Metapneumovirus cases on the rise

The human metapneumovirus (hMPV) is spreading quickly in Australia, with New South Wales already reporting more than 1000 infections in the last two weeks.

While hMPV infections are not endemic, Dr Larissa Dirr from the Institute for Glycomics at Griffith University warned that they pose an important threat to the health of infants, the elderly and immunocompromised people, such as transplant patients, who are most at risk of contracting hMPV and developing severe disease, such as pneumonia or bronchiolitis.

“The infection peak for hMPV is usually seen at the end of winter and early spring. Global studies have indicated that every child under the age of five has encountered hMPV at one point in their life, with the percentage of children who are hospitalised due to an hMPV infection being 10–12%,” Dirr said.

“Although there have been many advances made since its discovery, neither effective drugs nor vaccines are currently available to treat or prevent hMPV infections.

“At the Institute for Glycomics, our research focuses on how hMPV is able to bind to human cells and how the virus spreads in the human body. It has been already identified that one viral protein is essential in the lifecycle of hMPV and we are trying to understand how this protein interacts with the human host cell receptors. We then utilise this information to design effective drugs that can block the interaction between the viral protein and human host cell receptors, therefore preventing disease.”

Increased testing

The virus has just been discovered in humans in 2001 by a group of researchers in the Netherlands, Dirr noted.

For this reason, hMPV has been misconstrued as a ‘new’ virus but it “likely infected humans for decades if not centuries before its discovery — we just didn’t have the technology to identify it as the cause of common respiratory illnesses,” said Dr Mary Petrone, a Postdoctoral Research Associate in the Sydney Institute for Infectious Diseases, School of Medical Sciences at The University of Sydney.

“This is very different from SARS-CoV-2, which did not infect humans before 2019. Because it is highly likely that most Australian adults have been infected with hMPV before, we have some level of immunity against it. This was not the case for SARS-CoV-2 because our immune systems had no previous experience with that virus when we were first infected,” Petrone said.

“What we are currently experiencing in NSW is in line with epidemiological patterns in other parts of the world. Cases of hMPV spiked in the United States around March of this year, at the end of winter and beginning of spring. This was likely due in part to increased testing, but a study in the Lancet Microbe found that concentrations of hMPV in wastewater in California also increased. This suggests that there was a bona fide rise in hMPV cases along with other respiratory viruses.”

Vulnerable populations

“We are witnessing a similar pattern of cases here in NSW as we enter spring. Although we should take this seriously, as vulnerable populations including children and the elderly can experience severe disease from hMPV infection, there is no reason to think that what is happening here is an anomaly.”

Professor David Gordon, Head of Microbiology & Infectious Diseases, College of Medicine and Public Health at Flinders University, said the virus is not a notifiable infection, according to SA Health.

“It is probably always around and most frequent around winter/early spring as for RSV. Clinically and epidemiologically, it is similar to RSV, and along with RSV and influenza, is one of the leading causes of respiratory tract infections in children.

“More recently (in the past 10 years or so) it has been more recognised in adults and the elderly, and as a cause of pneumonia in immunosuppressed people where it can cause quite severe disease. There is no specific treatment other than supportive, and there are no vaccines currently available.

“Given the recent success with the development of RSV vaccines (including with mRNA technology), it is likely that this will spur interest in metapneumovirus vaccine development.”

Early detection

Paul Griffin, Director of Infectious Diseases at Mater Health Services, Associate Professor of Medicine at the University of Queensland, and Medical Director and Principal Investigator at Q-Pharm, Nucleus Network, said we currently do not have any vaccine or treatment for hMPV but fortunately, most people will recover relatively rapidly without any intervention. Basic infection control practices, including staying home if you’re unwell, good hand hygiene and mask-wearing work for this virus as well.

“The reason why it’s important there is awareness regarding this virus at the moment is that it does seem to be on the rise, which is not the first time we’ve seen this but it is a little unusual this time of year. While more common in children, it can cause more severe disease in vulnerable people, particularly the immunosuppressed and elderly people with comorbidities,” Griffin said.

“It is also a virus that is prone to causing outbreaks in nursing homes and hospitals, so identifying it early and implementing appropriate precautions is very important. Another key takeaway is that if you are unwell and test negative for COVID, flu and even RSV, it’s still important to take precautions, particularly staying away from others, until your symptoms settle. Also, consider getting a full respiratory virus PCR panel via a laboratory to identify what you are infected with.”

Image credit: iStockphoto.com/JUN LI