Toxoplasmosis is a widespread disease caused by the parasite Toxoplasma gondii (T. gondii). This single-celled organism affects almost all warm-blooded animals, including our beloved pets and humans, making it one of the most common parasitic infections globally. While cats play a crucial role in the T. gondii life cycle, they rarely suffer severe clinical disease from it. Although T. gondii generally poses minimal health risks to healthy adult humans (with some exceptions), the Centers for Disease Control and Prevention (CDC) has recognized toxoplasmosis as a significant neglected parasitic infection in people due to its high occurrence. It’s estimated that over 60 million individuals in the United States are infected.
The Complex Life Cycle of Toxoplasma gondii and Cats
The T. gondii parasite has a complex life cycle involving two types of hosts: definitive hosts, where the parasite sexually reproduces and produces oocysts (eggs), and intermediate hosts, where it asexually reproduces, forming tissue cysts. Cats, both wild and domestic, are the only known definitive hosts for T. gondii.
When a cat consumes infected prey or raw meat, T. gondii cysts are released into their digestive system. Here, the parasite undergoes sexual reproduction, leading to the production of oocysts. Infected cats then shed millions of these oocysts in their feces. Cats newly exposed to T. gondii typically start shedding oocysts within three to ten days after consuming infected material and continue for approximately 10 to 14 days. Oocysts are incredibly resilient and can survive in the environment for over a year.
Furthermore, some T. gondii parasites from ingested cysts penetrate the cat’s intestinal wall and multiply into tachyzoites. These tachyzoites spread beyond the intestine to other parts of the cat’s body. Eventually, the cat’s immune system forces the parasite into a dormant stage, forming tissue cysts in muscles and the brain. These cysts contain bradyzoites, a slow-multiplying form of Toxoplasma.
Other animals, including humans, act as intermediate hosts and can become infected by ingesting either tissue cysts or oocysts. Oocysts excreted in cat feces are not immediately infectious. They need to undergo sporulation, a process taking one to five days depending on environmental conditions, to become infectious. Cat feces containing sporulated oocysts are a source of infection whether found in litter boxes, gardens, or sandboxes used by outdoor cats. Once an intermediate host ingests sporulated oocysts, tissue cysts develop throughout their body and persist for life, remaining infectious to cats, humans, and other intermediate hosts that consume cyst-containing tissue. In some instances, T. gondii tachyzoites may be present in the milk of infected cows and goats.
Clinical Signs of Toxoplasmosis in Cats
Most cats infected with T. gondii exhibit no visible signs of illness. However, toxoplasmosis can manifest clinically, especially when a cat’s immune system fails to control the spread of tachyzoites. The disease is more likely to occur in cats with weakened immune systems, such as young kittens or cats with feline leukemia virus (FeLV) or feline immunodeficiency virus (FIV).
Common symptoms of toxoplasmosis in cats include fever, loss of appetite, and lethargy. Other symptoms can vary depending on whether the infection is acute or chronic and the location of the parasite within the body. In the lungs, T. gondii infection can lead to pneumonia, causing progressively worsening breathing difficulties. Liver infections may result in jaundice, characterized by a yellowish discoloration of the skin and mucous membranes.
Toxoplasmosis can also affect the eyes and central nervous system (CNS), leading to:
- Uveitis: Inflammation of the uvea, the pigmented part of the eye.
- Retinitis: Inflammation of the retina.
- Anterior chamber inflammation: Inflammation of the space between the lens and cornea.
- Abnormal pupil size and responsiveness to light.
- Blindness.
- Lack of coordination.
- Increased sensitivity to touch.
- Personality changes.
- Circling.
- Head pressing.
- Ear twitching.
- Difficulty chewing and swallowing.
- Seizures.
- Loss of bladder and bowel control.
Diagnosing Toxoplasmosis in Cats
Diagnosing toxoplasmosis typically involves considering a cat’s medical history, clinical signs, and laboratory test results. Measuring two types of antibodies to T. gondii in the blood – IgG and IgM – is helpful in diagnosing toxoplasmosis.
