Toxocariasis

Tiny worms live inside dogs and cats.

These worms lay eggs. The eggs leave the pet in their poop.

The eggs can stay in the dirt for a long time.

People can get sick if they swallow these eggs. This can happen by eating dirt or touching things with dirty hands.

Once inside, the tiny worms move through the body.

They can move to the lungs or the belly. Sometimes, they even move to the eyes. This can make it hard to see.

Most people do not feel sick at all. But some people might get a fever or a cough.

You can stay safe by washing your hands. Always wash your hands after playing with pets or dirt.

Tiny roundworms live inside dogs, cats, and foxes.

These worms are called roundworms. They lay many eggs.

The eggs leave the pet in their poop. The eggs need moist weather to grow. They can stay in the dirt for years.

Humans can get sick if they swallow these eggs. This might happen by eating dirt or touching dirty things.

Once inside a person, the tiny worms move through the body. Most people do not feel sick. However, some people may feel unwell.

There are three main ways the illness shows up. The first way is a mild illness. It can cause a fever, a cough, or a stomach ache. The second way is more serious. This is called visceral larva migrans. In this way, the worms move through organs like the lungs or liver. This can make it hard to breathe. The third way is rare. It is called ocular larva migrans. This happens when a worm moves into the eye. It can cause eye pain or even blindness.

You can stay safe by washing your hands. Always wash after playing with pets or dirt. You should also pick up pet poop in parks.

Toxocariasis is an illness caused by tiny roundworms. These worms are known as Toxocara canis in dogs and foxes. They are also known as Toxocara cati in cats.

While these worms live in animals, humans can become "accidental hosts." This means the worms enter a human body by mistake. Most of the time, people do not feel sick at all. However, these worms can sometimes cause serious health problems. It is important to understand how these tiny creatures move through the world.

The way the illness works depends on how the worms move. First, a person swallows infective eggs from the environment. These eggs might be in dirt or on surfaces.

Once inside, the eggs hatch into tiny larvae. These larvae begin to migrate, or move, through the body. They travel through different organs like the lungs or the liver. In some cases, the larvae can even reach the brain or the eyes. Because humans are not the right hosts, the worms cannot grow into adults. Instead, they eventually settle into a resting stage called encystment.

Scientists and doctors have studied these worms for a long time. We know that puppies and kittens are the main source of these eggs.

This is because mother animals can pass the larvae to their babies. This can happen through the placenta or through milk. In the United States, groups like the Companion Animal Parasite Council work to help. They help pet owners and veterinarians control how these worms spread. By teaching people how to keep pets healthy, we can keep humans safer too.

There are many specific facts about these roundworms. A single female Toxocara canis can lay 200,000 eggs in one day!

The eggs are very tough and can survive in the dirt for years. They need moist and humid weather to develop into the infectious stage. This development usually takes between two and six weeks. The eggs of Toxocara canis are about 75 to 90 micrometers in size. Toxocara cati eggs are slightly smaller and shaped more like an oblong. These tiny numbers show just how much work these small worms do.

You can stay safe by following a few simple steps. Always wash your hands after playing with pets or touching dirt.

It is also important to wash your hands before you eat. If you go to a park, make sure pet waste is cleaned up. In the U.S., up to 20% of playground soil samples have had these eggs. You can also keep sandboxes covered so cats do not use them as litter boxes. These habits act like a shield to keep the tiny worms away from you.

Toxocariasis is a zoonotic illness caused by certain species of roundworms. These parasites include Toxocara canis, which affects dogs and foxes, and Toxocara cati, which affects cats.

Humans are considered "accidental" or paratenic hosts. This means the worms enter a human body by mistake because humans are not the intended host. While many infections are asymptomatic, meaning they show no symptoms, the parasites can cause significant health issues. Understanding how these worms move through different hosts is vital for public health.

The life cycle of these worms is a complex process of migration. It begins when an animal, like a dog or cat, ingests infective eggs. These eggs hatch into second-stage larvae within the animal's intestines.

The larvae then enter the bloodstream and migrate to the lungs. From the lungs, they are coughed up and swallowed to return to the small intestine. In the correct host, they mature into adults to mate and lay eggs. However, in an accidental host like a human, the larvae cannot mature into adults. Instead, they migrate through various organs and eventually encyst, or settle into a resting stage, as second-stage larvae.

There are three distinct clinical syndromes of toxocariasis. The first is covert toxocariasis, which is a relatively mild illness often linked to chronic exposure. This syndrome can cause fever, abdominal pain, headaches, and coughing. It may also involve hepatomegaly, which is an enlarged liver, or lymphadenitis, which is inflammation of the lymph nodes. The second form is visceral larva migrans (VLM). VLM is a more severe condition caused by high parasitic loads or repeated infections. It is primarily diagnosed in young children because they are more prone to ingesting infective eggs. In VLM, the migrating larvae cause inflammation in internal organs. Depending on the organ affected, symptoms can include respiratory failure if the lungs are involved, or even meningitis and seizures if the brain is affected.

The third syndrome is ocular larva migrans (OLM). This form is rarer than VLM and often occurs when a single larva enters the host's eye.

OLM can cause inflammation of eye tissues, retinal detachment, or retinal granulomas, which are small clumps of cells. These ocular granulomas are sometimes misdiagnosed as retinoblastomas. Because the damage to the eye is permanent, OLM can lead to visual impairment or even total blindness. It often manifests in just one eye and can cause vision loss over several days or weeks.

Transmission to humans occurs primarily through the ingestion of infective eggs. These eggs are passed in the feces of infected dogs or cats.

For the eggs to become infectious, they must undergo an incubation period in moist, humid outdoor environments. This process typically takes between two and six weeks, though it can take up to a couple of months. Once developed, the eggs have a resistant outer shell. This shell protects them from environmental threats, allowing them to remain infectious for years. Humans can also be infected by eating undercooked meat, such as rabbit or chicken, that contains encysted larvae.

Research into these parasites highlights their incredible reproductive capacity. A single female Toxocara canis can produce approximately 200,000 eggs every day.

The size of the eggs also differs by species. Toxocara canis eggs are spherical and measure 75 to 90 micrometers in diameter. In contrast, Toxocara cati eggs are oblong and slightly smaller, measuring 65 to 70 micrometers. These numbers illustrate why controlling the parasite in animal reservoirs is so important for preventing human infection.

Preventing toxocariasis requires active management of pet health and environmental hygiene. Organizations like the Companion Animal Parasite Council (CAPC) work to reduce infections in dogs. Because pregnant or lactating animals can pass larvae to their offspring through the placenta or milk, they should follow strict deworming programs. In the United States, up to 20% of soil samples from playgrounds have tested positive for roundworm eggs. To reduce risk, people should wash their hands thoroughly after playing with pets or handling dirt. Additionally, covering sandboxes can prevent cats from using them as litter boxes, which helps keep the environment safer for everyone.