Rubella Also an enveloped SS RNA virus, transmitted by the respiratrory route. Again, generally considered to be benign childhood disease. The virus is an enteric virus and is shed in feces. Neuraminidase degrades mucous whereas h emagglutinin binds the virus to the cell surface. Type A pandemics occur approximately every 10 years and tend to be the most severe.
Virulence increases with passage through animals.
Occur approximately every 2-5 years. B. This is the reason why we do not develope resistance to flu infections. Thus antibodies generated against one type of protein may not recognise the new protein. This generally leads to flu epidemics. The changes introduced into the protein structures are more dramatic, and distinctly different flu strains emerge that cause global flu pandemics.