Ever heard of toxoplasmosis? Nope? That’s okay. A bit surprising though, given that nearly a third of the planet’s population is affected by toxoplasmosis. Yup, a third!
What is toxoplasmosis?
It’s caused by this parasite:
Toxoplasma gondii oocyst under the microscope.
Toxoplasma gondii is a single-celled organism found worldwide. It is particularly prevalent in hot, humid climates and at lower altitudes because its oocysts survive better in these environments.
Domestic and feral cats play an important role in the spread of this parasite, as cats are considered the organism's definitive host.
But our frisky felids are not always to blame (as one European study demonstrated - Sources of toxoplasma infection in pregnant women:
European multicentre case-control study; Cook et al.), and below we’ll get into some of the popular questions on this topic.
Toxoplasmosis and behavioural changes
Despite the global impact of toxoplasmosis, probably the most impressive fact about this parasite is the behavioural changes it causes in those who are infected. There have been numerous animal model studies that have demonstrated how infection with toxoplasmosis is associated with risky behaviours leading to predation. The best example of this is how infected mice are attracted to the smell of cat urine - potential prey such as mice are attracted to their natural predator. Such attraction enhances the likelihood of predation and, thus, the spread of toxoplasmosis because the parasite needs to infect cats for its sexual reproduction to take place.
Perhaps even scarier is that these behavioural changes are not limited to animals. Toxoplasmosis has also been linked to behavioural changes in humans.
Like what? Well, in people, it has been associated with schizophrenia, suicide attempts, and good ol’ “road rage.” But, the list doesn’t end there – in a 2018 study by Johnson et al., the authors reported infection prevalence as a consistent, positive predictor of entrepreneurial activity.
Infection with Toxoplasma gondii has been shown to have an influence on personality and risk-taking behaviours.
Nations with higher infection had a lower fraction of respondents citing ‘fear of failure’ in inhibiting new business ventures. Now, in no way are we suggesting that toxoplasmosis is a good thing when it comes to your aspirations to make millions of dollars.
So, how does Toxoplasma gondii induce such behavioural changes? The infection-associated changes in the brain leading to increased impulsivity are not completely understood, however, a few mechanisms have been proposed. These include changes in the production, metabolism, or synthesis of both hormones (e.g., testosterone) and neurotransmitters (e.g., serotonin, dopamine, and norepinephrine). Increases in testosterone have been linked to Toxoplasma gondii infection and can enhance risk-taking behaviour, aggression and impulsivity in humans.
What is the most common source of toxoplasmosis?
The parasite forms egg-like structures, known as oocysts, that are shed in animal faeces. Toxoplasma gondii can also form small pockets, or (tissue) cysts, in muscle tissue, which is another important means of transmission of the parasite.
Humans typically become infected by either eating food or drinking water that has been contaminated with oocysts shed in the faeces of infected cats or by eating meat containing tissue cysts. The same can be said for the transmission of the parasite with our beloved four-legged friends.
Now, avoiding the former sounds easy enough, but what about infected meat?
Can you get toxoplasmosis from raw meat?
In short, a resounding YES!
So, unfortunately, it’s possible to detect Toxoplasma gondii in a whole host of different meats and other foodstuffs, from venison to raccoons, and milk to bacon and cheese, you name it, and someone has probably (and thankfully) done a study to see if this parasite is present or not.
Eating raw or rare meat, particularly lamb, pork, kangaroo, and game meat, including offal (such as heart, liver, and tongue), is an easy way to put yourself and your pets at risk of toxoplasmosis. Poultry (including chicken, duck, and geese) is another possible source.
Are there other sources of toxoplasmosis?
Yes, the list does go on. And it includes:
Wild boar
Goat meat
Shellfish (such as oysters, clams, or mussels)
Milk (unpasteurised) – particularly goat’s milk
Raw/unpasteurised cheese
How common is Toxoplasma in meat?
A study by Iqbal et al., looked at the presence of Toxoplasma gondii DNA in retail meats in different Canadian provinces – the authors found parasite DNA in 4.3% (or 12 out of 281) packages of ground beef, chicken breasts, and ground pork.
If it’s any consolation, and perhaps might stop you from completely switching to being either a vegetarian or vegan, Toxoplasma isn’t generally frequently found in beef.
How can you minimise the risk of toxoplasmosis from food?
The first and probably most widely used recommendation is to cook the food.
Cook food to safe temperatures – now this depends on what meat you’re dealing with and also the cut of meat.
