Exposure to the virus, the mother's microbiome, and drugs each could cause harm.
Up to half of babies born to HIV-infected mothers become infected themselves either in utero, during labor, or through breastfeeding, unless the mothers and babies are treated with antiretroviral (ARV) drugs. But several studies suggest an additional burden for the many children in Nigeria who dodge transmission from their mothers, whether by luck or treatment: They may still suffer from growth retardation, immune abnormalities, and even an increased risk of mortality. “Exposed, uninfected children are a growing population, and they're neglected,” says virologist Nicaise Ndembi of the Institute of Human Virology, Nigeria (IHVN) in Abuja.
At the University of Benin Teaching Hospital in Benin City, Ndembi is a co–principal investigator (co-PI) of a study exploring what happens to those exposed, uninfected children and why. “There's a growing body of data that suggests they're very different from normal infants,” says another co-PI, epidemiologist Man Charurat of IHVN.
Theoretically, the harm could come from the mother's poor health, or from exposure to viral proteins or to the ARV drugs given to treat the mother and the baby to prevent transmission. “It's a really complicated picture,” says Claire Thorne, an epidemiologist at University College London who is trying to separate the effects of HIV exposure from exposure to ARV drugs.
The IHVN team is exploring whether an HIV-caused condition called “leaky gut” may transfer from mother to uninfected child. HIV preferentially destroys immune cells in the gut shortly after infection, leading to an overstimulated immune system, inflammation, and a permeable gut. That could alter the mother's microbiome, and she might pass the altered bacteria to her child during birth or breastfeeding. The Benin researchers suspect the child's altered microbiome then increases diarrhoea, impedes proper absorption of nutrients, and slows growth.
The IHVN study, which began in 2014 and will run through next year, compares 300 uninfected children, half of whom were exposed to HIV during their first 2 years of life. The researchers are analyzing stool samples from mothers and their children to see whether HIV alters the genera of bacteria that live in their guts. Researchers also are giving the children a dose of two sugars and then testing their urine to see whether their intestines have compromised permeability. “If we can identify problems, we can begin to look at interventions,” Ndembi says.
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