Antimicrobial resistance can trigger resurgence of this disease

Diphtheria is a highly contagious bacterial infection that primarily affects a patient’s nose and throat. Sometimes it can also affect the skin. It is easily preventable if caught on time, but can otherwise prove fatal. Today there are vaccines and most countries immunize babies against this disease. But in some low- and middle-income countries, diphtheria can still cause sporadic outbreaks in unvaccinated and partially vaccinated communities. According to reports, the number of reported cases of diphtheria worldwide is gradually increasing. In 2018, 16,651 cases were reported, more than double the annual average for 1996-2017 (8,105 cases). This is a worrying trend and scientists from the UK and India say it may be because diphtheria, a relatively easily preventable infection, progresses to become resistant to a number of classes of antibiotics and could potentially break down. future lead to vaccine leakage. The researchers, led by scientists at the University of Cambridge, say that the impact of COVID-19 on diphtheria vaccination schedules, coupled with an increase in the number of infections, risks the disease becoming a again major global threat. Read also – Antibiotic resistance occupies an important place; New class of drugs may help meet the challenge

Transmission of diphtheria

Diphtheria is primarily caused by the bacteria Corynebacterium diphtheriae and is spread primarily through droplets from coughs and sneezes, or through close contact with an infected person. In most cases, the bacteria can cause acute infections, caused by diphtheria toxin, a key target of the vaccine. However, non-toxigenic C. diphtheria can also cause illness, often in the form of systemic infections. Also Read – Scientists Find New Compound As COVID-19 Triggers Superbug Threat

More than half of the world’s reported cases were in India in 2018

In the aforementioned study, published in Nature communications, the researchers used genomics to map infections, including a subset of India, where more than half of the world’s reported cases occurred in 2018. Analyzing the genomes of 61 bacteria isolated from patients and by combining them with 441 publicly available genomes, build them a phylogenetic tree – a genetic “family tree” – to see how infections are linked and understand how they spread. They also used this information to assess the presence of antimicrobial resistance (AMR) genes and assess variation in toxins. Also read – Brucellosis has already entered India: are we heading for another pandemic?

Experts find 18 variants of diphtheria toxin

The researchers found clusters of genetically similar bacteria isolated from several continents, most often Asia and Europe. This indicates that C. diphtheriae has been established in the human population for at least over a century, spreading across the world as populations migrated. The main pathogenic component of C. diphtheriae is 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, several of which had the potential to alter the structure of the toxin.

What this means for diphtheria vaccines

The diphtheria vaccine is designed to neutralize the toxin. Thus, any genetic variant which modifies the structure of the toxin could have an impact on the effectiveness of the vaccine. While the data from this study does not suggest that the vaccine currently in use will be ineffective, the fact that there is an ever-increasing diversity of toxin variants suggests that the vaccine and treatments that target the toxin need to be regularly evaluated. .

Increased antimicrobial resistance

Diphtheria infections can usually be treated with a number of classes of antibiotics. Although cases of resistance to C. diphtheriae antibiotics have been reported, the extent of this resistance remains largely unknown. When researchers looked for genes that might confer some degree of antimicrobial resistance, they found that the average number of AMR genes per genome was increasing every decade. Genomes of bacteria isolated from infections of the most recent decade (2010-19) had the highest average number of AMR genes per genome, almost four times more on average than in the next highest decade , the 1990s.

The complex genome of C. diphtheriae acquires resistance to antibiotics

What is worrying for researchers is the fact that the C. diphtheriae genome is complex and incredibly diverse. He acquires resistance to antibiotics which are not even clinically used in the treatment of this disease. They suspect that there must be other factors at play, such as asymptomatic infection and exposure to a plethora of antibiotics intended to treat other illnesses. Erythromycin and penicillin are the antibiotics of choice traditionally recommended for treating confirmed cases of early-stage diphtheria, although there are several different classes of antibiotics available to treat the infection. The team identified variants resistant to six of these classes in isolates from the 2010s, higher than in all other decades.

(With contributions from agencies)

Posted: Mar 10, 2021 8:17 PM