4. Image by Arionfx Image by Adenosine

5. enzyme Virus Particle

15. American Red Cross nurses tend to flu patients in temporary wards set up inside Oakland Municipal Auditorium during the Spanish flu outbreak of 1918.

16. Image of patient infected with measles virus. Image of Measles Virus The Seneca Indians were infected with a measles outbreak because they lacked immunities to the virus.

18. Avian flu (influenza H5N1 viruses) released from infected human cell Swine flu (influenza H1N1 viruses)

22. Image by Mark Pellegrini