10.1. Infectious diseases
A subsection of Biology, 9700, through 10. Infectious diseases
Listing 10 of 208 questions
Cholera is a life-threatening and infectious disease caused by the bacterium Vibrio cholerae. One of the symptoms of the disease is severe diarrhoea. V. cholerae O1 and V. cholerae O139 are the two forms of the pathogen that are associated with cholera epidemics (large outbreaks). These two forms have different antigens that can be detected. If an outbreak of cholera is suspected but not confirmed, a standard home treatment for diarrhoeal diseases can be used immediately to help prevent severe illness as a result of dehydration. If cholera is the cause of the disease, this standard treatment also helps to prevent a larger outbreak of the disease. Outline the standard treatment that can be used for suspected cholera cases. Suggest and explain why this treatment can help to prevent a larger outbreak of cholera. Rapid diagnostic testing (RDT) can be used to diagnose cholera by detecting the presence of V. cholerae. One type of RDT involves using a dipstick that contains mobile and immobilised monoclonal antibodies. Monoclonal antibodies (mAbs) are specific in their action. shows a simplified diagram of an RDT dipstick that can be used to distinguish between V. cholerae O1 and V. cholerae O139. A faecal sample from a person with suspected cholera is collected and added to a reagent solution to form the test mixture. direction of flow of test mixture area where dipstick can be held 4 control area 3 test area containing immobilised monoclonal antibody that binds antigen-antibody complex O1 2 test area containing immobilised monoclonal antibody that binds antigen-antibody complex O139 1 area containing two different mobile monoclonal antibodies: • anti-O1 antibody • anti-O139 antibody area where dipstick is inserted into the test mixture The test mixture moves up the dipstick through area 1. The mobile monoclonal antibodies are attached to tiny gold particles. If these antibodies collect in test area 2 or 3, a coloured band becomes visible. A coloured band that becomes visible in area 4 confirms that the test strip is working and that the results are valid. Explain how the structure of the monoclonal antibodies in the dipstick allows them to be specific in their action. shows the results for samples taken from two different people, A and B, who are suspected of having cholera. person A person B With reference to , state and explain the conclusions that can be drawn from the results of the RDT dipsticks for each person. Table 2.1 shows the results of an investigation to evaluate the effectiveness of an RDT dipstick in diagnosing cholera. Samples taken from 156 people were tested using a dipstick and compared to the results obtained by culturing the pathogen in a laboratory for accurate identification. Table 2.1 number of test results using culture techniques (to obtain accurate identification) using dipstick correct diagnosis incorrect diagnosis positive results for cholera negative results for cholera With reference to Table 2.1, calculate the percentage chance of an RDT dipstick correctly confirming that a person with cholera has the disease. Using an RDT dipstick to diagnose cholera is much cheaper than culturing the pathogen and requires less technical skill. Suggest one additional advantage of using an RDT dipstick, rather than culture techniques, to diagnose cholera.
9700_s22_qp_22
THEORY
2022
Paper 2, Variant 2
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Use Name the organism that causes tuberculosis (TB). Explain how TB is transmitted from an infected person to an uninfected person. The World Health Organisation (WHO) collects data on TB from its six different regions as shown in Table 5.1. In 2003, it used these figures to estimate • the total number of people with the disease in each region • the number of deaths from TB. Many of those who died from TB were also infected with HIV. Table 5.1 WHO region number of cases per 100 000 population number of deaths from TB (including TB deaths in people infected with Hper 100 000 population Africa The Americas Eastern Mediterranean Europe South-East Asia Western Pacific Explain the advantage of expressing the number of cases and the number of deaths as ‘per 100 000 population’. Examiner’s Use Using the information in Table 5.1, outline the reasons why TB has a greater impact on the health of people in some regions rather than others. The number of cases of TB decreased considerably in many countries during the 20th century. Over the past 20 years, the number of cases worldwide has increased very steeply. A vaccine against TB has existed since 1921. Explain why TB has not been eradicated even though a vaccine has existed since 1921.
9700_w07_qp_2
THEORY
2007
Paper 2, Variant 0
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Questions Discovered
208