Anna Charlotte Ruys or Charlotte Defresne-Ruys (1898 – 1977) was a Dutch professor of bacteriology and epidemiology. She became a proponent of hygiene in public health and an activist against biological warfare. Early life and education Ruys was born in Dedemsvaart as a daughter of Bonne Ruys and Engelina Gijsberta Fledderus. Her younger sister, Mien, became a landscape architect and carried on their father's work. Ruys studied at the Gymnasium in Zwolle and then was awarded a bachelor's degree in Utrecht. She pursued a PhD in medicine at Groningen, graduating on 3 July 1925 after submitting a thesis on the cause of rat-bite fever. Career She was hired by plague specialist Professor J. J. van Loghem to work on a study of plague in ship- and harbour-rats for the ministry of health (GG and GD). In 1928 she became director of the laboratories of the GG and GD and formed a class on hygiene which she then taught. One of her early discoveries was a large group of women who were being treated for gonorrhea despite actually suffering from the minor infection vulvovaginitis, due to sloppy laboratory tests. Proper diagnosis enabled the women to return to work and avoid the embarrassment and social stigma of a sexually transmitted infection. In 1940 she was promoted by van Loghem to professor of microbiology of infectious diseases in Amsterdam with the speech Ziektekiemen. The next year she spoke at an event celebrating his 25th anniversary as professor and in 1948 she took over his professorship of bacteriology, epidemiology and immunology. During the war years she participated in the artsenverzet (doctors' resistance). After male students were removed forcibly from one of her classes, she refused to teach until she was fired in 1944. In February 1945 she was arrested on suspicion of hiding illegal radio transmitters and was locked in the Oranjehotel until 6 May 1945. After her release she married her long-time lover, the playwright on 22 June 1945. He had not been able to marry her before because his first wife would not grant him a divorce, and after 1934, she could not marry him because she would have to give up her work at the GG and GD due to the (ARAR) law of 1934 that stated a female government employee younger than 45 who married would be honorably discharged on the day of her wedding. The couple can, for instance,