Toxoplasmosis is a disease caused by a parasite, the Toxoplasma gondii. As many as 60 million people carry this parasite, but in most people their healthy immune systems prevent it from developing into toxoplasmosis. However, Toxoplasma gondii can be dangerous for pregnant women and people with weaker immune systems, and newborn babies.
Symptoms and Effects of ToxoplasmosisMost newborns infected with toxoplasmosis do not display symptoms. But without treatment, problems may develop later, including hearing loss. One in 10 newborns is "obviously infected" with such symptoms as an eye infection, jaundice (yellowish skin) or a low birth weight. Some of the infected newborns will die; some may develop cerebral palsy, vision problems, intellectual disability or hearing loss.
How Is Toxoplasmosis Acquired?
According to the March of Dimes, between 400 and 4,000 babies are born every year in the United States infected with toxoplasmosis. There are many ways a toxoplasmosis parasite can be acquired. Just a few of the known causes are: eating undercooked or contaminated meat, such as pork; drinking contaminated water; passing the parasite to a baby before or during birth; and contact with cat feces contaminated with Toxoplasma gondii.
Preventing the Effects of ToxoplasmosisToxoplasmosis effects can be prevented or reduced if the pregnant woman, her fetus or newborn is treated. Infection can be detected in a pregnant woman with standard amniotic fluid testing and ultrasounds. If an infection is detected, then a pregnant mother can be treated with the drug spiramycin. Her fetus can be treated with pyrimethamine and sulfadiazine.
After birth, an infected newborn can also be treated with pyrimethamine and sulfadiazine. Treatment with these and other drugs has already been found to possibly be effective in preventing hearing loss and other disabilities, including intellectual problems.
Toxoplasmosis and Hearing-Loss StudiesSeveral studies have been done to examine the effectiveness of treatment in preventing hearing loss associated with toxoplasmosis. For the most part, these studies have found that early and sustained treatment is the most effective way to minimize hearing loss in newborns with toxoplasmosis.
Researchers in Brazil looked at newborns who were identified with congenital toxoplasmosis. Twenty newborns (out of 30,808 babies) were identified at birth. Fifteen were asymptomatic and 19 had hearing screenings. Of these 19, six were found to have hearing loss (four had sensorineural hearing loss that ranged from mild to severe/profound; two had conductive hearing loss).
Treatment was limited. One newborn was treated for only three months; one had irregular treatment for 10 months, and two had consistent treatment for 12 months. However, the consistent treatment did not prevent or reduce hearing loss, perhaps because of the presence of other risk factors, such as low birth weight. The authors concluded that toxoplasmosis could cause hearing loss in as many as 20% of newborns, and it should therefore be considered a risk factor for hearing loss.
A Canadian review of five studies of newborns with toxoplasmosis found evidence of the benefits of early and sustained treatment. In newborns with limited or no treatment, there was a 28 percent presence of sensorineural hearing loss. In babies who had 12 months of treatment (the consistency of which could not be determined), starting after 2.5 months old, the presence of hearing loss was 12 percent. Finally, in babies who had 12 months of consistent, confirmed treatment that started before the infants were 2.5 months old, there was no hearing loss.
In Chicago, a study was done of 120 infants identified as having congenital toxoplasmosis. These infants were treated starting at birth and continuing for 12 months. The results showed that all the infants with mild cases of toxoplasmosis had normal outcomes, meaning they did not develop any problems. Infants with more severe cases of toxoplasmosis had normal outcomes in more than 72% of the cases, and none developed hearing loss.
A small Norwegian study was not able to confirm any association between toxoplasmosis and hearing loss. The study identified 40 women who were infected with the parasite before their babies were born, but none of the babies had hearing loss.
Toxoplasmosis As a Hearing-Loss Risk FactorIn 2007, the Joint Committee on Infant Hearing issued a position statement that included in utero toxoplasmosis infection as a risk factor for delayed-onset and progressive sensorineural hearing loss. Toxoplasmosis is listed as a risk indicator associated with permanent congenital, delayed-onset or progressive hearing loss in childhood; and as an in-utero infection, which also includes CMV, herpes, rubella and syphilis.
However, according to the March of Dimes, only two states - Massachusetts and New Hampshire - require newborns to be screened for toxoplasmosis. Why isn't newborn screening for toxoplasmosis more widespread in the United States? Possible reasons include inadequate evidence of the effectiveness of treatment, despite studies like the ones cited above. Low incidence of toxoplasmosis may be another reason; adding screening tests for newborns increases costs. Likewise, the screening of pregnant women also increases costs. Indeed, the American College of Obstetricians and Gynecologists does not recommend universal screening of pregnant women for toxoplasmosis.
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Congenital toxoplasmosis. Medline Plus. U.S. National Library of Medicine. http://www.nlm.nih.gov/medlineplus/ency/article/001360.htm
March of Dimes - Toxoplasmosis. http://www.marchofdimes.com/pregnancy/complications_toxoplasmosis.html
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