[Maximum number: 2]

Ebola virus disease (EVD) is the disease in humans and other primates that is caused by the Ebola virus. Fruit bats are the reservoir for the virus and are able to spread the disease without being affected. Humans can become infected by contact with fruit bats or with people infected by the virus, their body fluids or equipment used to treat them.

The table shows data for four African countries that were affected by the 2014-2015 Ebola outbreak.

(a)

An antiviral drug, T-705, was tested in order to establish whether it has potential to treat EVD. The graph shows the data from an in vitro trial of T-705 on cells that had been infected with Ebola virus five days previously. Virus concentration and live cells are shown as percentage of the control.

Based on these data, outline the evidence that T-705 has potential to be used as a treatment for EVD.

[ 2 ]

[Maximum number: 4]

The black-legged tick (lxodes scapularis) is an arthropod which sucks blood from humans and other mammals. It is encountered mainly in wooded and semi-wooded areas.
Some ticks can be infected by the bacterium Borrelia burgdorferi. When a tick bites a human, the bacterium is often introduced, causing Lyme disease. Lyme disease is a public health problem in North America and, if left untreated, can cause important neurological impairment. The diagram represents the two-year life cycle of a tick.

(a)

Using information from the text, identify one possible simple treatment for Lyme disease.

[ 1 ]

(b)

White-footed mice (Peromyscus leucopus) in eastern North America's wooded areas often host B. burgdorferi bacteria. To determine whether bacterial transmission from mice to tick nymphs could be prevented, mice were vaccinated with antigens from Lyme disease-causing B. burgdorferi. Scientists captured wild mice at two different sites in the woods once a month, over 4 months. Each time, they measured the levels of antibodies to B. burgdorferi present in the captured and re-captured mice, inoculated all of them, and released them into the woods. The control group was not vaccinated with B. burgdorferi antigen.

[ 3 ]

(i)

Suggest possible reasons for the observed pattern of presence of antibodies in vaccinated mice.

The summer after vaccination, the prevalence of B. burgdorferi infection in tick nymphs collected on mice from the two sites was measured.

[ 3 ]

[Maximum number: 3]

Ebola virus disease (EVD) is the disease in humans and other primates that is caused by the Ebola virus. Fruit bats are the reservoir for the virus and are able to spread the disease without being affected. Humans can become infected by contact with fruit bats or with people infected by the virus, their body fluids or equipment used to treat them.

The stacked bar graph shows the epidemiological data for the EVD cases in Conakry, the capital city of Guinea, surrounding suburbs and rural areas in Guinea from the beginning of January 2014 to the end of March 2015.

(a)

Explain how vaccination can lead to the production of B cells specific to the Ebola virus.

[ 3 ]

[Maximum number: 12]

According to the UN Inter-agency Group for Child Mortality Estimation, in the year 2000 there were 9.82 million deaths of children under the age of 5 . Many of these deaths were caused by infectious diseases. The pie chart shows estimates for the percentages of deaths that were attributable to two of the most frequent pathogens, Streptococcus pneumoniae and Haemophilus influenzae.

(a)

The deaths due to these two pathogens only included children who were not infected with HIV. Suggest a reason for excluding HIV-infected children from the statistics.

[ 1 ]

(b)

Vaccination programmes have led to decreases in child mortality. The graph shows global trends between 1980 and 2018 in the vaccination of children against seven different pathogens in the first year of their lives.

[ 2 ]

(i)

Using the graph, identify the percentage who had received the tuberculosis vaccine in 2012.

[ 1 ]

(ii)

Calculate the difference in time between 40 % of children receiving the hepatitis B vaccine and 40 % receiving the pneumococcal vaccine.

[ 1 ]

(c)

Children are immunized against diseases caused by Streptococcus pneumoniae with pneumococcal conjugate vaccine (PCV) and against diseases caused by Haemophilus influenzae with Haemophilus influenzae type b (Hib) vaccine.

The graphs show the estimated global percentages of children not vaccinated against S. pneumoniae and H. influenzae by the age of 5 and the estimated global death rates in children under 5 years, due to these pathogens, between 2000 and 2015.

Outline the conclusions that can be drawn from the graph showing data for PCV and S. pneumoniae.

[ 2 ]

(d)

Suggest reasons for the difference between the data for S. pneumoniae and H. influenzae.

[ 2 ]

(e)

Suggest reasons for the difference between the fraction attributed to S. pneumoniae in all cases of ARI and in cases where antibiotics were used to treat the infection.

[ 2 ]

(f)

Using the data, predict the effect of universal PCV vaccination in LMICs.

[ 1 ]

(g)

Outline likely health benefits of universal PCV vaccination of children, other than reducing the incidence of ARI.

[ 2 ]

[Maximum number: 1]

Dementia is a term used to describe a group of symptoms that are caused by a decline in brain function. People with dementia have problems with memory, language and behaviour.

Alzheimer's disease is the most common cause of dementia. Scientists investigated the effect of a drug called donanemab on people with Alzheimer's disease. They divided them into two groups:
- The treatment group received regular injections of a solution containing donanemab.
- The control group received regular injections of a solution without donanemab.

The scientists used the Alzheimer's Disease Rating Scale (ADRS) to measure brain function. The lower the score on this scale, the worse the brain function. The scientists calculated the mean ADRS score for each group at intervals over 76 weeks. They then calculated the mean change from their initial score at the start of the investigation (baseline).

Their results are shown in the graph.

(a)

In some drug trials, the control group is given a drug that is known to be effective against the disease. The treatment group is also given this drug, together with the new drug being tested. Suggest a reason for designing drug trials in this way for the control group.

[ 1 ]

[Maximum number: 1]

The table shows the number of amino acids that are different in the sequences of the protein FOXP2 from a human compared with four other primate species.

(a)

Some infectious diseases in humans are caused by viruses that originated in other primates.

[ 1 ]

(i)

State the term used for an infectious disease that can transfer from other species to humans.

[ 1 ]

[Maximum number: 4]

The growth of non-pathogenic Escherichia coli bacteria were studied in a microbiology laboratory at different temperatures with the antibiotic ampicillin. The number of bacterial colonies that grew were counted, and the mean and standard deviations calculated for five replicates per temperature.

At $25^{\circ} \mathrm{C}$ , the mean number of colonies counted was $70 \pm 8$ . The Petri dish shows the results obtained in one of the replicates at this temperature.

(a)

State the dependent variable in this experiment.

[ 1 ]

(b)

Explain the need for replicates in this experiment.

[ 2 ]

(c)

Suggest one reason for the presence of bacterial colonies despite the use of the antibiotic ampicillin.

[ 1 ]

[Maximum number: 3]

The photomicrograph shows a coronary artery and a cardiac vein.

(a)

(i)

The blood carried by arteries and veins contains antibodies. Explain antibody production by lymphocytes.

[ 3 ]

[Maximum number: 2]

The structure of part of the digestive system is shown in the diagram below.

(a)

(i)

Cells defend the body against pathogens. Outline how some of these cells ingest pathogens in the blood and in body tissues.

[ 2 ]

[Maximum number: 2]

The figure shows a transmission electron micrograph of rotavirus particles. Each rotavirus is about 70 nanometres in diameter.

(a)

Rotavirus causes diarrhea and vomiting. Explain why viral diseases cannot be treated using antibiotics.

[ 2 ]