How valuable are IgA and IgM anti-HIV tests for the diagnosis of mother-child transmission of HIV in an African setting?

BACKGROUND

Babies born to HIV-infected mothers retain anti-HIV of maternal origin until 15-18 months of age. Because of this, HIV proviral DNA and p24 antigen measurements have become the methods of choice for timely diagnosis of HIV infection in infancy. They are, however, too expensive for widespread use in the developing world.

OBJECTIVE

To evaluate a simple, inexpensive serological method for diagnosing mother-child transmission of HIV, in an African population, which takes account of the effects of placental transfer of maternal antibody and continued exposure to HIV through breast-feeding.

STUDY DESIGN

Plasma specimens for a prospective study of mother-to-infant transmission of HIV in rural Zaire were collected at birth, 3, 6, 9, 12, 18 and 24 months from 21 infected infants (PP group), 21 uninfected infants (PN group) born to seropositive mothers and 21 control infants (NN group) born to uninfected mothers. The specimens were retrospectively tested for IgG, IgM and IgA anti-HIV by immunoglobulin class-specific capture EIAs, and by a commercial anti-HIV EIA.

RESULTS

In neonatal specimens, IgA and IgM anti-HIV were present, respectively, in 13 of 14 (97%) and 8 of 14 (57%) of the PP group and in 6 of 11 (55%) and 2 of 11 (18%) of the PN group. Later, at 3 months and older, IgA and IgM anti-HIV were only detected in the PP group. They peaked at 18 months (93%) and 24 months (67%) respectively. Of the 21 PP group children, 8 (38%) were transiently IgG anti-HIV-negative in the first year, indicating that infection had probably taken place after birth; four of the 8 had no detectable IgA anti-HIV during the first year. None of the specimens collected from the NN group babies were reactive for IgA, IgM or IgG anti-HIV.

CONCLUSIONS

IgA and IgM anti-HIV may be passively transferred across the placenta. Where breast-feeding is prevalent, about half of the transmissions may occur after birth, thus delaying the diagnosis of mother-child transmission. Nevertheless, this simple, cheap IgA anti-HIV, EIA identified 65% of transmissions by 9 months of age, and 93% at 18 months of age. It is a more useful marker than IgM anti-HIV, and gave a much more rapid answer than did tests for IgG anti-HIV seroreversion.