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Mother to Child Transmission of HIV

Posted Oct 22 2008 4:32pm
When the AIDS epidemic commenced in the early 1980s, the high risk groups were identified as the 4 H’s: homosexuals, hemophiliacs, Haitians, and heroine users. Today, the face of the AIDS epidemic has transformed and women have the highest rates of infection. As more women become infected, the potential for vertical transmission from mother to child increases. Of the nearly seven million children newly infected with HIV in 2003, it is estimated that over ninety percent acquired the disease from mother-to-child-transmission. Similarly, it is estimated that over 90% of the HIV-infected children in sub-Saharan Africa acquired the infection vertically. While a combination of intervention methods can reduce the risk of vertical transmission to less than 2%, mother-to-child HIV transmission still persists worldwide, especially in developing countries which account for 95% of the vertically transmitted HIV cases.

Vertical HIV transmission is the cause of most cases of HIV in children below age 15, so it is important to understand how HIV passes from mother to child. Without intervention or treatment, the possibility of HIV transmission from mother to child is 15-30% in developed countries and 30-45% in developing countries. While 50-80% of infants are vertically infected during delivery, HIV transmission can also occur during pregnancy and after birth. During pregnancy, the fetus can become infected by contacting maternal blood through a placental hemorrhage or by swallowing infected amniotic fluid. Maternal factors which increase the chance of mother-to-fetus transmission include: maternal seroconversion during pregnancy, high viral load, malnutrition, other sexually transmitted diseases, and lack of or poor compliance with antiretroviral drug therapy.

During birth, factors that increase the risk of mother-to-child HIV transmission include: vaginal delivery, rupture of vaginal tissue, contact with maternal blood and vaginal secretions, and chorioamnitis. Pregnant women with chorioamnitis have a potentially increased white blood cell count that acts as a target for the HIV virus. Higher maternal viral load is positively correlated with vertical HIV transmission. Posnatally, the most significant risk factor is breastfeeding. The HIV virus has been isolated from breast milk, demonstrating the risk of long-term breastfeeding in infants. Transmission of HIV through breastfeeding occurs in 16-29% of cases. Specific risk factors during breastfeeding include: cracked nipples, mastitis (breast inflammation), breastfeeding for extended time periods, postnatal maternal seroconversion, high viral load, and low CD4 cell count. Mixed feeding of breast milk and other food sources has been shown to increase the risk of HIV transmission. Scientists hypothesize that an infant’s immune response is triggered by the introduction of new foods, attracting white blood cells to the gastrointestinal tract and increasing targets for the HIV viruses to spread infection.

The most successful methods of intervention to prevent mother-to-child HIV transmission include: antiretroviral medication for mother and child, caesarian section, and refraining from breastfeeding. While the recommended type and regimen of antiretroviral drugs for mothers varies, mothers on antiretroviral drugs have less than a 2% chance of transmitting HIV to their babies. The Pediatric AIDS Group Protocol 076 (PACTG 076) was an important study that demonstrated the effectiveness of using zidovudine in reducing vertical HIV transmission. This study showed that zidovudine given during pregnancy and labor and given to the baby during the first six weeks of life decreased the risk of vertical transmission by 66%. Another drug called nevirapine, a nonnucleoside reverse transcriptase inhibitor, is also effective in reducing vertical HIV transmission when given during pregnancy and after birth to the child. Aside from drug therapy, pregnant HIV positive women are also advised to have a cesarean section at 38 weeks to further reduce the risk of vertical transmission. Cesarean delivery reduces exposure of the infant to maternal fluids and tissues which is high during vaginal delivery. Finally, HIV positive women are encouraged to refrain from breastfeeding to reduce the risk of spreading HIV to their babies postnatally.

While the methods of preventing vertical HIV transmission are fairly effective, implementing these interventions in sub-Saharan Africa and other developing areas of the world is difficult due to cultural and economic barriers. While encouraging HIV-positive mothers to refrain from breastfeeding is a logical preventive measure against vertical HIV transmission, most women in poverty-stricken areas cannot afford to pay for formula or do not have access to clean drinking water to prepare the formula. Also, women who stop breastfeeding to protect their children from HIV risk the stigma of being labeled as HIV positive. These obstacles, combined with the lower level of access to antiretroviral drugs in developing countries, create obvious barriers to decreasing vertical HIV transmission worldwide.

I'm Meredith Prasse. Thanks for listening.
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