Question 19M.2.HL.TZ1.g
| Date | May 2019 | Marks available | [Maximum mark: 3] | Reference code | 19M.2.HL.TZ1.g |
| Level | HL | Paper | 2 | Time zone | TZ1 |
| Command term | Explain | Question number | g | Adapted from | N/A |
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.
[Source: Adriana Rico, et al. “Epidemiology of Epidemic Ebola Virus Disease in Conakry and Surrounding Prefectures,
Guinea, 2014–2015.” Emerging Infectious Diseases 22.2 (2016): 178–183. PMC. Web. 23 Mar. 2017.
https://wwwnc.cdc.gov/eid/article/22/2/15-1304_article]
The table summarizes epidemiological data from Guinea during the Ebola outbreak in 2014. The data are based on figures supplied by Ebola treatment centres. The last column refers to people who died in places other than Ebola treatment centres.
[Source: Adriana Rico, et al. “Epidemiology of Epidemic Ebola Virus Disease in Conakry and Surrounding Prefectures,
Guinea, 2014–2015.” Emerging Infectious Diseases 22.2 (2016): 178–183. PMC. Web. 23 Mar. 2017.
https://wwwnc.cdc.gov/eid/article/22/2/15-1304_article]
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 a percentage of the control.
[Source: Oestereich, Lisa & Rieger, Toni & Neumann, Melanie & Bernreuther, Christian & Lehmann, Maria & Krasemann,
Susanne & Wurr, Stephanie & Emmerich, Petra & de Lamballerie, Xavier & Ölschläger, Stephan & Günther, Stephan. (2014).
Evaluation of Antiviral Efficacy of Ribavirin, Arbidol, and T-705 (Favipiravir) in a Mouse Model for Crimean-Congo
Hemorrhagic Fever. PLoS neglected tropical diseases. 8. e2804. 10.1371/journal.pntd.0002804.]
In 2015, an experimental vaccine was trialled in Guinea in an area where new Ebola cases continue to develop. Among the nearly 6000 people who accepted the vaccine, no cases were recorded after vaccination. In comparison, there were 23 cases among those who did not accept the vaccine.
Explain how vaccination can lead to the production of B cells specific to the Ebola virus.
[3]
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 ✔
This was a timely question with Ebola epidemics again causing great problems in parts of Africa. Students were expected to have had some practice at analysing data relating to an epidemic because of this Skill in the programme: Analysis of epidemiological data related to vaccination programmes. It was assumed that candidates would understand terms such as ‘case’, ‘fatal case’, ‘infect’ and ‘treat’.
Vaccination is a major focus on 11.1 of the programme so it was perhaps surprising that answers here were not better. Given the current outbreaks of measles and other diseases that can be prevented by vaccination, this topic should be given greater prominence in some schools. There were a few impressive answers giving the details of the steps that lead up to production of antibodies against a specific pathogen, but less than a quarter of candidates scored all three marks. There were many misconceptions. The terms ‘resistant’ and ‘immune’ have different meanings in biology, which should be carefully distinguished. Some candidates think that a vaccine contains a small amount of the pathogen. Would those candidates be happy to be infected with Ebola viruses as long as it was only a few? There was too much talk of cells ‘remembering’ the antigen or the virus. Memory cell is perhaps an unfortunate term. They are only memory cells in the sense that if an antigen binds to the antibodies they display, after cell multiplication more of those antibodies are produced and they will bind to the same antigens on the surface of an invading pathogen. This is just a series of molecular processes, not true memory.
