EpidemicsGoogle Earth typhoid maps traces disease outbreaks
Recent advances in DNA sequencing have allowed scientists accurately to track the spread of some diseases by measuring mutations in the pathogen’s DNA when the DNA replicates; tracing the spread of typhoid, however, has proved challenging because these mutations are small in number and not detectable by most techniques in use
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 feces. Symptoms of the disease include fever, abdominal pain and vomiting.
Recent advances in DNA sequencing have allowed scientists accurately to track the spread of some diseases by measuring mutations in the pathogen’s DNA when the DNA replicates. Tracing the spread of typhoid, however, has proved challenging because these mutations are small in number and not detectable by most techniques in use.
A Wellcome Trust release reports that 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 - has proved challenging to health workers.
In research published today in the journal Open Biology, scientists at the Wellcome Trust Major Overseas Program in Vietnam and the Oxford University Clinical Research Units in Kathmandu, Nepal, and Ho Chi Minh City, Vietnam, have found a way accurately to map typhoid outbreaks in the city. Their research combines DNA sequencing technology and GPS signaling 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 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.”
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 hospitalized patient to isolate the organism and to allow analysis of the typhoid strain’s genotype - its genetic make-up. This genotyping used sequencing technology able to identify single changes in the “letters” of DNA — the A, C, T, and Gs that make up the code.
The researchers found extensive clustering of typhoid infections in particular locations. Yet, perhaps counterintuitively for a disease that spreads among humans, this clustering was unrelated to the density of the local population.
The release notes that, in fact, the study showed that people living near to water spouts, for whom these provide
