Immunisation

The diagram shows how human blood develops from blood stem cells.

Describe how stem cells are different from most body cells.

Describe the role of platelets in the body.

Explain how vaccination protects the body from disease.

Blood stem cells can be used to treat blood disorders such as sickle cell anaemia which affects red blood cells and leukaemia which affects white blood cells. Explain why blood stem cells can be used to treat a variety of blood disorders.

Rabies is a dangerous disease caused by a virus.

The rabies virus is a pathogen.

Which other groups of microorganisms include pathogens?

Rabies is transmitted to humans when they are bitten by an infected animal. Domestic dogs are dogs kept by people as pets or as working animals. Dogs and some wild animals are known to transfer rabies to humans.

In the 1940s, a rabies vaccine for animals was introduced in the United States and most domestic dogs were vaccinated.

The graph shows the number of cases of human rabies and domestic dog rabies in the United States from 1938 to 2018.

Number of domestic
Number of dog cases
human cases

The immune system of dogs works in a similar way to the immune system of humans.

Explain how the rabies vaccine prevents dogs from developing rabies.

Discuss the effects of the use of the rabies vaccine to immunise domestic dogs on the number of cases of rabies in humans.

Use information from the graph to support your answer.

A new RNA vaccine is being developed to treat rabies.

RNA that codes for parts of the rabies virus protein coat are injected into the body. Cells then take up the RNA and produce the viral proteins.

Describe how the cells use the RNA to produce the viral proteins.

Measles is a disease caused by a virus. The graph shows the number of cases of measles each year and the percentage of five year‑olds vaccinated between 1950 and 2016 in the United Kingdom.

percentage of five year-olds vaccinated

Determine the difference in the percentage change in the number of cases of measles between 1950 and 1965 and the percentage change in the number of cases of measles between 1968 and 1983.

Explain the relationship between the number of cases of measles and the percentage of five year‑olds vaccinated.

Use information from the graph in your answer.

Some children are receiving treatments that reduce the activity of their immune system.

Explain why vaccinations are not used on these children.

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow. Schistosomiasis Schistosomiasis is an infection caused by a parasitic worm called a schistosome. The immature or larvae of the worm live in rivers and lakes in tropical parts of the world. The diagram shows the life cycle of the schistosome worm.

_{Larvae releasedinto waterfreshwaterHatch in}

Some people in tropical parts of the world use water from these rivers and lakes for their daily lives. These people risk infection because the larvae burrow into their skin. The larvae are then transported to other parts of the body where they damage organs such as the kidneys, intestines, lungs and brain. The larvae develop into adult worms. The adult worms lay eggs in the human body. Some of these eggs are destroyed by the immune system, but most eggs survive. These eggs can get into water if faeces or urine from infected people pass into rivers or lakes. In the water, the eggs develop into small larvae which grow inside freshwater snails. Larvae are released from the snails and infect any person they contact. These larvae develop into adult worms inside the human body. Doctors diagnose schistosomiasis when they find eggs in the faeces or urine of infected people. Infected people also have blood cells in their urine and antibodies for the pathogen in their blood. At present, the drug praziquantel is used to kill the worms. A dose of 0.040 g per kg of body mass is usually effective. With no treatment, affected organs can be permanently damaged, leading to death. It is estimated that 240 million people (in the world) have schistosomiasis. Every year 8 × 10^–4 per cent of infected people die from the disease. A vaccine is being developed using a plasmid. The plasmid has DNA inserted that makes a protein found on the body surface of the adult schistosome worm. In one investigation, a vaccine made using the DNA plasmid was given to a group of infected people. The results showed a mean number of 21.53 worms per person in this group. In the control group, a mean number of 40.53 worms per person was found.

Which process is affected if kidneys are damaged (line 8)?

Suggest three ways to reduce the risk of being infected by schistosomes.

Name two different blood cells that would be found in the urine of infected people (line 17).

An infected person has a body mass of 120 kg. What dose of drugs would be effective for this person (lines 19 to 20)?

Using the estimated number of people in the world who have schistosomiasis (lines 21 to 22), calculate the number of people who die each year from schistosomiasis.

Which of these is the correct description of a plasmid?

Explain how a vaccine could protect people from schistosomiasis (lines 24 to 25).

Suggest what is given to the control group (lines 27 to 29).

A scientist claims that the investigation proves the vaccine is effective against schistosomiasis (lines 27 to 29). Comment on this claim.

Human populations are at risk from infectious disease.

Describe the different types of pathogen. Refer to a disease that each type of pathogen causes in your answer.

Explain how vaccination protects humans from pathogens.

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow.

Badgers and bovine tuberculosis

The bacterium Mycobacterium bovis causes the lung disease bovine tuberculosis (TB) in cattle. Infected cattle have damaged lungs, which causes gas exchange problems and makes them cough into the air. The pathogen spreads to humans if they inhale air containing the bacterium. Humans also become infected if they drink unpasteurised milk from infected cattle. Milk is usually pasteurised by heating it for a period of time at a high temperature.

Bovine TB can kill humans. In one year, 13 400 people died from a total of 149 000 reported cases of TB. Some of these cases were from Europe, where 103 people died from 1290 reported cases. The rest of the cases were from outside Europe.

Some farmers in the United Kingdom are concerned that badgers spread the TB pathogen to cattle.

The photograph shows a badger.

Badgers act as a reservoir for the TB pathogen and can live for several years without showing any signs of TB. Some farmers want badgers to be culled (killed) to stop the spread of bovine TB to cattle.

However, some scientists claim that only a fraction of cattle catch TB from badgers, and that culling badgers could spread the disease to new areas. This is because badger culling changes the behaviour of the badgers that survive. Normally, badgers live in social groups and will defend their territory from other badgers by being aggressive. This territorial behaviour reduces the spread of disease between groups. If badgers are culled, then their territories cannot be defended. Surviving badgers could move in to occupy the undefended territory, bringing TB with them. This could spread TB to new animals and new areas.

Some people believe that badgers should be vaccinated to stop the spread of TB. However, there is some concern that vaccination may increase the spread of TB because it might also change badger behaviour.

An investigation is needed to find out if badger vaccination can reduce TB both in badgers and in cattle.

Explain why cattle with damaged lungs have gas exchange problems (lines 2 to 3).

Explain the advantage of drinking pasteurised milk rather than unpasteurised milk (lines 4 to 5).

Suggest two reasons why there were fewer cases of bovine TB in Europe compared with outside Europe (lines 7 to 9).

The case to death ratio in Europe is 12.5: 1 (lines 7 to 9).

Calculate the case to death ratio from outside Europe.

Territorial behaviour reduces the spread of disease between badger groups (lines 19 to 20).

Suggest two other ways that badgers benefit from territorial behaviour.

Explain how vaccination reduces the risk of infection in badgers (line 24).

Describe how scientists could find out if badger vaccination reduces TB in cattle (lines 27 to 28).