- High IgG antibody levels in a healthy cat suggest a previous infection and immunity. These cats are unlikely to be shedding oocysts and are not considered a source of infection.
- High IgM antibody levels may indicate an active, recent infection.
- Absence of T. gondii antibodies in a healthy cat suggests susceptibility to infection, and the cat could shed oocysts for up to two weeks after initial infection.
Detecting oocysts in feces is not a reliable diagnostic method as they resemble oocysts of other parasites. Furthermore, cats only shed oocysts for a short period and may not be shedding when showing disease symptoms. A definitive diagnosis often requires microscopic examination of tissue samples to identify tissue changes and the presence of tachyzoites.
Treatment Options for Feline Toxoplasmosis
Treatment for toxoplasmosis in cats usually involves a course of the antibiotic clindamycin, which may be used alone or with corticosteroids if there is significant inflammation in the eyes or CNS. Ideally, treatment should start immediately after diagnosis and continue for several days after symptoms resolve. In acute cases, treatment may begin based on high initial IgM antibody levels. If clinical improvement is not observed within two to three days of treatment, the diagnosis of toxoplasmosis may be reconsidered.
Prognosis for Cats with Toxoplasmosis
The prognosis for cats with toxoplasmosis depends on the affected organs, the time between infection and treatment, and the cat’s response to therapy. Cats with CNS and eye symptoms may respond more slowly to treatment but often have a favorable prognosis if they show improvement within 2-3 days of starting treatment. However, the prognosis for cats with liver or lung involvement is generally less favorable.
Preventing Toxoplasmosis in Cats and Reducing Human Risk
Preventing toxoplasmosis in cats involves minimizing their exposure to infective oocysts and reducing oocyst shedding into the environment. Key preventive measures include:
- Feeding cats commercially prepared, cooked food. Heat effectively inactivates T. gondii cysts.
- Preventing cats from eating raw meat or prey.
- Limiting cats’ access to areas where food-producing livestock are housed or food is stored.
While cats are essential to the T. gondii life cycle, the risk of human infection from pet cats is relatively low. Owning a cat does not automatically mean you will get toxoplasmosis. Since T. gondii oocysts require at least 24 hours to sporulate and become infectious, daily removal of feces from the litter box while wearing gloves and washing hands afterward significantly reduces the risk of infection. Direct contact with an infected cat is unlikely to transmit the parasite, as they usually do not carry it on their fur. Cat bites and scratches are also unlikely routes of infection. Indoor cats that do not hunt or consume raw meat have a minimal risk of T. gondii infection.
In the United States, humans are more likely to contract toxoplasmosis from consuming raw meat and unwashed produce than from cat feces. Gardening in soil contaminated with cat feces also poses a risk, which can be mitigated by wearing gloves and washing hands after gardening.
Pregnant women and individuals with compromised immune systems are at higher risk of health complications from T. gondii exposure. Congenital toxoplasmosis, infection of a fetus during pregnancy, is a significant concern. Between one-third and one-half of infants born to mothers who acquire Toxoplasma during pregnancy are infected. While most infected mothers and infants are initially asymptomatic, many children may develop symptoms later in life, including vision and hearing loss, intellectual disabilities, and in severe cases, death.
In immunocompromised individuals, such as those with AIDS or undergoing immunosuppressive therapy, toxoplasmosis can cause lymph node enlargement, CNS and eye disorders, respiratory problems, and heart disease. Relapses are common in these patients, particularly those with AIDS, and the mortality rate is high.
Contrary to past advice, the CDC currently advises that pregnant women and immunocompromised individuals do not need to avoid cats. For the most current recommendations regarding toxoplasmosis risk in humans, please consult the CDC website.
For specific health concerns regarding toxoplasmosis in humans, please consult a healthcare professional.
Currently, there is no vaccine available to prevent toxoplasmosis in animals or humans.
Updated June 2018
