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

• Hidden Toxocariasis

What is Covert Toxocariasis? (Definition/Background Information)

• Covert Toxocariasis is a form of parasitic roundworm infection caused by Toxocara species. This type of toxocariasis infection is more commonly seen in children
• Toxocariasis is a parasitic infection in humans caused by roundworms belonging to the genus Toxocara. This infection is transmitted from animals (commonly cats and dogs) to humans, making it a zoonotic infection
• The infection occurs when a human ingests the parasite. This mostly occurs via contamination of one’s hands or food (prior to eating) with the feces of an infected animal. The infection can occur from ingestion of undercooked or raw meat/poultry that is infected
• Covert Toxocariasis is so named owing to its non-specific symptoms, such as cough, abdominal discomfort, trouble with sleep, and headaches. The infection may become chronic with recurrent symptoms, if inadequately treated
• Many Covert Toxocariasis cases resolve on their own; although, treatment with anti-parasitic medication may be required to eliminate infection from the body

Who gets Covert Toxocariasis? (Age and Sex Distribution)

• Covert Toxocariasis was first reported in Ireland, primarily affecting young children
• The infection is predominantly observed in individuals living in poverty (poor economic status)
• No gender bias has been reported in the occurrence of Covert Toxocariasis

What are the Risk Factors for Covert Toxocariasis? (Predisposing Factors)

The risk factors for Covert Toxocariasis are common with other types of toxocariasis and these include:

• Having a cat or dog, especially puppies and kittens: Young animals have a weaker immune system and decreased ability to fight infections and foreign pathogens. Toxocara can also be passed through milk from a lactating dog or cat to its offspring
• Owning a household pet that has not been treated for worms
• Breeding animals inside the house/household 
• Young children who frequently play outdoors: Children may come into contact with animal feces or soil contaminated by animal feces, which may then infect them via the oral route (mouth). Toys dropped to the ground may be inadvertently placed in the mouth
• Ingesting raw or undercooked meat infected with larvae of Toxocara

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 Covert Toxocariasis? (Etiology)

Covert Toxocariasis is caused by the parasitic roundworm belonging to the genus Toxocara. Individuals with this kind of infection may test positive for the presence of parasite, but exhibit vague (unclear or hidden) symptoms.

• Eggs of Toxocara species are often found in animal feces, or soil that has been contaminated by animal feces
• However, it may take between 2-4 weeks under ideal conditions (such as temperature and humidity) to become infective
• When Toxocara eggs containing embryos are ingested and enter the human gut, they hatch. The released larvae then infect the intestinal wall
• The larvae live inside the host, feeding-off the host cells by digesting them
• The larvae/worm can also move from one site to another within the human body via the bloodstream, causing inflammatory reactions at each site, resulting in symptoms

Occasionally, Covert Toxocariasis is used synonymously with Common Toxocariasis. However, the latter occurs primarily in adults.

What are the Signs and Symptoms of Covert Toxocariasis?

The signs and symptoms of Covert Toxocariasis may not be significantly visible. Or, the affected individuals may exhibit vague and mild symptoms, which may include:

• Fever and headaches
• Coughing; asthma-like symptoms
• Abdominal pain
• Repeated infections
• Swelling of lymph nodes
• Eosinophilia: Increased eosinophils in blood, indicative of an infection
• Enlarged liver or hepatomegaly
• Skin rashes and itchy skin

How is Covert Toxocariasis Diagnosed?

Covert Toxocariasis is diagnosed on the basis of the following tools:

• A thorough physical examination exam and evaluation of medical history
• Blood test for measuring the level of eosinophils
• Tissue biopsy to check for the presence of roundworm larvae; although, this test is not definitive. It is difficult to establish a diagnosis on the morphology of the parasite alone
• Confirmation of the presence of parasitic infection in the serum/intra-ocular fluids/cerebrospinal fluid, through antibody detection using enzyme-linked immunosorbent assay (ELISA)

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 Covert Toxocariasis?

Covert Toxocariasis often presents with mild symptoms and does not normally lead to complications. However, this type of infection can become chronic with recurrent infections.

How is Covert Toxocariasis Treated?

Typically, Covert Toxocariasis resolves itself over time. However, if symptoms persist or recur, anti-parasitic medication may be prescribed.

How can Covert Toxocariasis be Prevented?

Prevention of Covert Toxocariasis may be achieved by adhering to the following practices:

• Washing hands, especially after being outdoors, gardening, or handling animals or playing with pets, prior to eating or performing other related activities
• Frequently deworming household animals including cats and dogs
• Having thoroughly cooking food (especially meat)
• Clearing/disposing pet feces in a timely and appropriate manner
• Supervising young children while they play outdoors; ensuring that children avoid the ingestion of soil or dirt

What is the Prognosis of Covert Toxocariasis? (Outcomes/Resolutions)

• The prognosis for Covert Toxocariasis is generally good, since most cases resolve spontaneously
• However, persistent or severe symptoms should be addressed in a timely manner to avoid complications or progression to a more severe form of toxocariasis

Additional and Relevant Useful Information for Covert Toxocariasis:

The life cycle of Toxocara is as follows:

• The parasite eggs are passed through the feces of an infected animal
• The eggs become embryonated in the environment (outside the animal), if conditions, such as humidity and temperature, are ideal
• Once embryonated, the eggs are infective, and hatch once ingested by an animal or human
• The larvae infect the intestinal wall in the small intestine
• The roundworm develops into an adult, once it infects the small intestine and is able to lay eggs that are passed through the feces
• The cycle repeats when eggs are ingested by another animal or host

Humans are paratenic hosts i.e., hosts who are not necessary for the parasite to complete its life cycle. However, such hosts may still contribute towards maintaining the life cycle of the parasite.