Absence of Melaka-virus in European children with respiratory disease.

In July 2007 Chua et al. from Malaysia and Australia detected a previously unknown member of the reovirus family (respiratory enteric orphan viruses) which was named Melaka-virus. This virus was associated with acute respiratory disease in the 39-year-old male index patient and also somewhat later in two of his family members (Chua et al., 2007). Furthermore, 14 out of 109 human volunteers living on the same island as the index patients proved positive for antibodies against Pulau-virus that is closely related with Melaka-virus.

As our group is interested in the epidemiology of newly discovered viruses such as HMPV, human Bocavirus, and newly discovered Coronaviruses, in the cohort of hospitalized pediatric and adult high risk patients (2–5) we have screened 225 nasopharyngeal washes that were previously RT-PCR tested for RSV, HMPV, human Coronaviruses (NL63, OC43, 229E, HKU1, and SARS), and human Bocavirus (detailed protocols available on request and previously published in: 2–5) for the presence of Melaka-virus RNA. The RT-PCR detection protocol was kindly provided by Dres. Chua and Wang who initially described Melaka-virus (Chua et al., 2007).

In total 29 (12.66%) out of the 225 samples tested were positive for RSV, 1 was positive for HMPV, 1 was positive for HMPV, 1 was positive for Coronaviruses, 1 was positive for Influenza virus A, and 1 (0.44%, each) was positive for human Bocavirus. No double infections with any of the tested viruses were observed. Melaka-virus RNA was not found in any of the samples tested. Although the lack of a Melaka-virus RNA positive sample does not imply that it is absent in our clinical samples since it could have been below the detection limit of the RT-PCR assay, we can still conclude that Melaka-virus plays no or only a minor role in hospitalized European pediatric patients. This conclusion is based upon the negative RT-PCR results. In similar epidemiological studies that we have performed for other viruses, the phenomenon that a newly described virus was not found in patient populations with corresponding symptoms was not observed. In other words, following the first descriptions of HMPV, human Bocavirus, Coronaviruses NL63 and HKU1, at least a small percentage of patients turned out to be infected by these new viruses (Kupfer et al., 2006, Muller et al., 2007, Volz et al., 2007, Wilkesmann et al., 2006) contributing to the common cold. In contrast, no positive results were obtained for Melaka-virus which is suspected to be transmitted by bats as a zoonotic pathogen.

Taking into account that none of our patients had known or suspected contact with bats, nor travelled to a region in which Melaka-virus may be endemic, our results give rise to the hypothesis by Chua et al. (2007) that Melaka-virus may indeed be transmitted by bats rather than common cold pathogens. We finally conclude that Melaka-virus testing should preferably be carried out in populations with suspected contact to the virus such as inhabitants of the endemic regions or air travellers with symptoms of respiratory disease (Luna et al., 2007).