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Can’t Blame Kitty for This Infection, Study Finds

by Daniel on May 20th, 2011

Pregnant women are warned to avoid or minimize their exposure to various drugs, types of foods, and activities in order to prevent harm to their unborn babies. One such danger is infection by the protozoan (single-celled) parasite, Toxoplasma gondii.

Since it is known that domestic cats are primary carriers of this microbe, pregnant women are often advised to avoid changing litter boxes and other activities that might put them into contact with cats or their excrement. A study published in the July 15 issue of the British Medical Journal, however, suggests that other factors are more important in determining a woman’s risk of contracting this infection.

Toxoplasmosis, the disease caused by T. gondii, can cause fetal or newborn deaths, learning difficulties and eye damage in infants of mothers who become infected during pregnancy. While infected cats can pass the parasite to people, this is only likely during the first couple of weeks after the cat has itself been infected, according to the authors of the study. The infection can also be contracted by other means — such as eating undercooked infected meat or ingesting soil that has been contaminated by the microbe. It is important that women be educated about which activities are most likely to expose them to this parasite.

The authors of the British Medical Journal study interviewed pregnant women at six centers in Europe — Naples, Lausanne, Copenhagen, Oslo, Brussels and Milan. Their subjects included a total of 252 pregnant women who had been diagnosed with acute Toxoplasma infections (the cases), and 858 uninfected women from the same centers (the controls).

All the subjects were asked if they knew how to avoid Toxoplasma infection to evaluate their knowledge about the disease. The investigators then determined the subjects’ exposure to a variety of factors that might increase their risk of acquiring toxoplasmosis. These included occupation; diet; consumption of untreated water; usual consumption of raw, undercooked or dry-cured meats; and working in fields or gardens with hands contacting the soil; as well as exposure to cats and their feces.

By comparing the occurrence of the various risk factors in cases and controls, the authors were able to determine which exposures seemed most likely to increase the risk of acquiring toxoplasmosis. Their analysis indicated that raw or undercooked beef, poultry or lamb increased the risk of disease twofold to fourfold. Lamb seemed to be the most frequent culprit. Other food-related risks were consumption of unpasteurized milk and untreated water. Traveling outside Europe, the United States and Canada also strongly predicted Toxoplasma infection. Contact with cats or their feces was not, however, a risk factor for infection.

The authors calculated that between 30 percent and 63 percent of the toxoplasmosis at the different centers could be attributed to meat consumption. They noted that other studies have also implicated lamb, goat and pork as the parasite’s carriers more often than beef. While beef is less likely to be contaminated with the parasite than the other types of meat, the authors noted that beef is eaten more frequently than other meats and this could explain why their study indicated it as an important infection source.

“The single most important health message for pregnant women in all centers in the study is to avoid eating any meat that has not been thoroughly cooked,” the authors emphasized. They also expressed concern that in some of the centers they examined, from 2 percent to 51 percent of the subjects interviewed could not “cite any risk factors” for acquiring toxoplasmosis.

In an accompanying editorial, Dr. Richard Holliman of St. George’s Hospital and Medical School in London agreed: “Current health education may benefit from focus and refinement, concentrating on principal risk factors at the expense of less important issues.”

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