There are certain neglected parasitic infections that have the potential to cause serious health problems. Toxocariasis is one of these, and it has a significant impact on global public health.

Toxocariasis is an infection seen all over the world and it is caused by small worms found in the faeces of some animals, including dogs, cats, and foxes.

Due to its potential to spread to vital organs such as the lungs, liver, and brain, it is crucial to recognise toxocariasis and increase your knowledge about it. In this article, you can read about the important aspects of toxocariasis and find answers to your questions about this potentially dangerous infection.

Introduction to toxocariasis

Toxocariasis is a zoonotic infection, which means it is transmitted to humans from animals. The causative organism of toxocariasis is a nematode or roundworm, which belongs to the genus Toxocara.

Toxocariasis is commonly seen and particularly affects people living in poverty.¹ Although it has been reported in many countries worldwide, it is more widely found in hot and humid locations due to better survival of the parasite’s eggs in the soil.

It is important to understand the impact of toxocariasis on global public health and its potential to cause serious conditions in humans.³

Understanding the parasite (Toxocara spp.)

Explanation of toxocara worms and their lifecycle

Toxocara spp. are roundworms classified under the Ascaridoidea and include four species, namely Toxocara canis, Toxocara cati, Toxocara malaysiensis, and Toxocara vitulorum.

T. vitulorum, T. canis, and T. cati have been reported worldwide. However, T. malaysiensis has  only been reported in China, Malaysia, and Vietnam.¹

In developing countries, dogs and cats are the most common animal hosts of toxocariasis. However, in certain developed countries, such as the UK, urban and rural foxes act as the primary host of the infection.

Toxocara roundworms can have a one host or multiple host life cycle. Their lifecycle can be simply summarised as follows:

• Eggs are shed in the faeces of the definitive host (cats, dogs, or foxes)
• Eggs become infective in the external environment
• Infected eggs are ingested by a definitive host 
• Infected eggs hatch inside the definitive host’s body and the larvae migrate to several organs followed by returning to the gut or arresting in the tissues
• Adult worms develop in the gut of the definitive host
• Alternatively, infected eggs can also be consumed by a paratenic host (numerous mammal and birds including livestock)
• Infected eggs hatch inside the paratenic host’s body and the larvae migrate 
• The life cycle is completed when the definitive host consumes larvae within the paratenic host

How humans contract toxocariasis: ingestion of worm eggs?

Humans are accidental hosts and they become infected when they ingest infective eggs or undercooked meat of paratenic hosts. The infective eggs hatch inside the human body and larvae migrate to certain organs by circulation following the penetration of the intestine wall. Despite not developing further, larvae can damage these organs and this can lead to certain signs and symptoms.  

Common sources of contamination

Environmental contamination of soil with infected eggs in public parks and playgrounds is common in most countries, as most dogs and cats have access to those places.

Attachment of infective eggs to the hair of dogs, cats, and foxes can also result in transmission of the parasite to humans. Puppies and stray animals tend to carry a higher amount of eggs on their coats.¹ 

Consumption of contaminated undercooked beef, lamb, chicken or duck meat (particularly liver) can also cause humans to acquire the infection.

Signs and symptoms of toxocariasis

Signs and symptoms of toxocariasis depend on the amount of the parasite in the body, duration of the migration of the larvae, and the ageand immune status of the affected person. However, in most people, toxocariasis does not cause any symptoms.

When the larvae migrate to the major organs and cause systemic disease, it is described as visceral larva migrans (VLM). VLM can affect organs, including the liver, heart, lungs, kidneys, and muscle.¹

Possible common symptoms of VLM include the following:

• Fever
• Cough
• Wheezing
• Breathing difficulties
• Extreme tiredness
• Weight loss
• Tummy pain
• Vomiting
• Loose stools
• Itchy skin rash
• Enlarged liver
• Enlarged spleen

When toxocariasis involves the nerves, it is called “neurotoxocariasis” and its possible symptoms are as follows:

• Headache
• Fever
• Weakness
• Sensitivity to light
• Epileptic seizures
• Confusion
• Vision problems
• Tiredness
• Dementia
• Depression
• Balance problems
• Stiffness
• Urine retention
• Incontinence problems

Signs and symptoms related to ocular toxocariasis (when the parasite affects the eye) include:

• Eye pain and redness
• Scarring and damage to the back of the eye
• Vision problems

Covert or common toxocariasis (CT) is another clinical form of the disease, which might affect children and adults.¹ 

In adults, CT might present with symptoms such as:

• Breathing problems
• Rash 
• Itchiness 
• Tummy pain 
• Weakness

In children CT might present with the following symptoms:

• Fever
• Headache
• Loss of appetite
• Nausea and vomiting
• Behaviour and sleep problems
• Tummy pain
• Sore throat
• Symptoms related to pneumonia
• Itchy rash
• Enlarged liver

Diagnosis and medical evaluation

Diagnosis of toxocariasis is mainly based on medical history (especially the history of possible exposure to a contaminated soil or consumption of undercooked meat), physical examination, and lab and imaging tests.

