Before Dorothy M. Horstmann located the poliovirus in the bloodstream of humans and monkeys, it wasn't clear how this devastating virus was spread - or how vaccination could reduce the impact of the polio epidemic. Horstmann’s accomplishments led her to be the first woman full professor and the first female Endowed Chair at Yale University School of Medicine.

Dorothy Horstmann was born in 1911 in Spokane, Washington, and went to the University of California, Berkeley, for her undergraduate education. A musician and a poet, she taught piano to pay for medical school at the University of California, San Francisco, graduating in 1940.

She then applied for a medicine residency at Vanderbilt University in Nashville, but was rejected - because she was a woman. Six months later she was considering a private practice position in San Francisco when she received a letter from the chief of medicine, Hugh Morgan, who had forgotten that "Dr. Horstmann" was a woman and was offering her an unclaimed residency spot. She accepted, shocking Morgan when she arrived and was not the man he expected.   

When Horstmann joined the Yale School of Medicine as an instructor in preventative medicine in 1942, polio was the great challenge in infectious disease. While polio is an ancient virus, existing in the archeological record for thousands of years, epidemics are a relatively recent phenomenon. In 1893, the first large polio epidemic in the U.S. hit Boston, Massachussetts, with 132 cases and 18 deaths. Cases increased yearly; in 1916, there were more than 27,000 cases of polio and 7,000 deaths in U.S. Increased sanitation may have increased the risk of severe illness, as exposure to the poliovirus was delayed from infancy until late childhood or adulthood when paralysis was more common.

We know now that most cases of polio are asymptomatic or cause a mild gastrointestinal illness. Less than 1% of pediatric polio infections affect the motor neurons of the spinal cord and cause a flaccid paralysis, usually asymmetric, primarily affecting the lower extremities but sometimes affecting the cranial nerves and the muscles of respiration. 

Researchers had attempted previously to isolate the poliovirus from human blood, but by the time a clinical diagnosis of poliomyelitis was made, no virus could be found. Polio researchers working with monkeys used a strain that could only replicate in nervous tissue, adding to the idea that polio exclusively infected the nervous system, without any viremia at all.

In 1943, Horstmann and her colleagues in the Poliomyelitis Study Unit traveled to outbreaks along the East Coast, testing blood, stool and pharyngeal swabs from their patient. They found poliovirus in the gut, and not in the respiratory tract – suggesting a fecal-oral route of transmission. And, in one 9-year-old girl from New Haven with a mild illness, they finally found the virus in the bloodstream - one positive test in 111 blood samples from recently infected people.  

Horstmann went to the lab where she fed monkeys and chimpanzees oral poliovirus and detected the poliovirus in the bloodstream, 4-6 days later. This was it, finally: the pathophysiology of polio transmission. Horstmann’s work, confirmed by others, led to the development of the Sabin live-attenuated-virus polio vaccine and the Salk inactivated killed-virus polio vaccine.  

Horstmann was promoted to assistant professor in 1948, then associate in 1952. In 1956 she was given a joint appointment in epidemiology and pediatrics. In the late 1950s, Horstmann traveled through the Soviet Union to evaluate the efficacy and safety of Sabin's oral polio vaccine. 

In 1961, Horstmann became the first female full professor at Yale. She became the first woman to have an Endowed Chair there in 1969. In 1975 she was elected the first woman president of the Infectious Disease Society of America.

A newspaper article from 1955 describes her as tall, with "reddish blond curls, a nice smile, a memorable capacity for laughter and a very human approach to the laboratory, to the classroom and to the sickbed." One of her colleagues, epidemiology professor James Niedermann, described her as "a very elegant woman in addition to being a perfectly disciplined scientist." 

Horstmann lived to see polio on the verge of eradication - and to see Virginia Apgar take over the National Foundation (March of Dimes) when its focus switched from polio to birth defects in 1958 - though poliomyelitis continues to resurge when vaccinations abate in areas of political instability. 

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Horstmann retired in 1982, and an annual lectureship was established in her name in Pediatric Infectious Diseases and Epidemiology at Yale in 1991. She died in 2001 with Alzheimer's disease.

Carleton HA. Putting together the pieces of polio: how Dorothy Horstmann helped solve the puzzle. Yale Journal of Biology and Medicine. 2011 Jun;84(2):83-9.

Essay by Alison Christy, MD, PhD