Avian influenza A H5N1 virus: a continuous threat to humans

Abstract

We report the first case of severe pneumonia due to co-infection with the emerging avian influenza A (H5N1) virus subclade 2.3.2.1 and Mycoplasma pneumoniae. The patient was a returning traveller who had visited a poultry market in South China. We then review the epidemiology, virology, interspecies barrier limiting poultry-to-human transmission, clinical manifestation, laboratory diagnosis, treatment and control measures of H5N1 clades that can be transmitted to humans. The recent controversy regarding the experiments involving aerosol transmission of recombinant H5N1 virus between ferrets is discussed. We also review the relative contribution of the poor response to antiviral treatment and the virus-induced hyperinflammatory damage to the pathogenesis and the high mortality of this infection. The factors related to the host, virus or medical intervention leading to the difference in disease mortality of different countries remain unknown. Because most developing countries have difficulty in instituting effective biosecurity measures, poultry vaccination becomes an important control measure. The rapid evolution of the virus would adversely affect the efficacy of poultry vaccination unless a correctly matched vaccine was chosen, manufactured and administered in a timely manner. Vigilant surveillance must continue to allow better preparedness for another poultry or human pandemic due to new viral mutants.

Keywords: H5N1; avian; influenza virus; mycoplasma.

Figure 1

Phylogenetic relationships of the haemagglutinin genes from the virus strain of the 2010 Hong Kong patient and other avian H5N1 influenza virus strains. The phylogenetic tree was constructed using the neighbour-joining method. The numbers of clades and subclades are based on the World Health Organization nomenclature on H5N1 virus and are indicated on the right panel. Two human H5N1 isolates identified in 2010 in Hubei province and Hong Kong are indicated in red.