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[NAIROBI] Exposure to malaria in the womb leaves some babies more susceptible to both malaria and anaemia in childhood, a new study suggests.

Researchers writing in PLoS Medicine say these babies develop a 'tolerance' to malaria, meaning their bodies fail to recognise the malaria parasite as foreign. This early tolerance persists into childhood, the authors say, inhibiting the immune system from fighting a malaria infection.

The researchers studied nearly 600 newborns, some born to mothers who had had malaria while pregnant and some who hadn't. Of the children born to malaria-exposed women, the researchers were able to split the babies into two groups — those whose immune systems had responded to the malaria parasite and those who hadn't.

They followed the babies up twice a year for three years to check for signs of malaria infection and anaemia, and to analyse malaria-specific immune responses.

The researchers found that those babies whose immune systems had not responded to the parasite were 60 per cent more likely to contract malaria than non-exposed babies in their first three years. They also had a "slightly higher" risk than babies whose immune system had responded.

"Under normal circumstances, the body is very hostile to anything foreign," co-author Alex Wamachi, a researcher at the Kenya Medical Research Institute in Nairobi, told SciDev.Net.

Babies are generally protected by antibodies provided by their mothers for the first six months of life, the authors say. But once this immunity is gone children up to the age of three have an increased susceptibility to malaria.

This susceptibility, coupled with immune tolerance, says Wamachi, is "a recipe for disaster".

When undetected, the malaria parasite finds its way into red blood cells where it matures. Eventually it leaves to multiply, destroying many red blood cells in the process — reducing the body's capacity to carry oxygen and resulting in anaemia.

Wamachi says the factors determining newborn tolerance are unclear but could be related to a mother's own immune response during a malaria infection.

The researchers hope their findings will have implications for the design of future malaria vaccines for this age group.

"For now we are happy that at least we have identified a new piece of information," says Wamachi. "The greater challenge is what others or we can do with these findings."

Link to full paper in PLoS Medicine


PLoS Med 6(7): e1000116. doi:10.1371/journal.pmed.1000116 (2009)

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