1. 1
   A water treatment plant in a low-income coastal region has failed following severe flooding. Within a week, the local clinic reports a sharp rise in patients suffering from severe diarrhoea and dehydration. Laboratory testing on stool samples confirms the presence of Vibrio cholerae bacteria in the contaminated drinking water supply used by the community.

   (a)

   Which type of pathogen is Vibrio cholerae, the organism confirmed in the contaminated water supply?

   [1 mark]

   • AVirus
   • BBacteria
   • CFungus
   • DProtist

   (b)

   Which of the following is the main route by which cholera is spread between people?

   [1 mark]

   • AAirborne droplets
   • BAnimal vectors such as mosquitoes
   • CContaminated water
   • DDirect skin contact

   (c)

   Describe two ways the risk of further cholera cases in this community could be reduced.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A 34-year-old patient is diagnosed as HIV-positive following a routine blood test at a clinic. Over the following two years, the patient's white blood cell count steadily falls, and doctors note that the patient develops several infections that they had previously fought off easily, including a chest infection later confirmed as tuberculosis.

   (a)

   What type of pathogen is HIV?

   [1 mark]

   • ABacteria
   • BFungus
   • CProtist
   • DVirus

   (b)

   Which of these describes how HIV is most commonly spread between people?

   [1 mark]

   • ABody fluids, such as through unprotected sexual contact
   • BContaminated drinking water
   • CAirborne droplets
   • DAnimal vectors such as mosquitoes

   (c)

   Explain why this patient has become more likely to develop other infections, such as tuberculosis, since being diagnosed with HIV.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A forestry researcher is monitoring a woodland plantation of ash trees. Over several months, she records that many trees are shedding their leaves earlier than normal and developing dark, sunken lesions on their bark and stems. Neighbouring plantations several kilometres away begin showing the same symptoms shortly afterwards, and laboratory analysis confirms the presence of a fungal pathogen, consistent with Chalara ash dieback.

   (a)

   Describe how the ash trees in this plantation could defend themselves against attack from this fungal pathogen.

   [3 marks]

   (b)

   The researcher wants to confirm that Chalara ash dieback, rather than an environmental factor, is responsible for the symptoms seen across the plantations. Describe how she could investigate this, both in the field and in the laboratory.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A public health officer is reviewing two ongoing situations in the same region. First, several patients who were diagnosed as HIV-positive some years ago have since developed tuberculosis, despite having had no unusual exposure to the tuberculosis bacterium. Second, in a nearby village, a cluster of cholera cases has been traced to a shared well used for drinking water, at the same time as an outbreak of Chalara ash dieback has begun destroying ash trees in the surrounding woodland.

   (a)

   Explain why the patients who are HIV-positive have become more likely to develop tuberculosis, and outline how HIV itself is spread between people.

   [6 marks]

   (b)

   Evaluate how effective different measures would be at reducing the spread of the cholera outbreak in the village and the Chalara ash dieback affecting the ash trees, given the different pathogens and transmission routes involved.

   [6 marks]

   Total for question 4: 12 marks

End of questions