Cholera (also called Asiatic
cholera) is an infectious disease of the gastrointestinal tract caused by the
Vibrio cholerae bacterium. These bacteria are typically ingested by
drinking water contaminated by improper sanitation or by eating improperly
cooked fish, especially shellfish. Symptoms include diarrhea, abdominal
cramps, nausea, vomiting, and dehydration. Death is generally due to the
dehydration caused by the illness. When left untreated Cholera generally
has a high mortality rate. Treatment is typically an aggressive rehydration
regimen usually delivered intravenously, which continues until the diarrhea
· About one million
Vibrio cholerae bacteria must 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.
· 1,099,882 cases and 10,453 deaths were reported in the
Western Hemisphere between January 1991 and July 1995.
· On average, one case of cholera is reported in the
United States every week.
Vibrio cholerae causes
disease by producing a toxin that disables the GTPase function of G
proteins which are part of G protein-coupled receptors in intestinal cells.
This has the effect that the G proteins are locked in the "on
position" binding GTP (normally, the G proteins quickly return to
"off" by hydrolizing GTP to GDP). The G proteins then cause
adenylate cyclases to produce large amounts of cyclic AMP (cAMP) which
results in the loss of fluid and salts across the lining of the gut.
The resulting diarrhea allows
the bacterium to spread to other people under unsanitary conditions.
Although cholera can be
life-threatening, it is easily prevented and treated. In the United States,
because of advanced water and sanitation systems, cholera is not a major
threat. The last major outbreak of cholera in the United States was in
1911. However, everyone, especially travelers, should be aware of how the
disease is transmitted and what can be done to prevent it.
Carriers of the cystic
fibrosis gene are protected from the severe effects of cholera because they
don't lose water as quickly. This explains the high incidence of cystic
fibrosis among populations which were formerly exposed to cholera.
Recent genetic research has
determined that a person's susceptibility to cholera (and other diarrheas)
is affected by their blood type. Those with type O blood are the most susceptible.
Those with type AB are the most resistant, virtually immune. Between these
two extremes are the A and B blood types, with type A being more resistant
than type B.
The scientists with major
contributions to fighting cholera are John Snow, who found the link between
cholera and drinking water in 1854, and Robert Koch, who identified the
bacillus causing the disease.