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Germs that infect humans

Vibrio cholera

Vibrio cholera

© Dennis Kunkel Microscopy, Inc.

Microorganism: the bacterium Vibrio cholerae (subgroup 01)

Disease: cholera

Occurrence of the disease

History: seven major pandemics have been reported, the last of which was in 1961. In 1855 an English doctor, John Snow, discovered that water contaminated by the excrement of persons sick with cholera could be the means of transmission of the disease in England. At that time, two companies shared a monopoly on the distribution of water. Of the 10,000 persons who drank the water of the first company (Southwark and Vauxhall Company), 315 died; among the 10,000 who drank water from the second company (Lambeth Company), only 37 deaths were recorded. In fact, the two companies did not supply water from the same place. The first company supplied water from the Thames, in the heart of London, where the river was polluted by waste from the city. At that period, there was no water treatment. The second company supplied water from the same river, but upstream from the city.

Current situation: in industrialized countries cholera is practically nonexistent; nevertheless, certain regions are still vulnerable, generally because of poor sewage treatment. A few small epidemics (fewer than 300 cases) have been reported in the United States. Researchers believe that these localized epidemics could be related to the consumption of raw mollusks or crustaceans, which form an alternative reservoir of infection. The mortality rate is more than 50% without treatment, but less than one per cent with adequate medical care. At present, fewer than ten cases per year are reported in Canada.

Mechanism of action of the microorganism: the bacterium attaches itself to the intestinal mucous membrane. The bacteria themselves are not invasive, but they produce a poison known as an exotoxin. This poison penetrates the cells that line the intestine and stimulates the excretion of large quantities of water. The sick person becomes dehydrated, and experiences abdominal muscular cramps, vomiting, fever, and liquid diarrhea. An individual may lose from ten to 15 liters of water during the infection. If the dehydration becomes too severe, the infected person may die.

Symptoms of the disease: acute enteritis, cramps, vomiting, severe diarrhea.

Geographical distribution of the microorganism: many countries of central Africa, India, Pakistan, South Korea, Albania, and Malta. Cholera may also spread into southern Europe.

There are two types of cholera: the classic type and the E1 Tor type. Before the 1960s, the classic type was prevalent, whereas now the E1 Tor type is more frequent.

Incubation period: approximately three days

Contagious period: the contagious period lasts as long as the stool contains bacteria, normally several days after the patient is cured.

Transmission: the bacteria are found in food or water contaminated by fecal matter from infected persons.

Hosts: hosts for cholera include mollusks, crustaceans, and plankton.

Discoverer of the microorganism: Robert Koch in 1883.

Treatment: the main treatment for cholera consists of drinking plenty of water with added salt and sugar (sucrose); this allows the intestine to absorb salt and water, which will rehydrate the patient. In addition, some medicines such as antibiotics (streptomycin, tetracycline, trimethoprim-sulfamethoxazole, or ciprofloxacin) can be used. However, these antibiotics are less effective if the patient has not been rehydrated.

Prevention: water treatment

Vaccine: the cholera vaccine is made from parts of the bacterium or from killed bacteria. A booster is required after six months. Vaccination may be recommended in regions where cholera is endemic.