Presentation on theme: " Cholera is a highly infectious disease. Infection occurs by the oral route through contaminated food and drinks. Water born epidemics are reported. The."— Presentation transcript:
Cholera is a highly infectious disease. Infection occurs by the oral route through contaminated food and drinks. Water born epidemics are reported. The source of infection is either a case or a carrier. The pathogenesis of cholera is dependent on colonization of the small intestine by the organism and secretion of enterotoxin. V. cholera is not an invasive organism, so it does not reach blood stream (no bacteremia).
Subcultures are subsequently made on alkaline agar or TCBS (Thiosulfate-bile sucrose medium) medium on which V. cholerae produces yellow colonies.
The growth is subsequently identified by: 1. Microscopic examination Fresh examination demonstrates the actively motile vibrios under dark field microscopy 2. Gram-stained smears Show Gram-negative comma-shaped bacilli, non-spore forming and non-capsulated 3. Biochemical reactions and cholera red reaction 4. Agglutination with anti-O1 and anti O139 antisera.
Molecular methods: PCR amplification has been used for the detection of the cholera toxin A subunit gene in the rice water stools. DNA probe for detecting toxigenic V. cholerae. Treatment: The most important part is restoration of fluid and electrolyte balance to correct dehydration and acidosis by giving intravenous fluids. Antibiotics (tetracyclines) have a secondary role.
Prevention: Public health measures directed to sewage disposal, clean water supply, isolation of cases (similar to s. typhi) Chemoprophylaxis by tetracyclines to exposed persons. Vaccines: Extract of killed bacteria given I.M. Oral vaccine consisting of inactivated V. cholerae with B subunits. A live attenuating oral vaccine
The efficiency of this vaccine in protection is disputed as it stimulates antibacterial but not antitoxic antibodies. Attempts to develop new vaccines given orally to protect against cholera toxin are under trails.
VIBRIO PARAHAEMOLYTICUS This is a marine vibrios requires a high Na cl concentration to grow (halophilic). It produces blue-green colonies on TCBS medium. It is associated with food poisoning due to eating shell fish or raw fish the clinical picture caused by V. parahaemolyticus varies from mild to quite severe watery diarrhea. The illness is self limited.
Plesiomonas Related to vibrios, but halophilic. Plesiomonas shigeloides sometimes causes water-borne outbreaks of diarrhea in warm countries. (halophilic -requires a high conc. of Nacl to grow).