Featured Research

from universities, journals, and other organizations

Defining DNA Differences To Track And Tackle Typhoid

Date:
July 30, 2008
Source:
Wellcome Trust Sanger Institute
Summary:
For the first time, next-generation DNA sequencing technologies have been turned on typhoid fever -- a disease that kills 600,000 people each year. The study sets a new standard for analyzing the evolution and spread of a disease-causing bacterium: it is the first study of multiple samples of any bacterial pathogen at this level of detail. The results will help to improve diagnosis, tracking the disease and could help to design new strategies for vaccination.

Upper panel: Phylogenetic tree based on SNP data. Branch colours indicate lineages of Typhi; branch lengths are measured in number of SNPs. The central, small filled circle indicates the ancestral root and the dashed line represents the rest of the Salmonella lineage. Lower panel: Accumulation of gene-inactivating mutations in Typhi lineages. Points correspond to bifurcations in the tree above; y axis shows the total number of genes inactivated by deletion or nonsense mutation up to that bifurcation. Each line represents the accumulation of mutations in a particular isolate; different lineages of Typhi are coloured as above. LCA, last common ancestor.
Credit: Image courtesy of Wellcome Trust Sanger Institute

For the first time, next-generation DNA sequencing technologies have been turned on typhoid fever - a disease that kills 600,000 people each year. The results will help to improve diagnosis, tracking of disease spread and could help to design new strategies for vaccination.

The study sets a new standard for analysing the evolution and spread of a disease-causing bacterium: it is the first study of multiple samples of any bacterial pathogen at this level of detail. It uncovers previously hidden genetic signatures of the evolution of individual lineages of Salmonella Typhi.

The team developed methods that are being used to type outbreaks, allowing researchers to identify individual organisms that are spreading in the population: using Google Earth, the outbreaks can be easily visualized. The team hope that these mapping data can be used to target vaccination campaigns more successfully with the aim of eradicating typhoid fever.

Unlike most related Salmonella species, and in contrast to many other bacteria, Typhi is found only in humans and the genomes of all isolates are superficially extremely similar, hampering attempts to track infections or to type more prevalent variants. The detail of the new study transforms the ability of researchers to tackle Typhi.

"Modern genomic methods can be used to develop answers to diseases that have plagued humans for many years," explains Professor Gordon Dougan from the Wellcome Trust Sanger Institute and senior author on the study. "Genomes are a legacy of an organism's existence, indicating the paths it has taken and the route it is on. This analysis suggests we may have found Typhi's Achilles' heel: in adapting to an exclusively human lifestyle, it has become complacent, its genome is undergoing genetic decay and it's heading up an evolutionary dead end in humans.

"We believe that concerted vaccination programmes, combined with epidemiological studies aiming to track down and treat carriers, could be used to eradicate typhoid as a disease."

There are 17 million cases of Typhoid fever each year - although the World Health Organization cautions that this is a 'very conservative' estimate. Young people are most at risk: in Indonesia, nine out of ten cases occur in 3-19-year-olds.

"A key to survival of Salmonella Typhi is its ability to lie dormant in carriers, who show no symptoms but remain able to infect others," says Kathryn Holt, a PhD student at the Wellcome Trust Sanger Institute and first author on the study. "Our new tools will assist us in tracing the source of typhoid outbreaks, potentially even to infected carriers, allowing those individuals to be treated to prevent further spread of the disease.

"Using the genomic biology of this study, we can now type Typhi, identify the strain that is causing infection, identify carriers and direct vaccination programmes most efficiently. It is a remarkable step forward."

The study is a collaboration between researchers at the Wellcome Trust Sanger Institute, University College, Cork, Institut Pasteur in Paris and Oxford University Clinical Research Unit, Ho Chi Minh City, Vietnam. The team studied 19 isolates of Typhi from ten countries, using new sequencing methods that meant they could capture the rare signals of genetic variation in this stubborn genome. They produced more than 1.7 billion letters of genetic sequence and found evidence of fewer than 2000 mutation events, suggesting very little evolution since the emergence of Typhi at least 15,000 years ago.

Their analysis shows that the Typhi genome is decaying - as it becomes more closely allied to us, its human host, it is losing genes that are superfluous to life in the human body. More importantly, genes that contain instructions for the proteins on the surface of the bacterium - those most often attacked by our immune system defences - vary much less than do the equivalent genes in most other bacteria, suggesting that Typhi has a strategy to circumvent the selective pressures of our immune system.

"Both the genome and the proteins that make up the surface of Typhi - the targets for vaccines - show amazingly little variation," says Professor Julian Parkhill, Head of Pathogen Genomics. "We have been able to use novel technologies, developed for the analysis of human genome variation, to identify this variation: this would have been impossible a year ago. The technologies we have developed here could also be used in the battles against other disease-causing bacteria."


Story Source:

The above story is based on materials provided by Wellcome Trust Sanger Institute. Note: Materials may be edited for content and length.


Journal Reference:

  1. Holt et al. High-throughput sequencing provides insights into genome variation and evolution in Salmonella Typhi. Nature Genetics, 2008; DOI: 10.1038/ng.195

Cite This Page:

Wellcome Trust Sanger Institute. "Defining DNA Differences To Track And Tackle Typhoid." ScienceDaily. ScienceDaily, 30 July 2008. <www.sciencedaily.com/releases/2008/07/080727224103.htm>.
Wellcome Trust Sanger Institute. (2008, July 30). Defining DNA Differences To Track And Tackle Typhoid. ScienceDaily. Retrieved August 27, 2014 from www.sciencedaily.com/releases/2008/07/080727224103.htm
Wellcome Trust Sanger Institute. "Defining DNA Differences To Track And Tackle Typhoid." ScienceDaily. www.sciencedaily.com/releases/2008/07/080727224103.htm (accessed August 27, 2014).

Share This




More Health & Medicine News

Wednesday, August 27, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Predicting Heart Transplant Rejection With a Blood Test

Predicting Heart Transplant Rejection With a Blood Test

Ivanhoe (Aug. 27, 2014) Now a new approach to rejection of donor organs could change the way doctors predict transplant rejection…without expensive, invasive procedures. Video provided by Ivanhoe
Powered by NewsLook.com
Better Braces That Vibrate

Better Braces That Vibrate

Ivanhoe (Aug. 27, 2014) The length of time you have to keep your braces on could be cut in half thanks to a new device that speeds up the process. Video provided by Ivanhoe
Powered by NewsLook.com
Smartphone App Tracks Your Heart Rate

Smartphone App Tracks Your Heart Rate

Ivanhoe (Aug. 27, 2014) A new app that can track your heart rate 24/7 is available for download in your app store and its convenience could save your life. Video provided by Ivanhoe
Powered by NewsLook.com
Stroke in Young Adults

Stroke in Young Adults

Ivanhoe (Aug. 27, 2014) A stroke can happen at any time and affect anyone regardless of age. This mother chose to give her son independence and continue to live a normal life after he had a stroke at 18 years old. Video provided by Ivanhoe
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins