What Is Toxoplasmosis

Overview

Can owning a cat be detrimental to your health? Do all cats harbour the “deathly” Toxoplasma parasite?

What is Toxoplasmosis?

Toxoplasmosis is a zoonotic infection. Zoonoses are infections that are caused by pathogens that are  passed from animals to humans.^1,2 Toxoplasmosis is caused by the parasite Toxoplasma gondii, which is spread through food and water contaminated with the parasite from cat faeces.²

Cats are the primary hosts of the toxoplasma parasite T. gondii. Infected cats can excrete millions of this parasite in the form of oocysts in their faeces which then spread and contaminate the environment around them.^1,2 Oocysts are one of several stages in the life cycle of parasites like T. gondii, during which the parasite is encapsulated in a hard and thick wall, essentially in a dormant state until the right conditions for its growth are met. 

T. gondii oocysts contained in the cat faeces then infect soil and water from which humans and other animals can become infected.²

Editor’s note: It may be useful to include a diagram of the life cycle of T. gondii to complement this section. Perhaps one such as this Life Cycle (antimicrobe.org) from the CDC could help.

Causes of toxoplasmosis

Animals can become infected after ingesting water, soil, or plant material contaminated with T. gondii oocysts. After ingestion, these oocysts  invade the animal's muscle and neural tissues. These animals then become intermediate hosts of the parasite and can infect humans and other animals who consume their flesh.²

Humans can get infected via several routesincluding:²

• Consuming water, raw fruits, and vegetables contaminated with T. gondii oocysts 
• Eating the meat of animals infected with the parasite (intermediate hosts) either raw or not properly cooked
• Accidentally ingesting oocysts while changing cat litter or gardening due to not washing their hands properly after carrying out either activity
• Drinking milk from infected animals 
• During the birthing process through direct contact with the body fluids of the pregnant person if that person has been infected 
• From blood transfusion or organ transplantation, though this rarely occurs now due to extensive screening tests carried out before blood transfusion or organ transplantation

The World Health Organization (WHO) estimates that more than 1 million cases of T.gondii infection from contaminated food are recorded yearly in the European region.²

Given that cats are typically the main source of the infective stage of the parasite for humans, people often worry about owning cats. Fortunately, you can’t catch T. gondii by petting cats.³ Further,  it’s worth clarifying that not all cats are sources of this parasite only cats that have been infected can cause toxoplasmosis in humans.

Signs and symptoms of toxoplasmosis 

Toxoplasmosis usually doesn’t  cause any symptoms in healthy individuals. In fact, about 80% of individuals infected with T. gondii don’t have any symptoms and usually clear the infection.⁴ Symptoms and complications usually occur primarily in individuals with a compromised immune system (either due to chemotherapy, medication, or a disease) or pregnant women, as the state of pregnancy also affects the effectiveness of their immune response.⁴

The signs and symptoms of toxoplasmosis are very similar to having the flu.  Unlike the flu, which usually lasts at most 2 weeks, however, the symptoms of toxoplasmosis can last from a few weeks up to 6 months. 

The symptoms of toxoplasmosis include:^5,6

• High fever
• Generalised body pain
• Feeling tired
• Feeling unwell 
• Sore throat
• Swollen glands

The good news is that, in healthy individuals, once you have had toxoplasmosis, you develop lifelong immunity to it.⁵ This means you can not get toxoplasmosis ever again. The exception to this is when a woman with a weakened immune system has toxoplasmosis before getting pregnant.²

The medicines used to treat toxoplasmosis do not clear the infection. Instead, treatment renders the infection dormant, meaning that it can be reactivated during pregnancy, potentially leading the baby to be born with congenital toxoplasmosis or even causing a miscarriage or stillbirth.^1,2,7

Toxoplasmosis can also lead to complications, especially individuals with a weakened immune system,  including inflammatory conditions affecting the brain (encephalitis), heart (myocarditis), lungs (pneumonitis), and eye (chorioretinitis). 

Management and treatment for toxoplasmosis

A large proportion of healthy individuals don’t present symptoms of toxoplasmosis when infected, as their immune system usually clears the infection over time without needing treatment.

If necessary, however, the, treatment and management for toxoplasmosis are tailored to the symptoms presented, the health of the infected individual's immune system, and if there are any complications associated with the infection.

