It is estimated that more people died of the bacterial disease tuberculosis (TB) in 1999 than in any other year in history. Scientists are fighting the battle against the disease on several fronts. For example, the complete DNA sequence of 4 million base pairs of the causative agent has recently been determined. Epidemiological research is also important. In the suburbs of Cape Town, South Africa, for example, the disease is, as expected, most common in the poorer suburbs. But there is also a marked correlation between the incidence of TB and infections by intestinal parasites. This may be because such parasites stimulate T-lymphocytes to activate B-lymphocytes and suppress the activity of macrophages.

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1. Name the most common causative agent of TB.

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2. Explain what is meant by epidemiological research.

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3. State two reasons why TB was expected to be most common in the poorer suburbs of Cape Town.

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4. Suggest one reason why knowledge of the DNA base sequence of the causative organism could help in the fight against the disease.

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5. Summarise the main reasons why TB is still such a widespread disease.

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6. Describe briefly the differences in the way the B- and T-lymphocytes act during the immune response.

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7. Explain why suppression of macrophages lowers resistance to TB.

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