By Kate Kelland

(Reuters) – Scientists have mapped the genome of a strain of cholera extracted a century ago from a sick British soldier during World War One and found clues to how some cholera bacteria strains cause epidemics today.

The bug – thought to be the oldest publicly available sample of the V. cholerae bacterium – was isolated in 1916 from the soldier’s “choleraic diarrhoea” while he was convalescing in Egypt, the researchers said.

But their analysis of its genetic code showed it was a non-toxigenic strain and that the soldier was probably sick with some other infection.

The strain was, however, distantly related to strains of cholera bacteria that are causing current outbreaks and have sparked epidemics in the past.

“Even though this isolate (bacterial sample) did not cause an outbreak it is important to study those that do not cause disease as well as those that do,” said Nick Thomson, who co-led the study at the Wellcome Sanger Institute in Cambridge, UK.

“Studying strains from different points in time can give deep insights into the evolution of this species of bacteria and link that to historical reports of human disease.”

Cholera is a severe diarrheal disease caused by eating or drinking food or water contaminated with toxigenic cholera bacteria. It can spread rapidly in areas with poor sanitation and has cause several historical global epidemics, or pandemics.

Experts say one of these outbreaks, known as the “sixth pandemic”, coincided with World War One.

Outbreaks of cholera are currently spreading in several countries including Yemen and Mozambique. The World Health Organization says the disease is “a global threat”, and experts estimate there are between 1.3 and 4.0 million cases and between 21,000 and 143,000 cholera deaths worldwide each year.

Matthew Dorman, who co-led the research, said the analysis of also revealed the 1916 strain had certain faults, including lacking a flagellum – a thin tail that enables bacteria to swim.

“We discovered a mutation in a gene critical for growing flagella, which may be the reason for this,” Dorman said.

The research was published in the Proceedings of the Royal Society B journal on Wednesday.

(Editing by Frances Kerry)