The bacterium, Vibrio cholerae, is the causative agent of cholera. The El Tor strain of V. cholerae originally occurred only in Indonesia. In 1961, this strain began to spread replacing existing strains in other parts of Asia. El Tor is now widespread throughout Asia, the Middle East, Africa and parts of Eastern Europe, but has never established itself in Western Europe.

El Tor is hardier than the strain it replaced and the bacteria may continue to appear in the faeces for up to three months after patients have recovered. The bacteria may persist in water for up to fourteen days.

Question:


1. State two ways in which V. cholerae is transmitted from infected to uninfected people.

   [2]
   

   Some people infected with cholera have mild symptoms, or none at all, and are carriers of the disease.

   Question:
   

2. Suggest how laboratory tests could identify carriers of cholera.

   [2]
   Question:
   

3. Suggest four reasons why E1 Tor has not become established in Western Europe.

   [4]
   Question:
   

4. The United Nations, recognising that most of the outbreaks of cholera were the result of polluted water supplies, set up a 'Decade of Water' in 1981. Its aim was to provide safe water for everyone. Over the decade 1981/1990, the number of people lacking a safe water supply in developing countries dropped from 1800 million to 1200 million.

   Explain why cholera continues to be a worldwide problem, in spite of the 'Decade of Water' campaign.

   (In this question, 1-mark is available for the quality of written communication.)

   [8]
   

5. The antibiotic tetracycline is sometimes used as a treatment for cholera.

   Question:
   

   1. Suggest two ways in which tetracycline can affect V. cholerae.

      [2]
      Question:
      

   2. Explain why tetracycline should not be used routinely for all cases of cholera.

      [1]