Trends in Diphtheria Incidence

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Researchers from India, the U.K. and Russia have analysed a large collection of 502 genomes of the bacterium that causes diphtheria – Corynebacterium diphtheriae.

Key Takeaways

• There is an increasing trend in the number of cases of diphtheria globally, as the number of cases in 2018 (16,651) was double the 1996–2017 average (8,105).
  • 50% of the cases that came up in 2018 were in India.
• In order to map out the genetic spread of the organism, the group has done a phylogenetic analysis that basically gives a picture of the family tree of the species.
  • Unlike certain other bacteria, C. diphtheriae has shown a diversity in evolution, which makes it, as a species, more stable and powerful.

• They analyse the genes for their capacity towards Antimicrobial Resistance.
  • Compared to the 1990s, isolates from the decade spanning the years from 2010 to 2019 show the highest average number of antimicrobial resistance genes encoding resistance for sulphonamide, aminoglycoside, chloramphenicol and trimethoprim.
  • These antimicrobial resistance genes might have been transferred by the mobile genetic elements from other bacteria.
• Finally, the researchers study the variations (or mutations) in the tox gene, which is responsible for producing the diphtheria toxin – which is the main target of the vaccinations.
  • They identified 18 tox gene variants, with mutations estimated in its toxin structural impact.

About Diphtheria

• Diphtheria is a serious infection caused by strains of bacteria called Corynebacterium diphtheriae that make toxin (poison).
• It is an aerobic gram-positive bacillus.
  • Toxin production (toxigenicity) occurs only when the bacillus is itself infected (lysogenized) by a specific virus (bacteriophage) carrying the genetic information for the toxin (tox gene).
• Infects the throat and upper airways, and produces a toxin affecting other organs.
• Symptoms: Diphtheria usually begins with angina (a type of chest pain) and tonsillitis symptoms, sore throat, mild fever and swollen glands in the neck.
  • The toxin causes a membrane of dead tissue to build up over the throat and tonsils, making breathing and swallowing difficult.
• Transmission: Diphtheria bacteria spread from person to person, usually through respiratory droplets, like from coughing or sneezing. 
  • People can also get sick from touching infected open sores or ulcers.

• In countries endemic for diphtheria, the disease occurs mostly in sporadic cases or in small outbreaks.
• Fatality: The diphtheria toxin causes inflammation of heart muscle (myocarditis) and this can lead to death if not treated with Diphtheria antitoxin and proper antibiotics.
  •  It is fatal in 5-10% of cases, with a higher mortality rate in young children.
• Treatment: Involves administering diphtheria antitoxin to neutralize the effects of the toxin, as well as antibiotics to kill the bacteria.
  • The vaccine is a bacterial toxoid (a toxin whose toxicity has been inactivated).
  • Vaccination has reduced the mortality and morbidity of diphtheria dramatically.

Image Courtesy: TH

Source :TH