Cats carry ailments that may be lethal to people, and it is costing Australia $6 billion yearly

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Toxoplasmosis, cat roundworm, and cat scratch disease are caused by pathogens that depend on cats – pets or wildlife – for part of their life cycle. However, these diseases can be transmitted to humans, sometimes with serious health consequences.

In our study, published today in Wildlife Research, we looked at the incidence of these diseases in Australia, their health effects and the cost to our economy.

Professor Sarah Legge discusses the main results of the study.

Based on the results of a wide variety of Australian and international studies, Australian hospital data and information from the Australian Bureau of Statistics, we estimate that many thousands of people in Australia become sick or suffer minor injuries from cat-related illnesses each year.

Our estimates suggest that more than 8,500 Australians are hospitalized and about 550 die annually from the causes associated with these diseases.

We have calculated the economic cost of these pathogens in Australia to be more than A $ 6 billion per year based on medical care costs, lost income from leisure time and other related expenses.


Toxoplasmosis is a disease caused by the parasite Toxoplasma gondii. It is the most serious cat-related disease.

Newly infected cats shed millions of T. gondii oocysts (like tiny eggs) in their feces, and these can survive in the environment for many months.

People become infected when they ingest these oocysts, which are in the ground and dusty in places where cats defecate, especially in sand pits, vegetable gardens, or cat litter.

Humans can also become infected by eating uncooked meat if these farm animals have come into contact with oocysts in the cat pen.

Read more: Health Check: Which Insects Can You Catch From Your Pets?

Up to a third of people worldwide are infected with T. gondii, most of them without knowing it. Australian studies have reported infection rates between 22% and 66%.

Once infected, around 10% of people will develop disease; The other 90% have no symptoms.

Based on the total infection rate and the population of Australia, we estimate that there are more than 125,000 new infections in Australia each year.

Of these, around 12,500 people fall ill, mostly with unspecific flu-like symptoms that go away within a few weeks. 650 will require hospitalization and 50 will die, these more severe cases often including brain swelling and neurological symptoms.

People with weakened immune systems, such as B. People with cancer or HIV are at the highest risk.

Toxoplasmosis is caused by the parasite Toxoplasma gondii.
Yale Rosen / Flickr

Pregnant women who become infected for the first time may have a miscarriage or their babies may be born with congenital deformities.

Based on reported and estimated infection rates of T. gondii in newborns, approximately 240 infected babies are born in Australia each year.

More than 20%, or around 50, of these babies have symptoms that require lifelong care, including impaired vision or hearing, and intellectual disabilities. Another 90 babies develop symptoms later in life that are usually related to sight or hearing.

A woman holds her pregnant belly.

Toxoplasmosis poses unique risks for pregnant women.
Freestocks / Unsplash

Long-term effects of latent infection

Even if the initial infection causes little disease, the T. gondii parasite stays with us for life, trapped in a cyst, often in the brain. These “latent” infections can affect our mental health and behavior; B. on a delay in our response times.

Many studies have shown that people with T. gondii infection are more likely to have car accidents. A review of several studies found that car accident rates would theoretically be 17% lower in the absence of T. gondii infections.

T. gondii infections are also more common in people with mental disorders such as schizophrenia and in people who attempt suicide. Reviews in many studies suggest that without T. gondii infections, there could be 10% fewer suicides and 21% fewer diagnoses of schizophrenia.

Debate still persists as to whether the parasite is causing car accidents and mental disorders, or whether some other common factor explains the link. However, it is possible that infection with T. gondii is a risk factor for these problems, just as smoking is a risk factor for heart attacks.

Scientists are still discovering how T. gondii affects the brain, but studies in rodents suggest that it may be due to altered brain chemistry or inflammation.

Put everything together

If we accept that T. gondii infections increase the risk of car accidents, suicide, and schizophrenia, given the frequency of these accidents and health problems in Australia without T. gondii, we may be able to avoid:

  • 200 deaths and 6,500 hospitalizations due to automobile accidents

  • 300 suicides and 4,500 attempted suicide

  • 800 schizophrenia diagnoses per year.

If we combine the deaths from car accidents and suicide with the 50 deaths from acute toxoplasmosis, we get a total of 550 deaths from T. gondii infection per year.

The total number of hospitalizations for T. gondii includes 650 for acute toxoplasmosis, 50 for congenitally infected babies, 6,500 for car accidents, and 800 for schizophrenia. We did not admit hospitalizations for attempted suicide because we did not have statistics on this. So this could be a conservative estimate, regardless of the fact that other factors play a role in car accidents and mental health problems.

Cat scratchers and roundworms

Cat scratch disease is a bacterial infection (Bartonella henselae) that people can become infected with if they are bitten or scratched by an infected cat.

Typical symptoms are wounds, fever, pain and swollen glands. But more serious symptoms such as inflammation of the heart tissue, cysts in the organs, and loss of vision can also occur.

No prevalence figures are available in Australia. Based on rates in the US and Europe, where cat ownership patterns and cat infection rates are similar, we estimate that at least 2,700 Australians develop cat scratch diseases and 270 are hospitalized annually.

Read More: Your Cat Has Toxoplasmosis And Are You Concerned? join the club

Cat roundworm is a parasitic infection (Toxocara cati) that humans and other animals can become involved in by accidentally eating the parasite’s egg that infected cats shed in their feces.

Most catworm infections cause mild symptoms, but migration of the larvae across the body can cause tissue damage, which can be serious if it occurs in a place like the eye or heart.

An adult cat roundworm.
Beentree / Wikimedia Commons, CC BY

What can we do?

Around 700,000 wild cats and another 2.7 million domestic cats roam our cities and suburbs and serve as reservoirs for these diseases.

There are no human vaccines against these diseases. Treatment for T. gondii infection in cats is not considered beneficial because cats usually shed the oocysts without the owner even realizing that the cat has the parasite. Cats can be treated to rid them of roundworms, but treatment for B. henselae (the bacteria that cause cat scratches) may not be effective.

But if you are a cat owner, there are a few things you can do. Keeping pet cats indoors or in a securely enclosed outdoor area can reduce the chances of your pet contracting or passing on a disease-causing pathogen.

A cat sits on the windowsill and looks out at the street.

If cats are kept indoors all the time, there is a small risk that they will catch and spread the disease.
Jaana Dielenberg, Author provided

Cats should be kept away from vegetable gardens and children’s sand pits. Washing hands after handling cat litter and gardening, as well as washing vegetables thoroughly, can also reduce the risk of transmission.

Since T. gondii can be attacked by infected meat, it can also be helpful to cook meat well before eating and not to feed pets raw meat.

Read more: One cat, one year old, 110 native animals: lock up your pet, it’s a killing machine

Urban wildcat reservoirs could be reduced by preventing access to food sources such as farms, bins and tips. We could do this with improved waste management and fencing.

Humans should not feed wild cats, as this can lead to the formation of cat colonies, which are also more susceptible to infection.

Pet cats should also be desexual to avoid unwanted litters that end up as free-roaming ferals.

These steps would cost little to us and our pet cats, but could prevent unnecessary effects on our health and wellbeing.