Broad categories to consider include:
Whole cuts of meat (excluding poultry)
Ground meat (excluding poultry)
Poultry (whole cuts and ground)
Ideally, you want a digital meat thermometer/food thermometer to measure the internal temperature of cooked meat. It’s worth mentioning that colour is NOT a reliable indicator that meat has been cooked to a temperature high enough to kill harmful pathogens such as Toxoplasma.
If, like me, you prefer some of your meats on the rare end of the spectrum, or if you feed raw meat to your pets, there are other ways of reducing your and your pets’ risk of contracting toxoplasmosis – although I’m probably a lost cause.
Apart from cooking the meat, another effective means is freezing it to ensure that the oocysts, if present, are rendered non-viable.
Here’s what you do:
Freeze the meat for at least three days, then defrost the meat in a fridge or microwave.
Research has shown that freezing meat at -10 degrees Celsius for 3 days or at -20 degrees Celsius for 2 days killed the parasite and their cysts could not recover.
So, you might be thinking how cold a typical household freezer is. Great question – on average, this is around -18 degrees Celsius (or 0 degrees Fahrenheit – if you’re more familiar with those units). In short, using your household freezer to freeze the meat is more than adequate to render the oocysts nonviable.
Just to point out, while freezing can be useful in reducing the risk of parasites such as Toxoplasma, it’s not a ‘catch-all’ solution for possible food-borne parasites.
For example, freezing does not reliably kill other parasites, such as certain species of Trichinella that can be found in meat, nor harmful bacteria. That’s why cooking the meat is still considered to be the safest method to destroy (potential) parasites and pathogens.
Other things you can and should do in order to minimise the risk of toxoplasmosis include:
- Don’t drink unpasteurised goat’s milk
- Don’t eat raw or undercooked oysters, mussels, or clams
- Practice thorough cleaning of cutting boards, utensils, surfaces, and hands after contact with raw meat, poultry, seafood, or unwashed fruits or vegetables
- Clean cat litter daily. Toxoplasma does not become infectious until 1-5 days after it is shed in a cat’s faeces
- Wash your hands thoroughly after cleaning out a cat’s litter box
- At-risk individuals such as pregnant women, infants, and immuno-compromised persons should avoid contact with cat litter trays
What temperature kills toxoplasmosis in meat?
If you’re going to cook the meat – what do you need to do? As mentioned earlier, safe temperatures (measured with a food thermometer placed in the thickest part of the meat) depend on the type of meat that you’re dealing with, as well as the cut of meat.
For whole cuts of meat (excluding poultry):
Cook the meat to at least 63 degrees Celsius
Allow the meat to rest for three (to five) minutes before consuming (the rest period is important, as the temperature remains constant or may even continue to rise during this time, which destroys pathogens)
Includes: beef, lamb, and kangaroo in whole cuts like chops, steaks, pieces, and roasts
For ground meat (excluding poultry):
Cook the meat to at least 71 degrees Celsius
Ground meats do NOT require a rest time
For poultry (ALL) – whole cuts and ground:
Cook the meat to at least 74 degrees Celsius (or 75 degrees Celsius)
Poultry do not require a rest time
What about toxoplasmosis in treats?
This depends on how the treats are processed.
In other words, treats that are cooked or even air-dried are less likely to be contaminated with toxoplasmosis, provided the meat in question is cooked or heated to safe temperatures - refer to above section.
When it comes to freeze-dried treats because there is no kill step as part of the process, parasites and harmful bacteria can pose a potential problem. If meat is adequately frozen before freeze drying, this can reduce the risk of toxoplasmosis.
Take-home message:
Toxoplasmosis is widespread, affecting people and pets across the globe. There are various ways to reduce the risk of toxoplasmosis for both yourself and your pets. If you’re not cooking meat, be sure to freeze it, to render any Toxoplasma gondii oocysts that might be present, nonviable. Also, practice good hygiene, both in the kitchen and when it comes to managing cat litter and accidents around the house.
Resources:
A review on inactivation methods of Toxoplasma gondii in foods:
Centers for Disease Control and Prevention – Toxoplasmosis: General FAQs:
Cornell Feline Health Center – Toxoplasmosis in Cats:
Food Safety Information Council (Australia) – Toxoplasmosis:
Toxoplasma gondii in Australian macropods (Macropodidae) and its
implication to meat consumption:
Toxoplasma gondii in Foods: Prevalence, Control, and Safety