68 THE SCIENTIST | the-scientist.com
FOUNDATIONSNATIONAL INSTITUTES OF HEALTH OFFICE OF HISTORYBY ASHLEY YEAGERRethinking Raw Milk, 1918
A
lthough Louis Pasteur famously developed pasteuri-
zation to kill harmful bacteria in wine in 1864, a half
century later—in 1913, when bacteriologist Alice Evans
began her career at the US Department of Agriculture’s dairy
division—pasteurization of milk was still not mandatory. Evans
started out studying common milk-borne bacteria, particularly
Bacillus abortus, which can cause spontaneous abortion of
bovine fetuses. At the time, just a few studies hinted that the
bacterium could be harmful to human health, and the link
was far from certain. Still, “the idea of drinking milk contami-
nated with bacteria capable of causing disease in animals was
distasteful to me,” Evans recalled in the unpublished memoir
she wrote in 1963. That hunch led her to question whether
B. abortus was related to any bacterial species that cause dis-
ease in humans.
Talking with a USDA colleague, Evans learned about
Micrococcus melitensis, a bacterium that in humans causes
undulant or Malta fever (diagnosed mainly in the Mediterra-
nean nation of Malta) characterized by muscle and joint pain,
sweating, and a recurring fever. M. melitensis appeared to be
spherical, while B. abortus looked rod-shaped, so research-
ers didn’t think they could be related. But Evans knew that
both species were present in the udders of cows, so she won-
dered if scientists might be missing something. “I was amazed
to find that [both bacteria] behaved alike in the tests avail-
able in those days for bacterial identification,” she wrote in
her memoir.
Evans and her colleagues then infected pregnant guinea
pigs with M. melitensis from human patients and found that
the animals’ fetuses aborted, just as in cows infected with
B. abortus. Those results suggested that the species that
caused human illness was related to B. abortus. “Considering
the close relationship between the two organisms, and the
reported frequency of virulent strains of B. abortus in cow’s
milk, it would seem remarkable that we do not have a disease
resembling Malta fever in this country,” Evans wrote of the
US. This led her to ask: “Are we sure that cases of glandular
disease, or cases of abortion, or possibly diseases of the respi-
ratory tract may not sometimes occur among human subjects
in this country as a result of drinking raw cows’ milk?”
When Evans published her guinea pig results in 1918,
“making this connection was considered medical blasphemy,
and Evans set off a firestorm of protest and disbelief by physi-
cians, veterinarians, dairy industry representatives, and other
scientists,” Rita Colwell, a microbiologist at the University of
Maryland and former director of the National Science Foun-
dation, wrote in the Yale Journal of Biology and Medicine in- It took a few more years to turn the tide on pasteuriz-
ing milk nationwide. Finally, in the 1920s, after the child of
an officer in a dairy organization contracted brucellosis, an
illness caused by bacteria in raw milk, public health officials
and physicians started to recognize the dangers of drinking
unpasteurized milk. In 1924, spurred in part by Evans’s find-
ings, the US Public Health Service drafted a model ordinance
for states and localities to implement pasteurization require-
ments for milk meant to be consumed by humans, but the
practice didn’t become common across the country until later,
with the first federal pasteurization law passed in 1947.
Ultimately, “Evans’s work saved many lives and millions of
dollars in public health costs,” Colwell tells The Scientist. “She
was a true heroine of American microbiology.”gCONTAMINANTS: Alice Evans at work in her laboratory at what is now
the National Institutes of Health. Evans joined the agency—then called
the Hygienic Laboratory, part of the US Public Health Service—in 1918
and worked there until 1945.