What are the other Names for this Condition? (Also known as/Synonyms)

• Baylisascariasis
• Raccoon Roundworm Infection

What is Baylisascaris Infection? (Definition/Background Information)

• Baylisascaris Infection (or Baylisascariasis) is a parasitic infection caused by the roundworm Baylisascaris procyonis. It is emerging as an important worm infection transmitted from raccoons, primarily in young children. Due to lack of studies, the exact burden of infection is not presently known
• It is believed that most infections in humans are asymptomatic; the body tending to successfully clear the infection before any signs and symptoms appear. Nevertheless, in a few cases, it can cause irreversible damage to various organs (including brain and eye) and result in a serious life-threatening disease
• Baylisascariasis is a widespread infection found in raccoons which do not show any signs of infection and remain unaffected. The raccoons are the definitive hosts for the parasite i.e., they harbor the adult worms in their guts and spread the infection by shedding millions of roundworm eggs in feces
• Raccoons habitually defecate in communal sites called latrines. Rooftops, attics, in and around chimneys, tree stumps, woodpiles, decks, and lawns (near trees) are common urban and suburban locations. Rarely, domestic dogs can also serve as definitive hosts and spread the infection
• The freshly shed eggs are not infective and require 2-4 weeks to embryonate to become infective. Humans acquire Baylisascaris Infection by inadvertently ingesting the infective eggs. There is no human-to-human spread noted
• Baylisascaris Infection is difficult to diagnose. Several other conditions may present with similar signs and symptoms and the diagnosis is made by exclusion of other causes. The healthcare professional should keep a high index of suspicion in individuals with consistent signs and symptoms
• Treatment with antiparasitic drugs is effective only when taken promptly after exposure. The outcome is dismal if the larva migrates to the eyes, brain, or other vital organs, irrespective of treatment. However, Baylisascaris Infection can be easily prevented by following relatively simple preventive measures

Who gets Baylisascaris Infection? (Age and Sex Distribution)

• There is wide distribution of infected raccoons throughout the United States with highest burden in the following regions:

• Midwest
• Northeast
• Middle Atlantic
• West Coast
• Baylisascaris Infection is being increasingly recognized in humans. However, clinical disease seems to be rare with only about 25 cases reported In the United States to date
• Most of the infections occur in toddlers or young children
• Males are predominantly affected which is likely due to their outdoor playing habits

What are the Risk Factors for Baylisascaris Infection? (Predisposing Factors)

Factors that place individuals at a higher risk for Baylisascaris Infection may include:

• Contact with infected raccoons, their feces, or the contaminated environment
• Pica or geophagia, i.e., habit of eating soil
• Accidental contact with raccoon latrines
• Young children and toddlers playing outdoors

Among adults, the disease has been documented only in developmentally delayed individuals, as they tend to have poor hygiene and a habit of putting everything into their mouths.

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one's chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Baylisascaris Infection? (Etiology)

Baylisascaris Infection is caused by a parasite called Baylisascaris procyonis.

• It is a roundworm which is ubiquitously found in the intestines of raccoons. Therefore, it is also called raccoon roundworm
• The adult forms of this parasite reside in the intestines of raccoons and produce eggs in very large numbers. Consequently, the infected raccoons can shed millions of roundworm eggs in their stools. Such heavy contamination of environment poses high risk of infection to exposed individuals
• The infective forms of the parasite are embryonated eggs which contain the larvae. Humans are infected by swallowing these eggs that hatch in their intestines and release larvae. These larvae burrow into the intestinal wall and migrate throughout the body

Humans do not harbor adult forms of the parasite, and thus, the infection does not spread from one human to another.

What are the Signs and Symptoms of Baylisascaris Infection?

• The infective (embryonated) eggs when ingested, hatch in the human intestine and the released larvae burrow through the intestinal wall and starts migrating throughout the body, trying to find shelter in various organs
• Depending on the site of larval migration and the number of eggs ingested, clinical features may vary from few or no symptoms to dire outcomes
• The larvae may migrate to eyes (termed ocular larva migrans/OLM), brain and spinal cord (neural larva migrans/NLM), or other organs (visceral larva migrans/VLM)

The early signs and symptoms of the disease may be non-specific and vary based on the organs involved. These may include:

• Nausea
• Tiredness
• Abdominal pain
• Rash (predominantly on the face and trunk)
• Enlargement of liver
• Cough or chest pain

The signs and symptoms of ocular larva migrans (OLM) may include:

• Pain in eye
• Blurred vision
• Sensitivity to light
• Foreign body sensation in the eye
• Blindness, which is typically one sided

Neural larva migrans (NLM) often presents as acute eosinophilic meningoencephalitis, and the signs and symptoms include:

• Fever
• Headache 
• Weakness
• Irritability
• Confusion
• Seizures
• Loss of coordination
• Loss of muscle control and gait disturbance
• Coma
• Blindness

How is Baylisascaris Infection Diagnosed?

