause enteritis and mild diarrhea. Although dramatic cases of intestinal obstruction and intussusception associated with large numbers of worms in the small intestine have been reported in raccoons, such sequelae are considered rare and have not been described in dogs.

Diagnosis

• Eggs of B. procyonis can be difficult to distinguish from those of the more common Toxocara spp., although morphologic differences exist (see image under Life Cycle) and differentiation becomes easier with experience.
• PCR (provides differentiation between Baylisascaris and Toxocara species).
• Fecal antigen testing for Toxocara will also detect antigens from Baylisascaris in both dogs and raccoons.
• Routine testing and deworming of all dogs is recommended (see Treatment).

Treatment

• Most of the drugs known to remove T. canis from dogs (fenbendazole, milbemycin oxime, moxidectin, and pyrantel pamoate) will also remove Baylisascaris spp. although no treatments are label-approved for this use and retreatment may be needed to eliminate the infections.

Control and Prevention

• To avoid contamination with eggs of B. procyonis, raccoons should not be kept as pets and people and dogs should avoid areas frequented by raccoons.
• To treat potential newly acquired infections, dogs should be maintained on monthly intestinal parasite control products with efficacy against ascarids.
• Efficacy of the initial dewormings, monthly control product, and client compliance should be monitored by performing a fecal examination 2 to 4 times in the first year and 1 to 2 times per year thereafter, depending on the age of the animal and its prior history of infection. A confirmed infection of Baylisacaris in a dog likely means it has access to infected raccoon feces or infected paratenic hosts so would be at risk of future infections. Detection of Eimeria concurrent with Baylisascaris likely means that the dog is ingesting racoon feces because Eimeria is a common parasite of raccoons.
• Keeping dogs confined to a leash or in a fenced yard will prevent predation and scavenging activity and limit the opportunity for dogs to acquire infection with Baylisascaris via ingestion of paratenic hosts or from an environment contaminated with feces from raccoons.
• Prompt removal of feces from the yard will also help prevent ascarid eggs from remaining as the fecal material decomposes or is dispersed into the environment.
• Enforcing leash laws and requiring owners to remove feces deposited by their dogs can protect public areas from contamination with ascarid eggs.

Public Health Considerations

• Baylisascaris procyonis can cause disease in people following ingestion of larvated eggs from a contaminated environment. The larvae of B. procyonis migrate extensively in the central nervous system, commonly resulting in severe neurologic disease in affected individuals; B. procyonis can also produce visceral, ocular, and covert forms of disease.
• Prevention of disease caused by infection with B. procyonis requires preventing the ingestion of eggs from the environment. Young children should be closely monitored so that eating dirt and other forms of pica can be discouraged, particularly in public areas known to be frequented by dogs or populated with raccoons.
• Early, regular deworming is essential in preventing contamination of the environment with ascarid eggs, including those of B. procyonis. Treating dogs to prevent egg shedding is critical because the eggs are very hardy and long-lived in the environment. Once present, the eggs can be removed or destroyed only through extreme measures such as paving kennel areas or areas where pets defecate with concrete or asphalt, complete removal of topsoil, prescribed burns, or treatment with steam.

Selected References

• Kazacos KR, Jelicks LA, Tanowitz HB. 2013. Baylisascaris larva migrans. Handb Clin Neurol. 114:251-62.
• Bauer C. 2013. Baylisascariosis--infections of animals and humans with 'unusual' roundworms. Vet Parasitol. 193(4):404-12.
• Hernandez SM, Galbreath B, Riddle DF, Moore AP, Palamar MB, Levy MG, DePerno CS, Correa MT, Yabsley MJ. 2013. Baylisascaris procyonis in raccoons (Procyon lotor) from North Carolina and current status of the parasite in the USA. Parasitol Res. 112(2):693-8.
• Bowman DD, Ulrich MA, Gregory DE, Neumann NR, Legg W, Stansfield D. 2005. Treatment of Baylisascaris procyonis infections in dogs with milbemycin oxime. Vet Parasitol. 129(3-4):285-90.
• https://pubmed.ncbi.nlm.nih.gov/32660656/
• https://www.sciencedirect.com/science/article/pii/S2213224417300032?via%3Dihub
• https://pubmed.ncbi.nlm.nih.gov/31014845/