Introduction
Toxoplasmosis is an infection caused by the parasite Toxoplasma gondii. It is a common infection in cats that can have serious implications if left untreated. The parasite spreads through ingesting infected raw meat or contact with cat feces containing T. gondii oocysts. Toxoplasmosis is concerning in cats because it can lead to neurological problems, vision loss, and even death in some cases. Key questions around this condition include what percentage of house cats are infected, how do cats get infected, what are the symptoms, and how can it be prevented and treated.
Transmission
Toxoplasmosis spreads when cats ingest infected rodents, birds, or other small animals. Cats become infected by eating prey that contains Toxoplasma gondii tissue cysts. Inside the cat’s intestine, the cysts rupture and release infective bradyzoites that penetrate the intestinal epithelium and transform into tachyzoites that rapidly multiply and spread throughout the body. The tachyzoites eventually develop into bradyzoite tissue cysts, often localized in brain and muscle tissue. Cats remain infected for life. They shed millions of oocysts in their feces for one to three weeks after initial infection. Oocysts passed in feces are not immediately infectious but require 1-5 days of environmental exposure to become infective.
According to the CDC, “Cats get Toxoplasma infection by eating infected rodents, birds or other small animals, or anything contaminated with feces from another cat that is shedding the parasite.”
Source:
https://www.cdc.gov/parasites/toxoplasmosis/toxoplasmosis_catowners.html
Symptoms
Most cats infected with toxoplasmosis do not show any symptoms because their immune system usually keeps the parasite from causing illness. However, some cats can develop symptoms when first infected or if they have a compromised immune system.
Common symptoms of toxoplasmosis in cats include fever, loss of appetite, lethargy, and enlarged lymph nodes. More severe symptoms may include pneumonia and neurological signs like incoordination, circling, behavior changes, and seizures. In rare cases, toxoplasmosis can also cause inflammation in the eyes leading to vision problems.
The symptoms of an active toxoplasmosis infection usually last around 2-3 weeks as the cat’s immune system fights it off. However, cats with weakened immune systems may experience more prolonged or recurrent symptoms that require veterinary treatment.
Diagnosis
Toxoplasmosis is difficult to diagnose definitively in cats. Vets will typically run blood tests first to check for antibodies against T. gondii, which would indicate exposure. The most common blood tests are the modified agglutination test (MAT) and the indirect fluorescent antibody test (IFA). A positive antibody test means the cat has been exposed to T. gondii at some point but does not necessarily mean they have an active infection.
If symptoms warrant further testing, vets may examine CSF (cerebrospinal fluid) surrounding the brain and spinal cord. They may also take tissue samples for biopsy. PCR (polymerase chain reaction) tests on these samples can sometimes detect T. gondii DNA and confirm active infection. However, negative PCR results do not rule out toxoplasmosis as the cause of symptoms.
Overall, diagnosis involves assessing the presence of clinical signs, antibody test results, and response to anti-parasitic treatment. There is no single definitive diagnostic test for toxoplasmosis in cats.
Sources:
https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/toxoplasmosis-cats
https://vcahospitals.com/know-your-pet/toxoplasmosis
Treatment
There is no specific treatment for cats that are infected with toxoplasmosis but do not show any signs of illness. However, cats that develop clinical signs of toxoplasmosis are treated with antibiotics, usually clindamycin. According to the Cornell Feline Health Center, clindamycin is effective against toxoplasmosis and can be given by mouth. The antibiotic treatment typically lasts for 4-6 weeks. Cats with central nervous system or ocular issues may respond more slowly to antibiotic therapy but tend to have better prognoses if their clinical signs improve within the first couple weeks of treatment.
Other antibiotics like azithromycin may also be used. In some cases, the veterinarian may prescribe a combination of antibiotics to treat the infection. Corticosteroids may be administered as well to reduce inflammation. Treatment is aimed at eliminating the active infection and managing any symptoms the cat is experiencing.
Prevalence Data
Studies estimate that globally, about 30-40% of cats are infected with Toxoplasma gondii. However, seroprevalence rates can vary greatly by region. A 2020 study analyzing data from 79 countries found toxoplasmosis seroprevalence ranging from 0% to 97% in domestic cats [1].
