Influenza: virological aspects, epidemiology and virological diagnosis

Influenza is a major public health issue because of its morbidity and increased mortality observed during epidemics, and because it may develop into a pandemic. A, B and C influenza viruses are RNA segmented viruses with high genetic plasticity including drift leading to new A and B variants responsible for epidemics, and shift resulting in new type A viruses responsible for pandemics. Hemagglutinin and neuraminidase glycoproteins are the targets of neutralizing antibodies. Gene reassortments can occur between human A influenza viruses and the avian reservoir, the pig possibly being an intermediary host. Virulence factors are not well documented, but they might be multigenic. Virological diagnosis is based on direct detection of virus antigens and culture, required for the discovery of new circulating variants in order to adapt vaccinal composition. Influenza epidemiological surveillance is carried out by alert networks. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.