OCR, specimen paper

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]
    Answer:

    faeces from infected person;via drinking water;via food;direct to mouth of uninfected person;carrier not washing hands after using toilet, food preparation etc;carried by flies to food;via seafood;via water used to irrigate vegetables.


    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]
    Answer:

    test for antibodies (against V.cholerae);isolate/grow bacteria from faeces/rectum/intestinal tissue;some method of identification;microscopy;use of monoclonals (® if injected);fluorescent dye.


    Question:

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

    [4]
    Answer:

    sewage treatment;water supply not contaminated/clean water supply;transmission cycle broken/not established;drinking water, chlorinated/purified;good sanitation, explained/described;good food hygiene;vaccination, antibiotics


    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]
    Answer:

    programme not effective;still 1200 million who can transmit cholera;do not have access to clean water;rural areas not reached;growth of population;growth of shanty towns;poor sanitation;natural disasters;new facilities not maintained;wars/civil unrest;no effective vaccine;overcrowding; [7 marks max]

    Q – legible text with accurate spelling, punctuation and grammar; [1 mark]


  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]
      Answer:

      bacteriostatic/stop growth/cell wall synthesis/ cell membrane synthesis;stops division/protein synthesis/transcription;disrupts cell wall/membrane function;disrupts translation/DNA replication;acts as enzyme inhibitor;causes lysis;


      Question:

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

      [1]
      Answer:

      resistance of bacterium;may recover with oral rehydration only;immune


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