What is toxoplasmosis?

Discovered in 1908, toxoplasmosis is an intracellular parasitic infection caused by the protozoan Toxoplasma gondii. It infects multiple warm-blooded including humans, livestock, birds etc., however, cats are the definitive hosts to Toxoplasma gondii. This means that the parasite is only able to sexually reproduce in cats, both wild and domesticated species. Most people have heard of toxoplasmosis due to the risks infections pose to pregnant women. If infection occurs during pregnancy it can cause abortion and congenital defects to the fetus. Toxoplasmosis infection in humans is extremely common with between 30 – 50% of the population having been exposed. [1]

Symptoms

Most healthy adults are asymptomatic, that is they don’t have any symptoms, others have only mild symptoms such as:

• Enlarged lymph nodes
• Flu-like symptoms
• Fever
• Muscle aches and pains

Severe toxoplasmosis in humans can sometimes occur and cause damage to the eyes, brain, and other organs. This is more likely to happen in immunocompromised individuals such as people with HIV, organ transplant recipients and patients undergoing some forms of chemotherapy.

Diagnosis

Serologic testing to look for IgG and IgM antibodies in the blood.

Treatment

If a pregnant woman is diagnosed with toxoplasmosis, she will be treated with antibiotics to help prevent transmission to the fetus.  The earlier treatment starts the better.

If upon testing the fetus is shown to be infected also, two types of antibiotics will be prescribed.

Diagnosing toxoplasmosis in the fetus

• Amniocentesis: Testing of amniotic fluid.
• Cordocentesis: Testing of blood from the umbilical cord.
• Fetal ultrasound: This may be able to detect fetal abnormalities caused by the infection.

How does the fetus become infected and what effect does it have?

Fetal infection occurs via placental transmission. The earlier in the pregnancy, the lesser chance of transmission, but the effects are more severe. The later in the pregnancy, the greater the chance of transmission, but the effects are milder. [2] When a fetus becomes infected in the uterus it is known as ‘congenital toxoplasmosis’. Not all women who become infected will pass it on to their fetus.

Toxoplasmosis symptoms in newborns

• Low birth weight
• Chorioretinitis (inflammation of the choroid and retina of the eye)
• Jaundice, yellow gums, skin and eyes
• Intracranial calcifications
• Rash
• Swollen lymph nodes
• Hepatosplenomegaly (enlarged liver and spleen)
• Hydrocephalus (accumulation of cerebrospinal fluid in the ventricles of the brain)

Many infants display no symptoms at birth (subclinical infection) but may develop disabilities later in life. This includes:

• Mental retardation
• Blindness or visual impairment
• Hearing loss

Treat infants with congenital toxoplasmosis with antibiotics for the first year and carefully monitor past infancy.

Prevention

Cats aren’t the only source of infection to humans, people can also become infected via improperly cooked meat, improperly washed vegetables, drinking untreated water (from a stream or river for example) and gardening.

• Avoid cleaning the litter trays, if this is not possible wear gloves and a mask. Scoop solids daily and dispose of them in the garbage.
• Scoop litter trays at least once a day.
• Cook meat thoroughly.
• Wash your hands after handling animals.
• Wear gloves while gardening.
• Wash fruit and vegetables thoroughly before eating.
• Wash your hands after handling raw meat, fruit, and vegetables.
• Don’t let your cat(s) hunt.
• Cover sandboxes to prevent cats from defecating in them.
• Don’t drink unpasteurised milk.
• Thoroughly cleaning chopping boards and utensils. Use separate boards for fruit/vegetables and meat.
• Keep the litter tray away from the kitchen and other eating areas.

Should a pregnant woman rehome her cat?

No, this isn’t necessary, however, it is recommended you request a blood test to determine if you have been exposed in the past. This means your immune system has already built up a resistance, therefore, you are very unlikely to become re-infected.

What else can I do to avoid toxoplasmosis?

If you are planning to become pregnant, ask your doctor for a blood test to look for antibodies to toxoplasmosis.  Seek medical advice immediately if you are already pregnant and think you have been exposed.

References:

[1] Cornell University College of Veterinary Medicine

[2] Congenital Toxoplasmosis