Salmonella Typhi colonies

CDC

Researchers have sequenced the genome of the bacterium responsible for typhoid fever, a move they say will improve diagnosis and tracking of the disease and aid new vaccination strategies.

Around 600,000 people die from typhoid fever each year, with the disease killing 10–30 per cent of untreated people. Although controlled by vaccination and antibiotics, the disease persists due to antibiotic resistance, especially in South-East Asia.

An international team of researchers, led by the United Kingdom's Wellcome Trust Sanger Institute, sequenced 19 isolates of Salmonella Typhi from ten countries. They found that the Typhi genome had evolved little since its emergence around 15,000 years ago.

The researchers say this is consistent with Salmonella Typhi having become an infectious agent exclusive to humans, with asymptomatic carriers the main source of infection. This means it can be targeted through vaccination — and typhoid could potentially be eradicated.

The sequencing of Typhi now means that it can be classified in the field, to determine the strain of Typhi causing an outbreak of typhoid fever. This allows researchers to identify individual organisms spreading the disease in given populations, which can be used in conjunction with Google Earth's maps to visualise outbreaks.

The researchers hope that this mapping can be used to conduct more successful vaccination campaigns.

Gordon Dougan, from the Wellcome Trust Sanger Institute and senior author of the study, told SciDev.Net that the mapping could be used to study diseases such as typhoid and cholera that have troubled humans for centuries, adding that, individual viruses or bacteria or whole populations can be studied real-time in the field.

"The new technology enables us to see the evolutionary fingerprints in the DNA of organisms like Typhi," he says.

The mapping technology will revolutionise public health approaches such as monitoring and vaccination programmes of managing disease like typhoid fever, especially in the developing world, he adds.

He says that the mapping technology is easily accessible to scientists from the developing world, where they can use the databases of The Sanger Institute through its open access policy.

Link to full article in Nature Genetics