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Salmonella food poisoning that struck hundreds of police officers during
the Pope’s visit to Canada in 1984 has given scientists valuable clues about
a common type of arthritis called Reiter’s syndrome.

Researchers had long suspected a link between bacterial infections and
this type of arthritis in people with a genetic susceptibility to the disease.
The link was confirmed when 470 police officers assigned to cover Pope John
Paul II’s outdoor mass at a Jesuit shrine in Ontario went down with food
poisoning after eating their packed lunches. By turning the officers’
gut-wrenching experience into an epidemiological study, Robert Inman,
a rheumatologist at the University of Toronto, was able to pinpoint the
gene responsible.

Inman and his colleagues sent a questionnaire to all the officers attending
mass that day, and so identified those who developed pain and swelling in
their joints after a bout of diarrhoea. A follow-up visit by one member
of the research team confirmed that they were suffering from Reiter’s syndrome,
an arthritis that affects the joints of the hands and feet, the shoulders
and the small of the back.

Comparing the group who had food poisoning but not arthritis with the
group who had food poisoning and arthritis, the researchers pinpointed a
gene called HLA-B 27 as the predisposing factor. Once they had discovered
this, they could investigate the gene’s role in the development of the disease.

There are two possible ways the disease could develop, says Inman. When
infection strikes, the immune system somehow becomes confused and starts
attacking its own cells – an autoimmune reaction. Alternatively, it might
be that people with this B 27 gene are incapable of clearing all the invading
bacteria, resulting in long-term infection. This in turn might set off the
chronic inflammation behind the arthritis.

But how does salmonella, a bacterium that attacks the lining of the
stomach, affect the joints? Inman believes fragments of protein from the
bacteria lodge in the joint. ‘Possibly blood cells may pick up parts of
the bacteria at the level of the gastrointestinal tract and migrate through
the blood and through the lymph system of the body and deposit some of these
fragments in the joints. These then trigger and perpetuate this inflammation.
But it isn’t known what the intervening steps are.’

The researchers hope they can transfer some of the lessons they have
learnt from this isolated epidemic of Reiter’s syndrome to other types of
arthritis. Other studies have shown that Reiter’s syndrome can be triggered
by several types of bacteria. And there are suspicions that other forms
of arthritis have the same kind of link between genes and environmental
triggers. There may be a variety of steps to a final common pathway, says
Inman. ‘The bacteria in the setting of the B 27 gene may just be one.’