By Will Dunham

WASHINGTON, Feb 6 (Reuters) - The AIDS virus can be passed from an infected mother to her baby if she pre-chews the child's food as sometimes occurs in developing countries, U.S. government scientists said on Wednesday.

The U.S. Centers for Disease Control and Prevention said it had identified three cases -- two in Miami and one in Memphis, Tennessee -- in which a child was infected in this way between 1993 and 2004. The mother was involved in two of the cases and a relative who acted as a caregiver was involved in the third.

In developing countries, some mothers pre-chew food for babies. These women may lack access to packaged baby food or may not have a way to blend baby food. This practice is thought to be very rare in the United States or other wealthy nations.

The researchers, who presented their findings at a scientific meeting in Boston, said the infected women's saliva itself did not transmit the virus to the child, but rather it appears blood present in the saliva caused the infection.

The researchers said HIV transmission appears to have occurred when the children ingested pre-chewed food that contained blood from the bleeding gums of HIV-infected women, and this entered the children's bloodstreams through a cut, sore or inflammation of the mouth or digestive tract.

They said they ruled out other possible means of infection such as breast-feeding or blood transfusion.

"Pre-mastication is a newly recognized route for HIV transmission that warrants further investigation in order to continue reducing cases of HIV transmission in the U.S.," the CDC said in a summary of the findings by epidemiologist Dr. Ken Dominguez and other researchers.

"The findings could have more significant implications for developing countries," the CDC added.

In one case, a girl, age 9 months, was diagnosed with HIV in 2004. The HIV-positive mother reported giving pre-chewed food to the child, who is still alive, receiving HIV drugs.

In a second case, a 3-year-old boy was diagnosed with HIV in 1995. The infant's mother had AIDS and had given pre-chewed food to the child, who died of AIDS in 1996.

In a third case, a boy, age 15 months, was diagnosed with HIV in 1993. The boy's mother is HIV-negative but his HIV-positive great-aunt served as a caregiver and had given him pre-chewed food. The researchers said the mother did not know the aunt was HIV-positive until after she died of AIDS. The boy is still alive, getting HIV drugs.

"The researchers advise that health care providers and HIV-infected child caregivers should be aware of the potential health risks and should advise those caregivers against the practice of pre-chewing food for their infants," the CDC said. (Editing by David Alexander and Cynthia Osterman)

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