WORLD OF MICROBIOLOGY AND IMMUNOLOGY Salmonella503•
sored by the National Foundation for Infantile Paralysis. More
than one million children between the ages of six and nine
took part in the trial, each receiving a button that proclaimed
them a “Polio Pioneer.” A third of the children were given
doses of the vaccine consisting of three injections—one for
each of the types of polio virus—plus a booster shot. A control
group of the same number of children was given a placebo,
and a third group was given nothing.
At the beginning of 1953, while the trial was still at
an early stage, Salk’s encouraging results were made public
in the Journal of the American Medical Association.
Predictably, media and public interest were intense. Anxious
to avoid sensationalized versions of his work, Salk agreed to
comment on the results thus far during a scheduled radio and
press appearance.
Despite the doomsayers, on April 12, 1955, the vaccine
was officially pronounced effective, potent, and safe in
almost 90% of cases. The meeting at which the announce-
ment was made was attended by five hundred of the world’s
top scientists and doctors, 150 journalists, and sixteen televi-
sion and movie crews. The success of the trial catapulted Salk
to instant stardom.
Wishing to escape from the glare of the limelight, Salk
turned down the countless offers and tried to retreat into his
laboratory. Unfortunately, a tragic mishap served to keep the
attention of the world’s media focused on him. Just two weeks
after the announcement of the vaccine’s discovery, eleven of
the children who had received it developed polio; more cases
soon followed. Altogether, about 200 children developed par-
alytic polio, eleven fatally. For a while, it appeared that the
vaccinationcampaign would be railroaded. However, it was
soon discovered that all of the rogue vaccines had originated
from the same source, Cutter Laboratories in California. On
May 7, the vaccination campaign was called to a halt by the
Surgeon General. Following a thorough investigation, it was
found that Cutter had used faulty batches of virus culture,
which were resistant to the formaldehyde. After furious debate
and the adoption of standards that would prevent such a reoc-
currence, the inoculation resumed. By the end of 1955, seven
million children had received their shots, and over the course
of the next two years more than 200 million doses of Salk’s
polio vaccine were administered, without a single instance of
vaccine-induced paralysis. By the summer of 1961, there had
been a 96% reduction in the number of cases of polio in the
United States, compared to the five-year period prior to the
vaccination campaign.
After the initial inoculation period ended in 1958, Salk’s
killed-virus vaccine was replaced by a live-virus vaccine
developed by Sabin; use of this new vaccine was advanta-
geous because it could be administered orally rather than
intravenously, and because it required fewer “booster” inocu-
lations. To this day, though, Salk remains known as the man
who defeated polio.
In 1954, Salk took up a new position as professor of pre-
ventative medicine at Pittsburgh, and in 1957 he became pro-
fessor of experimental medicine. The following year he began
work on a vaccine to immunize against all viral diseases of the
central nervous system. As part of this research, Salk per-formed studies of normal and malignant cells, studies that had
some bearing on the problems encountered in cancer research.
In 1960, he founded the Salk Institute for Biological Studies in
La Jolla, California; heavily funded by the National
Foundation for Infantile Paralysis (by then known as the
March of Dimes), the institute attracted some of the brightest
scientists in the world, all drawn by Salk’s promise of full-
time, uninterrupted biological research.
Salk died on 23 June 1995, at a San Diego area hospi-
tal. His death, at the age of 80, was caused by heart failure.See alsoAntibody and antigen; Antibody formation and kinet-
ics; Immunity, active, passive and delayed; Immunization;
Poliomyelitis and polioSSalmonellaALMONELLA
Salmonellais the common name given to a type of food poi-
soning caused by the bacteriaSalmonella enteritidis(other
types of illnesses are caused by other species of Salmonella
bacteria, including typhoid fever. When people eat food con-
taminated by S. enteritidis,they suffer gastroenteritis(inflam-
mation of the stomach and intestines, with diarrhea and
vomiting).
Salmonella food poisoningis most often caused by
improperly handled or cooked poultry or eggs. Because chick-
ens carrying the bacteria do not appear ill, infected chickens
can lay eggs or be used as meat.
Early in the study of Salmonellafood poisoning, it was
thought that Salmonellabacteria were only found in eggs
which had cracks in them, and that the infecting bacteria
existed on the outside of the eggshell. Stringent guidelines
were put into place to ensure that cracked eggs do not make it
to the marketplace, and to make sure that the outside of
eggshells were all carefully disinfected. However, outbreaks
of Salmonellapoisoning continued. Research then ultimately
revealed that, because the egg shell has tiny pores, even
uncracked eggs which have been left for a time on a surface
(such as a chicken’s roost) contaminated with Salmonella
could become contaminated. Subsequently, further research
has demonstrated that the bacteria can also be passed from the
infected female chicken directly into the substance of the egg
prior to the shell forming around it.
Currently, the majority of Salmonellafood poisoning
occurs due to unbroken, disinfected grade A eggs, which have
become infected through bacteria which reside in the hen’s
ovaries. In the United States, he highest number of cases of
Salmonellafood poisoning occur in the Northeast, where it is
believed that about one out of 10,000 eggs is infected with
Salmonella.
The most effective way to avoid Salmonellapoisoning
is to properly cook all food which could potentially harbor the
bacteria. Neither drying nor freezing are reliable ways to kill
Salmonella.While the most common source for human infec-
tion with Salmonellabacteria is poultry products, other carri-
ers include pets such as turtles, chicks, ducklings, and iguanas.womi_S 5/7/03 8:20 AM Page 503