Resistant typhoid pathogens are spreading


Reason for concern: in recent years, typhoid bacteria have increasingly developed new resistance to antibiotics, as revealed by genetic analyses. The mutations make the pathogens immune to modern emergency antibiotics and are now spreading from India. This development is worrying, underline the researchers of the journal “The Lancet Microbe”. In extreme cases, this could mean that no oral typhoid fever remedy is working.

More than eleven million people contract typhoid fever each year and about 100,000 die from it, mainly in South Asia and Africa. The causative agent of this bacterial infection, Salmonella enterica serovar Typhi, is usually transmitted through contaminated water or food. Although the infection can be easily treated with antibiotics, antibiotic resistant strains are increasingly spreading.

From South Asia to the world

Kesia Esther da Silva of Stanford University and her colleagues have now studied the extent and where these resistant and multidrug-resistant typhoid bacteria are now prevalent. For their study, they analyzed bacterial DNA from 3,489 pathogen samples collected in South Asia between 2014 and 2019. In addition, they evaluated another 4,169 samples from more than 70 countries and collected over the last 100 years.

Analyzes revealed that multidrug-resistant strains of the pathogen type that are immune to older classes of antibiotics have been circulating in South Asia for decades. They are mainly native to India and have been introduced to other countries and regions from there more than 197 times since 1990 alone, as the team reports. The most common transmissions have occurred in South Asia or to Southeast Asia, but resistant strains of typhoid have also reached Africa, North America and Europe.

New resistances on the rise

However: In the meantime, new resistant forms are spreading in addition to these “classic” multi-resistant typhoid bacteria. They have evolved mechanisms that also make them immune to modern classes of antibiotics such as cephalosporins, quinolones and macrolides. As early as the 1990s, there were strains of bacteria resistant to fluoroquinolones. In 2010, these already accounted for 95% of the type specimens from India, Pakistan and Nepal, as reported by da Silva and colleagues.

Spread of type variants (FQ-NS: resistant to fluoquinolone; MDR: multi-resistant; XDR: extremely multi-resistant) © da Silva et al. / The Lancet Microbe, CC-by 4.0

Over the past 20 years, at least seven strains of bacteria have developed resistance to azithromycin, a commonly used macrolide antibiotic. The research team also identified several strains of cephalosporins with corresponding resistance genes. As with the first multi-resistant typhoid bacteria, most of these new strains developed in India.

“A real cause for concern”

“The rate at which highly resistant strains of Salmonella Typhi have evolved and spread in recent years is a real concern,” said lead author Jason Andrews of Stanford University. “This underscores the urgent need to expand and intensify prevention efforts, especially in the most vulnerable countries.”

Researchers see a particular danger in the fact that typical pathogens can exchange newly acquired resistance genes with each other. This can then result in bacterial strains that are insensitive both to older active ingredients and to newer quinolone and macrolide antibiotics. “Such organisms would escape treatment with established oral antimicrobial agents,” da Silva and colleagues write. “This would lead to increased hospital admissions and increased morbidity and mortality.”

A global problem

According to the research team, their findings are also a clear indicator that India remains a significant hotspot for the emergence of antibiotic resistance – something more urgently needed here. “The fact that resistant strains of the typhoid bacterium have spread so often internationally also underscores that controlling typhoid fever and resistance must be seen as a global, not a local, issue,” says Andrews. (The Lancet Microbe, 2022; doi: 10.1016/S2666-5247(22)00093-3)

Source: The Lancet

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