Acute respiratory infections
New virus, new problem

Acute respiratory infections (ARI) are the most frequent cause of death in children in the developing world. Although it is now well accepted that bacteria such as pneumococcus and haemophilus and viruses, especially Respiratory Syncytial Virus (RSV), are among the main causes of ARI, it is not known what other factors contribute to a significant number of these episodes.

A new virus called metapneumovirus (HMPV) was identified in the Netherlands in 2001 and has since led to a rethink about ARI. Following the discovery, the virus has been reported in other European countries, Asia and North America, suggesting that it has a worldwide distribution. To learn more, researchers from the Liverpool School of Tropical Medicine set out to describe the epidemiological and clinical characteristics of children with ARI due to HMPV and/or RSV in Aracaju, northeast Brazil.

The research studied 111 children with symptoms of bronchiolitis attending health facilities in 2002 and 110 children in 2003. Bronchiolitis is an ARI affecting young children that resembles asthma and is mostly caused by RSV. The research indicated that up to 25% of the children had HMPV in 2002, while none had HMPV in 2003. HMPV and RSV had similar physical signs and both were present in a number of children. HMPV coincided in time with RSV, but was more prevalent in children attending peripheral clinics than referral hospitals. Similarly children with just HMPV were less likely to have low oxygen levels and lower respiratory rates than those with RSV, suggesting that HMPV had milder symptoms. This is in contrast to studies from the UK that reported severe cases of children in intensive care with both RSV and HMPV.

Are Brazilian and European HMPV one and the same? This is not yet clear. An explanation to reconcile these findings is the possibility that there are different HMPV subgroups producing clinical syndromes of varying severity. Other studies have since been completed in Sana’a, Yemen where preliminary findings suggest that HMPV also plays a major role in severe bronchiolitis. Researchers also found that the frequency of this virus changes in these settings from as little as 2-3% in one year to 25% in the next.

A strong link has been established between RSV infection, particularly in the first year of life, and a higher risk of asthma. Recently, researchers have also described an association between HMPV and acute wheezing in children with asthma. It is possible that the coincidental timing of RSV and HMPV could have led us to miss the culprit?

From these findings researchers and policy-makers should:

• further investigate the role of HMPV in ARI and asthma. Future studies should aim to establish the medium term clinical outcome of these infections
• identify funding for the introduction of existing vaccines in developing countries to prevent death due to ARI ( e.g. pneumococci)
• examine newly discovered pathogens as a possible means of facilitating the development of new vaccines for the prevention of ARI.

Luis E. Cuevas
Liverpool School of Tropical Medicine
Pembroke Place
Liverpool L3 5QA
UK

lcuevas@liv.ac.uk

See also:

'Human metapneumovirus and respiratory syncytial virus in Brazilian children with acute lower respiratory infections', Emerging Infectious Diseases, by L.E. Cuevas et al, October 2003 (forthcoming)

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