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HIV spreads through exchange of body fluids: sexual contact, sharing needles, or from mother to baby during pregnancy. Free GCSE Biology notes and 14 FAQs.
Common Viral Diseases is part of Communicable diseases in GCSE Edexcel Higher Biology.
4 min
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39
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GCSE Edexcel Higher
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HIV spreads through exchange of body fluids: sexual contact, sharing needles, or from mother to baby during pregnancy. Free GCSE Biology notes and 14 FAQs.
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Use this lesson to stay inside Communicable diseases while connecting the detail back to the wider Topic 5: Health, disease and the development of medicines topic.
Read the core explanations from Common Viral Diseases before testing yourself from memory.
Viruses are microscopic parasites that can't survive on their own. They hijack your cells, turning them into virus factories that pump out thousands of copies. This cellular takeover is what makes you feel ill.
Unlike bacteria, viruses can't be treated with antibiotics. Your immune system has to fight them off, or in some cases, antiviral drugs can slow them down. This is why prevention through vaccination is so crucial for viral diseases.
Measles starts like a bad cold - fever, runny nose, and cough. Then comes the telltale red rash that spreads from the head downwards. What makes measles particularly dangerous is its complications: pneumonia, brain inflammation, and in severe cases, death.
The measles virus spreads through tiny droplets when infected people cough or sneeze. These droplets can hang in the air for hours, making measles one of the most contagious diseases known. One infected person can spread it to 12-18 others in an unvaccinated population.
Trap: Many students think measles is 'just a childhood illness'. Actually, measles can be fatal - this is why the MMR vaccine is given to young children as part of the routine vaccination programme.
HIV is particularly cunning because it targets the very cells designed to protect you - your immune system's helper T cells. Initially, HIV causes flu-like symptoms that many people dismiss. The virus then lies dormant for years, slowly destroying immune cells.
When the immune system becomes severely damaged, the person develops AIDS (Acquired Immune Deficiency Syndrome). At this stage, the body can't fight off infections that healthy people easily overcome, leading to life-threatening complications.
HIV spreads through exchange of body fluids - sexual contact, sharing needles, or from mother to baby during pregnancy. Unlike measles, HIV cannot spread through casual contact, saliva, or airborne droplets.
Modern antiretroviral drugs can control HIV effectively, allowing people to live normal lifespans. These drugs stop the virus reproducing, giving the immune system a chance to recover.
TMV doesn't infect humans, but it's devastating for plants. The virus creates a distinctive 'mosaic' pattern of light and dark green patches on leaves. These discoloured areas can't photosynthesise properly, so the plant struggles to make glucose for growth.
TMV affects many crop plants including tomatoes, peppers, and tobacco. Infected plants show stunted growth, reduced fruit production, and may die if the infection is severe. This makes TMV a serious agricultural problem worldwide.
The virus spreads through direct contact - contaminated tools, hands, or insects can transfer the virus between plants. Unlike animal viruses, TMV is extremely stable and can survive on surfaces for months.
Understanding how viruses spread is crucial for prevention. Each virus has evolved different transmission strategies that affect how we control them.
Worked example: Analysing Viral Transmission Routes
Compare the transmission methods of measles, HIV, and TMV. Explain why each method suits the virus's survival strategy.
Answer: Each virus has evolved transmission methods that suit its biology: measles spreads rapidly through air, HIV persists long-term through intimate contact, and TMV survives on surfaces to infect plants through wounds.
Viral disease questions often test your understanding of symptoms, transmission, and prevention. Here's how to tackle them systematically.
Common exam mistake: Students often confuse HIV with AIDS. HIV is the virus; AIDS is the late-stage condition when the immune system is severely damaged. You can have HIV without having AIDS if it's controlled with drugs.
For 6-mark questions about viral diseases, structure your answer around: symptoms → transmission → effects on the body → prevention/treatment. This logical flow shows the examiner you understand the complete disease process.
Published by Revise Right. Use the official specification reference to check the requirements for your course. Content updated: 2026-03-23.
Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
HIV spreads through exchange of body fluids: sexual contact, sharing needles, or from mother to baby during pregnancy. Unlike measles, HIV cannot spread through casual contact, saliva or airborne droplets, and antiretroviral drugs can control it effectively.
The MMR vaccine protects against measles and is given to young children as part of the routine vaccination programme. Vaccination and isolation are the main ways of preventing measles spreading.
AIDS stands for Acquired Immune Deficiency Syndrome. It is the late-stage condition when HIV has severely damaged the immune system, so the body cannot fight off infections that healthy people easily overcome.
HIV is the virus, while AIDS is the late-stage condition when the immune system is severely damaged. HIV attacks and destroys the body's immune cells, and if untreated it leads to AIDS, when the body cannot fight off infections; people can have HIV without AIDS if it is controlled with drugs.
Tobacco mosaic virus (TMV) is a plant virus that causes distinctive mosaic patterns of discolouration on leaves, reducing photosynthesis and stunting plant growth. It affects crops including tomatoes, peppers and tobacco, and spreads through direct contact such as contaminated tools, hands or insects.
The complications of measles include pneumonia, brain inflammation and, in severe cases, death. Measles is not just a childhood illness, which is why the MMR vaccine is given to young children.
Tobacco mosaic virus spreads through direct contact: contaminated tools, hands or insects can transfer the virus between plants. TMV is extremely stable and can survive on surfaces for months.
Measles is a highly contagious viral disease causing fever and a distinctive red skin rash that spreads from the head downwards. It spreads through airborne droplets from coughs and sneezes, and one infected person can spread it to 12-18 others in an unvaccinated population.
Antibiotics cannot treat viral diseases because viruses are not bacteria: they are microscopic parasites that hijack cells, turning them into virus factories. The immune system has to fight them off, antiviral drugs can slow some down, and vaccination is crucial for prevention.
Measles is one of the most contagious diseases known: one infected person can spread it to 12-18 others in an unvaccinated population. Its droplets from coughs and sneezes can hang in the air for hours.
HIV damages the immune system by attacking helper T cells, the very cells designed to protect the body. After flu-like symptoms, the virus lies dormant for years, slowly destroying immune cells until AIDS develops.
HIV is treated with antiretroviral drugs, which stop the virus reproducing and give the immune system a chance to recover. These drugs can control HIV effectively, allowing people to live normal lifespans.
HIV cannot spread through casual contact, saliva or airborne droplets. It spreads through exchange of body fluids: sexual contact, sharing needles, or from mother to baby during pregnancy.
Tobacco mosaic virus causes a mosaic pattern of light and dark green patches on leaves, and these discoloured areas cannot photosynthesise properly. The plant struggles to make glucose for growth, so it shows stunted growth and reduced fruit production.