10. Infectious Disease

Question 1

Disease

Answer 1

Abnormal condition affecting an organism that reduces the effectiveness of the functions of the organism; usually presented with symptoms

Question 2

Suggest and explain why cholera outbreaks are common after natural disasters. [2m]

Answer 2

• sewage and drinking water mixed
• contaminated water supply
• people are unable to practise good hygiene
• unable to thoroughly cook food

Question 3

Suggest why the case fatality rate of cholera varies between countries. [3m]

Answer 3

• treatment of cholera involves supply of oral rehydration therapy
• & provision of safe drinking water
• better response to emergencies in some countries
• may depend on remoteness of regions affected by cholera / ways in which emergency supplies/personnel can reach affected areas

Question 4

8 biological reasons for the difficulties in developing and introducing control methods for malaria

Answer 4

1. Plasmodium is inside RBCs / liver cells
2. antigenic concealment
3. antibodies are ineffective (short stage in plasma when antibodies are effective)
4. Plasmodium is eukaryotic, has many genes/antigens
5. difficult to develop vaccine
6. resistance to drugs used (eg. chloroquine) to treat malaria
7. Anopheles breeds in small pools of water, difficult to control all breeding places
8. mosquitoes become resistant to insecticides (eg. DDT, dieldrin)

Question 5

Describe and explain the difference between the global distribution of Anopheles and the global distribution of malaria. [3m]

Answer 5

• not all countries with Anopheles have malaria
• malaria only / mainly in subtropical and tropical areas
  explanations:
• Plasmodium not present in all areas where Anopheles is located
• conditions (where Anopheles located) not always suitable for life cycle of Plasmodium
• some areas have eradicated the disease but still have the vector
• some countries have effective treatment for malaria

Question 6

Discuss the consequences of multiple resistance for health authorities. [4m]

Answer 6

• need to find new antibiotics
• so cost of research
• higher death rates
• increased treatment/hospitalisation times
• increased costs of treatment ; allow cost once
• fewer antibiotics left that are effective

Question 7

Outline the role of the mosquito in the transmission of malaria. [2m]

Answer 7

• VECTOR
• taking BLOOD from a person during a blood meal
• Plasmodium enter person with anticoagulant/saliva

Question 8

9 methods that can be used to prevent the spread of cholera

Answer 8

1. treat drinking water
2. provide sewage treatment plants
3. keep sewage and drinking water sources separate
   eg. avoid defaecating near rivers used for washing
4. vaccination / provide vaccines
5. ref. to education in ways to prevent spread
6. encourage hand washing
7. cook food thoroughly
8. oral rehydration therapy
9. use of antibiotics

Question 9

2 ways in which M. tuberculosis may survive within a macrophage

Answer 9

1. produces inhibitors for lysosomal enzymes

2. is resistant to digestive enzymes