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Parasite expert warns Australian dog owners to be on lookout for potentially harmful infection

A parasite expert has warned Australian dog owners to be on the lookout for a potentially harmful infection that can impact the health of dogs and humans.

Recent warm and wet weather across the country poses an increased risk of exposure to Toxocara roundworms, according to University of Melbourne parasitologist Dr Vito Colella.

This parasitic roundworm can cause toxocariasis, a usually mild but chronic disease that results in a range of health issues.

Toxocara roundworms are found in the small intestines of dogs and cats, with the eggs from the female parasites passing through the animals and into the environment via faeces.

This is particularly problematic for dogs who often pass faeces in public places, such as parks, hence spreading the roundworms to other dogs as well as humans.

Both parties can become infected by eating the soil that has been contaminated with the eggs.

The eggs are microscopic, Colella said, so even a “minimal amount of fecal material that is heavily contaminated” is enough to cause an infection.

In dogs the infection is usually mild and symptoms include diarrhoea, vomiting, failure to gain weight and a swollen belly.

“The majority of dogs develop something … called pot-bellied syndrome,” Colella said.

“The belly, especially in puppies, is dilated, it’s particularly swollen.

“The Toxocara parasites … can take up the nutrients that should have gone to the animal.”

Intestinal obstruction can also sometimes occur, Colella said.

Toxocara roundworms under a microscope.
Toxocara roundworms under a microscope. Credit: Getty Images

This can lead to perforation of the small intestine (a hole that develops in the wall of the organ), releasing the roundworms into the abdominal cavity.

Anaphylaxis can then occur, resulting in the death.

In humans, children are more commonly affected by the disease than adults simply due to the likelihood of them playing with, and picking up, soil.

“They could get infected from the environment where the dogs live, especially public parks or if they are in the garden, if the faeces are not picked up in a short time and disposed of properly,” Colella said.

A range of health issues can occur if a human becomes infected with Toxocara roundworms.

It can cause abnormal blood test results, enlargement of the liver, loss of appetite, muscle and joint pains, abdominal pain and rashes.

These symptoms occur because the worm larvae migrates through the body, causing tissue damage.

If the larvae migrate to the eye for example, permanent vision loss can occur.

It is extremely rare for toxocariasis to cause severe disease or death.

“There are cases in which the parasites cause brain and heart dysfunction that have led to death, but the mortality rate of this infection is very, very low,” Colella said.

A cross-section of Toxocara larvae in liver tissue.
A cross-section of Toxocara larvae in liver tissue. Credit: Centres for Disease Control and Prevention

The impact of warm and wet weather

This year’s winter in Australia is expected to be warmer than usual, according to the Bureau of Meteorology, posing ideal conditions for Toxocara parasites.

The parasite’s larval eggs will develop into the infectious stage during humid weather conditions, with the optimal temperature about 20C.

Anything below 10C or above 37C will stop the larval eggs from reaching this stage.

Wet weather also plays a part in spreading contaminated soil.

“If faeces are left outside in the park or in the garden for a couple of days, and then it rains, there will be a sort of wash effect on the faeces that means that the eggs then can travel,” Colella said.


Both dogs and humans can be treated fairly easily for Toxocara roundworms through the use of different drugs.

Most humans recover without specific treatment.


To protect both animals and humans, Colella said it was important for dog owners to stay on top of their pet’s health.

This includes doing simple things such as deworming their dogs monthly, annually treating them for external parasites and going for regular check-ups with the vet.

Dog owners should pick up their pet’s faeces as quickly as possible, and ensure they dispose of it correctly.

Colella said they should also wash their hands after interacting with soil or objects that could potentially be contaminated.

“This is important for all dog owners, but particularly so for those with young children who we know are at greatest risk,” he said.


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