Cholira

1. Cholira • 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).

2. Clinical findings: • The incubation period of cholera is 1- 4 days • There is sudden onset of nausea effortless vomiting and profuse diarrhea (up to 20 liter/day rice watery diarrhea with fishy odor) with abdominal cramps. • There is rapid loss of fluids and electrolytes leading to severe rapid dehydration acidosis, collapse and anuria, and hypovolaemic shock which leads to cardiac failure, renal failure and death in 12-24 hours - The mortality rate is 25 - 60% without treatment.

3. Clinical features: A diagnosis of a suspected (first or primary) case in a non- endemic area: • Isolation of the organism with full systematic identification is required before being considered and notified as cholera. • Inoculation of stool (rice-watery) in alkaline peptone water (pH 7.5-9.5) and incubation at 37⁰C for 6-8 hours. The alkalinity of the medium allows the vibrios to overgrow the other intestinal flora - The organisms form a surface pellicle growth.

4. Subcultures are subsequently made on alkaline agar or TCBS (Thiosulfate-bile sucrose medium) medium on which V. cholerae produces yellow colonies.

5. The growth is subsequently identified by: • Microscopic examination Fresh examination demonstrates the actively motile vibrios under dark field microscopy • Gram-stained smears Show Gram-negative comma-shaped bacilli, non-spore forming and non-capsulated • Biochemical reactions and cholera red reaction • Agglutination with anti-O1 and anti O139 antisera.

6. 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.

7. 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

8. 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.

9. 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.

10. Non O1 non O139 cholera • Cause mild, sometimes bloody diarrhea associated with abdominal cramps. Also wound infection in patients exposed to aquatic environments. Aeromonas species • Related to vibrios, but halophilic. • Aeromonashydrophila cause diarrhea. • Aeromonassalmonicida is economically important pathogen of fish.

11. Plesiomonas • Related to vibrios, but halophilic. • Plesiomonasshigeloides sometimes causes water-borne outbreaks of diarrhea in warm countries. • (halophilic -requires a high conc. of Nacl to grow).