New Delhi: The bacteria causing diphtheria has developed resistance to several commonly used antibiotics, leading to a spurt in cases the world over, a study by Cambridge University, along with experts from the Union Ministry of Health and Family Welfare and several Indian institutes, has reported in an article published in Nature Communications.
What’s more, they have warned that at this rate, it is possible that the diphtheria vaccine becomes less effective over time.
Diphtheria is among the oldest vaccines in the Indian immunisation programme and the disease had gone down dramatically before making a comeback in recent years — a revival most experts till now attributed to rising vaccine hesitancy. The current paper changes that.
In 2018, about half of all the diphtheria cases in the world were in India. According to data from the National Health Profile 2019, India had 5,21 diphtheria cases and 149 deaths in 2017. The provisional figures for 2018 put the burden at 11,720 cases and 180 deaths.
Different degrees of antibiotic resistance
Diphtheria is caused by Corynebacterium diphtheriae. Researchers analysed 502 C. diphtheriae genomes by sequencing 61 novel Indian isolates and combining these with 441 publicly available genomes. The isolates in the study cover 16 countries and territories and they were collected across a period of 122 years.
“Within the Indian isolates, C. diphtheriae from Himachal Pradesh (isolated in 1973) had no detectable AMR (antimicrobial resistance) genes. Isolates from Haryana harboured genes encoding resistance to four classes of antibiotic, whereas isolates from Delhi, Kerala and Tamil Nadu had genes for resistance to five. Isolates from the most populous state of India, Uttar Pradesh, showed resistance to six classes, including the only isolate of our study with macrolide resistance. Five isolates from Kerala (all isolated in 2016) and one from Uttar Pradesh (isolated in 2017) showed no AMR genes present in their genomes,” the study noted.
It also raised a red flag about continued efficacy of the vaccine currently in use given the high rate of change in the organism.
“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 anti-toxin treatment failure in future,” the researchers wrote.
They added that while the current vaccine against diphtheria continues to remain largely effective, it is necessary to conduct further in vitro (outside of a living organism) and in vivo (within a living organism) studies to investigate the benefit, if any, the six variants with “non-synonymous allelic mutations that impact protein structure may provide to C. diphtheriae”, especially those estimated to have moderate and high impacts on structure, the researchers added.
About the disease
Diphtheria is primarily a respiratory infection affecting the throat and upper airways. One type, more common in the tropics, can also cause skin ulcers. It is more common in children in the age group of 1-5 years.
In 2018, among the more severe outbreaks reported in India was one in Delhi when 25 children died in September, 22 in October and 12 in November. Despite the fact that the vaccine has been in use since 1978, periodic outbreaks continue to be reported across the country.
In 1978, India launched the Expanded Programme on Immunisation with BCG (against TB), DPT (diphtheria, pertussis, tetanus) and cholera vaccines. In 1985, it came to be called the Universal Immunisation Programme (UIP). The diphtheria vaccine is now incorporated as a pentavalent vaccine, (containing vaccine against diphtheria, pertussis, tetanus [DPT], Hepatitis B and Haemophilus influenzae type B).
(Edited by Manasa Mohan)