Last Updated on February 26, 2021 by Julia Wilson
Toxoplasmosis is an infection caused by a single-celled parasite by the name of Toxoplasma Gondii. Its distribution is worldwide. Only cats are the definitive hosts; however, the parasite can infect a wide range of other intermediate hosts including wild and domestic animals (including birds) as well as humans. From 1988-1994, researchers in the United States found 65% of people over the age of 12 tested positive for antibodies to T. gondii. Closer to home in Australia, between 20 – 40% of women of childbearing age have evidence of previous infection. Infection rates vary from country to country, but overall, it is estimated that 30% of the human population has been infected with T. gondii.
Infection of T. gondii occurs via the fecal-oral route, via an intermediate host which has cysts in their tissues or transplacental (from an infected mother to her unborn baby) and via the mother’s milk.
Cats are the only definitive hosts to T. gondii, which means that after ingestion of infective oocysts, the parasite is to sexually reproduce. Millions of oocysts appear in the cat’s feces between 3-10 days after infection. Once outside the cat’s body, oocysts become infective in 1-5 days. Cats continue to shed the oocysts in their feces for 14 days.
Oocysts are shed in the cat’s feces can cause environmental contamination of the following:
Environmental survival time of oocysts:
- Oocysts can survive up to 18 months in warm soil or water.
- 46 days in uncovered feces.
- 334 days when covered.
Other sources of infection:
- Consuming intermediate hosts (such as rodents) which contain cysts in their tissues
- Consuming raw or undercooked meat that contains cysts in their tissues
How do cysts get into animal tissues?
The entire life-cycle of T. gondii has been covered in detail here so I won’t go over that ground again. Cyst formation occurs in the tissues when the host’s own immune system mounts an attack against the parasite. In response, tachyzoites (T. gondii pseudocysts) convert to bradyzoites and form cysts within the tissues. Tissue cysts can remain in the host for an entire lifetime. The location of these cysts varies from species to species, but commonly affected parts include the brain, eyes, heart and skeletal muscles. At this point, if the host (for example a rat, bird, cat, etc.) consumes infected tissue containing cysts, they become infected.
Why is this so important?
For immunocompetent people, toxoplasmosis is a mild and self-limiting infection that may go undetected. If symptoms are present, they may include:
- Swollen lymph nodes
- Muscle soreness
- Flu-like symptoms
However, it is a different story if a primary toxoplasmosis infection occurs during pregnancy which can pass through the placenta and cause catastrophic damage to the fetus, including:
- Hydrocephalus (water on the brain)
- Hearing loss
- Hepatosplenomegaly (enlarged liver and spleen)
- Learning disabilities and mental retardation
- Low birth weight
We know that rats infected with T. gondii exhibit behavioural changes, namely, instead of being fearful of cat urine, they are attracted to it. This has led researchers to question if T. gondii affects human behaviour too, but the jury seems to be out on this (read here and here).
With the potential risks to the unborn baby, should a pregnant woman get rid of her cat?
So far, this article has painted a pretty bleak picture of toxoplasmosis infection, and it IS a serious topic. If you have had toxoplasmosis in the past, you are not at risk; the danger is if the pregnant woman develops infection for the first time during pregnancy, or if cysts in the tissues become reactivated due to immunosuppression.
One study found the biggest source of T. gondii infection in pregnant women is the consumption of undercooked meat. DVM360 reports that the most common sources of infection are raw or undercooked meat, unpasteurised goats milk, raw vegetables, contaminated water, and gardening.
With proper safety precautions, exposure can be greatly reduced. Cats are only a risk if they acquire infection and shed oocysts at the same time as a woman is pregnant.
It is not necessary to get rid of the cat before, during or after pregnancy. You can not catch toxoplasmosis from petting your cat. I tested negative to T. gondii during both of my pregnancies and remained that way, despite living with multiple cats.
How will I know if I have been infected in the past or recently?
A blood test to look for T. gondii antibodies can tell you if you have had toxoplasmosis (seropositive) and if the infection was in the distant past, or is current. This test looks for two types of antibodies, IgM antibodies indicate a current infection and IgG antibodies will be present due to a past infection.
It is recommended that if you are planning to become pregnant, or already pregnant that you ask your doctor for a blood test to see if you are seropositive or seronegative. It is also possible for veterinarians to perform the same test on cats.
What happens if my blood test reveals toxoplasmosis infection for the first time?
If the blood test reveals that a pregnant woman has an active infection for the first time, your practitioner will prescribe the antibiotic Spiramycin to decrease the risk of vertical (placental) transmission.
- If you are pregnant, do not scoop out litter trays, if this is not possible, wear rubber gloves and a mask. Scoop solids into a plastic bag, tie it shut and dispose of in the outside garbage. Wash hands thoroughly afterwards.
- Remove solids from litter trays twice a day (morning and night).
- Wash fruit and vegetables thoroughly before consumption.
- Wash hands before and after handling meat.
- Use a separate chopping board for meat and fruit/vegetables.
- Wash all utensils and chopping boards thoroughly in hot soapy water or the dishwasher.
- Cook meat (excluding chicken) to at least 145° F (63° C) and it is no longer pink inside.
- Cook chicken and ground meat (mince) to at least 74°C (165° F).
- Don’t eat raw oysters or clams.
- Always wash your hands before eating.
- Avoid contact with soil and sand, wear gardening gloves when gardening and wash your hands once you are finished.
- Feed your cat a commercial diet of canned and/or dry food. If you do want to continue feeding a raw diet, freeze at either -10 degrees C for 3 days or -20 degrees C for 2 days to kill tissue cysts.
- Keep your cat indoors to prevent hunting or environmental exposure to infective oocysts.
- Do not drink unpasteurised milk.
- Cover outdoor sandpits when not in use.
- Empty the contents of litter trays in the garbage outside.
- There is only a 10-14 day window when a newly infected cat sheds T. gondii oocysts in the feces.
- It takes at least 24 hours for oocysts in the cat’s feces to become infective.
- A person must have had no prior exposure to T. gondii to become infected and pass on the infection to an unborn baby unless a previous toxoplasmosis infection is reactivated. This only occurs in people whose immune systems are compromised, such as those who have AIDS.
- Washing hands, fruit and vegetables, freezing and/or cooking meat, and daily removal of cat feces greatly reduces the chances of infection.
- You must ingest the infective oocysts via feces, environmental contamination, or via meat that contains cysts.
- Cats can not infect you via bites, scratches, or when you pet them.
- The average indoor cat lives for 12 years and if infected with T. Gondii will shed oocysts for two weeks, which accounts for approximately 0.35% of the cat’s lifespan. When you factor in that oocysts don’t become infective for 1-5 days, you can see that the chance of infection via the average indoor cat is slim. Undercooked meat and unwashed fruit and vegetables and contaminated soil post a much greater risk.