S Typhi strains have spread to many countries nearly 200 times since 1990: Study
The effectiveness of antibiotics to treat typhoid infections is threatened by the emergence of the resistant S Typhi strains.
According to a study published in The Lancet Microbe journal, the largest-ever genome analysis of Salmonella enterica serovar Typhimurium (S Typhi), shows that resistant strains – almost all originating in South Asia – have spread to other countries nearly 200 times since 1990.
Calling the finding of the study as a cause for worry, a scientist from AIIMS, Delhi said, “The bacteria causing typhoid has become a “smart bacteria” which has been able to find mechanisms to evade the usual antibiotics. It’s worrying, and the current antibiotic regimen needs to be reviewed urgently.”
The Lancet study noted that typhoid fever is a global public health concern, causing 11 million infections and more than 1,00,000 deaths per year.
While it is most prevalent in South Asia, which accounts for 70 per cent of the global disease burden, it also has significant impacts in sub-Saharan Africa, Southeast Asia, and Oceania, highlighting the need for a global response, they said.
“The speed at which highly-resistant strains of S Typhi have emerged and spread in recent years is a real cause for concern, and highlights the need to urgently expand prevention measures, particularly in countries at greatest risk,” said the study’s lead author, Jason Andrews, from Stanford University.
“At the same time, the fact that resistant strains of S Typhi have spread internationally so many times also underscores the need to view typhoid control, and antibiotic resistance more generally, as a global rather than local problem,” Andrews said.
In the new study, the researchers performed whole-genome sequencing on 3,489 S Typhi isolates obtained from blood samples collected between 2014-2019 from people in Bangladesh, India, Nepal, and Pakistan with confirmed cases of typhoid fever.
A collection of 4,169 S Typhi samples isolated from more than 70 countries between 1905 and 2018 was also sequenced and included in the analysis. Resistance-conferring genes in the 7,658 sequenced genomes were identified using genetic databases.
Strains were classified as multidrug-resistant (MDR) if they contained genes giving resistance to classical front-line antibiotics ampicillin, chloramphenicol, and trimethoprim/sulfamethoxazole.
The authors also traced the presence of genes conferring resistance to macrolides and quinolones, which are among the most critically important antibiotics for human health.
Since 2000, MDR S Typhi has declined steadily in Bangladesh and India, and remained low in Nepal, though it has increased slightly in Pakistan.