Diphtheria
Diphtheria (Gr. diphtheria = membrane; ia = condition) is an acute contagious respiratory disease caused by Corynebacterium diphtheriae which is a gram-positive, nonmotile, aerobic bacterium forming irregular rod-shaped or club-shaped cell during growth. The pathogen enters the body via the respiratory passage with cells lodging in the throat and tonsils. The inflammatory response of throat tissues to the pathogen leads to the formation of a characteristic lesion referred to as pseudomembrane.

The latter consists of damaged host cells and the cells of bacteria. Certain strains of C. diphtheriae are lysogenized by bacteriophage β and these strains secrete powerful exotoxin called diphtheria toxin that inhibits eukaryotic protein synthesis and thus kills the host cells. The diphtheria toxin, if absorbed in the circulatory system and distributed throughout the body, damage the peripheral nerves, heart and kidneys.

Penicillin, erythromycin or Gentamycin antibiotics are generally effective against the disease. Prevention is by active  immunization with the DPT (diphtheria-pertussis-tetanus) vaccine.