A respiratory virus discovered last year in the Netherlands has been isolated for the first time in Australian children, with researchers now suggesting it is likely to be relatively common worldwide.
The human metapneumovirus (hMPV), a paramyxovirus most closely related to avian pneumovirus, was first reported by Dutch researchers in 28 children with symptoms ranging from upper respiratory tract infection to severe bronchiolitis and pneumonia (Nat Med 2001; 7: 719–24).
Albert Osterhaus, from the Erasmus Medical Centre in Rotterdam, reported that serological studies showed that virtually all children in the Netherlands had been exposed to hMPV by the age of 5, and that it had been circulating in human beings for at least 50 years.
The virus was not identified earlier because of its poor replication in standard culture assays and because it appears to take up to 10 days after inoculation to cause cytopathic changes, he suggested.
At the time the Dutch results were published, Michael Nissen, Theo Sloots, and their team at the Royal Children's Hospital in Brisbane, Australia, were seeking a molecular diagnosis in the 25–33% of children with unexplained illness consistent with viral pneumonia or bronchiolitis.
Using a random sample of nasopharyngeal aspirate specimens, they screened for hMPV by PCR based on the known sequence of the virus after excluding nine common viruses (respiratory syncytial virus [RSV], influenza A and B, parainfluenza 1, 2, and 3, rhinovirus, coronavirus, and adenovirus) and atypical bacteria.
Of the 200 samples screened, three were identified as homologous with hMPV, and viral growth was subsequently confirmed in cultures from two samples (Med J Aust 2002; 176: 188).
The findings of this preliminary study led Nissen to predict that “hMPV is also relatively common in the Australian community”, a view reinforced by extension of the screening study to 525 samples, of which 40 tested positive for hMPV in 38 children with an average age of 2·4 years.
Studies of antibody responses in selected, positive samples showed antibody titres at 3 to 6 months after infection, “but we are not entirely sure how long lasting the immunity is”, reports Nissen.
The virus has been identified in several European countries and North America as well as Australia. “Given some additional preliminary data from other countries as well, we think indeed that the virus occurs worldwide”, says Osterhaus.
The Australian and Dutch teams agree that the findings could have implications for infection control. Nissen warns that: “It may be important to isolate children with the virus, as occurs with RSV”.