Coinfections with Other Respiratory Viruses
Coinfections of HCoV-NL63 and other respiratory viruses, including other HCoVs, influenza A virus, respiratory syncytial virus, parainfluenza virus and human metapneumovirus (hMPV), are common.[19,23,27,30,31,43,44,72,73] Interestingly, coinfected patients are more likely to be hospitalized, indicating the severity of this kind of superinfection. In a study from Germany, respiratory syncytial virus A and HCoV-NL63 was the most common coinfection identified in children less than 3 years of age. This is probably due to the high incidence of respiratory syncytial virus A in winter and the overlap in the seasonality of the viruses. Co-infection in hospitalized children with HCoV-NL63 and bocavirus is reported. The viral load of HCoV-NL63 is lower in coinfected patients than in patients infected with HCoV-NL63 only.[5,30] The clinical significance of these coinfections are not clear, but various plausible explanations for the lower HCoV-NL63 viral load have previously been discussed: HCoV-NL63 causes the initial infection that weakens the immune system enough for a second viral infection to gain a foothold. By the time this second infection shows symptoms, the HCoV-NL63 infection might have already been brought under control by the host immune system; HCoV-NL63 and the other virus may be in competition for the same cellular receptor or target cell in the respiratory organs; the activation of the innate immune response triggered by the second respiratory virus may cause inhibition of HCoV-NL63; or prolonged persistence of HCoV-NL63 at low levels of expression.[30,74] Even though these reports may reflect biological complexity or interaction, it is important to keep in mind that virtually all the published studies comprise solely of cohorts of children hospitalized for ARTI and thus are extremely biased.
Future Microbiol. 2011;6(2):153-159. © 2011 Future Medicine Ltd.
Cite this: Human Coronavirus NL63 - Medscape - Feb 01, 2011.