HIV, the virus that causes AIDS, is ravaging Africa. In some regions south of the Sahara Desert, more than 35 percent of the population is infected. Each year, as many as 700,000 children acquire HIV from their infected mothers during pregnancy, labor, or breast-feeding.
In developed countries, by contrast, mother-to-child HIV transmission has been virtually eradicated. Pregnant women take anti-HIV drugs to minimize the chance of passing the virus to their babies. Delivery by cesarean section removes the danger of HIV reaching a baby during birth. And use of infant formulas eliminates the possibility of infection through a mother’s breast milk. As a result, fewer than 2 percent of babies born to HIV-positive mothers in developed countries become infected.
Science News headlines, in your inbox
Headlines and summaries of the latest Science News articles, delivered to your email inbox every Thursday.
Thank you for signing up!
There was a problem signing you up.
But in Africa, up to 40 percent of the children of HIV-infected mothers are either infected at birth or become infected soon afterward. Cesarean sections are too risky or simply unavailable in many African hospitals, and the World Health Organization (WHO) estimates that only 9 percent of pregnant HIV-infected women in sub-Saharan Africa receive anti-HIV drugs.
Moreover, researchers have concluded that a significant number of African babies acquire HIV infection through the very substance that protects them in so many other ways: breast milk.
Subscribe to Science News
Get great science journalism, from the most trusted source, delivered to your doorstep.
“We already know how to prevent breast-feeding transmission: Don’t breast-feed,” says Lynne Mofenson of the National Institute of Child Health and Human Development in Bethesda, Md. But that ideal is “not an option in [developing] countries.”
In the developed world, with an abundance of clean water and easy access to medicines and health services, feeding infants on formula presents no unusual difficulties or dangers. But in Africa, where food may be scarce and women sometimes can’t afford enough formula or don’t have access to clean water, many infected women have tried to heed WHO advice to bottle-feed their newborns but have ended up supplementing their children’s diets with breast milk.
Now, research is revealing a cruel irony. This part-formula–part-breast regimen may be the worst strategy of all for the babies it’s supposed to protect. Recent studies show that supplementing breast milk with other food exacerbates the risk of HIV transmission from mother to child in several ways. In addition, babies don’t get the full nourishment and disease-preventing benefits of breast milk, while being exposed to heightened risks of malnutrition and gastrointestinal diseases from inadequate formula and the polluted water with which it’s sometimes mixed.
On the basis of mounting anecdotal evidence and, now, a large and lengthy study of HIV and breast-feeding, many researchers and health authorities have concluded that women in developing countries should return to feeding babies only breast milk in order to reduce their chances of HIV infection as well as save them from a host of other ills.
Breaching the barrier
Studies have shown that children whose infected mothers don’t get antiretroviral drugs or other interventions during pregnancy have a 15 percent to 25 percent chance of acquiring HIV before or during birth. If the child of an infected mother is fortunate enough to make it into the world HIV-free, he or she still has an additional 5-to-20 percent chance of picking up the virus through breast milk. The longer an infected mother breast-feeds, the greater the chance that she will give the virus to her child, studies show.
Viruses such as hepatitis B and hepatitis C can’t pass through breast milk, but HIV finds a way. Some 45-to-60 percent of breast-milk samples from HIV-infected women contain the virus, researchers have found. A baby won’t be barraged with HIV every time it breast-feeds, but since a child takes milk several times a day, each baby of an infected mother is presumed to be regularly exposed to HIV.
Further increasing the likelihood of HIV transmission are various types of tissue damage. Throughout the body, intact membranes are effective in blocking HIV. But ruptured, pierced, and even just inflamed tissues present breaches where HIV can slip into the bloodstream or invade immune cells that congregate in disturbed areas. Thin mucous membranes, such as those lining the vaginal wall, are especially vulnerable, which is why normal childbirth by HIV-positive women is risky.
Similarly, if the tissue lining an infant’s gut is inflamed or if a baby has sores in its mouth, HIV in breast milk has an easier infectious path. And when mothers acquire the common bacterially-caused inflammation known as mastitis, which blocks and inflames milk ducts, breast milk becomes “a much better conduit for HIV,” says Tracy Creek of the Centers for Disease Control and Prevention (CDC) in Atlanta. Milk from an infected breast has a higher concentration of virus than milk from a healthy breast does, she says.
