Toxoplasmosis (Toxoplasma gondii) is a single-celled parasite that infects many warm-blooded animals, including cats, dogs, and also 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. The parasite often doesn't cause any significant symptoms or concerns in a cat unless your pet has a weak immune system.
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 involving different cystic forms and hosts. There are two types of hosts for T. gondii. A definitive host houses the parasite as it reproduces itself via the production of eggs, called oocysts that will then shed in the host's feces. An intermediate host houses the parasite as it clones itself without the production of eggs.
Domestic and wild cats are the only type of definitive hosts of T. gondii and humans are considered intermediate hosts. Though it was a mystery why cats where the chosen definitive host for the parasite, research has shown that T. gondii can only reproduce in a cat because the feline contains a very specific type of essential fatty acid.
Symptoms of Toxoplasmosis in Cats
Most healthy cats never become clinically ill from an infection by T. gondii. The risk of clinical disease if your cat does become infected is low. Some of the organisms in a cat may deeply embed themselves within the intestinal walls 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.
Occasionally, though, if a cat's immune system isn't strong enough to fight the organisms that could potentially migrate from the gastrointestinal tract, the cat will begin showing mostly mild clinical signs of the disease. A young kitten or a cat with a weaker immune system that is already ill with feline leukemia virus (FeLV), or feline immunodeficiency virus (FIV) might present the following symptoms if infected with T. gondii:
A cat infected with the parasite may have a fever, which is one of the most common symptoms. Though it's best left to your vet to take your cat's temperature with a thermometer, you can see signs of a fever. Your cat may shiver, feel listless, lose its appetite, and possibly have a rapid heartbeat.
Loss of Appetite
Another common, but non-specific symptom your cat may show is a lack of appetite. Disinterest in food may accompany trouble breathing. If a cat can't smell its food it is likely to stop eating.
Any time a cat is ill, it will feel listless, including if it is infected with this parasite.
If the parasite has migrated into the lungs, your cat may have difficulty breathing. This condition may lead to pneumonia and the breathing will become continually worse. As a result, your cat may have difficulty swallowing while eating.
If the parasite is in the ocular area, your cat will show a host of symptoms, from inflammation, abnormal pupil sizes, sensitivity to light, and potential blindness.
If the parasite has found a home in your cat's liver, your pet may appear jaundiced, though it may be subtle and difficult to observe. The cat's skin and mucous membranes, including the eyes, ears, and gums may take on a yellowish tinge.
When toxoplasmosis affects the central nervous system, your cat may begin to have tremors or seizures. A seizure could be a symptom of another disease so do not ignore this symptom and call your vet immediately.
The presence of the parasite may trigger changes in your cat's behavior. Some personality changes may include avoidance of being touched, walking in circles, pressing its head against a surface, constant ear twitching, incontinence, or loss of control of defecation.
Causes of Toxoplasmosis
Cats become infected by hunting small animals, such as birds and rodents, that are infected with the parasite. Contaminated food, especially from feeding a cat a raw diet, is another route by which your cat can become infected with the parasite.
When a cat (the definitive host) 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 goes into the cat's gastrointestinal 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 three days post-ingestion and can continue to shed them anywhere from one week up to three 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 (produce spores), a process that can take between one and five 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.
Diagnosing Toxoplasmosis in Cats
Your veterinarian can use a special blood test to diagnose toxoplasmosis. If your cat tests positive for toxoplasmosis then your cat has been exposed to the parasite at some point in its life but that does not reflect on whether your cat is actively shedding oocysts at that time. If your cat tests negative for toxoplasmosis then your cat has not been exposed to the parasite.
If your cat does start exhibiting signs of toxoplasmosis, it is easily treated with a simple course of antibiotics. If your cat has significant inflammation associated with an infection with the eyes or nervous system, your vet may also prescribe a course of corticosteroids.
Prognosis for Cats With Toxoplasmosis
The prognosis for a cat that shows symptoms of toxoplasmosis is guarded depending on the damage already done to the organs where the parasites have lived or the systems impacted by the infection. If the infection has affected the lungs or the liver the prognosis may not be favorable.
How to Prevent Toxoplasmosis
Toxoplasmosis in cats is something that all cat owners should be aware of, but more so if pregnant or immune-suppressed people will come into contact with your pet. Here are a few steps to take to reduce the risk of your cat and others coming into contact with the parasite:
- Keep your cat indoors to limit its contact with prey that is infected with the parasite.
- Change the cat litter box daily but avoid this task if you are pregnant or immunocompromised.
- Avoid handling stray kittens who may be infected.
- Feed your cat a diet of cooked commercial or homemade food rather than a raw diet of meat that can be infected. 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 without actually cooking the food.
Is Toxoplasmosis Contagious to Other Animals
Toxoplasmosis can be contagious to other animals but only in a specific way. 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 its 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.
Is Toxoplasmosis Contagious to Humans?
Toxoplasmosis can be contagious to humans. Most people that contract T. gondii won't become sick or symptomatic from the parasite. If you have concerns about contracting T. gondii from your cat, rest assured that basic good hygiene (washing your hands thoroughly afterward) can prevent you from becoming infected. If you're pregnant, wearing gloves while cleaning the cat box is an added safeguard, or completely avoiding it and letting someone else temporarily take over the task is best.
If a pregnant woman does become infected early in the pregnancy, the risk is low that the parasite will migrate into the fetus, but that percentage rises if the mother is infected later in the pregnancy. The majority of these women will remain asymptomatic. But if a child becomes infected in utero and if it makes it to term, it may have birth defects, neurological defects, and/or ocular problems. The defects rarely occur at birth but symptoms may develop later in life.
Having a cat is not the only way that a human can come into contact with the parasite. 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.
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Toxoplasmosis in Cats. Cornell University College of Veterinary Medicine.
Toxoplasmosis in Cats. Cornell University College of Veterinary Medicine.
Toxoplasmosis FAQs. Centers for Disease Control and Prevention.
Chaudhry SA, Gad N, Koren G. Toxoplasmosis and Pregnancy. Can Fam Physician. 2014;60(4):334-336.