Reduce risk of parasite: Hearing loss may be linked to toxoplasma

Originally published in The Ottawa Citizen June 11, 2004

Original Title: Stay away from Puss ‘n Boots

We live with a multitude of bacteria and parasites in our environment. Many do not cause disease in healthy individuals.Toxoplasma gondii is a protozoan that is relatively harmless for most healthy people. Although pregnant women have the same risk of contracting the parasite as the general population, they should take precautions to reduce their risk of exposure to toxoplasma.

There are about 250 new cases of toxoplasmosis (toxoplasma infection) per year in Ontario.

Toxoplasmosis can cause harm to a developing fetus. About 10 infants will be infected per year in Ontario. Approximately 32 to 40 per cent of Canadian women are immune to toxoplasma due to previous exposure; they will be able to protect their unborn child. Indeed, mothers exposed to toxoplasma six months before pregnancy do not pass the infection on to their child.

Infected pregnant women will not have many symptoms. It is the fetus that is at risk. Toxoplasma will cross through the placenta to the fetus an average of 30 to 40 per cent of the time. The transfer risk, about 15 per cent, is lowest in the first trimester but it can cause severe nervous system disease, spontaneous abortions and stillbirths. By the third trimester the transmission rate is about 60 per cent but the fetal disease is mild.

About 70 to 90 per cent of infected newborns will not have any initial symptoms. Indeed, it may take years to develop. However, if left untreated 85 per cent will develop blindness or impaired vision due to chorioretinitis (inflammation of the retina and surround eye structures). Ten to 30 per cent will experience moderate hearing loss and 25 to 75 per cent will manifest some developmental delay and brain damage.

Some of the signs that do suggest toxoplasmosis at birth include fever, enlarged liver and spleen, small head size (microcephaly), jaundice, seizures and rash. An infant that has water accumulation in the brain (hydrocephalus), chorioretinitis and calcium deposits on the inside of the skull strongly suggest congenital toxoplamosis.

Prevention is paramount during pregnancy.

Many people focus on cats as the primary risk of toxoplasma infection. Once a cat is infected it will only spread toxoplasmosis for a few weeks thereafter. Kittens are more likely to spread the infection because they have not yet become immune to the disease.

Daily cat litter changes done by a healthy, non-pregnant individual will prevent the parasite’s eggs from becoming infectious spores. It takes four days to change from egg to spore. Keep your cat indoors to reduce your chances of catching toxoplasmosis. Feed it dry or canned cat food and not uncooked or undercooked meat scraps.

Despite the cat precautions, cats and cat litter are not the major source of infection.

Indeed, 25 per cent of fresh pork and lamb have cysts containing toxoplasma. Eating raw or partly cooked meat, handling it or touching the cutting board or dish that it was in contact with it, and then putting your hands to your mouth, can transfer the infection.

Since toxoplasma is found in the soil, be sure to wash all raw fruits and vegetables. Avoid unpasteurized goat’s milk or cheese.

Other prevention methods include:

* Wear gloves while gardening because cats often use gardens as litter boxes.

* Wash all cutting boards, dishes and other items with hot soapy water after they have been in contact with raw meat, poultry, seafood and raw fruits and vegetables.

* Cook meat until it is no longer pink. The meat thermometer should read 160 degreesF (71 degreesC). Do not taste meat until it is well-cooked.

* Avoid drinking the water when travelling to underdeveloped countries.

Toxoplasma is treatable but its success depends upon early diagnosis. Routine screening is not done in Canada because of the relatively low prevalence and the blood tests would not provide an accurate assessment of infection.

The bottom line is for pregnant women to reduce their exposure to sources of toxoplasma. If you suspect you are at risk of exposure to toxoplasma and are pregnant, please consult your physician.

© Dr. Barry Dworkin 2004

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