For these reasons, organizations such as the American Academy of Pediatrics have recommended since the mid-1980s that infected women in developed countries avoid breast-feeding. In 1992, WHO extended that advice to women in poorer areas, unless formula feeding was unsafe or impractical. Studies completed in the early 1990s, showing that more babies died from acquiring HIV during breast-feeding than died of diseases caused by formula feeding (SN: 6/2/01, p. 340), supported those recommendations.
“Avoiding HIV transmission at all costs was a reasonable position to take at the time,” says Nigel Rollins, a physician at the University of KwaZulu-Natal in Congella, South Africa, who has studied HIV and breast-feeding.
Despite all this bad news, not all babies of infected mothers get HIV. In fact, 60 percent or more of babies born HIV-free and subsequently breast-fed survive the daily doses of the virus without picking it up. But the reasons remain murky. Examinations of HIV in expressed breast milk have revealed immune cells containing HIV as well as the virus on its own.
However, breast milk also contains HIV antibodies that inhibit the virus’ passage into mucosal cells in the baby’s gut and on into the blood. Other proteins, such as epidermal-growth factor, boost repair of breaches of the thin membrane separating the digestive tract from blood vessels. This probably bars some HIV from entering the blood.
Another protein that seems to inhibit HIV’s operation include the broad-acting anti-infectious agent lactoferrin. This molecule occurs in high concentrations in colostrum, the fluid that a mother’s breast produces in the days immediately after her baby is born. Also, milk contains proteins of a type known as mucins, which may protect infants against HIV. Mucins are also found in the lining of the gut and in saliva.
As in any person repeatedly exposed to HIV, however, these defenses can protect babies only so long.
Breast is best
About 8 years ago, researchers looking at vitamin A deficiency and HIV transmission in South Africa and Kenya suggested that exclusive breast-feeding lowered HIV transmission to babies, compared with mixed feeding. However, “those studies were not sufficiently rigorous … to conclusively guide policy,” Rollins says. Without hard evidence of an advantage for exclusive breast-feeding, a WHO-policy update in 2000 maintained the formula-feeding recommendation, he says.
To clarify the evidence, Rollins and his colleagues at the University of KwaZulu-Natal set out to determine whether exclusive breast-feeding might reduce HIV-transmission rates in the first 6 months of a baby’s life.
The researchers didn’t randomly assign women to breast-feed or formula feed, but studied healthy and HIV-infected women who chose to breast-feed only, bottle-feed only, or supplement breast-feeding with formula, milk, or solid foods.
After studying more than 2,700 women for 7 years, the researchers published their results in the March 31 Lancet. They found that babies fed exclusively breast milk had about a 4 percent risk of picking up the virus from age 6 weeks to 6 months. That was less than half the risk of HIV infection of babies fed with breast milk plus formula or other milk products. Moreover, babies fed solids as well as the breast milk were 11 times as likely to become infected as were breast-only babies. Only two formula-only babies became infected during the study, and both had been breast-fed before their mothers switched them to formula.
“What this research shows is that breast milk [on its own] is not really that transmissive,” Rollins says. Older studies indicating that about 15 percent of breast-fed babies acquire HIV from infected mothers failed to distinguish between babies exclusively breast-fed and those who received food supplements, says Rollins.
Wendy Holmes, an HIV researcher at the Macfarlane Burnet Institute for Medical Research and Public Health in Melbourne, Australia, describes the work by Rollins’ team as “extremely meticulously done.” The strengths of the study, she says, are its large sample size and detailed, weekly observations of babies’ feeding habits and the health of both mothers and babies. In a Lancet editorial accompanying the report, she points out that the study also accounted for potentially confounding data, such as the mother’s education and socioeconomic status, whether HIV drugs were taken, and duration of labor. Measuring infection rates among children 6 weeks to 6 months of age made sure that the differences in infection rates between exclusive breast-feeding and mixed-feeding babies weren’t attributable to pregnancy or labor, adds Holmes.
