Immunisation

Mothers infected with the human immunodeficiency virus (HIV) are usually discouraged from breastfeeding as the virus can be transmitted from mother to baby during breastfeeding.

Apart from breastfeeding, suggest and explain one other way in which HIV can be transmitted from an HIV-positive mother to their baby.

The role of breastfeeding in providing temporary immunity against other diseases is recognised as being extremely beneficial to newborn babies.

In 2010, the World Health Organisation (WHO) issued guidelines recommending the breastfeeding of babies born to HIV-positive mothers for at least one year, using antiretroviral therapy (ART) to minimise the risk of transmission.

Name the type of immunity acquired by breastfeeding.

ART involves taking a combination of medicines every day. These medicines often include an inhibitor of the enzyme reverse transcriptase.

Explain how this inhibitor can minimise the risk of HIV transmission.

HIV testing can be used to determine the presence of HIV.

The graph shows the results for an HIV-exposed baby who is born without HIV infection and remains uninfected throughout breastfeeding.

Outline a method used to test for HIV infection.

Calculate the mean rate of decrease in HIV antibody concentration, per day, for the first year after being exposed to HIV.

Give your answer to 2 significant figures.

Mean rate =........ a.u. per day

Sketch a line on the graph to suggest the expected HIV antibody concentration for an HIV-exposed baby who is not infected with HIV at birth but was infected during breastfeeding at 10 months of age.

Research shows that HIV testing cannot be used to definitively diagnose infection in young babies and that babies under 18 months of age may record a false-positive test for HIV infection.

Explain why a false-positive test may be recorded in babies under 18 months of age.

* Developing a vaccine that can prevent HIV infection in uninfected people is the highest HIV research priority given its potential for controlling and ultimately ending the HIV/AIDS pandemic.

Discuss the biological and ethical issues associated with the development and use of vaccines for preventing diseases such as those caused by HIV infection.

Extra answer space if required.

Diphtheria is a bacterial disease of humans that can be treated by vaccination using an antitoxin. The antitoxin is a solution of antibodies specific to the antigens on the surface of the bacterium.

Which of the options, A to D, describes the type of immunity provided by the antitoxin?

A artificial active

B artificial passive

C natural passive

D natural active

This question is based on the Advance Notice article ‘Do Pathogens Gain Virulence as Hosts Become More Resistant?’ on the Insert.

The myxoma virus (MYXV) is a pathogen that causes myxomatosis in its hosts.

Describe how a virus replicates.

Explain why myxomatosis could not be described as endemic in Australia before 1950.

Explain why the myxomatosis outbreak in the 1950s could be described as an epidemic.

HIV is a retrovirus but MYXV is not.

Use this information and your knowledge to complete the following table by placing a tick (if the feature is found in HIV or MYXV.

The graph shows how the virulence of MYXV changed over the period from 1950 to 1990.

Describe how the virulence of MYXV strains varied during the period 1950 to 1990.

The article describes the interactions between pathogen virulence and host resistance to infection.

Explain how immunological and genetic factors would allow a population of wild rabbits to become more resistant to infection by MYXV.

The article discusses how resistance to infection can be affected by two common agricultural practices: vaccination and selective breeding.

Explain how vaccination is used to protect poultry against pathogens such as Marek’s disease virus (MDV).

Explain why vaccination might not prevent epidemics of Marek’s disease in poultry.

Evaluate the suggestion that birds should be bred for susceptibility to MDV rather than resistance.

Immunity can be categorised as

• active or passive

• natural or artificial.

Complete the following table by putting ticks (✓) in the correct boxes to show whether each example is active or passive and natural or artificial.

Scientists investigated the link between breastfeeding in mice and the risk of offspring developing asthma.

They used a model system of asthma called allergic airway disease (AAD).

Two groups of mice were compared:

• Group I: mice who were born to normal mothers (no AAD) and then breastfed by their own mothers.

• Group II: mice who were born to normal mothers but then breastfed by foster mothers with AAD.

After 4 weeks the offspring were exposed to a protein to induce AAD.

The concentration of IgE in the blood of the offspring was determined. IgE is a type of antibody that increases in concentration during allergic reactions. The results are shown in the graph.

Name a statistical test the scientists could have used to compare the results of the two groups. Give a reason for your choice.

State which group of offspring showed more AAD. Give a reason for your choice.

The statistical analysis showed there was a significant difference in the concentrations of IgE antibodies in the two groups.

Breastfeeding is associated with a reduced risk of asthma in children.

Explain whether the results support the conclusion that breastfeeding could reduce the risk of asthma in children.

Scientists are producing a vaccine against a disease-causing bacterium.

The table below shows the locations and mutation rates of four proteins, A to D, in the bacterium.

Which of the proteins, A to D, is most suitable as the basis of a vaccine against this bacterium?

The MenB vaccine was developed to protect against disease caused by the bacterium Neisseria meningitidis. Infection with this bacterium (meningococcal infection) is a major cause of meningitis and blood poisoning, particularly in babies and young children.

The MenB vaccine was introduced into the routine UK vaccination schedule on 1st September 2015. It is available to all new babies born on or after 1st July 2015.

The MenB vaccine is a subunit vaccine.

Explain what is meant by a subunit vaccine.

Parents have been reassured that the MenB vaccine cannot cause meningitis in their children.

Explain why the MenB vaccine cannot cause the disease.

The MenB vaccine has also been shown to be effective against other types of meningococcal infection.

Suggest why.

* Evaluate the importance of herd immunity in the prevention of epidemics.