Tiny Placental Ruptures Send HIV From Mother to Child
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HIV is likely passed from mother to child through tiny tears in the placenta that occur during labor, researchers here reported.
So-called “microtransfusions” allow the mother’s HIV-laden blood to infect the infant, according to epidemiologist Steven Meshnick, M.D., Ph.D., of the University of North Carolina.
The finding, based on a case-control study in Malawi, means transmission takes place during labor and not as the infant passes through the birth canal, Dr. Meshnick and colleagues said in the Nov. 21 online edition of the Public Library of Science journal PLoS Medicine.
While it is well-known that between 25% and 35% of HIV-positive mothers will pass the virus to their children (in the absence of prophylaxis) and about half of that infection will occur at birth, the mechanism of the intrapartum transmission has not been clear, Dr. Meshnick said.
One idea has been that transmission takes place when the infant’s mucosa come in contact with HIV-contaminated blood or other secretions during the passage through the birth canal, Dr. Meshnick said.
Evidence for that idea is that elective Cesarean sections reduce mother-to-child transmission. Evidence against it is that emergency Cesarean—undertaken once labor has begun—do not reduce mother-to-child transmission, Dr. Meshnick and colleagues noted.
The discovery of a large maternal enzyme—placental alkaline phosphatase, or PLAP - provided the key to a better understanding of mother-to-child transmission, he said. The protein is too large to pass the intact placenta, so if it is found in umbilical vein serum, it indicates that there have been microtransfusions during labor.
Those microtransfusions - as well as allowing placental alkaline phosphatase to pass the placenta - would also allow HIV to reach the infant, Dr. Meshnick and colleagues hypothesized.
To test their hypothesis, they carried out a case-control study in Malawi, using an HIV-positive sub-population of a larger study, the Malaria and HIV in Pregnancy (MHP) prospective cohort study.
The researchers randomly selected 149 HIV-positive women from the MHP study to serve as a reference group, and compared them to all cases of in-utero and intrapartum mother-to-child transmission in the larger HIV-infected group.
The study found:
- The presence of PLAP in the cord blood was significantly associated with intrapartum mother-to-child transmission. The relative risk increased by a factor of 2.82 for every log10 increase in cord PLAP (with a 95% confidence interval of 1.04 to 7.67).
- For emergency Cesareans, there was no association, although the data suggest a trend toward reduced risk. Numbers were too small to analyze instrumental vaginal, elective Cesareans, and breech deliveries.
- There was, as expected, no association between PLAP in the cord blood and in-utero mother-to-child transmission.
“It looks like direct mother-to-child blood mixing occurring during labor leads to infection,” Dr. Meshnick said.
The finding suggests that such measures as sanitizing the birth canal before delivery are unlikely to be effective in preventing mother-to-child transmission, he said.
The reviewers of the study felt that although the results are preliminary, and many questions remain, that “the design of the study enabled an efficient first test of the maternal-fetal microtransfusion hypothesis.”
Source: PLoS Medicine
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