MINSTRY OF HEALTH HOMS DIRECTORATE OF HEALTH Cholera epidemiology

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MINSTRY OF HEALTH HOMS DIRECTORATE OF HEALTH
Cholera epidemiology

• Dr. Hisham Aldabbagh

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• Cholera is still a subject of intense interest
  for modern-day epidemiology
• in the 1800s a causal link between cholera
  transmission and exposure to contaminated water
  was established
• More recently, researchers have begun to
  understand more about the mechanisms of
  infectiousness of the cholera pathogen Vibrio
  cholerae

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• Cholera has been very rare in industrialized
  nations for the last 100 years however, the
  disease is still common today in other parts of
  the world, including the Indian subcontinent and
  sub-Saharan Africa
• Cholera is an acute, diarrheal illness caused by
  infection with the bacterium Vibrio cholerae. it
  is often mild or without symptoms, but sometimes
  it can be severe. Approximately one in 20
  infected persons has severe disease characterized
  by profuse watery diarrhea, vomiting, and leg
  cramps. In these persons, rapid loss of body
  fluids leads to dehydration and shock. Without
  treatment, death can occur within hours.

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• A person may get cholera by drinking water or
  eating food contaminated with the cholera
  bacterium. In an epidemic, the source of the
  contamination is usually the feces of an infected
  person. The disease can spread rapidly in areas
  with inadequate treatment of sewage and drinking
  water.
• The cholera bacterium may also live in the
  environment in brackish rivers and coastal
  waters. Shellfish eaten raw have been a source of
  cholera, The disease is not likely to spread
  directly from one person to another therefore,
  casual contact with an infected person is not a
  risk for becoming ill.

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• Vibrio cholerae is a Gram-negative bacterium that
  produces cholera toxin, an enterotoxin, whose
  action on the mucosal epithelium lining of the
  small intestine is responsible for the disease's
  infamous characteristic, exhaustive diarrhea
• The major reservoir for cholera was long assumed
  to be humans themselves, but considerable
  evidence exists that aquatic environments can
  serve as reservoirs of the bacteria

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• In endemic regions, such as South Asia, cholera
  is seasonal, with explosive outbreaks occurring
  once or twice a year, depending on the region.
  Periodically, pandemic waves of cholera roll
  across the world causing a heavy death toll.

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• 1816-1826 - First cholera pandemic began in
  Bengal, and then spread across India by 1820.
  Then extended as far as China and the Caspian Sea
• 1829-1851 - Second cholera pandemic reached
  Europe, London and Paris in 1832. In London, the
  disease claimed 6,536 victims in Paris, 20,000
  succumbed (out of a population of 650,000) with
  about 100,000 deaths in all of FranceThe epidemic
  reached Russia , Quebec, Ontario and New York in
  the same year and the Pacific coast of North
  America by 1834.

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• 1849 - Second major outbreak in Paris. In London,
  it was the worst outbreak in the city's history,
  claiming 14,137 lives, over twice as many as the
  1832 outbreak. In 1849 cholera claimed 5,308
  lives in the port city of Liverpool, England, and
  1,834 in Hull, England.An outbreak in North
  America took the life of former U.S. President
  James K. Polk. Cholera spread throughout the
  Mississippi river system killing over 4,500 in
  St. Louis and over 3,000 in New Orleans as well
  as thousands in New York In 1849 cholera was
  spread along the California and Oregon trail as
  hundreds died on their way to the California Gold
  Rush, Utah and Oregon.

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• 1852-1860 - Third cholera pandemic mainly
  affected Russia, with over a million deaths. In
  1853-4, London's epidemic claimed 10,738 lives.
• 1854 - Outbreak of cholera in Chicago took the
  lives of 5.5 of the population (about 3,500
  people).
• 1863-1875 - Fourth cholera pandemic spread mostly
  in Europe and Africa

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• 1866 - Outbreak in North America. In London, a
  localized epidemic in the East End claimed 5,596
  lives. Also a minor outbreak at Ystalyfera in
  South Wales. Caused by the local water works
  using contaminated canal water, it was mainly its
  workers and their families who suffered, 119
  died. In the same year more than 21,000 people
  died in Amsterdam, The Netherlands

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• 1881-1896 - Fifth cholera pandemic The 1892
  outbreak in Hamburg, Germany killed 8,600 people.
  This was the last serious European cholera
  outbreak.
• 1899-1923 - Sixth cholera pandemic had little
  effect in Europe because of advances in public
  health, but major Russian cities and the Ottoman
  Empire were particularly hard hit by cholera
  deaths.

