What is Toxoplasmosis?

Toxoplasmosis is a parasitic infection caused by the parasite Toxoplasma gondii. T. gondii is a single-celled parasite that primarily inhabits the small intestines of cats and can spread to other animals, humans, and surfaces through contaminated cat faeces. Globally, around one in three people are infected with T. gondii, but most people who are infected do not show symptoms.¹

Symptoms of Toxoplasmosis

Toxoplasmosis presents in different forms, including acute, chronic, and congenital infections.

Acute Toxoplasmosis

In healthy individuals, acute toxoplasmosis often causes mild, flu-like symptoms, such as:

• Fever
• Swollen lymph nodes
• Headache
• Muscle ache²

However, acute toxoplasmosis does not threaten a healthy individual since our immune system can fight the parasite forcing it into an inactive, dormant state (forming cysts). Even after the initial infection clears, T. gondii remains in the body indefinitely (in its bradyzoite form, see Figure 1), but usually without causing further harm.

Chronic Toxoplasmosis (Reactivation)

Chronic toxoplasmosis occurs in people who are suffering from a weakened immune system. This can occur in people suffering from HIV/AIDS, cancer, or those undergoing immunosuppressive therapy. If a person has already come into contact with T. gondii, then a weakened immune system will cause T. gondii to reactivate and initiate more severe symptoms such as:

• Confusion
• Poor coordination
• Seizures
• Blurred vision
• Eye pain
• Vision loss³

Congenital Toxoplasmosis

If a pregnant woman contracts toxoplasmosis, the parasite can cross the placental barrier, infecting the unborn baby.⁴ This typically occurs as T. gondii hides in placental white blood cells, which then carry the parasite into the foetal bloodstream. Once in the foetal circulation, T. gondii can infect organs such as the brain, eyes, and liver.⁴ This can cause adverse effects on the baby later in life, including:

• Stillbirth 
• Hydrocephalus (fluid buildup and inflammation of the brain)
• Vision problems
• Seizures
• Developmental delays
• Learning disabilities⁴

How is Toxoplasmosis transmitted?

Toxoplasmosis spreads primarily through exposure to the parasite Toxoplasma gondii, with several key transmission routes posing risks, particularly for pregnant women. One of the most common sources of infection is consuming undercooked or raw meat containing tissue cysts, particularly from pork, lamb, or venison.⁵ T. gondii can also be contracted through the consumption of unwashed raw fruit and vegetables that have been contaminated with cat faeces or by directly coming into contact with cat faeces (such as when cleaning litterboxes).⁵

Figure created with Biorender.com

Figure 1 - This figure presents the development and transmission of Toxoplasma gondii from the cat to humans through undercooked meat. 1) The definitive host is the host in which T. gondii can fully develop into its sexually mature form, which is in the cat. 2) Unsporulated oocysts are then shed through the cat’s faeces; these are eggs which have not fully developed yet. 3) After 1-5 days, oocysts become sporulated, meaning that they are infectious. 4) Sporulated oocysts can be found in soil, grass and water, which can be consumed by intermediate hosts such as cows, rodents, and pigs. 5) T. gondii forms enclosed cysts in the muscles of cows, chickens, and pigs, these tissue cysts contain inactive T. gondii can survive in meat if it is raw or undercooked. 6) If a person eats this raw/undercooked meat, they ingest the T. gondii parasite, which can cross the placenta and reach an unborn foetus, or reproduce in the stomach and intestines and spread through the body.⁵   

Prevention of Toxoplasmosis 

As there are many ways of contracting toxoplasmosis, prevention of this disease is crucial. There is a range of prevention strategies to protect against toxoplasmosis in both pregnant mothers and their unborn fetuses. Effective strategies focus on food safety, hygiene and responsible pet care. 

Cooking prevention 

Thorough cooking and proper kitchen hygiene are vital safeguards. All meat—including beef, pork, and poultry—should be cooked to an internal temperature of at least 70°C until no pink remains. 

