Raccoon Roundworm

Introduction

• What is it? -> Intestinal parasite found in the feces of raccoons 

• Scientific name -> Baylisascaris procyonic 

  • Procyonis comes from procyon lotor, which is the scientific name for raccoon

• Why is it important? -> Important pathogen affecting wildlife and domestic animals, causing severe neurologic damage 

Now considered common in Texas and can be found in central, eastern, and coastal areas (including Brazos County!)

The Parasite

• B. procyonis is a large, tan-colored parasitic nematode 

• Adult females are 20 to 22 cm long, and males are 9 to 11 cm long 

• Eggs -> thick-shelled and golden brown 

  • Microscopic 

  • Thick shell is important for protecting the egg from things like temperature, drying out, or other environmental conditions 

• Typically found in the small intestines or tissues of animals 

  • Migration is what makes the parasite so dangerous because it leaves behind physical damage in tissues and organs (lungs, eyes, brain)

• Definitive host ->  raccoons 

  • Parasite is able to complete its entire lifecycle within the raccoon

History

• 1931

  • First isolated from raccoons in the New York Zoological Park (as Ascaris columnaris) 

  • Later recognized as a distinct species (Ascaris procyonis) in raccoons in Europe

• 1968 

  • The genus Baylisascaris was defined and included eight recognized and two provisional species previously classified as members of the Ascaris or Toxascaris genus 

• 1984

  • First confirmed cases in humans

  • 2 young boys experienced neurologic symptoms after being exposed to the parasite 

  • First time scientists realized that is was more than just a disease that affects wildlife, has major global health implications

Hosts and Reservoirs

• Primary hosts -> raccoons 

  • Parasite can complete its life cycle and breed within a raccoon host 

• Other hosts -> domestic dogs, rodents, rabbits, primates, and birds (over 150 species)

  • Not common in livestock 

  • It is zoonotic, yet rare 

    • 35 confirmed cases in humans since 1984

• Raccoons are well-adapted hosts for B. procyonis; 

  • They exhibit a high susceptibility to infection, and they release a significant number of eggs into the environment each day, typically at latrines 

    • Latrines become contaminated with the parasite

How Infection Works

• Two types of life cycles for B. procyonis, direct and indirect 

• Type of life cycle depends on the host 

• Direct (monoxenous): only raccoons 

• Indirect (heteroxenous): paratenic hosts (birds and mammals)

  • Intermediate host

• Both allow the parasite to survive and persist in its environment

How Infection Works (Direct)

• Adult worms live in the small intestine 

• Eggs laid by the female worms are passed in feces and reach the ground 

  • Not immediately infectious 

• Takes a minimum of about 2 weeks for larvae to develop from first stage to third stage

• Once ingested by raccoon, larvae invade intestinal wall to complete development 

• Male and female worms, mate, and start oviposition 50 to 76 days after infection

How Infection Works (Indirect)

• Eggs are passed in feces and ingested by paratenic hosts 

• Larvae penetrate the intestinal wall and migrate through the bloodstream to reach other organs and tissues 

• Two to four weeks after infection, the larvae grow in their third stage of development 

• Become encapsulated by granulomas in various organs and tissues

Remain dormant in granulomas in paratenic hosts until ingestion by predatory raccoons, then continue into adulthood

Transmission

• Infected raccoons can shed millions of raccoon roundworm eggs per day in their feces 

  • Average 20,000 to 26,000 eggs per gram of feces 

• Optimal conditions: 

  • 75 F

  • 100% Humidity 

  • Eggs persist extremely well in their environment  

    • 92% of eggs were still alive and able to infect a host after 2 years 

    • True regardless of soil type, amount of moisture, and amount of shade 

• Infant raccoons are directly infected within the first few months 

  • Ingest eggs from mother’s contaminated teats or fur, contaminated den, or from nearby raccoon latrine sites 

• Older raccoons may become infected indirectly by killing or scavenging infected prey

  • 100% of raccoons that consumed an infected rodent became infected themselves

Clinical Signs

• Raccoons -> often asymptomatic, causing no clinical signs 

  • Unless the parasite load is large enough to cause intestinal obstruction 

• Other Hosts -> lethargy, depression, unkempt coat, seizures, blindness, or death 

  • Can invade CNS and eyes, causing neurologic and ocular signs 

• Because of the physical damage left behind by these migrating larvae, many times if the neurologic signs do start to show, it likely signals that the animal will die or be left with permanent neurologic damage

Population Effects

• Highly common 

  • Infecting 40-60% of adult raccoons and up to 90-95% of juveniles in certain areas

• 80% of raccoons acting as carriers in Texas 

  • Creates significant environmental contamination 

• Rarely causes high mortality in raccoons 

• Mortality rate is high for those who develop severe symptoms (other hosts)

Population-limiting factor for these prey species

Diagnosis

• Definitive Hosts (and dogs) -> Fecal Floatation 

  • Process of mixing stool with high density solution to make parasite eggs float 

    • Analyze eggs with microscope 

  • Can also use PCR to confirm presence 

• Other Hosts -> clinical signs of neurologic impairment 

  • Diagnosis is challenging 

    • Worms in these cycles never mature into adults and can’t produce eggs 

    • Fecal flotation would be ineffective because there are no eggs in the feces 

  • No eggs in feces for floatation 

  • Also confirmed post-mortem via histopathology 

  • Diagnosis relies on identifying characteristic neurologic and ocular signs

Prevention

• Prevention is the most important strategy for managing raccoon roundworm 

• Raccoons and other definitive hosts can be treated with common antiparasitic drugs used in domestic dogs and cats 

How to avoid infection/spread:

• Avoid direct contact with raccoons and raccoon latrines 

• Avoid using pet doors 

• Do not use self-feeders for outside pets 

• On a community level, identification and evaluation of contaminated areas 

Best Method -> combination of treatment and removal of contaminated raccoon latrines

Key Takeaways

• Cause -> intestinal parasite, Baylisascaris procyonis 

• Location -> in small intestines or tissues of host, eggs excreted via feces, larvae is ingested 

• Hosts -> Raccoons (definitive) and domestic dogs, rodents, rabbits, primates and birds 

• Clinical signs -> lethargy, depression, unkempt hair coat, blindness, or death (raccoons asymptomatic) 

• Treatment -> common antiparasitic drugs 

  • Dewormers