CHICAGO – Something called the metapneumovirus, discovered just two years ago, is turning out to be an exceedingly common cause of human misery, responsible for garden-variety colds in grown-ups and more severe coughing, wheezing and congestion in children.

Researchers are beginning to piece together the scope of this ubiquitous but overlooked bug, which now appears to afflict just about everybody, probably over and over.

Even though the virus seems to be rarely serious, its vast presence intrigues microbiologists, and it is one of the most talked-about topics at this week’s meeting in Chicago of the American Society for Microbiology.

Experts say the metapneumovirus is almost certainly not a new bug but something that has been around for eons. Rhinoviruses are long considered the classic cold bug.

Like many other respiratory bugs, this one is most likely to cause severe illness in infants encountering it for the first time. Although repeat infections are thought to be common, they result in much less intense illness, often just an ordinary cold or perhaps no symptoms at all. However, the bug may cause more serious problems in the elderly and people with other medical conditions.

Research suggests that the metapneumovirus is second only to respiratory syncytial virus as a cause of severe lower respiratory infections in the young, occurring about two-thirds as often. Both viruses are members of the paramyxovirus family.

A team led by Dr. James Crowe Jr. of Vanderbilt University looked at nasal specimens taken from 2,000 children after they were treated for lower respiratory infections since 1976.

The newly discovered virus turned out to cause about 12 percent of these severe illnesses. They also caused 15 percent of common colds in children, including one-third of the colds complicated by middle-ear infections.

“When we put this in perspective, it appears to be the second most common cause of respiratory illnesses in children,” he said.

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