1. Epidemiology of Cholera
Ashry Gad Mohamed
Professor of Epidemiology
College of Medicine & KKUH

2. Greek word for the gutter of a roof, comparing the deluge of water following a rainstorm to that of the anus of an infected person

3. Acute intestinal infection caused by the bacterium Vibrio cholerae characterized by:
profuse watery diarrhoea with flecks of mucous material (rice water stools), vomiting, abdominal pain
Rapid onset of dehydration causing severe weakness, poor skin turgor, sunken eyes and cheeks

4. Often muscular cramps, cyanosis, subnormal temperature, tachy-cardia, hypotension; renal failure may follow inadequate treatment
Without treatment a healthy person may become hypotensive within one hour & may die within 2-3 hours.
More commonly: from 1st liquid stool to shock 4-12 hours.

5. Mechanism
Entrotoxin activates adenylate cyclase enzyme in intestinal wall that is converted into pump that extract water & electrolytes from blood and tissues to intestinal lumen with shedding of mucous and epithelial cells giving rice water severe diarrhea

6. Infectious agent: Vibrio cholerae
epidemic cholera is caused by two biotypes of Vibrio cholerae :
the classical biotype serogroup O1, and
since 1961 (7th pandemic), the biotype El Tor
Serogroup O1 includes serotypes Inaba, Ogawa and Hikojima
Serogroup O139: in 1992/93, a new Vibrio cholerae O139 strain appeared

7. Vibrios are one of the most common organisms in surface waters of the world. They occur in both marine & fresh water habitats and in association with aquatic animals.

8. Most infections are subclinical cases, but excrete the organism in faeces for 7-14 days.
Only 10% of the infected persons develop typical cholera.
90% of episodes are mild or moderate.
Case fatality without treatment = 25-50%.
Case fatality with treatment (ORS) = 1%

9. During the 19th century, the classical biotype of V
During the 19th century, the classical biotype of V. cholerae serogroup O1 caused pandemic cholera, spreading from India to most of the world; currently confined to the Indian subcontinent
Since 1961, the biotype El Tor of V. cholerae serogroup O1 has spread through Asia into Africa, Europe (small epidemics), and South America (since 1991): 7th cholera pandemic
V. cholera serogroup O139 was mainly isolated in Asia and represents currently 15% of isolates

10. During 2000, 56 countries have officially reported cases and deaths; however, > deaths/year are estimated in developing countries, about one third in children <5 years

11. Current epidemic 7th epidemic
Due to V cholerae 01,
V eltor &
V cholerae 0139
Started 1961 in Indonesia.
Bangladesh 1963
India
West Africa 1970
Latin America 1991
Bangladesh (V cholerae 0139)
South East Asia
South Africa 2000

14. Selected morbidity indicators
Cholera
Malaria
Poliomyelitis
Measles
Pulmonary tuberculosis
Diphtheria
Tetanus
Neonatal tetanus
AIDS
Meningococcal meningitis

15. Incubation period: 1-5 days.
Modes of transmission:
1-Contaminated water and food.
2-Rarely direct from person to person.
Reservior
1-Aquatic environment (Brackish water & sea food)
2-Human beings

16. Communicability (stool-positive stage):
Usually ends few days after recovery, occasionally several months carrier state, antibiotics can shorten the period of communicability

17. Prevention and control
Hygienic disposal of human faeces.
Adequate supply of safe drinking water.
Good food hygiene
Cooking food thoroughly & eating it hot.
prevent contact of cooked food with raw contaminated food, water or ice.
Avoid raw vegetables unless peeled
Boil it, cook it, peel it or forget it.
- Mass chemoprophylaxis has no effect

18. Vaccination:
The previous parenteral cholera vaccines had little efficacy and are not recommended for use in endemic areas, during outbreaks, or in people traveling to endemic areas.
Oral immunization:
(1) killed bacterial vaccines
(2) live genetically engineered mutants deleted of toxin genes
(3) avirulent vectors genetically engineered to express protective cholera antigens.

19. an oral vaccine containing killed V cholerae O1.
Oral killed vaccines
an oral vaccine containing killed V cholerae O1.
successful immunity for 6 months, which later waned.
Unfortunately, in patients who need the vaccine most (children), the immunity was poor.
Need multiple dosages.
This vaccine is now disrepute

20. It is effective in children and healthy volunteers.
Oral live vaccines
Appears to be safe and induces protective immunity as soon as 8 days after immunization, even after a single dose in adults.
It is effective in children and healthy volunteers.
Confer 80% immunity against El Tor cholera.
However, its efficacy in endemic and
non-endemic areas and across all populations
is yet to be established.

