Diphtheria could become a major global threat

Researchers found that Diphtheria has started to become resistant to several classes of antibiotics

April 16, 2021
The Scitech

A team of researchers from India, the UK and Russia, has found that Diphtheria, which is a relatively easily-preventable infection, has started to become resistant to several classes of antibiotics, and in future, it may even become immune to vaccination. Diphtheria is a highly contagious infection. It can affect the nose and throat, and sometimes the skin. If left untreated it can prove fatal. In high-income countries, all babies are vaccinated against the infection. However, in low- and middle-income countries, the disease can still cause sporadic infections or outbreaks in unvaccinated and partially-vaccinated communities.

The researchers used genomics to map the infections, including a subset from India, where over half of the globally reported cases occurred in 2018. By analysing the genomes of 61 bacteria isolated from patients and combining these with 441 publicly available genomes that had been collected from across the world over 122 years (1896-2018), they build a phylogenetic tree - a genetic 'family tree' - to see how the infections are related, understand how they spread and assess the presence of antimicrobial resistance (AMR) genes and determine toxin variation. The main disease-causing component of C. diphtheriae is the diphtheria toxin, which is encoded by the `tox’ gene. It is this component that is targeted by vaccines. In total, the researchers found 18 different variants of the `tox’ gene, of which several had the potential to change the structure of the toxin.

The team looked for genes that might confer some degree of resistance to antimicrobials and they found that the average number of antimicrobial resistance genes per genome was increasing each decade. Genomes of bacteria isolated from infections from the most recent decade (2010-19) showed the highest average number of AMR genes per genome, almost four times as many on average than in the next highest decade, which was the 1990s.

In a report on their study published in Nature Communication, the team said, “While our data does not, at present, highlight any efficacy concern in the currently used tox variant type 16 based diphtheria toxoid vaccine, the continually increasing toxin diversity and prevalence of non-toxigenic strains do however forecast a real possibility of vaccine escape and antitoxin treatment failure in future. While the current vaccine against diphtheria continues to remain largely effective, it is vital to conduct further in vitro and in vivo studies”.

Source: India Science Wire