Family outbreaks have also been described that involve multiple children who played in an infected sandbox or dirt pile.5 Similarly, an outbreak has been reported in a riding stable that was home to infected cats. Infective oocysts were thought to have become aerosolized and breathed in by the patrons.6 Multiple other possible modes of transmission are being investigated, including sexual transmission among humans.7
Human infections are not always benign
In most human T. gondii cases, the infected individual experiences mild, flu-like symptoms, often with enlarged lymph nodes, or has no symptoms.1 Thus, most people who have been infected with T. gondii are unaware because clinicians do not routinely test for it.
There are 3 exceptions to this otherwise benign clinical picture. The first is cerebral toxoplasmosis, which occurs in individuals who are immunosuppressed because they have AIDS or are receiving treatment for cancer or organ transplantation. Cerebral toxoplasmosis can be severe and was a common cause of death in patients with AIDS before the development of effective AIDS treatments.
The second exception is congenital toxoplasmosis, when an infection occurs in a pregnant woman. Such infections can cause severe damage to the developing fetus, including abortion, stillbirth, and brain damage. Congenital toxoplasmosis infections occur in approximately 1 of every 10,000 births in the United States, or approximately 3,800 each year.8 As a result, pregnant women are advised not to change their cat’s litter and to be tested for evidence of T. gondii infection.
The third exception is eye disease. Toxoplasmosis is one of the most common causes of eye disease, especially of the retina. Each year in the United States, approximately 4,800 individuals develop systematic ocular toxoplasmosis.9
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