The tragedy of mother-to-child HIV transmission

By, Courtenay Bartholomew, Trinidad and Tabago Express, March 26, 2008

The most biologically intimate association between two individuals is that of a mother and the foetus developing within her womb. Indeed, one of the most tragic consequences of HIV infection in women, who become pregnant is the transmission of that deadly virus to their unborn offsprings.

Alarmingly, more than 60,000 babies worldwide inherit HIV from their mothers every year. Can you really fathom the dimension of this tragedy? It is indeed a tragedy when the mother does not know that she is HIV-infected at the time of her pregnancy as is frequently the case, but it is a felony when she knows that she is HIV-infected and still becomes pregnant while neither on treatment nor taking other precautions.

Now, without treatment, the overall risk of transmission from an infected mother to her infant is around 30 per cent but there are wide variations. In the early stages of infection and in the more advanced stages with severe immuno-suppression, the viral load is greater than at other times and transmission from mother to child is therefore considerably higher during these periods.

Infection may be transmitted in utero or during the delivery process (intrapartum) as the baby moves down the birth canal and is bathed with the mother's blood.

Infection may also be acquired after birth (postpartum) by breast feeding and so, we advise all HIV-positive mothers not to breast feed their babies and milk formulae are given free of charge. About 23 per cent of infections occur in utero and as early as the first trimester of pregnancy, however, most transmissions occur at the time of delivery or during the birth process.

Antibodies to a virus are a legacy of and a response to previous infections and remain in the blood indefinitely even when the virus has disappeared. These antibodies then protect the individual from being re-infected with the same virus. Not so with the retrovirus of AIDS. Viruses and antibodies co-exist in these patients because the antibodies are not powerful enough to suppress or kill the virus. Therefore, to test for the presence of HIV, we only need to test for the antibodies, which is much simpler and less dangerous than testing for the virus itself (much cheaper also).

All babies of infected mothers, whether the mother's virus is transmitted to the child or not (and remember, as I said above, only about 30 per cent of mothers transmit their HIV virus to their babies), carry "passively" the antibodies of the mother through the cord blood.

However, these harmless passively-acquired maternal antibodies may take up to 18 months in some cases to be cleared from the baby's blood and it is only then that one can say with certainty that the baby does not carry the virus. However, for the past two years we now have more sophisticated equipment in our MRF laboratory and use the ultra-sensitive polymerase chain reaction (PCR) technique, which can identity viral infection within two months.

Because of the ridiculously high price of antiretroviral drugs, which third world countries could not afford and about which history will have a lot to say in years to come, there was a time when we were only able to prevent the baby from being HIV infected by giving the mother a short course of a single drug treatment (AZT) from 28 or 32 weeks of her pregnancy, during labour, and for a week to the baby after delivery. This reduced the percentage of HIV-positive babies drastically from about 30 per cent to about 6.8 per cent.

Unfortunately, therapy was then stopped and so, while many of the babies survived, the mother was not able to get long-term treatment. The tragedy of this is not worth recalling.

Now, all mothers attending the antenatal clinics of hospitals are tested for HIV antibodies (with their consent). This being so, we have found that 8 per cent of the mothers first became aware of their HIV positivity this way. This is interesting. Once they are tested positive they are then referred to the Medical Research Centre where we assess the immunological status of the mothers (CD4 counts) and their viral loads. Depending on those levels, we then treat the mothers at a certain time in their gestation period and treatment continues during labour, after labour and onwards. In other words, we now treat both mother and child. We use the World Health Organisation's (WHO) therapeutic recommendation for mother to child transmission. To date we have treated 203 mothers and only 7 (3.4 per cent) of their babies have been infected. But even that is not good enough.

We are now considering a more aggressive approach by treating the mothers with triple therapy earlier in their pregnancy although we are very concerned that since non-compliance of therapy increases with time, we may theoretically be putting the mothers at risk of developing drug resistance in time to come the earlier we begin treatment. Whether our concern is valid would only be determined in comparative long-term studies. In the meanwhile, we are aiming for a zero transmission of virus from mother to child without compromising the mother in the long-term.

- Prof Bartholomew is the Executive Director of the Medical Research

Source: http://www.trinidadexpress.com/index.pl/article_opinion?id=161298516