Google GPS, gene sequencing combo tracks typhoid outbreaks

LONDON, UK: Scientists working in Nepal have tried out a combo of cutting edge gene sequencing technology and global positioning system (GPS) to map typhoid's spread and trace its source.

More than 150 years ago, John Snow mapped cholera cases in Soho, London, tracing the source of the outbreak to a contaminated water pump.

Typhoid fever is caused by two bugs, Salmonella typhi and Salmonella paratyphi. They are found in Kathmandu and usually spread through water or food contaminated with faeces. Symptoms include fever, abdominal pain and vomiting.

Recent advances in DNA sequencing help precisely track disease spread by measuring mutations in the pathogen's DNA, the journal Open Biology reports.

However, tracing the spread of typhoid has proved challenging as these mutations are small in number and not detectable by current techniques, according to an Oxford University release.

Tracing outbreaks of typhoid in Kathmandu also carries its own problem: street names are not used in Nepal, so capturing the addresses of typhoid cases and accurately mapping the outbreaks have proved challenging to health workers.

Scientists at the Wellcome Trust Major Overseas Programme in Vietnam and the Oxford University Clinical Research Unit in Nepal have found a way to accurately map typhoid outbreaks in the city.

Their research combines DNA sequencing technology and GPS signalling, and maps the data onto Google Earth.

"Until now, it has been extremely difficult to study how organisms such as the typhoid-causing bacteria evolve and spread at a local level," explains Stephen Baker from the Oxford University unit in Vietnam.

"Now, advances in technology have allowed us for the first time to create accurate geographical and genetic maps of the spread of typhoid and trace it back to its sources," said Baker.