This article is more than 5 years old. Information may no longer be current.
Genetic study reveals dysentery’s global history
Click Here to Manage Email Alerts
An analysis of hundreds of Shigella dysenteriae type 1 isolates from around the world suggests the epidemic infection has affected humanity since the 18th century, and was largely spread globally through World Wars and European colonialism.
Furthermore, evidence also suggests S. dysenteriae type 1 (Sd1) may have developed drug resistance as early as the 1960s, with the most affected strain resulting in a rash of outbreaks during its transition from Asia to Africa.
Nicholas Thomson
“Analyzing the full genomes of all these S. dysenteriae strains collected over a huge time frame and from such an array of different countries provided us with an unprecedented insight into the historical spread of this pathogen,” Nicholas Thomson, PhD, microbiologist and bioinformatician from the Wellcome Trust Sanger Institute, said in a press release. “This was needed because there are still many unanswered questions [concerning] this infamous and important bacterial pathogen.”
The researchers conducted a whole-genome sequence analysis on 325 Sd1 isolates collected from 1915 to 2011 in 66 different countries. These included 14 isolates collected during World War I (1914-1918), as well as isolates collected from every major dysentery outbreak reported since the 1960s. The researchers detected single-nucleotide polymorphisms by mapping short-read sequences against reference genomes, and on these performed a maximum likelihood phylogenetic analysis. Four major genetic lineages — along with some sublineages — were identified through these methods. Data also supported the use of a Bayesian phylogenetic approach to provide nucleotide substitution rate and divergence time estimates for a subset of the isolates.
The analysis revealed that Sd1’s initial spread predated World War I, with movements into Asia, Africa and the Americas during the late 1800s coinciding with historical European emigration. In addition, substitution rate calculations dated the strains’ most recent common ancestor to 1747 (95% CI, 1645-1822), an estimate the researchers wrote falls in line with recorded outbreaks in Western and Northern Europe. Other 20th century transmission events included the introduction of Sd1 from Europe to Madagascar from 1915 to 1967, a movement from Asia to Poland from 1910 to 1944 and several waves originating in India that led to numerous outbreaks in Africa.
Antibiotic resistance genes were observed among Asian and American isolates beginning in the 1960s, the researchers wrote, with the most recent lineage appearing to be the most affected. Resistant Sd1 have since become predominant, with fewer than 1% of isolates collected from 1991 to 2011 remaining susceptible to antibiotics.
“This bacterium is still in circulation, and could be responsible for future epidemics if conditions should prove favorable — such as a large gathering of people without access to drinking water or treatment of human waste,” François-Xavier Weill, MD, PhD, research director at the Institut Pasteur, Paris, said in the press release. “This study highlights the need for an effective vaccine, which will be crucial for controlling this disease in the future in view of the reduced efficacy of antibiotics.” – by Dave Muoio
Disclosure: The researchers report no relevant financial disclosures.
Click Here to Manage Email Alerts