Some pathogens (such as the bacterium Yersinia pestis, which may have caused the Black Plague, the Variola virus, and the Malaria
protozoa) have been responsible for massive numbers of casualties and
have had numerous effects on afflicted groups. Of particular note in
modern times is HIV, which is known to have infected several million
humans globally, along with the Influenza virus. Today, while many medical advances have been made to safeguard against infection by pathogens, through the use of vaccination, antibiotics, and fungicide, pathogens continue to threaten human life. Social advances such as food safety, hygiene, and water treatment have reduced the threat from some pathogens.