Diphtheria toxin (DT) is a 62 kDa protein that belongs to the family of ADP-ribosylating bacterial toxins. It is secreted by toxic strains of the gram-positive bacillus Corynebacterium diphtheriae carrying a lysogenic bacteriophage, which contain the toxin encoding gene (Freeman, 1951). It was first identified in 1888 as the causative agent for the infectious disease known as diphtheria. The bacterium is spread from person-to-person through infected aerosols distributed by coughing or sneezing, and through contact with surfaces contaminated with infected secretions.
The disease caused by C. diphtheriae primarily affects the throat and upper respiratory tract, but the toxin can affect other organs. The symptoms of the disease are sore throat, malaise, low-grade fever and swollen neck glands. The toxin can also cause a membrane of dead cells to form over the throat and tonsils resulting in breathing difficulties, and in some cases death from asphyxia. In severe cases, the toxin may cause neurological complications or heart failure. Patients with diphtheria are currently treated with antibiotics to kill the bacteria, and antitoxin to neutralise the effects of the diphtheria toxin (CDC).
Since 1945, diphtheria vaccines and vaccination programs have been successful in reducing cases of diphtheria worldwide by 99%. However, diphtheria is still a significant problem in some countries and outbreaks have been reported in the former Soviet Union, India, Myanmar, Malaysia and the Philippines, which may be due to poor immunisation programs or poor vaccine quality. In addition, waning immunity to diphtheria toxin may occur in individuals who have been immunised in childhood but have not been exposed to diphtheria in later life. Various global studies report that diphtheria seronegativity increases with age, suggesting that booster vaccinations may be necessary in adults (WHO, 2017) (CDC).
- Freeman VJ, Morse IU. (1952). Further observations on the change to virulence of bacteriophage-infected a virulent strains of Corynebacterium diphtheria. J Bacteriol. Mar;63(3):407-14.
- Center for Disease Control and Prevention: Diphtheria
- World health Organization: Diphtheria vaccine. Review of evidence on vaccine effectiveness and immunogenicity to assess the duration of protection ≥10 years after the last booster dose. April 2017
- Center for Disease Control and Prevention: Diphtheria, prevention
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