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• 1961-1970s - Seventh cholera pandemic began in
  Indonesia, called El Tor, and reached Bangladesh
  in 1963, India in 1964, and the USSR in 1966.
  From North Africa it spread into Italy by 1973.
  In the late 1970s, there were small outbreaks in
  Japan and in the South Pacific. There were also
  many reports of a cholera outbreak near Baku in
  1972

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• January 1991 to September 1994 - Outbreak in
  South America. Beginning in Peru there were 1.04
  million identified cases and almost 10,000
  deaths.
• In 1992 a new strain appeared in Asia,
  nonagglutinable vibrio (NAG) named O139 Bengal.
  It was first identified in Tamil Nadu, India and
  for a while displaced El Tor in southern Asia
  before decreasing in prevalence from 1995 to
  around 10 of all cases. It is considered to be
  an intermediate between El Tor and the classic
  strain and occurs in a new serogroup.

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• Iraq outbreaks
• - 2oo7 15000 cases
• - 2008 700 cases

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• November 2008 - Doctors Without Borders reported
  an outbreak in a refugee camp in Congo's eastern
  provincial capital of Goma. Some 45 cases were
  reportedly treated between November 7th through
  9th.

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• November 2008 - More than an estimated 11,000
  people in Zimbabwe are believed to be infected
  with more than 970 recorded deaths observed
  during a current and ongoing outbreak. The number
  of people infected is believed to be
  significantly higher. The outbreak is a result of
  mismanagement of water purification
  infrastructure. Subsequent outbreaks are being
  observed in neighbouring countries as the medical
  infrastructure in Zimbabwe is severely crippled
  by hyperinflation leading to several Zimbabwean
  citizens seeking medical care elsewhere.

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• Until the 1970s, V. cholerae was thought to be a
  human-specialized parasite, incapable of
  persisting outside its host. But in the 1990s, it
  became clear that V. cholerae was a successful
  member of the brackish water microbial community,
  living in association with plankton in an
  unculturable but viable state

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• Volunteer studies suggest that cholera infection
  requires consumption of a heavy infectious dose,
  which is unlikely to be found in the environment
  in the beginning of the epidemic season, even
  considering the blooming of aquatic V. cholerae..

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Susceptibility

• Recent epidemiologic research suggests that an
  individual's susceptibility to cholera (and other
  diarrheal infections) is affected by their blood
  type Those with type O blood are the most
  susceptible while those with type AB are the most
  resistant. Between these two extremes are the A
  and B blood types, with type A being more
  resistant than type B

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• About one million V. cholerae bacteria must
  typically be ingested to cause cholera in
  normally healthy adults, although increased
  susceptibility may be observed in those with a
  weakened immune system, individuals with
  decreased gastric acidity (as from the use of
  antacids), or those who are malnourished

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The Hyperinfectious State

• The passage of V. cholerae through the human gut
  would promote the expression of genes that would
  make the bacteria more infective, that is, more
  capable of surviving and growing in the
  intestinal environment
• This hyperinfectious state would be lost after
  a few hours outside the gutthat is, after being
  outside the gut for more than 18 hours
• The infectious dose is 700 times smaller if
  consumed water contains HI bacteria. Infected
  persons shed HI bacteria into their feces, which
  decay to the non-HI state in an average of 18
  hours

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• Explosive outbreaks depend on the number of cases
  produced by contact with recently shed bacteria(
  HI bacteria )
• This would be the case in a community where poor
  basic hygienic conditions make contact with
  recently shed bacteria a probable event.

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• Any public health action to reduce direct
  transmission will have a large impact on the rate
  of disease spread. In other words, any measure
  that delays fecaloral transmission, even the
  simple act of washing hands before a meal, would
  have a stronger than previously expected impact
  on cholera transmission
• Thus, public health strategies based on
  increasing hygiene standards would be effective ,
  even if more permanent improvements, such as
  proper sewage treatment, were impossible

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How long will the cholera epidemic last?

• Predicting how long a cholera epidemic will last
   is difficult. The cholera epidemic in Africa has
  lasted more than 30 years. In areas with
  inadequate sanitation, a cholera epidemic cannot
  be stopped immediately.
•  There are no signs that the global cholera
  pandemic will end soon.
• Major improvements in sewage and water treatment
  systems are needed in many countries to prevent
  future epidemic cholera

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Distribution of cholera
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Is a vaccine available to prevent cholera?

• A recently developed oral vaccine for cholera is
  licensed and available in some countries (Dukoral
  from SBL Vaccines). The vaccine appears to
  provide somewhat better immunity and have fewer
  adverse effects than the previously available
  vaccine. However, CDC does not recommend cholera
  vaccines for most travelers, nor is the vaccine
  available in the United States .

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• Sensitive surveilence and prompt reporting allow
  for containing cholera epidemics rapidly. Cholera
  exists as a seasonal disease in many endemic
  countries, occurring annually mostly during rainy
  seasons. Surveillance systems can provide early
  alerts to outbreaks, therefore leading to
  coordinated response and assist in preparation of
  preparedness plans.

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• Efficient surveillance systems can also improve
  the risk assessment for potential cholera
  outbreaks. Understanding the seasonality and
  location of outbreaks provide guidance for
  improving cholera control activities for the most
  vulnerable. This will also aid in the developing
  indicators for appropriate use of oral cholera
  vaccine.

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• Thanks for your concern