Gene sequencing, GPS used to trade the spread of typhoid

Researchers funded in part by the Wellcome Trust recently began using gene sequencing technology and global positioning system case localization to trace the spread of typhoid fever and its sources.

The scientists, working out of Kathmandu, Nepal, have been able to accurately plot the spread of the disease by measuring mutations in the pathogen’s DNA that occur when it replicates, according to

The technique was fraught with challenges. The DNA changes are relatively small in number and not detectable by most techniques in use to analyze typhoid. Tracing typhoid in Kathmandu is especially difficult because street names in the Nepalese capital are generally not used.

To capture the needed information, health workers visited patients’ homes and then used GPS locators to capture their exact location. Hospitalized patients could then have the typhoid parasite isolated in their blood so its DNA could be sequenced.

The results were then plotted using Google Earth and distinct patterns emerged. Contrary to some expectations, population density was not shown to be an overriding factor in the location of typhoid cases. The study showed that those living next to water sources and those living at lower elevations are at an increased risk of contracting the disease.

"Until now, it has been extremely difficult to study how organisms such as the typhoid-causing bacteria evolve and spread at a local level," Dr. Stephen Baker of the Oxford University Clinical Research Unit said, reports. "Without this information, our ability to understand the transmission of these diseases has been significantly hampered. 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."