Baylisascaris Infection is difficult to diagnose. Several other conditions may present with similar signs and symptoms and the diagnosis is made by exclusion of other causes. The physician should keep a high index of suspicion.

• It is very important to inform the physician about any suspected exposure to raccoons
• The various tests used may include:

• Blood and cerebrospinal fluid (CSF) examination: The results would be consistent with parasitic infection, but may tend to be non-specific
• Tissue biopsy: It can be helpful if a section of larva is contained in the sample, although obtaining an appropriate piece of tissue where larva is present can be challenging
• Eye examination: Ophthalmoscopy may reveal a motile larva with larval tracks or consistent lesions
• Serologic testing: There is no serological test commercially available. The detection of antibodies in CSF or serum is being performed at Centers for Disease Control and Prevention (CDC) for suspected cases
• Neuroimaging: Neuroimaging abnormalities in acute neural larva migrans become apparent only in the later stages of the illness and do not contribute to an earlier diagnosis

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Baylisascaris Infection?

The various complications from Baylisascaris Infection may include:

• Persistent vegetative state
• Severe residual neurologic deficits
• Blindness and visual impairment
• Organ damage and failure

Severe infections are highly fatal with almost 50% mortality rate. Almost all the survivors have been left with serious complications causing permanent disability and requiring total nursing care.

How is Baylisascaris Infection Treated?

• There are few antiparasitic drugs which are effective in killing the larvae, but treatment for Baylisascaris Infection is effective only when taken promptly after exposure to the infection
• Steroids can be used adjunctively to reduce the damage caused by inflammation
• The larvae in the eye can be killed with laser photocoagulation
• The healthcare provider may undertake symptomatic treatment, as necessary

How can Baylisascaris Infection be Prevented?

Preventative measures for Baylisascaris Infection may include: 

• Avoid contact with raccoons and their feces
• Educating public regarding the dangers posed by the parasite (raccoon roundworms)
• Avoid racoons as pets and stay away from their latrine areas
• Monitor children closely in potentially contaminated areas
• Wash hands after working or playing outside
• Wear disposable gloves, masks, and boots while handling racoons or their feces
• Burn the latrines and any contaminated material as the eggs are highly resistant to environmental conditions (forces of nature) and commonly used decontaminants

What is the Prognosis of Baylisascaris Infection? (Outcomes/Resolutions)

• The treatment for Baylisascaris Infection is effective only when taken promptly after exposure. Once the signs and symptoms of larva migrans appear, widespread irreversible damage has already occurred in various organs, including the brain and eye
• The administered antiparasitic drugs can kill the larvae but they cannot reverse the damage caused by the migration of the larvae. Therefore, prognosis is generally unfavorable irrespective of treatment
• Despite treatment, the majority of documented cases of neural larva migrans have had no neurologically intact survivors

However, if appropriate preventive measures are followed, which are relatively simple, most cases of Baylisascaris Infection can be easily prevented.

Additional and Relevant Useful Information for Baylisascaris Infection

There are few reports of infection in animals other than raccoons (e.g., kinkajous, coatis, olingos, and ringtails) and the potential for spread from them to humans.

Other conditions which may present with similar signs and symptoms and need to be excluded include:

• Angiostrongyliasis: It is caused by a roundworm endemic to regions such as Southeast Asia and the Pacific Basin
• Gnathostomiasis: It is a caused by a roundworm endemic to regions where raw fish dishes (e.g., sushi and ceviche) are popular, particularly in Japan, Thailand, Vietnam, and Mexico
• Neurocysticercosis: It is an infection of brain caused by the larval form of the tapeworm called Taenia solium
• Other less common parasitic causes of eosinophilic meningoencephalitis include:
  • Cerebral paragonimiasis
  • Cerebral toxocariasis
  • Neurotrichinosis
  • Schistosomiasis
• Disseminated Coccidioides immitis infection: It is a fungal infection and is perhaps the most common cause of eosinophilic meningitis in the United States
• Acute disseminated encephalomyelitis: It is an attack of inflammation in the brain and spinal cord. It is a non-progressive illness, and generally has a good prognosis