Avoid tasting raw meat during preparation, and ensure all utensils and surfaces are washed with hot, soapy water after contact with uncooked meat. Pregnant women should strictly avoid raw or undercooked meat throughout pregnancy. Fruits and vegetables must be washed thoroughly, especially if homegrown or harvested from soil, as they may carry oocysts from contaminated cat faeces. Peeling or cooking produce further reduces risk.⁶

Hand hygiene

Our hands are the gateway for Toxoplasma gondii to enter the body, and so they should be regularly washed with warm water and soap. Especially after gardening, cleaning litterboxes, cooking, and touching sand as it is possible to come into contact with contaminated cat faeces,so pay particular attention to hygiene afterwards.

Litter box handling

Pregnant women should ideally avoid changing cat litter. If unavoidable, disposable gloves should be worn and hands washed meticulously afterwards. Litter boxes must be cleaned daily, as oocysts in fresh faeces take 1–5 days to become infectious (see Figure 1).

Cats should also be kept indoors to prevent them from hunting and eating rodents infected with toxoplasmosis. Keeping cats away from the kitchen during cooking is also necessary to avoid contamination.⁶

Treatment

Treating toxoplasmosis during pregnancy presents significant challenges, as management depends on both the gestational stage at which maternal infection occurs and whether transmission to the foetus has taken place.This is why prevention of toxoplasmosis is key. Diagnosis typically involves serological blood tests to detect Toxoplasma gondii antibodies, while confirmation of foetal infection requires amniotic fluid analysis and ultrasound examination.⁶

If the baby is not infected, the mother can be treated early with spiramycin. This is a pregnancy-safe antibiotic. This medication concentrates in the placenta, helping prevent vertical transmission.

However, when diagnostic testing confirms congenital infection, a more aggressive therapeutic approach becomes necessary. The standard regimen combines pyrimethamine (an antiparasitic agent contraindicated in the third trimester), sulfadiazine (a bacteriostatic antibiotic), and folinic acid (leucovorin) to mitigate pyrimethamine's potential bone marrow toxicity. This combination therapy carries greater risks but becomes essential when foetal infection is established.

FAQs

Why is toxoplasmosis particularly dangerous during pregnancy?

It can cross the placenta and infect the unborn baby, possibly causing a miscarriage, stillbirth or developmental issues in the baby such as brain damage and learning disabilities.

How is it diagnosed?

Diagnosis involves blood tests to detect Toxoplasma-specific antibodies (IgG and IgM). For pregnant women, additional testing of amniotic fluid (via amniocentesis) and detailed ultrasound scans help determine if the foetus has been affected.

Can it be prevented?

Yes, cook meat thoroughly, wash produce, wash hands, avoid handling cat litter, when possible, or wash hands thoroughly afterwards.

Is treatment safe in pregnancy?

Yes, when it is administered correctly and adjusted for the trimester of pregnancy.

Summary

Toxoplasmosis is a parasitic disease caused by the parasite Toxoplasma gondii, an organism that primarily inhabits the intestinal tract of cats and is shed in their faeces. The parasite's lifecycle involves intermediate hosts including livestock and rodents, which become infected through contact with contaminated soil, water or vegetation containing infectious oocysts from cat faeces. Within these animal hosts, T. gondii forms dormant tissue cysts in muscle, containing inactive bradyzoites that can persist in undercooked meat.

When humans consume inadequately cooked infected meat, the parasite reactivates into its proliferative tachyzoite form, disseminating throughout the body to establish infection.

Acute toxoplasmosis occurs in generally healthy individuals and causes little to no symptoms. This is just an infection, though the parasite remains latent in cyst form for life. However, in immunocompromised patients - particularly those with HIV/AIDS or undergoing cancer treatment - reactivation can lead to severe complications including encephalitis, ocular toxoplasmosis and potentially fatal systemic infection.

Congenital toxoplasmosis occurs as a pregnant mother contracts Toxoplasma gondii and transmits it to the unborn foetus. This can cause miscarriage and stillbirth or severe developmental issues in the unborn foetus as it grows. Adverse effects include learning disabilities, blindness, seizures and brain damage.

Transmission occurs not only through undercooked meat but also via contaminated water, unwashed produce, and exposure to environments containing infectious cat faeces, such as litter boxes or garden soil. Preventive measures for pregnant women emphasise thorough cooking of meat, avoidance of litter tray handling, and rigorous hand hygiene after contact with potential sources of contamination. These precautions are particularly crucial as treatment options during pregnancy are limited and dependent on precise timing of infection.