In North America and Europe, estimated seroprevalence in domestic cats is around 30-40%. However, rates are much higher in some areas like Central and South America (61-83%) and parts of Africa (51-98%). Indoor cats generally have lower rates than outdoor cats. One study in the U.S. found indoor cats had 18.5% seroprevalence compared to 61.5% in outdoor cats [2].
Overall, about one-third of house cats globally are estimated to have toxoplasmosis. However, infection rates vary widely based on location and whether cats have outdoor access.
Risk Factors
Certain behaviors and conditions put cats at a higher risk for contracting toxoplasmosis.
Outdoor access is a major risk factor, as cats can become infected by eating infected prey like birds and rodents. Cats that hunt are more likely to ingest tissue cysts and become infected. According to the CDC, over 90% of cats contract toxoplasmosis this way.
Younger cats are at higher risk, as they have not yet developed immunity from prior exposure. Kittens less than 1 year old are more susceptible according to the Cornell Feline Health Center. Older cats that go outdoors are still at risk if they hunt prey.
Stray cats and feral cats also have very high rates of toxoplasmosis infection, often over 95%, due to greater exposure from hunting and eating raw meat outdoors (CDC).
Prevention
To prevent toxoplasmosis in cats, it’s important to take measures to reduce their exposure to infective oocysts. For indoor cats, this means keeping them indoors and not allowing them to roam outside where they could ingest infected soil, water or prey (CDC, 2022). Cats should be fed commercial dry or canned cat food and never raw meat, which could be a source of infection (CDC, 2022).
All new kittens and cats being adopted from shelters should be tested for toxoplasmosis and treated with anti-parasitic medication if positive. Indoor cats should be periodically tested and dewormed as a preventative measure (Cornell Feline Health Center, 2022). Litter boxes should be cleaned daily, wearing gloves, and hands washed thoroughly afterwards since oocysts shed in feces can infect humans and other cats.
For cats with outdoor access, options include supervised time outdoors on a leash or in an enclosed “catio”, or restricting outdoor access at night when hunting is more likely. This reduces their chances of ingesting infected prey. However, the only sure way to prevent infection is to keep cats strictly indoors.
Implications for Owners
Toxoplasmosis is usually harmless for cats, but can pose risks for some human owners. For people with healthy immune systems, the CDC states the risk is low as “healthy individuals who become infected after birth have few symptoms because their immune systems usually keep the parasite from causing illness.” However, the Mayo Clinic notes that “for people with weakened immune systems, toxoplasmosis can cause serious long-term or life-threatening problems.” This includes those with HIV/AIDS, organ transplant recipients taking immunosuppressant drugs, and infants born to mothers who became infected with toxoplasmosis during pregnancy.
The highest risk is for pregnant women or women planning to become pregnant. According to the CDC, contracting toxoplasmosis for the first time during pregnancy or just before pregnancy can cause miscarriage, stillbirth, and severe illness in newborns. Preventative measures are recommended such as avoiding changing cat litter, wearing gloves when gardening, washing hands after touching raw meat, and avoiding the consumption of raw/undercooked meat. For cat owners trying to conceive or who are pregnant, limiting exposure to sources of toxoplasmosis is advisable. However, indoor cats who do not hunt prey or consume raw meat pose little risk.
While concerning, toxoplasmosis rarely has severe effects on healthy cat owners. Proper hygiene around potential sources can prevent infection. For those with compromised immunity or who are pregnant, limiting contact with the parasite is recommended. Overall, owning a house cat presents a low risk for acquiring toxoplasmosis in humans.
Conclusion
In summary, toxoplasmosis is a parasitic infection caused by Toxoplasma gondii that can infect most warm-blooded animals, including cats. While infected cats usually show no symptoms, toxoplasmosis infection during pregnancy can cause serious birth defects in humans. Studies show between 30-40% of cats are infected with toxoplasmosis in the United States. Kittens and outdoor cats have a higher risk of contracting the parasite. Simple precautions like keeping cats indoors, wearing gloves when cleaning the litter box, washing hands afterwards, and properly cooking meat can prevent transmission. If you are pregnant or immunocompromised, consider having someone else clean the litter box daily. While toxoplasmosis is common in cats, the risks can be easily managed with proper handling and care.