Viruses Cause Disease Inside the Body's Cells
Virus
A pathogen, much smaller than a bacterium, that can only reproduce inside a living cell, which it damages or destroys.
- Viruses are pathogens that reproduce inside living cells, damaging and destroying them.
- There is no medicine to cure a viral disease, so preventing its spread is important.
- Measles, HIV and tobacco mosaic virus are three viral diseases to know.
A virus can only reproduce inside a host cell, which is why viral diseases are so hard to treat with medicines.
Measles
Measles
A viral disease that causes fever and a red skin rash and is spread by droplets from coughs and sneezes.
- Measles is a viral disease with symptoms of fever and a red skin rash.
- It is a serious illness that can be fatal if complications arise.
- It is spread by the inhalation of droplets from coughs and sneezes.
- Most young children are vaccinated against measles to prevent it.
- There is no treatment, so an infected person is isolated to stop the virus spreading.
Because most children are vaccinated, measles is now rare in the UK.
HIV and AIDS
HIV
A virus that attacks the body's immune cells and is spread by sexual contact or by the exchange of body fluids such as blood.
- HIV first causes a mild, flu-like illness.
- It then attacks the body's immune cells.
- It is controlled with antiretroviral drugs, which stop it damaging the immune system.
- If it is not controlled, it leads to late-stage HIV infection, called AIDS.
- In AIDS the immune system is so badly damaged that it can no longer fight other infections or cancers.
- HIV is spread by sexual contact or by the exchange of body fluids, such as when drug users share needles.
HIV is not spread by everyday contact; it needs the exchange of body fluids such as blood.
Tobacco Mosaic Virus in Plants
Tobacco mosaic virus
A virus that infects plants such as tomatoes, giving a mosaic pattern of discolouration on the leaves that reduces photosynthesis.
- Tobacco mosaic virus (TMV) is a widespread plant pathogen affecting many species, including tomatoes.
- It gives a distinctive mosaic pattern of discolouration on the leaves.
- The discoloured leaves carry out less photosynthesis, so the plant grows less well.
- It is spread by contact between plants and by insect vectors, and there is no treatment.
- Farmers grow TMV-resistant strains and use good field hygiene to limit its spread.
- Give the two main symptoms of measles.
- How is measles spread, and how is it prevented?
- What does HIV attack, and what is AIDS?
- How is HIV spread?
- What effect does TMV have on a plant, and why does this reduce growth?
