Toxoplasma gondii (T. gondii) is a single celled parasite that infects most warm-blooded animals, including cats and humans. It is a parasite that, while a real concern for certain groups in the population, is often misunderstood when it comes to our feline companions.
What Is Toxoplasmosis?
Toxoplasmosis is a disease process that is caused by the parasitic organism T. gondii and, while it is one of the most common parasitic diseases, it does not usually cause any clinical symptoms in cats (or people). T. gondii has a fairly complex life cycle. It involves different cystic forms, definitive hosts (those in which the parasite can reproduce by forming eggs, also called oocysts, that are then shed in the host's feces), as well as intermediate hosts (those in which the parasite must reproduce by cloning itself and then clustering those clones within cysts). Domestic and wild cats are the definitive hosts of T. gondii and will shed oocysts in their stool. Any other animal a T. gondii organism infects is an intermediate host.
Cats become infected by hunting animals that are infected with the parasite. When an intermediate host becomes infected with T. gondii the organism replicates and the cysts that develop will collect in various parts of the host animal's body. The host animal will carry these cysts throughout the course of it's life. If the host animal is ever consumed, whether by a predator that kills it or a scavenger that consumes it after death, those cysts then infect the animal that eats the host. Any predator, including cats, is at risk of infection by T. gondii The exact prevalence in cats isn't fully known, but it is believed that anywhere from 15-40% of cats have become infected with Toxoplama as some point.
It should be noted that with the growing popularity of raw feeding, contaminated food is another route by which your cat can become infected with the parasite. If you have your heart set on feeding your cat raw food, there are commercial freeze dried brands that undergo high pressure pasteurization (HPP) to effectively kill any pathogens that without actually cooking the food. Of course, it's always easier to avoid the problem altogether and feed your cat a cooked diet, whether commercial or homemade.
When a cat ingests the T. gondii organism from an infected intermediate host, the parasite is released from the cysts that were formed in the intermediate host and into the GI tract. Once this happens, the parasite can begin reproducing by forming oocysts that are shed in the cat's stool. Cats can begin shedding oocysts in as little as 3 days post ingestion and can continue to shed them anywhere from 1 week up to 3 weeks. Infected cats do not shed oocysts continually, though.
Furthermore, an oocyst is not immediately infectious upon excretion in a piece of stool. The oocyst must first sporulate, a process that can take between 1 and 5 days, depending on environmental conditions. Oocysts can also survive a very long time in the environment. Sometimes well over a year, depending on the conditions.
T. gondii is tricky, though. When an organism infects a definitive cat host, not all the parasite will remain the cat's GI tract. Some will deeply embed themselves within the intestinal walls of the cat and multiply there. Still others will migrate even further within the cat. Regardless of where these T. gondii end up, though, the cat's immune system will force these specific organisms into a dormant, cystic form. These cysts are just as infectious to a predator as cysts formed in an intermediate host.
Can You Get Toxoplasmosis From Your Cat?
Cats are the most popular household pet in the US. Their ability to shed oocysts for days to weeks at a time would seem to make this parasite a growing public health concern. Are cat owners more significantly at risk of infection than non-cat owners? Well, the same routes of infection in cats hold true in people. Eating contaminated raw or undercooked meat and/or not adequately washing produce that has been grown in contaminated soil are also ways that people can become infected. Of course, if your cat is in fact infected and actively shedding oocysts when you clean out her litterbox and then fail to wash your hands after, that is also a route of infection.
So while, yes, having poor hygiene after cleaning out the cat box is one way a person can become infected with T. gondii, it isn't the only way.
People also typically have the same risk of disease as cats. Most people that contract T. gondii won't become sick from the parasite. However, if a women is infected while she is pregnant, there is about a 20-50% risk of fetal infection. The majority of these will remain asymptomatic, but if a child becomes infected in utero, if it makes it to term, it may have birth defects, neurological defects, and/or ocular problems.
Cat can be tested for toxoplasmosis by your veterinarian. The test is a special blood test that will most likely need to be sent off to an outside lab, so you may not get results for a few days. If your cat tests positive for toxoplasmosis than your cat has been exposed to the parasite at some point in her life but that does not reflect on whether your cat is actively shedding oocysts at that time. If your cat tests negative for toxoplasmosis than your cat has not been exposed to the parasite.
Toxoplasmosis is easily treated with a simple course of antibiotics. If your cat has significant inflammation associated with her infection, your vet may also prescribe a course of corticosteroids.
Most cats don't get clinically ill from infection by T. gondii, though. Occasionally, though, if a cat's immune system isn't strong enough to fight the organisms that migrate from the GI tract, the cat will begin showing clinical signs of the disease. These can include fever, loss of appetite, and lethargy, but can also include a myriad of other symptoms. Depending on where the parasite migrates, these other symptoms may include pneumonia or breathing problems, inflammatory eye problems, jaundice and liver disease, and even tremors/seizures. If your cat does start exhibiting signs, though, treatment is a simple course of antibiotics. If there is inflammation associated with the eyes or nervous system, your vet may also add in a round of corticosteroids.
Toxoplasmosis in cats is something that all cat owners should be aware of but not necessarily something that they need to lose sleep over. The benefit of being a definitive host to the parasite is that it does not benefit the parasite to make the host animal clinically sick. So risk of clinical disease if your cat does become infected is low. If you have concerns about contracting T. gondii from your cat, rest assured that basic good hygiene can prevent you from becoming infected. If you're pregnant, wearing gloves while cleaning the cat box is an added safeguard. Of course, you can also simply snuggle your cat while your significant other cleans the cat box for you. Historically there has been a lot of misinformation concerning toxoplasmosis and cats. If you are concerned that your cat might be at risk for toxoplasmosis your veterinarian can help you decipher fact from fiction.