Caused by the Gram-negative bacterium Vibrio cholerae, cholera is a serious gastrointestinal infection, and the pathogen has been investigated for its potential as a biological warfare (BW) agent. In 1939, the United States investigated cholera for its potential as a biological weapon, as did German military scientists, although none of these investigations got much further than defensive research. Meanwhile, cholera was used by Japan against Chinese forces in World War II, although at least one of these operations backfired, resulting in many Japanese casualties as well. While its capacity to cause disease in food- and water-borne routes is well known, it is not clear that cholera would have much potential in its aerosolization. Cholera could present a threat in terms of sabotage and/or terrorist activities. However, cholera bacteria are vulnerable to chlorination, making it less of a threat for modern water handling systems.
In nature, cholera is spread by the fecal-oral route and infects only humans. In order to start an infection via the ingested route, an inoculum of approximately 1,000 to 100 million organisms are required. The actual cause of disease is generated by a toxin that is produced and excreted by the organism. Cholera toxin dramatically increases the flow of water and electrolytes into the gastrointestinal space. Following an incubation period of about one to five days, symptoms of cholera include severe and watery diarrhea, (so-called “rice-water” stool) followed by dehydration and loss of electrolytes, which can be deadly, especially for infants. Mortality rate of cholera is approximately 40 percent without treatment. Water and mineral replacement therapy is usually successful, with antibiotics showing some benefit in reducing the length of diarrheal symptoms. A vaccine for cholera is available and routinely administered in the developing world, but is usually not indicated in industrialized countries. The actual efficacy of this vaccine, furthermore, is in some doubt, as it is preventative over 3 to 6 months only 50 percent of the time, and, in any case, does not prevent subsequent transmission. Once relatively common, cholera is no longer a serious threat for developed countries, but remains a significant killer in the developing world, especially in Asia and South America. |
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