Most influenza viruses enter human or animal cells through specific pathways on the cells' surface. Researchers at the University of Zurich have now discovered that certain human flu viruses and avian flu viruses can also use a second entry pathway, a protein complex of the immune system, to infect cells. This ability helps the viruses infect different species – and potentially jump between animals and humans.
The majority of type A influenza viruses circulating in birds and pigs aren't normally a health risk for humans. However, the viruses may pose a threat if there is an outbreak like the one currently in dairy cattle in the US or during seasonal epidemics. In rare cases, a virus can jump from animals to humans – with potentially devastating consequences such as a global pandemic.
Most influenza viruses enter host cells by using their envelope proteins, which stand up from the surface like spikes. The so-called hemagglutinin binds to sialic acid, a chemical group on the surface of human cells and the cells of various animal species. An international research team led by Professor Silke Stertz from the Institute of Medical Virology at the University of Zurich (UZH) has now shown that flu viruses also have a second method to infect host cells.
Human influenza A viruses of subtype H2N2 and related H2N2 avian influenza viruses can enter cells through a second receptor. They use an alternative entry pathway." Professor Silke Stertz, Institute of Medical Virology, University.