Last week, a woman brought in Blue for his six-monthly check-up and annual vaccination.
Blue is a house cat in a good state of health and very pleasant temperament. During Blue’s check-up, his owner asked me if there was a way to prevent her cat from getting toxoplasmosis as she and her husband were planning to have a family.
Of all the diseases humans can get from cats, toxoplasmosis is possibly the most well known and heavily publicised. However, considerable misinformation about this disease abounds and this mostly relates to the role cats play in contributing towards the contagion of the disease in humans.
Toxoplasmosis comes from being infected with a single-celled microscopic parasitic organism called Toxoplasma gondii (T. gondii). It is a highly successful parasite that is not only present worldwide but can also virtually infect any warm-blooded animal to different degrees. Despite this, T. gondii rarely causes any significant illness in people or animals. To understand why, we need to look at cats’ role in the disease.
Although warm-blooded humans or animals are needed for the parasite to survive, the parasite needs to be present inside a cat for it to complete its full life-cycle and be able to spread and contaminate the environment. But whereas cats are critical to the survival and spread of T. gondii infections, humans usually get infected with T. gondii by consuming undercooked meat that contains the parasite.
The interesting thing is that even cats usually get infected by eating raw or inadequately cooked meat infected with T. gondii. Such meat can include beef, lamb or pork and, more commonly, wild prey such as mice or other small rodents.
This is why cats infected with T. gondii are more likely to be stray cats or cats allowed to roam outside and become active hunters. Domestic cats that are fed undercooked or raw meat will also have a much higher risk of being infected with T. gondii.
Depending on their lifestyle, it is estimated that of the cats that may be infected with T. gondii, only very few will ever show clinical signs. When symptoms do become apparent, they can include fever, loss of appetite, weight loss and general lethargy. In its more severe form, it can cause pneumonia, inflammation of the eyes and even neurological disturbances.
Simple everyday hygiene measures can be taken to reduce the risks of infection, making it safe to own and enjoy the companionship of a cat
A few days after a cat has been infected for the first time, it will shed millions of T. gondii eggs in its faeces. The eggs are shed only for a short period of time, typically less than 14 days. The cat’s immune response will then kick in and block the production of T. gondii eggs altogether. It is rare for a cat to repeat shedding eggs after their first infection but if this does occur, it usually results in a much smaller number of eggs being shed.
So how do humans come into the picture?
Humans can act as intermediate hosts for T. gondii. This means that humans can become infected but never shed T. gondii in their faeces as cats do. Humans become infected through the ingestion of T. gondii eggs from, for example, accidental contamination with cats’ faeces actively suffering from the disease, touching soil contaminated with spores that sprouted on T. gondii eggs, eating fruit and vegetables that were similarly contaminated and not properly washed before consuming or by eating cysts found in raw or undercooked beef, lamb or pork meat.
Farm animals destined for human consumption would have become infected by similarly accidentally ingested T. gondii eggs from cats living in their surrounding environment. In this case, these animals too serve only as intermediate hosts, but the fact is that the infection can pass to humans. In this respect, fresh meat is the most risky since freezing meat for several days will kill most tissue cysts.
It is estimated that more than 500 million people are infected worldwide and, just as with cats, the vast majority will exhibit no significant clinical signs. There are exceptions though and, when this happens, the effects on people usually depends upon their state of health or development.
In healthy humans with a normally functioning immune system, the clinical signs of toxoplasmosis are usually mild and may actually pass undetected or masked as mild, flu-like symptoms. However, individuals with compromised or impaired immune systems, such as those receiving anti-cancer therapy or those with acquired immunodeficiency syndrome (HIV/AIDS) may suffer severe symptoms.
There are also high-risk groups who are more likely to be at risk from contracting a more severe form of this disease. These include pregnant women, as well as babies inside their womb, newborns and infants and the elderly. Should they be unlucky enough to get infected, symptoms of infection in this group could manifest itself as miscarriage, stillbirth, physical and/or mental birth defects, problems affecting the nervous system and eyes and encephalitis (inflammation of the brain).
The bottom line is that research indicates that owning cats or having contact with cats does not increase the risk of T. gondii infection in humans. If you fall into this category and have questions about this disease, your vet will be able to give you guidelines on how to reduce even further your chances of contracting this disease, such as careful handling of litter trays and cat faeces, or accidental contamination thereof if you have cats around you, or avoidance altogether if you or your family members are in any way immunosuppressed.
If your vet suspects a T. gondii infection in your cat, they can diagnose this disease through a number of ways: direct faecal analysis, identifying the parasite during active infestation, DNA identification of T. gondii, known as Polymerase Chain Reaction (PCR), or by serum antibody testing. The latter would often be the method of choice, as it has a higher success rate of detecting infection, would be positive from two weeks post infection and detection can persist for many years.
The risks of acquiring toxoplasmosis from a cat are extremely small and most people are infected through other routes. Simple everyday hygiene measures can be taken to reduce the risks of infection, making it safe to own and enjoy the companionship of a cat such as Blue.
thisweekwiththevet@gmail.com
Dr Martin Debattista is a veterinary surgeon.