Parasite Provides First Clue to AIDS, Toxoplasmosis and Pregnancy

by Food and Drug Administration (FDA)

(Page 2 of 4)

Parasite Provides First Clue to AIDS

"In fact, it was because of unexplained cases of pneumocystis- -an airborne respiratory infection caused by Pneumocystis carinii — that AIDS was first recognized in 1981," Wykoff says. "Pentamidine, the drug used to treat the disease, was available only through CDC. When the agency noticed an increase in the number of requests for pentamidine, it began an investigation that eventually led to identification of AIDS as a new disease."

As HIV infections have increased, so has the incidence of pneumocystis pneumonia. According to CDC's HIV/AIDS Surveillance, 19,503 new cases of pneumocystis pneumonia were diagnosed in HIV-infected patients in 1992. Early symptoms are fever, cough, and shallow, rapid breathing. Chest x-ray shows parasitic infiltration of the lungs. As the disease progresses, cyanosis may develop — a bluish discoloration of the skin resulting from insufficient blood oxygen.

Pneumocystis is the leading cause of death in people with AIDS, Wykoff says, but adds that control of the disease has improved since the introduction of preventive treatment with aerosolized pentamidine isethionate (NebuPent), approved by FDA in 1989. In 1992, Mepron (atovaquone) was approved to treat the pneumonia, joining Bactrim and Septra (combination products containing trimethoprim and sulfamethoxazole), both approved in 1976. Injectable pentamidine was approved to treat pneumocystis pneumonia in 1984.

"Cryptosporidiosis is another parasitic infection of major concern in HIV-infected and other immune-suppressed patients," says Wykoff, "although it was unknown until relatively recently — the last decade or so — and people are still not sure how common it is."

The parasite infects cells in the intestinal wall and releases a toxin that causes a profuse, watery diarrhea and abdominal cramping. In healthy people, the disease is self-limiting; symptoms usually last a week or two, and then rapidly abate. Immune-suppressed patients, however, are unable to clear the infection, and endure unremitting diarrhea. In these individuals, cryptosporidiosis becomes a debilitating wasting disease. According to the American Public Health Association's Control of Communicable Diseases in Man, 10 to 20 percent of AIDS patients develop cryptosporidiosis sometime during their illness. No drug is available to effectively combat the parasite, although several are under study. Current treatment is limited to rehydration therapy (replacing and maintaining fluids and electrolytes). Besides drinking plenty of fluids, patients may be given a liquid formula such as Pedialyte (for children) or Rehydralyte (for children and adults), which contains water, dextrose, potassium citrate, sodium chloride, and sodium citrate. Cryptosporidium is transmitted through the fecal-oral route. Careful hand washing and good sanitation practices are essential in preventing disease spread. Adequate water filtration should prevent waterborne transmission such as occurred in Milwaukee.

Besides immune-suppressed patients, others at increased risk include children, foreign travelers, homosexual men, and close contacts of infected patients, such as family members, health-care workers, and day-care workers. A third parasitic infection associated with HIV is toxoplasmosis, caused by Toxoplasma gondii. As with Pneumocystis carinii, T. gondii is common in the U.S. population. An estimated 40 percent of Americans are or have been infected, but most either don't get sick or they develop a relatively harmless illness — slight fever, muscle pain, sore throat, headache, and inflammation of the lymph nodes lasting days or weeks.

But again, infection in immune-suppressed people is much graver. According to CDC, toxoplasmosis is the most common opportunistic infection of the central nervous system in HIV-infected patients, and causes encephalitis (inflammation of the brain) or brain lesions in as many as 30 percent of AIDS patients. Symptoms include paralysis, mental deterioration, severe headache, seizures, and coma, usually ending in death. Toxoplasmosis is acquired by eating raw or undercooked meat contaminated with the parasite, or by exposure to contaminated cat feces. (See accompanying articles, "For Safe Food, Handle with Care" and "Toxo- Tabby.")

Toxoplasmosis and Pregnancy

Toxoplasmosis can also be transmitted to a fetus through the placenta. The fetus is presumed to be at risk only if the mother has a primary, active infection during the pregnancy; a former infection is believed not to be dangerous. CDC estimates there are between one and three congenital Toxoplasma infections per 1,000 live births in the United States each year. Only 10 percent of those infants develop symptoms, but of them, 85 percent develop severe neurologic and developmental problems, and approximately 12 percent die. Of those who have no symptoms at birth, up to 85 percent may develop chronic recurring eye disease and learning disabilities. Toxoplasmosis can also cause miscarriage, stillbirth, and pre-term birth. Acute toxoplasmosis is usually treated with Daraprim (pyrimethamine) together with sulfadiazine for three to four weeks. Immune-suppressed patients should continue treatment for up to six months or longer, however, and may need reduced dosages throughout their lifetimes to try to prevent recurrence.

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