Disease Research Report
December 9, 2010
Cholera is an infection of the small intestine that causes a large amount of watery diarrhea. Cholera is a bacterial disease (caused by the bacterium Vibrio cholerae) usually spread through contaminated water. The bacteria, which are found in fecal-contaminated food and water and in raw or undercooked seafood, produce a toxin that affects the intestines causing diarrhea, vomiting, and severe fluid and electrolyte loss. This overwhelming dehydration is the outstanding characteristic of the disease and is the main cause of death. Cholera has a short incubation period (two or three days) and runs a quick course. In untreated cases the death rate is high, averaging 50%, and as high as 90% in epidemics, but with effective treatment the death rate is less than 1%. Historical Perspective
During 1883, cholera was epidemic in Egypt. A German physician and bacteriologist, Robert Koch traveled with a group of German colleagues from Berlin to Alexandria, Egypt in August, 1883. Following necropsies, they found a bacillus in the intestinal mucosa in persons who died of cholera, but not of other diseases. He reasoned that the bacillus was related to the cholera process, but was not sure if it was causal or consequential. He stipulated that the time sequence could only be resolved by isolating the organism, growing it in pure culture, and reproducing a similar disease in animals. He was not able to obtain such a pure culture, but did try to infect animals with choleraic material. None became infected. His thoughts and early findings were sent in a dispatch to the German government and shared with the German press. On January 7th 1884, Koch announced in a dispatch that he had successfully isolated the bacillus in pure culture. One month later he wrote again, stating that the bacillus was not straight like other bacilli, but "a little bent, like a comma." He also noted that the bacillus was able to proliferate in moist soiled linen or damp earth, and was susceptible to drying and weak acid solutions. Finally, he pointed out that the specific organisms were always found in patients with cholera but never in those with diarrhea from other causes, were relatively rare in early infection, but were extensively present in the characteristic "rice water stools" of advanced cholera patients. He was, however, still unable to reproduce the disease in animals, reasoning correctly that they are not susceptible. In May, 1884 Koch and his colleagues returned to Berlin where they were treated as national heroes. Epidemiology
Cholera is a disease that occurs in low income regions of the world where sanitation, food and water hygiene are inadequate. Imported cases occasionally occur in travelers returning from endemic areas. In areas without clean water or sewage disposal (as may occur after natural disasters or in displaced populations in areas of conflict), cholera can spread quickly and have a case fatality rate of as high as 50% in vulnerable groups with limited medical care. The World Health Organization (WHO) reports the emergence of new strains of Vibrio cholerae which now predominates in parts of Africa and Asia, and the emergence and spread of antibiotic resistant strains.
Annual global figures (2009) reported to WHO included 221,226 cases and 4,946 deaths from 45 countries. The majority of cases (98%) were reported from Africa where an outbreak, that started in 2008 and lasted for almost a year, spread to South Africa and Zambia. By the end of July 2009, over 98,000 cases and 4,000 deaths were reported in this outbreak. Asia reported an 82% decrease in cases in 2009 compared to 2008, however, reports of acute watery diarrhea, many of which may be cholera, were not included.
When cholera first appears in epidemic form in an unexposed population, it can affect all age groups. In contrast, in areas with high rates of endemic disease, most of...