C. Diphtheriae Past Paper PDF

## C. Diphtheriae: - Classified as childhood disease, of bacterial etiology. - Have not high incidence rate due to the vaccination programs. - Gram +ve bacilli, club-shaped, arranged, V or L forms (letter-shape). - They have metachromatic granules that represent energy storage sites (when stained w...

## C. Diphtheriae: - Classified as childhood disease, of bacterial etiology. - Have not high incidence rate due to the vaccination programs. - Gram +ve bacilli, club-shaped, arranged, V or L forms (letter-shape). - They have metachromatic granules that represent energy storage sites (when stained with methylene blue). - There are 3 species: - C. diphtheriae gravis. - C. diphtheriae intermedius. - C. diphtheriae mitis. ### Mode of Transmission: - By airborne droplets, respiratory tract infection. - Corynebacteria occur as NF in the upper respiratory tract. - The organism can also infect the skin by direct contact. ### Risk Factors: - Unvaccinated child, or doesn't complete the dose. - Person is immunodepleted, has chronic disease, taking corticosteroids for a long period, transplant patient. ### Pathogenesis: - The bacteria invade tissues locally, multiply and produce a potent exotoxin, which is the cause of the main pathology. * Note: A lot of bacteria are associated with production of toxin. - Which the pathology relay on, also the lab investigation, treatment mechanism. - The toxin inhibits elongation factor 2 (EF-2) which is important for protein synthesis, thus it causes protein synthesis inhibition in all eukaryotic cells. - The toxin is produced by the virally infected bacteria (lysogenized). ### Clinical Findings: - The incubation period is 2-6 days. - The most commonly affected sites are: - The tonsils. (common site). - Soft palate. - Larynx. - Nose. - The most characteristic feature is the formation of a thick, gray, adherent pseudomembrane over the tonsils and throat. - It is dirty brown or green in color. - Made up of bacteria, desquamated epithelial cells, leukocytes, fibrin, blood. - It can be dislodged only with difficulty, and if this is done, the tissue below bleeds. ### Clinical Findings: - Fever: sore throat. - Cervical lymphadenopathy: (bilateral). - The most important facial characteristic: Bull-neck appearance. ### Complications: - Airway obstruction by the membrane. - Myocarditis: sequelae arrhythmias & shock. - Neurological weakness (paresis=partial paralysis) or paralysis. - Rarely: perforation of the soft palate. (comment: the swallowed food may enter pro to infection). ### Lab Diagnosis: - Specimen: Throat swab. - Gram stains: the finding of many tapered, pleomorphic gram +ve rods. - Stain with methylene blue for the metachromatic granules. - Culture on: - Löffler's medium, or - Tellurite plate agar (the gray black colony is diagnostic), or - Blood agar. - The test for the toxin production: - Animal inoculation test. - The gel diffusion precipitation test "Elek's test". * Note: A patient is presented with clinical manifestations of C. diphtheriae & bull-neck, lymph adenopathy, pseudomembrane, febrile, not vaccinated- definitely diphtheria without investigation. ### Treatment: - The treatment of choice is antitoxin (toxoid): 20,000-100,000 units intravenously in forearm for 5-10-15 min. - After a preliminary intradermal test for hypersensitivity, the reaction appears as erythema, eg. in penicillin. - It should be given immediately on the basis of clinical suspicion, because there is delay in the laboratory diagnosis. - The antitoxin neutralizes the unbound toxin, thus reducing the toxin and minimize the outcomes: - Cell wall inhibits. - Macrolytes. - Penicillin G or erythromycin to: - Inhibit growth of the organism. - Reduce toxin production. - Decrease the incidence of chronic carriers (communicable disease). * Note: Erythromycin is a substitute for penicillin G in cases of allergies. ### Prevention: - Diphtheria toxoid is prepared by treating the toxin with formalin. - It is given as a combination: diphtheria toxoid, tetanus toxoid, acellular pertussis vaccine, DPT. - At 3 doses, one month intervals starting on the 45th day of birth. - Vaccination is given to the child or pregnant: antitetanus (DPT).