A-LevelBiologyInfectious diseases9700/23 · May/June 2017 · Q39 Marks

Name the causative organism of tuberculosis (TB).

(a)Name the causative organism of tuberculosis (TB).[1]
(b)Fig. 3.1 shows the number of deaths from TB and the number of new cases of TB from 1925 to 2010 in Canada. [Figure 3.1] The vaccine for TB was introduced in Canada for widespread use from 1948. Antibiotics, such as streptomycin, were introduced in Canada from 1940. Use the information in Fig. 3.1 to comment on the effect of the introduction of the vaccine and antibiotics on the number of new cases and deaths from TB.[5]
(c)In 2010, Swaziland had one of the highest death rates from TB in the world. Swaziland also had a high number of new cases of HIV infection in its population in 2010. People who are infected with HIV are described as HIV+ and people who are not infected with HIV are described as HIV-. Table 3.1 shows the number of deaths from TB in Swaziland in 2010. [Table 3.1] Using the information in Table 3.1, suggest why the number of deaths per 100000 population of people who are HIV+ is much higher than that in people who are HIV-.[3]

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Mark scheme

Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.

[1] Mycobacterium tuberculosis I Mycobacterium bovis ; correct spelling
[max 5] 1 deaths decrease to zero / new cases fall to 4 per 100 000, (in 2010); A other values that confirm decrease (after introduction of antibiotics) 2 deaths relatively constant / approx. 52 per 100 000, until 1943–6 (accept any in range) ; A for a few years A idea that rate of decrease not improved 3 number of new cases initially stops increasing / plateaus ; 4 (overall) number of new cases increases before decreases ; 5 data to support mp 3 or 4; e.g. 88–90 per 100 000 (1940–44) rises to / drops from, 104 per 100 000 in 1946; (after introduction of vaccination) 6 no change in trend of decrease in deaths / deaths continue to decrease ; 7 decrease from 36–40 per 100 000 (in 1948); 8 short plateau / 100 per 100 000 (until 1950), in new cases, then decreases ; 9 antibiotics may not have been in widespread use at first; ora 10 vaccine, reduces spread / gives (herd) immunity; 11 ref. to decrease less steep initially as time needed to build up herd immunity ; 12 AVP; e.g. suggestion why increase in new cases after introduction of antibiotics suggestion why cases have not decreased to zero not possible to tell relative effect of vaccine v antibiotic
[max 3] some people who are HIV+ will have developed HIV / AIDS ; HIV/AIDS weakens immune, system / response ; ora allow ecf for HIV+ people detail of why immune response weakened ; people with HIV/AIDS, prone to opportunistic diseases ; A TB is an opportunistic disease A more susceptible to, diseases / TB (Table 3.1 shows that) a greater proportion / AW, people die of TB if they are HIV+ ; AW e.g. greater chance of dying from TB if HIV+ dormant TB more likely to become the active form in, HIV+ people / people with HIV/AIDS; AW AVP; a high proportion of deaths from HIV / AIDs is due to TB mortality HIV+ people do not respond well to treatment for life-threatening diseases inability to pay for treatment for all conditions for HIV+ people