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

• Roundworm Infection due to Toxocara Spp.

What is Toxocariasis? (Definition/Background Information)

• Toxocariasis is a parasitic infection in humans caused by roundworms belonging to the genus Toxocara. This infection is transmitted from animals to humans and is termed a zoonotic infection 
• The most common infectious species of Toxocara are Toxocara canis (found in dogs) and Toxocara cati (found in cats)
• 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
• Many cases of Toxocariasis are asymptomatic; but, when symptoms do develop, they usually fall into several categories, depending on the migration of parasite and its location within the body. Based on this consideration, the following types of Toxocariasis are described:
  • Visceral Larva Migrans (VLM)
  • Covert Toxocariasis
  • Common Toxocariasis
  • Ocular Larva Migrans (OLM)
  • Neurotoxocariasis 
• The symptoms of Visceral Larva Migrans may include coughing, abdominal pain and enlarged liver. Those affected by Covert and Common Toxocariasis may exhibit mild and vague symptoms
• Individuals with Ocular Larva Migrans may experience swelling in the eyes and vision abnormalities, whereas those with the Neurotoxocariasis may have memory lapses, cognitive problems, and issues with gait
• Treatment for various forms of Toxocariasis primarily involves the administration of anti-parasitic drugs to eliminate the parasite from the body. Surgical intervention may be required to physically remove larvae from the affected organs or tissues. The treatment for OLM is focused on minimizing damage of the affected eye
• Delay in treatment or untreated infection can lead to complications, such as organ damage, cardiac arrest, epilepsy, idiopathic Parkinson’s disease, dementia and vision loss, among others. Nevertheless, the infection can be cured with prompt and adequate treatment

Who gets Toxocariasis? (Age and Sex Distribution)

• Toxocariasis is reported globally, in individuals of all ages and both genders. It is predominantly diagnosed in individuals living in poverty and poor economic status
• Individuals of all races and ethnicities are equally susceptible to infection
• The visceral type of infection is more common in children, whereas the ocular type frequently affects teenagers and adults
• Covert Toxocariasis is more prevalent in children, and was first reported in Ireland
• Common Toxocariasis typically affects adults of both genders, and was originally reported in certain rural areas of Midi-Pyrénées region of France
• Neurotoxocariasis is reported primarily in adults; although, a few cases of infection have been observed in children 

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

Some of the risk factors related to Toxocariasis are as follows:  

• 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 health care provider.

What are the Causes of Toxocariasis? (Etiology)

Toxocariasis is caused by the parasitic roundworm, belonging to the genus Toxocara.

• 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

The major types of Toxocariasis infections are:

• Visceral Larva Migrans (VLM): It occurs when the Toxocara parasite larvae travel or migrate to multiple tissues, such as to the liver, lung, muscle, brain, and heart
• Covert Toxocariasis: Often, the affected individuals are children, who may test positive for Toxocara infection, but exhibit little or vague symptoms of the infection. However, this form of infection may become chronic
• Common Toxocariasis: It is a chronic condition first reported in adults, in the rural areas of France. It is characterized by chronic weakness and fatigue

Occasionally, Covert Toxocariasis is used synonymously with Common Toxocariasis, owing to similar manifestations. However, the infections are differentiated on the basis of whether they predominantly affect children (Covert Toxocariasis) or adults (Common Toxocariasis).

• Neurotoxocariasis: It is a result of the parasite localizing in the brain and causing neurological symptoms
• Ocular Larva Migrans (OLM): This type occurs when Toxocara has traveled to the eye of the host, causing lesions in the eye. Typically, only one eye is infected

What are the Signs and Symptoms of Toxocariasis?

The signs and symptoms of Toxocariasis depend on the site of migration/area of infection, as well as the “parasitic burden”. It is a term used to describe (roughly) the number of eggs or larvae an individual has in his/her system or body.

The severity of symptoms may vary among the affected individuals, with some being asymptomatic. Young children, who are unable to articulate symptoms experienced, may be more severely affected. The following are some reported presentations of the various subtypes:

Signs and symptoms of Visceral Larval Migrant Toxocariasis:

• Fever and headaches
• Eosinophilia: Increased eosinophils in blood, indicative of an infection
• Abdominal pain or discomfort
• Coughing
• Weakness or tiredness
• Muscle pain
• Enlarged liver

Signs and symptoms of Covert Toxocariasis: Generally observed in children, the symptoms may be milder and unclear in comparison to VLM.

