Diphtheria remains in the news

Contributed by Dr Rohit Vashisht

In early July 2019, 2 children from Sathyamangalam in Tamil Nadu's Erode district succumbed to diphtheria. Around this time, several other cases of diphtheria were being reported from the state. The latest information shows that at least 50 people have been admitted to the Coimbatore Medical College and Hospital with diphtheria. Diphtheria from Greek word diphtheria meaning leather, is an infection caused by the bacterium Corynebacterium diphtheriae which primarily infects the throat and upper airways. The major virulence results from the action of its potent exotoxin, which inhibits protein synthesis in mammalian cells but not in bacteria. The illness has an acute onset and the main characteristics are sore throat, fever, painful swallowing and cervical lymphadenopathy. Within the first few days of respiratory tract infection, toxin, elaborated locally induces a dense necrotic coagulum composed of fibrin, leukocytes, erythrocytes, dead respiratory epithelial cells, and organisms. Removal of this adherent graybrown” pseudomembrane” reveals a bleeding edematous submucosa. The toxin effects all cells in the body, but most prominent effects are on heart (myocarditis), nerves (demyelination) and kidneys(tubular necrosis). The disease is spread through direct physical contact or from breathing in the aerosolized secretions from coughs or sneezes of infected individuals. Isolation of Corynebacterium diphtheria can be done by throat culture from a clinical specimen or histopathologic diagnosis of diphtheria by Albert stain can be made.

Vaccination against diphtheria has reduced the mortality and morbidity of diphtheria dramatically. However diphtheria is still a significant child health problem in countries with poor EPI coverage. In countries endemic for diphtheria, the disease occurs mostly as sporadic cases or in small outbreaks. Diphtheria 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 (erythromycin or procaine penicillin G for 14 days).

Diphtheria vaccine is a bacterial toxoid. The vaccine is normally given in combination with other vaccines as DTwP/DTaP vaccine or pentavalent vaccine. For adolescents and adults the diphtheria toxoid is frequently combined with tetanus toxoid in lower concentration (Td vaccine).

WHO recommends a 3-dose primary vaccination series with diphtheria containing vaccine followed by 3 booster doses. The primary series should begin as early as 6-week of age with subsequent doses given with a minimum interval of 4 weeks between doses. The 3 booster doses should preferably be given during the second year of life (12-23 months), at 4-7 years and at 9-15 years of age. Ideally, there should be at least 4 years between booster doses.