Researchers have shed light on how an anaemic blood disorder actually protects children from more severe anaemia caused by malaria.
Alpha thalassaemia, an inherited condition, is common in many areas of the world where malaria is endemic, particularly Africa and southeast Asia. People with the condition have red blood cells smaller than normal — causing a mild form of anaemia — but abnormally high levels of them.
A link between alpha thalassaemia and protection from malaria, particularly severe malarial anaemia (SMA), was made in the 1990s. Children with a specific type of the condition — homozygous alpha thalassaemia — are 60 per cent less likely to develop SMA when suffering from malaria.
The new study, published this week (18 March) in PLoS Medicine, suggests how this protection works.
Researchers reanalysed data from the 1990s from studies of over 800 children from the north coast of Papua New Guinea, where alpha thalassaemia affects around 70 per cent of the population. They found that a typical child loses 30–40 per cent of their red blood cells during a malaria attack.
They then modelled the effect a malaria attack would have on both normal children and children with alpha thalassaemia. This showed that children with homozygous alpha thalassaemia have to lose more red blood cells than their normal counterparts to get SMA.
The researchers say these children appear to have a "haematological advantage" — because they have more red blood cells to begin with, their pool of haemoglobin remains at a safe level despite losing a large number of red blood cells during a malaria attack.
"Anaemia protecting against anaemia is quite surprising," says Karen Day, chair of the Department of Medical Parasitology at the New York University Medical Center and a co-author of the study.
SMA contributes significantly to the morbidity and mortality associated with malaria, she says.
"SMA is having less than 50 grams of haemoglobin per litre of blood. Alpha thalassaemia may keep children above that danger level in the face of a malarial attack," she told SciDev.Net.
Stephen Allen, reader in paediatrics at the UK-based Swansea University and a co-author of the paper, says the study highlights the importance of research into the relationship between inherited blood cell abnormalities and malaria.
He hopes the study will encourage further research, adding that there is no obvious, direct route into new interventions for protection or treatment at present.
"Further research needs to assess how protection against anaemia may impact on other severe manifestations of malaria and also evaluate other protective mechanisms that are likely to occur in these children."
PLoS Medicine doi: 10.1371/journal.pmed.0050056 (2008)