In the mid-nineteenth century, John Snow mapped cases of cholera in Soho, London, and traced the source of the outbreak to a contaminated water pump. Now, in a twenty-first century equivalent, scientists funded by the Wellcome Trust working in Kathmandu, Nepal, have combined the latest in gene sequencing technology and global positioning system (GPS) case localisation to map the spread of typhoid and trace its source.
Typhoid fever is caused by two bacteria Salmonella typhi and Salmonella paratyphi. Both of these bacteria are found in Kathmandu and they usually spread through water or food contaminated with faeces. Symptoms of the disease include fever, abdominal pain and vomiting.
Recent advances in DNA sequencing have allowed scientists to accurately track the spread of some diseases by measuring mutations in the pathogen's DNA when the DNA replicates.
However, tracing the spread of typhoid has proved challenging as these mutations are small in number and not detectable by most techniques in use.
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 hence accurately mapping the outbreaks has proved challenging to health workers.
In research published today in the journal Open Biology, scientists at the Wellcome Trust Major Overseas Programme in Vietnam and the Oxford University Clinical Research Units in Kathmandu, Nepal, and Ho Chi Minh City, Vietnam, 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 Dr Stephen Baker from the Oxford University Clinical Research Unit in Vietnam. "Without this information, our abi
|Contact: Craig Brierley|