CENTRE FOR INFECTIONS / PUBLIC HEALTH ENGLAND / SCIENCE PHOTO LIBRARY CENTRE FOR INFECTIONS / PUBLIC HEALTH ENGLAND / SCIENCE PHOTO LIBRARY
Influenzavirus B. Coloured transmission electron micrograph (TEM) of particles of the influenza B virus, which is the cause of influenza (flu) in humans. The virus particles have an enveloped outer coat, or capsid, bearing the proteins (green) haemagglutinin (H) and neuraminidase (N), which allow the virus to enter and leave host cells. As with all viruses, influenza cannot reproduce by itself, instead entering cells and hijacking their biochemical machinery to produce more copies of the virus. Flu usually causes lethargy, aching muscles, fever and nausea. Influenza B, however, is less virulent than influenza A, due to the limited host range and its slower rate of evolution (by 2 to 3 times).
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