Human metapneumovirus plays big role in infant respiratory infections

Two or three years into the future, physicians will be able to determine the cause of many common childhood respiratory illnesses. A cure will probably still be a distant concept, but the immediate knowledge may provide much-needed comfort to parents worried about coughing, wheezing, sniffling and feverish children.

It may also empower primary care physicians to wave off the demanded antibiotics prescription because the viral cause will be easier to pinpoint. Additionally, then, this knowledge could trigger a slowing of the emergence of antibiotic resistance and reduce incidents of drug-related side effects.

This vision of the future comes in the wake of a study in the Jan. 29 New England Journal of Medicine. The report documents that the human metapneumovirus appears to cause 12% of lower and 15% of upper respiratory infections in infants, making it the second-most-common known viral cause of respiratory illness.

"Physicians should be very encouraged that researchers are now able to identify one of the most common causes of childhood illness that previously was a frustrating condition [because] in many cases we were not able to identify the virus," said James E. Crowe, Jr. MD, lead author on the paper and associate professor of pediatrics at Vanderbilt University in Nashville, Tenn. "This is not an Ebola, an emerging scourge. This has been with us, and now that we know about it, we'll be better prepared to treat patients."

This virus, discovered by Dutch scientists in 2001, may also be slightly more serious than others. According to the study, presence of the virus is more strongly associated with asthma exacerbations and middle-ear infections. Also, 2% of children infected are sick enough to be hospitalized. Other studies have suggested that the virus may play a significant role in adult respiratory illnesses, particularly those serious enough to require hospitalization.

"It's probably more important than a number of viruses," said Kenneth McIntosh, MD, lead author on the accompanying editorial and emeritus chief of infectious disease at Children's Hospital in Boston.

For virologists, this marks the rare instance in which a virus is discovered that not only has been there all along, but also makes a significant impact on human health.

"We in the respiratory virus field are very excited," said Ann Falsey, MD, associate professor of medicine at the University of Rochester School of Medicine and Dentistry in Rochester, N.Y., who has studied the virus in adults. "This doesn't happen very often."

For physicians who see a multitude of respiratory illnesses every winter, the finding offers an explanation for some previously unexplained viral infections -- though not all. In this study, 40% remained unexplained even with top-of-the-line laboratory testing.

"The more and more names you can put to viral infections, the better off we'll be," said Alexandra Freeman, MD, an infectious disease fellow at Children's Memorial Hospital in Chicago. "And, hopefully, we will have a vaccine or some kind of therapy."

Experts maintain that much work remains before physicians who care for children start regularly making the diagnosis of human metapneumovirus infection.

"There's not going to be a lot of big change right now, but over time I suspect this is going to be bigger," said Dr. McIntosh.

A test for the virus, already used in research settings, is the most likely next step. Experts expect it to take a place beside those for influenza and respiratory syncytial virus, both of which are already in use.

Although there is no effective drug for the metapneumovirus, information from the test will be useful in making decisions about supportive care and guiding parents. A positive test will also provide information about what not to do, such as prescribing antibiotics.

"If we can put a name on these illnesses and tell patients' families what the virus is, we also know something about the prognosis," said Dr. Crowe. "We can reassure families about what's likely to happen."

Links to other diseases

Wider availability of testing will also make much-needed epidemiological data easier to gather. This study confirms presence of the virus in very young children, but scientists are eager to learn more about its impact on ill children, adults or the elderly. Many are particularly intrigued by its possible role in asthma.

"We may find that this virus has some interesting associations with other lung diseases," said Jeffrey Kahn, MD, PhD, assistant professor in pediatric infectious disease at Yale University, New Haven, Conn., who is also researching the virus. "We can add human metapneumovirus to the growing list of respiratory pathogens, and we'll see over the next couple years what the true impact of this virus is -- the spectrum of disease and the epidemiology."

Experts also hope that work towards developing a vaccine and specific treatments will accelerate because the virus and its high prevalence have now been discovered.

But scientists also point out that respiratory syncytial virus, also an extremely common respiratory illness cause, was discovered decades ago, yet there are still few treatment options and no vaccine on the horizon. Still, the availability of testing and prophylactic for high-risk children has made significant progress against this virus.

"It's been a very frustrating virus, but [with] the advent of the bird flu and SARS and all the rest of the things that come along -- there's always a good reason to understand the way respiratory viruses replicate, mutate and spread," said Dr. Falsey.