Symptomatic individuals who are healthy and not pregnant are usually treated with a cocktail of an antiparasitic sulfonamide medicine, given in combination with a reduced form of folic acid to reduce the side effects of the antiparasitic agent, as well as an antibiotic.⁹

The same protocol is used for symptomatic individuals with a weakened immune system; however, , a longer duration of treatment is recommended. In these cases, treatment continues for up to 6 weeks after symptoms have resolved and can be continued up to 6 months after diagnosis.⁹

Pregnant women, infants, and babies with toxoplasmosis also receive a similar treatment regimen. Women who are less than 18 weeks pregnant are treated with an antibiotic if toxoplasmosis is not suspected or detected in the growing foetus. The antibiotic used reduces the mother-to-child transmission of the parasite.⁹ If, however, toxoplasmosis is detected after 18 weeks of pregnancy or if congenital toxoplasmosis is suspected, the same regimen used for symptomatic individuals is used.⁹

FAQs

How is toxoplasmosis diagnosed 

The diagnosis of toxoplasmosis can be made by:^8,10

• Testing a part of the blood called serum for antibodies that indicate infection (this is referred to as serologic testing)
• Testing  tissue samples taken from individuals suspected of being infected with T. gondii.
• Testing a sample of amniotic fluid in pregnant women, using molecular testing methods such as Polymerase Chain Reaction (PCR), which can detect the DNA of the parasite

Alternatively, isolating the parasite from cats belonging to individuals suspected of having toxoplasmosis is also a form of diagnosis.

In the UK, information on T. gondii diagnosis can be obtained from the Toxoplasma reference lab in Swansea. This data is analysed by Public Health England and Public Health Wales quarterly (UK GOV) to guide disease control interventions.¹¹

How can I prevent toxoplasmosis 

Toxoplasmosis can be prevented by the following practices:^5,6,8,12

DOs

• Cook meat properly (whole meats at 63 ^oC, ground meat at 71^oC, and poultry at 74 ^oC) before eating or freeze meat to below - 0 ^oC for several days before cooking
• Wash fruits and vegetables thoroughly before eating, especially those that are eaten raw.A good practice is to soak raw fruits and vegetables in distilled vinegar before washing them. The WHO's five keys to safer food provides guidelines on practices that will help reduce food-borne infections
• Wear gloves when gardening and wash your hands with soap and water afterwards
• Wash utensils that come in contact with raw meat and wash hands with soap and water after preparing raw meat 
• Feed cats packaged or cooked food which will prevent the need to hunt for pray and encourage them to stay indoors
• Make a habit of washing your hands thoroughly before and during meal preparation and eating
• If you own cats or work with cats, change cat litter daily and when doing so, avoid shaking the litter to prevent the dispersal of the oocysts in the air. When disposing of cat litter, bury it deep in the soil, burn it, or dispose of it in bins destined for landfill disposal. Again hands should be washed with soap and water afterwards
• Pregnant women should avoid changing cat litter. If you can not get someone else to do it for you, wear gloves when changing cat litter and wash hands with soap and water afterwards

Dont’s

• Do not eat raw, under cooked, or cured meats like salami or pharma ham
• Avoid touching sheep or lambs that are pregnant 
• Do not consume unpasteurised goats milk or products made from it 
• Do not allow stray cats to have access to sandboxes where children play. Keep sandboxes covered when not in use

Medical prevention

HIV-positive patients have a weakened immune system and are at risk of toxoplasmosis or reactivation of a previous infection. To prevent this, they are put on a preventative cocktail consisting of two antibiotics and a reduced version of folic acid which is taken throughout the individual's life.

In individuals with a weakened immune system that test positive for toxoplasmosis but don’t present any symptoms , the risk of complications due to toxoplasmosis infection is reduced by giving a high dose of an antiparasitic agent and a sulfonamide antibiotic.

Who are at risk of toxoplasmosis 

Toxoplasmosis in healthy individuals is usually not a cause for concern, even if you have symptoms, as these usually resolve with time. Toxoplasmosis is an opportunistic infection, therefore you are more at risk when your defences are down and your body's immune system is not working effectively to protect you from diseases.

Individuals that are at a high risk of toxoplasmosis and of experiencing serious complications when infected include:^5,6,11

• Pregnant women, astoxoplasmosis can result in miscarriage, stillbirth, and congenital toxoplasmosis for the foetus
• Individuals with a weakened immune system as toxoplasmosis infection can result in complications affecting the brain, eyes, lungs, and heart

How common is toxoplasmosis

From 2008 to 2012, only 190 cases of toxoplasmosis were detected in pregnant women in the UK, and toxoplasmosis is detected in about 1 in 10,000 babies born in the UK every year.³

In addition, about 350 cases of toxoplasmosis infection are diagnosed each year in the UK.¹¹

When should I see a doctor 

See your GP or healthcare provider if you suspect you have toxoplasmosis and:^5,6

• You’re pregnant 
• You have a compromised immune system 

Summary

It can be quite alarming to discover that domestic cats can cause a disease like toxoplasmosis in humans. Fortunately, toxoplasmosis rarely causes symptoms in healthy individuals.

The main route through which the toxoplasma parasite is transmitted to humans is through contaminated food and water. The WHO's 5-step Safe food is an excellent resources that lists practices that can help reduce the risk of food-borne diseases such as toxoplasmosis.

Given that toxoplasmosis is usually asymptomatic in healthy individuals, most people clear the infection without realising they have it. For individuals who experience symptoms, treatment is readily available. 

This is more complicated, however, for those with a weakened immune system and pregnant women due to the risks of complications. Nevertheless, several treatment options are available to reduce the risk of complications and prevent mother-to-child transmission of the infection.