who discovered infectious diseases are spread by microorganisms
Germ theory of disease Microorganisms are said to have been first directly observed in the 1670s by Anton van Leeuwenhoek, an early pioneer in microbiology. Yet Athanasius Kircher may have done so prior. When Rome was struck by the bubonic plague in 1656, Kircher spent days on end caring for the sick. Searching for a cure, Kircher observed microorganisms under the microscope and invented the germ theory of disease, which he outlined in his Scrutinium pestis physico-medicum (Rome 1658).[16] Building on Leeuwenhoek's work, physician Nicolas Andry argued in 1700 that microorganisms he called "worms" were responsible for smallpox and other diseases.[17]
Smallpox By the end of 1975, smallpox persisted only in the Horn of Africa. Conditions were very difficult in Ethiopia and Somalia, where there were few roads. Civil war, famine, and refugees made the task even more difficult. An intensive surveillance and containment and vaccination program was undertaken in these countries in early and mid-1977, under the direction of Australian microbiologist Frank Fenner. As the campaign neared its goal, Fenner and his team played an important role in verifying eradication.[82] The last naturally occurring case of indigenous smallpox (Variola minor) was diagnosed in Ali Maow Maalin, a hospital cook in Merca, Somalia, on 26 October 1977.[20] The last naturally occurring case of the more deadly Variola major had been detected in October 1975 in a two-year-old Bangladeshi girl, Rahima Banu.[26]