Worst of both worlds
As for how formula and other food can increase the risk of HIV infection while not carrying the virus themselves, Holmes endorses the suggestion made by other researchers that large proteins and other molecules found in foods such as formula, cow’s milk, and grain inflame a baby’s immature digestive system.
“The newborn gut is meant to only have breast milk and is not really meant to see anything else,” Holmes says. “So it can become irritated, especially with solids like rice and maize.”
Inflamed areas in the mucosal membranes of a baby’s gut would attract white blood cells, increasing the opportunity for HIV infection, Holmes says. Inflammation might also tend to open up gaps between the cells lining the membrane, letting more of the virus cross into the blood. A mother who feeds formula or other food part of the time and breast-feeds to fill in is therefore increasing her baby’s vulnerability to HIV infection. On top of that, the same feeding regimen increases the mother’s risk of developing a mild version of mastitis, because milk not emptied from the breast inflames the tissue. That inflammation encourages more HIV to move from the mother’s blood into her milk.
The Lancet study indicates that mixed feeding is a double whammy. Getting an insufficient dose of nutrients from breast milk not only seems to increase the likelihood of HIV infection for babies but also leaves them vulnerable to malnutrition, diarrhea, and diseases carried in contaminated water.
Avoiding breast-feeding to prevent HIV infection poses other problems in Africa. Confirming previous results, the Lancet study showed that babies fed exclusively on formula were twice as likely as their breast-fed counterparts to die by 3 months of age from diseases other than AIDS.
“There are millions, millions of children per year who die from diarrhea, and breast-feeding is an incredibly important survival instrument,” Rollins says. “We can honestly say with certainty that breast-feeding in comparison to formula feeding saves lives” in Africa.
At an October 2006 meeting in Geneva, WHO members refined the breast-feeding recommendation for HIV-infected women to emphasize that the first choice for babies during their first 6 months is exclusive breast-feeding, unless the conditions for bottle-feeding are “acceptable, feasible, affordable, sustainable, and safe.” That is, women should exclusively breast-feed if they don’t have access to clean water, good health care and medicines, and formula.
For women who do breast-feed their babies, the focus of research will now move toward making breast-feeding safer. One of the biggest challenges will be to make sure that women who want to breast-feed do so exclusively—something difficult to guarantee in practice. Factors outside a woman’s control, such as her health, work responsibilities, or how well the baby breast-feeds might force her to supplement the baby’s diet with nutrients from other sources. Rollins says that with the right education and support, women can, and do, breast-feed exclusively. While previous studies showed dismally low rates of exclusive breast-feeding, Rollins and his colleagues reported that, in their study, 83 percent of women exclusively breast-fed for 6 weeks, and 67 percent were able to keep that up for 6 months.
In studies under way in Botswana, HIV-infected women are being given antiretroviral drugs while breast-feeding. The evidence so far shows that the practice decreases the amount of virus in milk. Researchers in Tanzania and Rwanda presented the preliminary data at an AIDS meeting in Australia in July (SN: 10/25/03, p. 270). Other researchers are investigating possible advantages in feeding babies banked breast milk and in killing HIV by flash heating mothers’ expressed milk.
Researchers are also working on what to do when a baby reaches 6 months of age, the time when it’s grown enough to require more nutrients than breast milk can supply. “We’ve reached remarkable consensus among experts” that breast-feeding is best during the first 6 months for babies of HIV-infected mothers in poor countries, says Jean Humphrey of the Johns Hopkins Bloomberg School of Public Health in Baltimore, Md., speaking from Zimbabwe. “The issue really now is the switch in the focus of what to do after 6 months.” WHO currently recommends that mothers wean babies rapidly to avoid prolonged exposure to mixed feeding.
“We’ve come a long way in our understanding about how to reduce mother-to-child-transmission,” Humphrey says. She points out that the United States has reduced its mother-to-child HIV-infection rate from as high as 30 percent to less than 2 percent. “You can do that in the developing world,” she says. “It’s just about trying to figure out how to make that work.”