Antibiotic-resistant strains of typhoid bacteria continue to spread from South Asia

Antibiotic-resistant strains of Salmonella Typhicthe typhoid bacteria, have spread from South Asia to other countries nearly 200 times since 1990, new research suggests.

Each year, an estimated 11 to 20 million people suffer from typhoid and 128,000 to 161,000 victims die from the disease, says the World Health Organization (WHO). Typhus spreads through water contaminated with the feces of an infected person. Symptoms include prolonged fever, nausea, rash, headache, and diarrhea or constipation.

S. Typhi can only infect humans, and by studying how closely related bacteria found in different places are, we found that typhoid had spread many times over from South Asia, the home of typhoid, to many parts of the world.”


Gagandeep Kang, study co-author and professor at the Wellcome Trust Research Laboratory in the Department of Gastrointestinal Sciences at Christian Medical College, Vellore, India

The international team of researchers, funded by the Bill & Melinda Gates Foundation, say their findings highlight the need to treat drug-resistant typhus as a global problem.

Kang tells SciDev.Net that the study has the largest set of sequence data of S. Typhi† “By analyzing the genetic makeup of the bacteria, collected from different places and at different times, it was possible to build a narrative of what the bacteria have been doing over the decades,” she says.

Published in The lancet microbethe study involved whole genome sequencing (a comprehensive method for examining whole genomes) of 3,489 S. Typhi samples obtained between 2014 and 2019 from people living in Bangladesh, India, Nepal and Pakistan. Sequence was also run at 4.169 S. Typhi samples taken from more than 70 countries between 1905 and 2018. A total of 7,500 genomes were sequenced and resistance-conferring genes identified.

The researchers say that while resistance to multiple, first-line antibiotics has generally declined in South Asia since 2000, strains with resistance to key antibiotics such as macrolides and quinolones have increased and are often transferred to other countries. Globally, 70 percent of the typhoid disease burden is attributed to South Asia, followed by the sub-Saharan regions and Southeast Asia.

resistant S. Typhi tribes have spread between countries at least 197 times since 1990, the study said. Primarily native to South Asia, these strains have spread to Southeast Asia, East and South Africa and have been reported in Canada, UK and US. The study said that since 2000, multidrug-resistant S. Typhi has steadily declined in Bangladesh and India and remained low in Nepal.

In Pakistan, however, the declining trend of multidrug resistant typhus in South Asia has been reversed by the emergence in 2016 of extensively drug resistant (XDR) S. Typhi, which then quickly replaced less resistant strains.

According to a report by the US Centers for Disease Control and Prevention, between 2006 and 2015, 79 percent of US isolates from typhoid fever patients traveling to Pakistan were resistant to fluoroquinolone. From 2016 to 2018, typhoid fever was diagnosed in 29 US patients who had traveled to Pakistan and five of them were infected with XDR S. Typhi

Fluoroquinolones, the mainstay against multidrug-resistant S. Typhi in the 1990s, became ineffective in the 2010s, and in 2016 Pakistan saw an outbreak of S. Typhi that was resistant to fluoroquinolones and third-generation cephalosporins, the study said. By 2021, resistance to azithromycin was found to have emerged in multiple S. Typhi tensions, threatening the efficacy of all oral antimicrobials for the treatment of typhoid fever.

There is a possibility that the international burden of typhoid fever is increasing as a result of urbanization and climate change. “In addition, increasing resistance to antibiotics makes it easier for typhoid to spread through overcrowded urban populations and inadequate and/or flooded water and sanitation,” says the WHO.

“Typhoid-resistant genes are present in multiple countries and will pose challenges in creating effective antimicrobial regimens,” said Amesh Adalja, senior scientist at the US-based Johns Hopkins Center for Health Security. SciDev.Net.

“While there have been improvements in water and sanitation in South Asia, antibiotic-resistant S. Typhi strains are dangerous and we must try to control them by reducing the irrational use of antibiotics, improving the availability of diagnostics and introducing the highly effective conjugated typhoid vaccines,” Kang said.

Source:

Reference magazine:

da Silva, KE, et al. (2022) The International and Intercontinental Spread and Expansion of Antimicrobial-Resistant Salmonella Typhi: A Genomic Epidemiological Study. The Lancet microbe. doi.org/10.1016/S2666-5247(22)00093-3

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