Toxocara Canis Disease Facts and Information

Toxocara canis is a parasitic worm that affects dogs and can be transmitted to humans through contaminated soil, feces, or contaminated food and water.

This parasite can be found in approximately 14% of dogs worldwide, making it a widespread issue.

The eggs of the parasite can survive in the environment for up to 10 years, allowing them to be easily spread through soil and water.

In the United States, it's estimated that over 1.5 million children under the age of 12 are infected with Toxocara canis each year.

Toxocara Canis is a parasitic nematode that affects carnivores, including dogs.

It's a relatively complex life cycle, even without an intermediate host involved.

The genus Toxocara covers a large group of these parasites, and Toxocara canis is commonly known as the dog roundworm.

Humans can become accidental hosts by ingesting raw vegetables or meat containing embryonated eggs or larvae of Toxocara canis.

This can lead to visceral larva migrans (VLM) and other forms of toxocariasis.

Toxocariasis in humans is caused by infection with larvae of Toxocara spp., which are common ascarid roundworms of mammals.

The dog roundworm T. canis is presumed to be the most common cause of toxocariasis in humans.

It's not known whether other closely-related Toxocara species, like T. malaysiensis of cats, can infect humans.

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Toxocara canis infects almost all wild and domestic canids, and patent infections are more common in puppies than older dogs.

Puppies are frequently infected before birth due to transplacental transmission from their mother.

Both Toxocara canis and T. cati can infect a wide range of mammals and birds, including livestock.

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Toxocara canis infects almost all wild and domestic canids, and patent infections are more common in puppies than older dogs. This is likely because puppies are more susceptible to infection due to their immature immune systems.

T. cati, on the other hand, is found in both wild and domestic felids of all ages, but patent infections are slightly more common in kittens. This highlights the importance of early infection in young animals.

Paratenic hosts, which are animals that can harbor the parasite without showing symptoms, include numerous species of mammals and birds. Livestock, such as cattle, sheep, and chickens, can also serve as paratenic hosts, and consuming undercooked meat from these animals can lead to human infection.

Cockroaches and earthworms have been experimentally infected with Toxocara, and they may potentially serve as paratenic or transport hosts. This emphasizes the importance of proper food handling and waste disposal to prevent the spread of the parasite.

There are two types of toxocariasis that can affect humans, and it's essential to know what they are to understand the risks.

Ocular toxocariasis is a type of toxocariasis that occurs when the parasite gets into the eyes. This can cause eye inflammation, damage to the retina, or even vision loss, and typically only affects one eye.

Visceral toxocariasis is another type, where the parasite moves into organs like the liver or central nervous system.

Toxocara canis is a parasite that's found on every continent, making it a truly global problem.

Prevalence of the parasite is highest in developing countries, where access to healthcare and sanitation may be limited.

In these areas, the parasite is common in both dogs and cats, and it's also frequently found in people, especially children who come into contact with contaminated soil or feces.

The parasite is also found in developed countries, but the number of infections is higher among people in lower socioeconomic strata, who may not have access to the same level of healthcare and sanitation.

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Toxocara canis and T. cati are found all over the world, but they're more common in developing countries.

The parasites are widespread globally, but the highest number of infections in both animals and people can be found in developing countries.

In developed countries, the majority of infections are detected among people in lower socioeconomic strata.

This means that people living in poverty or with limited access to healthcare are more likely to be infected with Toxocara canis and T. cati.

Toxocara eggs are transmitted to humans through contaminated feces of dogs or cats. This is a key factor in the dissemination of toxocariasis.

Earthworms can facilitate the transmission of toxocariasis by altering the distribution of Toxocara eggs in soil.

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Toxocara canis infections can be quite varied in their presentation.

Most cases of toxocariasis are asymptomatic, but when symptoms do occur, they can be quite nonspecific.

In preschool children, the larvae tend to invade multiple tissues, including the liver, lung, and skeletal muscle, causing symptoms like fever, myalgia, weight loss, cough, rashes, and hepatosplenomegaly, often accompanied by hypereosinophilia.

The larvae can also migrate to the central nervous system, causing eosinophilic meningoencephalitis, which can be life-threatening in severe cases.

In older children or young adults, the larvae tend to affect the eyes, causing various ophthalmologic lesions and potentially leading to diffuse unilateral subacute neuroretinitis (DUSN).

Here are some common symptoms associated with ocular toxocariasis:

It's worth noting that ocular toxocariasis typically affects only one eye.

Diagnosis can be tricky because the symptoms of toxocariasis look similar to other infections. Toxocariasis can be hard to diagnose because its symptoms look similar to the symptoms of other infections.

A healthcare provider will take a sample of your blood or eye fluid for testing to confirm the infection. These tests look for the antibodies your immune system produces when you get infected.

They may also ask if you've been around substances that might have been contaminated with Toxocara eggs, like dirt or pet waste.

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Diagnosis of toxocariasis relies mostly on indirect means, such as serology, because larvae are trapped in tissues and not readily detected morphologically.

Visualization of larvae in histologic sections provides an unequivocal diagnosis, but the probability of capturing a larva in a small biopsy specimen is low.

Since the larvae do not develop into adults in humans, a stool examination would not detect any Toxocara eggs.

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Laboratory diagnosis of toxocariasis involves a combination of clinical signs, compatible exposure history, laboratory findings, and the detection of antibodies to Toxocara.

A presumptive diagnosis of toxocariasis is often based on clinical signs, such as eosinophilia, and a compatible exposure history.

Antibody detection tests are the only means of confirmation of a clinical diagnosis of visceral larva migrans (VLM) and ocular larva migrans (OLM).

The currently recommended serologic test for toxocariasis is enzyme immunoassay (EIA) with larval stage antigens extracted from embryonated eggs or released in vitro by cultured third-stage larvae.

The Toxocara excretory-secretory (TES) antigens are preferable to larval extracts because they are convenient to produce and do not require an absorption-purification step for maximum specificity.

A titer of ≥1:32 is considered positive in the TES-ELISA used at CDC, which measures total Toxocara-specific immunoglobulin.

Evaluating the assay in groups of patients with presumptive diagnoses of VLM or OLM indicated a sensitivity of 78% and 73%, respectively, at a titer of ≥1:32.

The assay detects infections caused by both T. canis and T. cati, but cannot differentiate between the two.

A measurable titer does not necessarily indicate current clinical Toxocara infection, and positive serological results should always be interpreted with consideration of the patient’s clinical picture.

Paired serum samples demonstrating a significant rise in antibody level over time may be useful to confirm active infection.

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Treatment is often straightforward, but it depends on where the parasite has taken hold. Most cases of toxocariasis can be treated with drugs that will kill the parasite.

If the parasite has infected an eye, you may need to take extra steps to protect it. Other drugs or surgery may be needed to keep the eye from being damaged.