Evans was offered the federal position as a bacteriologist finding methods to improve the flavor of cheddar cheese in the Dairy Division of the Bureau of Animal Industry at the United States Department of Agriculture. She accepted the offer in Madison, Wisconsin and worked there for three years. In those three years, she was coauthor of four scientific papers written on dairy science research. In 1913, she left to Washington, D.C. to work in the new laboratories of the Dairy Division. There she began her own study of bacteria that multiplies in a cow's utter and is discharged into the cow's milk. Bang's disease (Bacillus abortus or brucellosis) causes contagious abortion in healthy cows, and was considered not harmful to humans. Evans decided to investigate this; she wondered whether the disease in cows could be the cause of undulant fever in humans. She reported her findings to the Society of American Bacteriologists in 1917 and published her work in the Journal of Infectious Diseases in 1918.[2]
She was met with skepticism, particularly because she was a woman and did not have a Ph.D. She warned that raw milk should be pasteurized to protect people from various diseases. During the 1920s, scientists around the world made the same findings, and eventually Brucella was confirmed as the disease that caused what was then known as undulant fever and Malta fever. Her findings led to the pasteurization of milk in 1930. As a result, the national incidence of Brucellosis was significantly reduced.
Evans joined the United States Public Health Service in 1918, where she contributed to the field of infectious illness, like epidemic meningitis and influenza at the department's Hygienic Laboratories. There, she was infected herself with undulant fever in 1922, a disease incurable then that impaired her health for twenty years. She officially retired in 1945 but continued working the field. She lectured woman about career development and pursuing scientific careers.[3] She died of a stroke on September 5, 1975 in Alexandria, Virginia.
Evans donated a collection of her papers to the National Library of Medicine in 1969.[4]