Early diagnosis of toxocariasis is important to prevent complications and improve the outcome.¹ Therefore, it is very important to seek help from a healthcare professional without delay.

The most common method to diagnose toxocariasis is a blood test method called ELISA. This method detects the antibodies against the parasite in the human body. Antibodies are the proteins produced by our immune system to fight against infections.⁴

Various imaging methods such as magnetic resonance imaging (MRI), computed tomography (CT), ultrasound, and some imaging techniques to visualise the eyes and vision might be also helpful to diagnose toxocariasis.¹

Treatment and management

Treatment is usually recommended to those with symptoms. Therefore, if you are suspected of having toxocariasis, it is very important to get medical help for an appropriate assessment and treatment.

The main treatment for toxocariasis is antiparasitic medication such as albendazole or mebendazole. They are effective medications to kill the worms in the body.

Ocular toxocariasis can be treated with medications or by a surgery depending on the severity of the disease. However, the first choice of treatment is a medical therapy with corticosteroids in patients with active inflammation. Corticosteroids work by decreasing the inflammation, thus the damage, caused by the worms to the eyes.⁵

Although corticosteroids have been used to treat neurotoxocariasis, no evidence is present regarding the use of antiparasitic medications in neurotoxocariasis and ocular toxocariasis.

Covert/common toxocariasis is mostly a self-limiting infection and it resolves within three months.⁶

Prevention strategies for toxocariasis

Prevention of toxocariasis is possible. Moreover, certain preventive strategies are also important to prevent reinfection regardless of the type of toxocariasis infection.⁶

The following strategies are effective ways to prevent toxocariasis:^1,6

• Pet dogs and cats should be de-wormed periodically and from a young age
• Pets should be taken to the vet regularly, and should be given antiparasitic medications when necessary and according to the vet’s advice
• Pet faeces should be safely disposed of as soon as possible
• Household gardens, sandpits and playgrounds should be protected against animal faeces
• Parents should educate their children about hygiene measures, and the dangers of contact with dirt
• Vegetables and fruits harvested from possibly contaminated soil should be thoroughly washed before consuming
• Raw and undercooked meat should be avoided
• In the case of having chronic earth-eating (geophagia), counselling should be received from a healthcare professional
• Personal hygiene, including handwashing, is crucial, particularly when handling food and following contact with animals
• Wearing proper gloves is very important while gardening

Risk factors for toxocariasis

Toxocariasis risk factors include:

• Consuming raw or undercooked meat or offal
• Heavy drinking of alcohol
• Living in a rural area
• Geophagia (earth-eating)
• Contact with animals 
• Owning a dog
• Contact with a contaminated environment
• Smoking
• Living in hot, humid regions where the eggs survive better in soil

Summary

Toxocariasis is a serious global health concern caused by worms found in animal faeces, primarily dogs, cats, and foxes. Humans can contract the infection through contaminated soil or undercooked meat. Symptoms range from fever and cough to vision problems and organ enlargement. Timely diagnosis, typically done through blood tests and imaging, is vital. Treatment involves antiparasitic medications, and prevention includes regular pet de-worming, safe disposal of animal waste, and personal hygiene. Public awareness and adherence to preventive measures are crucial in combating this neglected parasitic infection.

FAQs

How common is toxocariasis in the UK?

Toxocariasis is relatively rare in the UK, but exact prevalence is challenging to determine due to under-reporting.

Can toxocariasis be cured?

Yes, toxocariasis can be cured with appropriate medical treatment, often involving antiparasitic medications.

Does toxocariasis go away on its own?

In some cases, especially mild ones, the infection might resolve on its own, but medical intervention is recommended for a complete cure.

Should I worry about toxocariasis?

While it is not common, awareness and preventive measures, especially for pet owners and children, are important to avoid the infection.

What is the prognosis for toxocariasis?

The prognosis is generally good with timely diagnosis and treatment. Early intervention leads to better outcomes.

How long can Toxocara live in humans?

Toxocara larvae can survive in human tissues for several months to years, causing potential health issues.

What is the difference between toxoplasmosis and toxocariasis?

Toxoplasmosis and toxocariasis are different parasitic infections caused by separate organisms. Toxoplasmosis is caused by Toxoplasma gondii, while toxocariasis is caused by roundworms belonging to the Toxocara genus. Both require medical attention for proper diagnosis and treatment.