When it comes to HIV transmission and breast feeding, the prevailing wisdom has been that a HIV infected mother risks passing on the virus to her child, if the child was not already infected†in utero, through her breast milk. However, a new study has added weight to scientists’ suspicions that breast milk may in fact contain properties that block the transmission of HIV and thus that the infection risk must come from some other variable.
Scientists have long been aware of breast milk’s ability to block HIV transmission in vitro, that is to say in isolated experiments that do not directly involve living subjects. However, breast milk’s inhibitory properties had not been demonstrated in vivo, or with living subjects . This, for Angela Wahl of the University of North Carolina, created a line of investigation that needed to be addressed–was breast milk really the culprit for early-life transmission, or does breast milk have transmission retarding properties?
So to test inhibitory power of breast milk, Wahl’s team took test subjects, in this case mice that had humanized bone marrow, liver tissue and thymus tissue, referred to as BLT mice, and one group of sample swallow†a HIV-laced fluid absent of breast milk , and breast milk tainted with the HIV virus.
They found that in the mice that were given the tainted breast milk, HIV transmission did not occur.
In stark contrast to the robust transmission of cell-associated HIV after oral exposure in the absence of breast milk, cell-associated HIV was not capable of establishing a productive infection when oral exposures occurred in the presence of breast milk. Specifically, we did not detect HIV RNA in the plasma of BLT mice that were exposed orally to HIV-infected cells re-suspended in the breast milk of donors 1 or 2 at any time point post-exposure (Figure 7D). Furthermore, the lack of HIV transmission was confirmed at necropsy when no HIV DNA was detected in the peripheral blood or tissues of any BLT mouse exposed to cell-associated HIV in the presence of human breast milk (Table 3). Collectively, these data demonstrate that BLT mice are susceptible to oral transmission of cell-associated HIV and that human breast milk possesses innate factors that can potently inhibit oral transmission of both cell-free and cell-associated HIV.
This sets the stage for further study into the role that breast milk, alongside retrovirals, may be able to play in HIV prevention strategies. To reiterate though, it does not demonstrate that breast milk alone could be some kind of miracle cure for the global HIV crisis–at least, not yet.
“This study provides significant insight into the amazing ability of breast milk to destroy HIV and prevent its transmission.
“No child should ever be infected with HIV because it is breastfed. Breastfeeding provides critical nutrition and protection from other infections, especially where clean water for infant formula is scarce.
“Understanding how HIV is transmitted to infants and children despite the protective effects of milk will help us close this important door to the spread of Aids.”
What is it in breast milk that acts as a barrier method helping to prevent HIV transmission then? Scientists are as yet unsure, though the study’s authors do point out that when in previous in vitro studies an inhibitory effect was not demonstrated, scientists were using skimmed breast milk rather than whole breast milk. This leads to several tantalizing avenues of inquiry. Scientists speculate that if they are able to pin down precisely what it is in breast milk that is acting as a barrier to infection, they may be able to use that so as to stop other infection methods such as sexual transmission.
So why do children become infected with HIV during early childhood if it is not in fact from breast milk? Researchers are not quick to draw conclusions on this point, but a number of theories exist, including that the mothers may have cracked or broken areas surrounding the nipple which may create the potential for HIV transmission.
Chiefly, this study suggests that the associated benefits of breast feeding, that is to say protections from infections that result in diarrhea, pneumonia and sepsis, may not have to be sacrificed under the false assumption that breast milk is the culprit for HIV transmissions, and that through also administering antiretroviral drugs it may be possible for HIV-infected mothers to still harness breast milk’s well established benefits in child health protection.