A little-known virus could be the second leading cause of hospital visits among infants in the developed world, new data suggest.
Human metapneumovirus (hMPV) was discovered in 2001 by researchers in the Netherlands. They found that, by the age of five, all Dutch children had antibodies against the virus, which causes flu-like symptoms and sometimes pneumonia.
This pattern is widespread, suggest results from the first systematic studies of the distribution and health impact of the virus. These were presented last week at the Interscience Conference on Antimicrobial Agents and Chemotherapy in Chicago.
Respiratory infections are the main reason for hospitalisation in under-fives in the west. About 12% of blood samples from under-fives with respiratory illness tested positive for hMPV, paediatrician James Crowe and colleagues at Vanderbilt University Medical Centre in Nashville, Tennessee, told the conference. Only respiratory syncytial virus was more prevalent - this virus, which causes severe wheezing and pneumonia in children, accounted for 50% of illness. "Metapneumovirus could be one of the most common causes of illness in infants," says Crowe.
The incidence of hMPV is high in the children of Canada, Israel and Britain, other groups told the same meeting. Recent studies found the same thing in Australia and Hong Kong. In all cases, antibody tests show that 100% of children are exposed by the age of five.
Israeli researchers found high levels of hMPV in children arriving from Ethiopia. Disease experts had worried that the virus was not present in Africa, so its arrival there could represent a potential public-health disaster. "It's fair to conclude that the virus has a worldwide distribution," says Dana Wolf of the Hadassah Medical School in Jerusalem.
Metapneumovirus is not new: antibodies against it can be traced back to 1953 in blood samples from the Netherlands. Re-infections are less severe than those of rapidly mutating, more deadly viruses such as flu.
"I'd say rhinovirus is still the lead player," says the paediatrician Peter Heymann of the University of Virginia Health System in Charlottesville. Rhinovirus causes the common cold, and so is responsible for far more illness overall.
But hMPV may be more dangerous for the immune-deficient and elderly. Ann Falsey of the University of Rochester School of Medicine, New York state, suggests it may account for 10% of elderly patients hospitalised with respiratory infections, compared with 12% for flu.
