Kathmandu, October 17, 2011 Scientists map Nepal typhoid using Google Earth

PTI

Scientists claim to have mapped typhoid outbreaks in the Nepalese capital accurately using latest gene sequencing technology and Google Earth.

In the research, published in the journal Open Biology, an international team of researchers used Global Positioning System (GPS) signalling and the latest DNA sequencing techniques to map the spread of typhoid and trace its source in Kathmandu.

They discovered the bugs behind the typhoid outbreaks — Salmonella typhi and Salmonella paratyphi bacteria — are usually spread through water or food contaminated with faeces in the city.

“Until now, it has been extremely difficult to study how organisms such as the typhoid-causing bacteria evolve and spread at a local level,” study researcher Dr. Stephen Baker, of Oxford University Clinical Research Unit in Vietnam, said.

“Without this information, our ability to understand the transmission of these diseases has been significantly hampered,” he explained.

“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.”

To capture the information, health workers would visit a patient’s home and use GPS to capture the exact location.

They would also take a blood sample from the hospitalised patient to isolate the organism and to allow analysis of the typhoid strain’s genotype — its genetic make-up.

This sequencing technology able to identify single changes in the “letters” of DNA — the A, C, T and Gs that make up the code.

The study showed that people living near to water spouts, for whom these provide their main source of water, and people living at a lower elevation are at substantially greatest risk of contracting the disease.

According to the researchers, their work has also shed light on the role of asymptomatic carriers of the disease in the spread of typhoid. As these carriers do not show symptoms, they are likely to be unaware of their infection and can unwittingly spread the disease.

The most famous of such cases was a cook in New York in the early twentieth century, nicknamed “Typhoid Mary”, who is believed to have spread the disease to dozens of people.