Toxoplasma gondii is a coccidian, an obligate intracellular parasite that infects virtually all warm-blooded species, including humans. Infection with T. gondii is very common: between 30-40% of the world’s population is seropositive.
Toxoplasmosis in humans can present in various ways:
- In immunocompetent individuals, it causes subclinical symptoms or mild flu-like illness.
- In immunocompromised individuals (such as AIDS patients, patients undergoing chemotherapy or taking immunosuppressive drugs, leukaemia or lymphoma patients, etc.), severe and even fatal forms of the disease may occur, with symptoms of pneumonia, myocarditis and meningoencephalitis. In these individuals, the clinical picture may be due to a recent infection, but more often it is due to the reactivation of an old infection as a result of immunosuppression.
- In pregnant women not previously exposed to T. gondii (seronegative), infection can cause miscarriages, neonatal deaths, significant congenital malformations, and severe neurological sequelae in the foetus. The severity of the symptoms caused by infection with Toxoplasma gondii during pregnancy varies with the age of the foetus at the time of infection; it is greater in infections contracted during the first trimester of pregnancy.
However, if the pregnant woman was infected prior to pregnancy (and therefore has antibodies against T. gondii), the foetus will never be infected, as her immunity protects her against new infections.
In Spain, the detection of antibodies against Toxoplasma gondii is part of the routine tests carried out during gynaecological check-ups that women attend during pregnancy.
Toxoplasmosis in cats is a rare disease. Cats are the definitive host for this parasite, and the vast majority of carrier cats never show clinical signs of disease at the time of infection. When these signs do occur, the severity of the condition depends on the organ affected and the degree of necrosis caused by the parasite.
- In immunocompromised cats and kittens, it can cause severe symptoms such as pneumonia, liver disease, pancreatitis, myocarditis, and encephalitis.
- In immunocompetent cats, it can occasionally induce symptoms such as fever, myositis, and eye disease, mainly uveitis.
Since cats are the only animals that can eliminate infectious forms of the T. gondii parasite in their faeces, doctors and gynaecologists often warn pregnant women or women planning to have children about the potential dangers of contact with cats.
There is ample scientific evidence showing that transmission of T. gondii to humans through contact with the faeces of an infected cat is unlikely and that the vast majority of people who become infected do so through the ingestion of undercooked meat, vegetables contaminated with oocysts of the parasite, or through direct contact with contaminated soil. It is therefore wrong to assume that whenever a person becomes infected with T. gondii, the source of the infection has been contact with a cat.
Cats infected with T. gondii are responsible for spreading the parasite into the environment in their faeces, but . To be infectious, the oocysts must sporulate, which occurs within 24 hours, and freshly eliminated cat faeces do not pose a real risk of infection, as they contain oocysts that have not yet sporulated and are not infectious for 5 days after the faeces are deposited.
During primary infection with T. gondii, cats release unsporulated oocysts in their faeces for only one to three weeks, after which they remain carriers of cysts in their muscles and viscera. From this point onwards, they no longer eliminate oocysts in their faeces and therefore pose no risk to humans.
Cats become infected by:
- – Eating meat and tissue infected with cysts from undercooked meat.
- – Eating meat and tissue infected with cysts from prey hunted in their habitat.
- – By drinking uncontrolled water (water from pots, rivers, etc.) contaminated with sporulated oocysts.
- – During pregnancy, through transplacental spread in seronegative mothers.
- – During lactation.
- – Through a blood transfusion from a cat with an active infection.
Therefore, cats should preferably be fed commercial cat food. Any other food must be cooked at high temperatures for 10 minutes, and if feeding them raw meat, it must be frozen at temperatures below -20ºC for 2 days. You should try to prevent them from hunting, and to do this you can use bells to warn their prey or take them on controlled outings under supervision.
People become infected by:
- Eating undercooked or raw meat.
- Handling raw meat without gloves.
- Drinking raw goat’s milk.
- By eating contaminated fresh vegetables that have not been washed properly.
- During gardening or in children’s playgrounds, if the sand is contaminated (infection requires unwashed hands to be put in the mouth). By drinking water contaminated with sporulated oocysts.
- Ingesting faeces from cats infected with Toxoplasma gondii that are in the oocyst elimination phase. At least 24 hours must have elapsed since defecation.
- Infection does not occur by touching or petting cats. Small animal veterinarians, who are in frequent physical contact with cats, do not have a higher seroprevalence than people in other professions.
Measures to be taken to prevent infection by a pregnant woman or any other person:
- Meat should always be cooked at high temperatures for 10 minutes, or frozen at -20ºC for two days if it is to be consumed rare.
- Vegetables should always be washed thoroughly before consumption.
- Only drink potable water or water from a known source, or filter/boil water if its source is unknown.
- Wear gloves when gardening and handling raw meat, or wash your hands thoroughly afterwards.
- Cat litter trays should be cleaned daily with a scoop. Pregnant women should avoid handling the litter tray, but if this is not possible, it is advisable to wear disposable gloves and a mask. The best method for disinfecting the tray is boiling water or pressurised steam, as sporulated oocysts are resistant to most disinfectants.
Current scientific evidence shows that the transmission of toxoplasmosis from cats to humans, including pregnant women and AIDS patients, is highly unlikely if basic hygiene rules are followed. We therefore consider it completely unjustified to abandon or reject cats in the event of a pregnancy in the family, even if this is the advice of some doctors.
Cats provide numerous psychological benefits and emotional well-being to people who enjoy their company, especially when they are part of the family as one of its members.
The usefulness of blood tests to determine whether a cat is seropositive or seronegative is debatable, as they do not indicate whether or not the cat is shedding oocysts at that time, and the preventive and hygienic measures that pregnant women should take are the same in both cases.
(Original article owned by GEMFE (Group of Specialists in Feline Medicine of AVEPA (Association of Spanish Small Animal Veterinarians)
