Pathogens and communicable disease – GCSE Combined Science Biology

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A pathogen is a tiny living thing that causes disease. When it spreads from one host to another, the disease is called communicable. A host is the organism it lives in.

This matters because these diseases make people and plants ill. Knowing how a pathogen spreads tells you how to stop it. That is how doctors, farmers and gardeners keep us safe.

By the end you will be able to name the four types of pathogen. You will say how each spreads and how to reduce the spread. You will also know six named diseases.

Four types of pathogen

There are four types of pathogen. Bacteria are tiny single cells. They reproduce quickly inside the body and make toxins, which are poisons that damage tissues.

Viruses are much smaller than bacteria. They live and reproduce inside your own cells and damage them. Fungi can grow on or in the body. Protists are single-celled organisms, and many are carried by a vector.

Not all microorganisms are harmful. Many bacteria in your gut are helpful. Only the pathogens cause disease.

How pathogens spread

Some pathogens spread through the air. When you cough or sneeze, tiny droplets carry them out. Another person breathes them in.

Pathogens also spread by direct contact, by dirty water and by food that is not cooked properly. Some spread through body fluids such as blood.

A vector is an animal that carries a pathogen from one host to another. A mosquito is the vector for malaria. The vector is not the pathogen. Think of a delivery van that carries a parcel but is not the parcel.

Viral diseases

Measles is caused by a virus. It causes a fever and a red skin rash. It spreads in droplets from coughs and sneezes. It can be serious, so most children are vaccinated.

HIV is a virus that spreads by sexual contact or by body fluids, such as blood on shared needles. It attacks the immune system. If it is not treated it can lead to AIDS. Antiretroviral drugs control the virus.

Tobacco mosaic virus infects plants. It makes patches on the leaves, so less photosynthesis happens and the plant grows poorly.

Bacterial diseases

Salmonella is a bacterium. It causes fever, stomach cramps, vomiting and diarrhoea. It spreads through food that was not cooked properly or was handled with dirty hands.

Gonorrhoea is a bacterial infection that spreads by sexual contact. It causes pain when urinating and a thick yellow or green discharge. Antibiotics can treat it, but some strains are now resistant. A condom helps to prevent it.

Remember, antibiotics kill bacteria. They do not kill viruses.

Cholera is a bacterial disease that causes severe diarrhoea and dehydration. It spreads in water or food that has been contaminated with the faeces of an infected person. Clean drinking water, good sewage treatment and rehydration treatment reduce its spread and its harm.

Tuberculosis (TB) is a bacterial disease of the lungs. It spreads in droplets when an infected person coughs. It damages lung tissue and causes coughing and weight loss. It is reduced by vaccination, good ventilation, isolating people who are infected and treating them with antibiotics.

Fungal and protist diseases

Rose black spot is caused by a fungus. It makes purple or black spots on rose leaves. The leaves turn yellow and fall off, so there is less photosynthesis.

It spreads by water and wind. Gardeners use fungicides, which are chemicals that kill fungi. They also strip off infected leaves and burn them.

Malaria is caused by a protist. A mosquito is the vector. It causes a recurring fever and can be fatal.

Stopping the spread

Match the control to the way the disease spreads. Good hygiene, such as washing hands and cooking food well, stops spread by food and contact.

To stop malaria, control the vector. Drain standing water and use insecticides and mosquito nets. Isolating ill people stops them passing on a disease. Vaccination protects people before they meet the pathogen.

A condom reduces the spread of infections such as HIV and gonorrhoea. Plants can be protected too. Remove infected plants and use fungicides.

Recap

The four types of pathogen are bacteria, viruses, fungi and protists.

They spread by air, contact, water, food and vectors.

Measles and HIV are viruses. Salmonella and gonorrhoea are bacteria. Rose black spot is a fungus. Malaria is caused by a protist.

Control the spread by hygiene, controlling vectors, isolation, vaccination and condoms.