21. - Protect against El Tor O1 and O139 Bengal strains
For a vaccine to be useful in endemic areas, it should do the following:
Produce long-lasting immunity
Be compatible with the Expanded Program on Immunization
Be able to produce immunity rapidly, ideally after one dose, to be useful in epidemics
- Protect against El Tor O1 and O139 Bengal
strains

22. Because the secondary attack rate of cholera in the household is high, selective antimicrobial prophylaxis of contacts has been attempted. This is not feasible as a routine public health measure.

23. Food products from cholera infected regions:
- Vibrio cholerae 01 survives 5 days in ambient temperature & 10 days at 5-10 degrees.
-It survives freezing & low temperature.
-It is sensitive to acidity & drying.
-It is sensitive to Gamma irradiation & temperature above 70 degrees.

24. Epidemiology of
Typhoid fever

25. An acute infection with prolonged fever due to Salmonella typhi sometimes lead to severe complications.
Globally 16 million cases with deaths annually.
Salmonella paratyphi A & B lead to milder disease.
S.t. / S.p = 10 – 1
Peak age years.

26. Disease caused by S. typhi is typhoid fever.
In past, many deaths were due to typhoid fever worldwide.
Now mostly
localized to developing countries.
People not only become ill and die but can become colonized by S. typhi resulting in being carriers and spread typhoid fever.

27. Incubation period for S. typhi is a week to a month post-ingestion.
Bacteria multiply in liver and spleen then released systemically
(blood). Results in high fever, chills, anorexia.

28. Poorer Countries are Vulnerable
Typhoid Fever seems to matriculate in places with poor sanitary conditions.
Places where water is not sanitized provides the perfect environment for Typhoid Fever.

29. Typhoid Fever
Ingest S. typhi
Bacteria invades intestinal cells and translocates to systemic organs
Multiplies to high number in liver and spleen
Spreads to bloodstream
Bacteria move to gallbladder
Bacteria persists
in gallbladder
Shed in Bile
Bacteria shed in
feces
DEATH
TYPHOID

34. Risky groups Children and young adults in endemic areas.
Contacts of chronic carriers.
Microbiology technicians.
Food handlers.
Travelers and military personnel

35. Incubation period:
10-14 days.
Modes of transmission:
Water contaminated with fecal materials.
Contaminated food.
Food handlers.
Reservoir:
Only human (cases & carriers)

36. Typhoid carriers
About 1–5% of people who are infected with S. typhi become asymptomatic chronic carriers.
The carrier state may follow acute or mild illness or subclinical infection.
The incidence of chronic carriage is higher among women and persons with biliary tract abnormalities.
Antibiotic use and antibiotic resistance may also affect the propensity to become a chronic carrier.
A chronic urinary carrier state occurs in individuals with schistosome infection.
Carriers who handle food without observing proper hygiene can transmit infection to others.

37. Transmission
Typhoid is spread by the faecal-oral route. Occasionally transmission may be direct, but usually it occurs following the ingestion of contaminated water or food.
In developing countries with contaminated water supplies and primitive sewage disposal systems, water is the most likely vehicle of transmission.

38. Epidemics originating from water contamination are particularly explosive.
because
a water source may serve a large population.
Water dilutes gastric acid which would otherwise inactivate pathogenic agents.
Water and other beverages remain in the stomach only very briefly

39. In more developed countries, with good sanitation, typhoid transmission is more likely to be associated with food contamination by an undetected carrier or a breakdown in proper practices of personal and food hygiene.

40. Communicability
Typhoid is communicable as long as S. typhi organisms are excreted, usually from the first week and throughout convalescence.
About 10% of untreated typhoid fever patients will excrete bacteria for 3 month after onset of symptoms.

41. Prevention and control
Basic sanitary and hygienic measures
Purifying water supplies.
Improving water delivery and sewage control.
Construction and use of latrines.
Boiling water
Supervision of foodhanders.

42. Vaccines
Three vaccines to typhoid fever:
Killed whole bacteria with side effects.
2. Capsular material (Vi antigen) that is safer and more effective.
3. Live oral vaccine, attenuated S. typhi strain (Ty21a).
Oral vaccines are still being developed to distribute in developing countries. Ty21a is also being used to carry foreign antigens from Shigella and V. cholerae.

43. Number of doses necessary Time between doses
Vaccine Name
How given
Number of doses necessary
Time between doses
Total time needed to set aside for vaccination
Minimum age for vaccination
Booster needed every...
Ty21a (Vivotif Berna, Swiss Serum and Vaccine Institute)
1 capsule by mouth 4
2 days
2 weeks
6 years
5 years
ViCPS (Typhim Vi, Pasteur Merieux)
Injection 1
N/A
2 years

44. Indication of vaccination:
Travellers to endemic areas.
People in refugee camps.
Microbiologists.
Treatment:
Antibiotics : Ciprofloxacin, pefloxacin & cephalosporins

45. Thank you