Question 1
1
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.
13 marks
Question 1(b)
1(b)
Using information from the text, identify one possible simple treatment for Lyme disease.
Easystructured1 marks
Answer
antibiotics / named antibiotics
Question 1(f)
1(f)
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.
0 marks
Question 1(f)(ii)
1(f)(ii)
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.
Mediumstructured3 marks
Answer
ii a low antibody level initially as mice not previously exposed to antigen/bacteria Ignore any references to non-vaccinated/control mice - this means that no marks are awarded for them because the question is about vaccinated mice, but there is no penalty for including this information in an answer. 3 max b vaccination causes antibody production/development of immunity c increased proportion of mice have been vaccinated in each successive month d second vaccination/booster shot increases antibody level/speeds up antibody production e memory cells produced so greater/faster antibody production f many/rising numbers of nymphs which may spread the bacteria/antigens to mice
Question 1
1
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.
0 marks
Question 1(g)
1(g)
Explain how vaccination can lead to the production of B cells specific to the Ebola virus.
Mediumstructured3 marks
Answer
a. vaccine contains Ebola antigens b. vaccine «could» contain weakened/attenuated/dead/killed form of «Ebola» virus/virus genetically modified to express an Ebola/viral protein c. phagocyte/macrophage engulfs the antigen/presents the antigen to T cell d. antigen recognized by «specific» T cells/binds to T cells e. «activated» T cells activate «specific) B cells f. «activated» B cells make the antibodies «against Ebola» g. B cells divide forming «clone of» plasma cells/producing more B cells specific to Ebola 3 max
Question 1
1
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.
16 marks
Question 1(b)
1(b)
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.
Mediumstructured1 marks
Answer
a. difficult to know what infection causes death in children with HIV; b. HIV lowers immunity/fewer T cells/reduces antibody production/more likely to catch infectious disease; c. deaths of HIV-infected children should be attributed to HIV; 1 max
Question 1(c)
1(c)
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 marks
Question 1(c)(i)
1(c)(i)
Using the graph, identify the percentage who had received the tuberculosis vaccine in 2012.
Easystructured1 marks
Answer
89 %; Allow 88 to 91\%.
Question 1(c)(ii)
1(c)(ii)
Calculate the difference in time between 40 % of children receiving the hepatitis B vaccine and 40 % receiving the pneumococcal vaccine.
Mediumstructured1 marks
Answer
13 years; Allow any value between 13 and 14 years inclusive.
Question 1(d)
1(d)
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.
Mediumstructured2 marks
Answer
a. number of deaths (due to S. pneumoniae) and percentage of children not vaccinated (with PCV) both fall (along the years) OR number of deaths (due to S. pneumoniae) decreases while percentage of vaccinated children (with PCV) increases (along the years); b. positive correlation between number of deaths and percentage of children not vaccinated / OR negative correlation between number of deaths and percentage of children vaccinated / vaccination reduces the number of deaths; c. increased reduction in the number of deaths from 2010 onwards; d. still large number of deaths/large number of children unvaccinated in 2015; Comparative terms expected (do not award mp for just stating values). Mpb: do not allow "directly or inversely proportional". Mpb: Do not just accept "positive correlation" or "negative correlation" without a clear indication of the variables being correlated 2 max
Question 1(e)
1(e)
Suggest reasons for the difference between the data for S. pneumoniae and H. influenzae.
Mediumstructured2 marks
Answer
a. Hib vaccination program started earlier/PCV vaccination program started later OR Hib vaccine developed before PCV vaccine; b. deaths due to H. influenzae drop earlier than deaths due to S. pneumoniae because of earlier vaccination; c. more deaths due to S. pneumoniae than H. influenzae (in any year) as lower % of children vaccinated against S. pneumoniae (compared H. influenzae); Mp a to c: accept vice versa. Comparative terms expected (do not award mp for just stating values). Mpa and mpb: there must be a clear reference to time. Mpc: there must be clear indication to vaccination. Allow no points for bacterial virulence / disease severity, etc., as bacterial pathogenicity is not addressed on graphs. 2 max
Question 1(g)
1(g)
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.
Mediumstructured2 marks
Answer
a. highest attributed fraction (in both age groups) is in cases where antibiotic used; b. ARI cases due to S. pneumoniae can be severe so antibiotics are often prescribed; c. all cases include other causes / viral ARI which may not require antibiotics; d. antibiotics administered without prescription or physician consultation/to reduce symptoms; Mpa: Comparative terms expected (do not award mp for just stating values). 2 max
Question 1(i)
1(i)
Using the data, predict the effect of universal PCV vaccination in LMICs.
Mediumstructured1 marks
Answer
(worldwide) drastic/huge/important/significant decrease/decrease of 42 million ARI cases (treated with antibiotics); There must be an indication of magnitude of decrease in the answer for the mark to be awarded. Accept 30 to 50 million for the decrease. 1 max
Question 1(j)
1(j)
Outline likely health benefits of universal PCV vaccination of children, other than reducing the incidence of ARI.
Mediumstructured2 marks
Answer
a. less use of antibiotics; b. less antibiotic resistance (in pathogens) / antibiotics more successful at treating infectious/bacterial diseases; c. decrease in health care costs / less money spent on antibiotics; d. decreased mortality / protection of immune-deficient patients/non-vaccinated population/ achieve herd immunity; Since the question already states "other than reducing the incidence of ARI", this reason should not be accepted. 2 max
Question 2
2
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.
structured0 marks
Question 2(c)
2(c)
Suggest one reason for the presence of bacterial colonies despite the use of the antibiotic ampicillin.
Mediumstructured1 marks
Answer
a. bacteria resistant to ampicillin; b. plasmid carrying resistance; 1 max
Question 3
3
The image shows a castor bean tick (Ixodes ricinus) which is commonly found in woodlands or forest areas. This tick can carry bacteria that cause Lyme disease in humans.
structured6 marks
Question 3(b)
3(b)
A vaccine has been developed to protect people against the symptoms of Lyme disease. The graph shows the relative number of antibodies specific to these bacteria in the blood of a person before vaccination. \begin{aligned} & \\ & \text { Relative } \\ & \text { number of } \\ & \text { antibodies } \\ & \text { in blood } \end{aligned}
2 marks
Question 3(b)(i)
3(b)(i)
Suggest what can be concluded from the graph about the person before they were vaccinated.
Mediumstructured1 marks
Answer
a. (person had been) previously infected / have immunity / have memory cells (to the bacterium); b. had been bitten by an (infected) tick before; c. their immunity is diminishing/reducing; 1 max
Question 3(b)(ii)
3(b)(ii)
Sketch a line on the graph to show how the number of antibodies would change over time after vaccination.
MediumPractical1 marks
Answer
line rises (to reach a peak) and (then) line falls; Example sketch: Allow any gradient. Allow peak at any value. Allow any end point after a fall. Do not accept two peaks.