• Fever and headaches
• Coughing; asthma-like symptoms
• Abdominal pain
• Repeated infections
• Swelling of lymph nodes
• Eosinophilia
• Enlarged liver
• Skin rashes and itchy skin

Signs and symptoms of Common Toxocariasis:

• Digestive problems, abdominal pain
• Eosinophilia
• Lethargy; chronic weakness
• Breathing difficulties
• Itching skin and skin rashes (infrequently noted)

Signs and symptoms of Ocular Larval Migrant Toxocariasis:

• Low-grade fever
• Eosinophilia
• White spots in the eye (or granulomas, often misdiagnosed as retinoblastoma)
• Swelling or inflammation of the eye
• Vision changes and vision loss

Signs and symptoms of Neurotoxocariasis:

• Headaches
• Nausea
• Clumsiness
• Walking difficulties; problems with gait
• Issues with memory and concentration

How is Toxocariasis Diagnosed?

A diagnosis of Toxocariasis is made by the following tests and exams:

• A thorough physical examination and a complete medical history investigation
• Eye exam, in case of Ocular Larva Migrans
• 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 Toxocariasis?

Generally, Toxocariasis is not known to cause serious complications. However, complications may arise based on the location of the infecting roundworms in the body. The rare but potential complications may include:

Potential complications due to Visceral Toxocariasis:

• Bowel dysfunction
• Infection of the lungs (pneumonia)
• Damage to the infected organ, which over time, can cause organ failure
• Convulsions (epilepsy)
• Heart attack

Potential complications due to Covert Toxocariasis:

• Chronic infection
• Recurrent symptoms

Potential complications due to Common Toxocariasis:

• Chronic infection
• Excessive weakness and lethargy

Potential complications due to Neurotoxocariasis:

• Convulsions (epilepsy)
• Increased number of eosinophils in peripheral blood (eosinophilia)
• Inflammation of blood vessels in the brain and/or spinal cord
• Inflammation of brain (encephalitis)
• Idiopathic Parkinson’s disease
• Dementia

Potential complications due to Ocular Toxocariasis:

• Vision damage due to tractional and retinal detachment
• Complete loss of vision
• Removal of the affected eye - that may be warranted due to excessive damage of the eye, or due to misdiagnosis of the condition as retinoblastoma

How Is Toxocariasis Treated?

The treatment for Toxocariasis may vary from one individual to another, depending on the location and seriousness of infection.

Treatment measures for Visceral Toxocariasis include:

• Usually treated using anti-parasitic drugs, such as albendazole
• Surgical removal of the infection may also be necessary

Treatment measures for Covert and Common Toxocariasis include:

• These infection types often resolve spontaneously
• If symptoms persist, anti-parasitic drugs are prescribed

Ocular Toxocariasis is more difficult to treat and the methods adopted address deterioration of vision and damage to the affected eye. The treatment measures may include:

• Topical steroids to reduce eye inflammation
• In severe cases, periocular steroid injections may be administered
• Use of prescription anti-parasitic medication has found limited success. The medicine of choice is albendazole
• Vitrectomy: It is the surgical removal of the vitreous gel from the middle of the eye. This surgery is performed to correct retinal detachment and improve vision

Treatment measures for Neurotoxocariasis include:

• Use of anti-parasitic drugs with simultaneous administration of dexamethasone, if necessary
• Use of corticosteroids

How can Toxocariasis be Prevented?

Prevention of 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 Toxocariasis? (Outcomes/Resolutions)

• Most cases of Toxocariasis resolve without causing any serious damage following suitable treatment. With adequate and prompt treatment, the infection can subside in a matter of days or weeks
• A delay in diagnosis and treatment may cause severe damage of infected tissue and interfere with the function of several organs. This may lead to organ failure
• In some rare instances, mostly due to a lack of treatment, some cases are fatal

Additional and Relevant Useful Information for 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