Unlike other diarrheal diseases, this one is unlikely to be resolved by providing access to clean water. As developing countries become more industrialized the numbers of infections with dysentery-causing Shigella flexneri are known to decline, associated with improved health, lifestyle and perhaps most importantly access to clean water, but the incidence of another form of the dysentery-causing bacterium, Shigella sonnei, actually increases.
The team pinpointed that S. sonnei was first established in Europe just a few centuries ago, but in the last few decades has spread to the rest of the world. They also found that a key factor in the spread of this pathogen was a rise in multidrug resistance - the ability to survive exposure to a wide array of antibiotics. Because S. sonnei is easily transmitted and has high levels of drug resistance, the researchers suggest that drug treatment and better sanitation alone will not be sufficient for controlling the disease. Vaccine development will be crucial.
Dysentery is a disease primarily associated with developing countries and more than one million people, mostly young children, are estimated to die from dysentery caused by Shigella each year. Whilst most people have heard about dysentery, few know about the bacteria that causes it, Shigella. This is because it is relatively understudied and little is known about their population structure or its origins. Traditionally, S. flexneri has been the most common form of Shigella bacterium to cause dysentery in developing countries with S. sonnei more prevalent in industrialized countries. Yet, this is beginning to change with S. sonnei becoming increasingly common as developing countries rapidly industrialize.
"Although S. sonnei is a relatively new species of bacterium, during its spread it has diversified into an array of different distinguishable clones or strains found right across the world," says Doctor Kathryn Holt, first author from the University of Melbourne. "This is hard to see using traditional methods, but by sequencing the genomes of over 100 different forms of the bacteria, we were able to get a glimpse into its past and really start to understand how it is evolving and moving around the world."
To investigate why the bacterium was spreading so effectively, the team looked at the S. sonnei's genetic evolution and found that only a few types of genes were selectively evolving over time, particularly those involved with drug resistance. This suggests that a major driver in the spread of this bacterium was its apparent ability to become resistant to drug treatment.
MEDICA.de; Source: Wellcome Trust Sanger Institute