Children under five living in sub-Saharan Africa are at greater risk than older children of developing a long-term parasitic disease, research suggests.
Infants experience significantly greater exposure to the parasitic worms that cause the chronic disease schistosomiasis, a study shows.
Under-fives are vulnerable because they spend time near rivers and lakes in which parasites that cause the disease live.
Previous studies missed pre-schoolers significant exposure to infected water in rivers close to family homes.
Researchers found that preschool-age children can suffer parasitic disease for as long as five years before they receive treatment.
Mass administration of anti-parasite medication is currently taking place in 28 African countries.
Despite infection afflicting as much as 60 per cent of the preschool population in these countries, the age group is not included in any of the treatment programmes.
Researchers claim that current clinical testing of schistosome vaccines is neglecting preschool children by targeting only primary pupils. They say that this raises the potential of future vaccinations continuing to exclude the younger age group.
Schistosomiasis affects 200 million people worldwide and is endemic in 43 African countries, with 90 per cent of cases occurring in sub-Saharan Africa.
Researchers from the University of Edinburgh, who carried out the study, found that infection can occur in babies as young as six months in high transmission areas.
Schistosomiasis, commonly known as bilharzia, is second only to malaria as the most significant parasitic disease affecting children in Africa. The disease, transmitted by freshwater snails, affects general health, growth, mental development and future reproductive health.
The Edinburgh study reaffirms the 2010 WHO recommendation that preschool-aged children should be included in national schistosome control programmes to redress the current health inequity.
The collaborative study between the University of Edinburgh and the University of Zimbabwe was published in Pediatrics and funded by the Thrasher Research Fund.
Dr Francisca Mutapi, who led the study, said: "Availability of anti-parasite drugs and improvements in point-of-care infection and disease diagnosis for pre-school children should remove the remaining barriers to delivering a schistosome mass drug administration programme on par with WHO recommendations."
"We must continue to work toward delivering an integrated, inclusive, sustainable and globally implemented control program for schistosomiasis."
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