Edexcel Biology Gcse - Communicable Diseases Part 3

fever and headache

joint and muscle pain

muscle weakness

Patients then develop diarrhoea, vomiting, stomach pain and internal bleeding.

The virus is transmitted in body fluids. It is possible to catch it from a dead person several days after they have died. It is also possible to catch it from the clothes or possessions of a dead person, having sex with an infected person or from unsterilized needles shared with an infected person.

There is currently no licensed treatment for Ebola.

Not all bacteria are pathogens which cause disease. Many bacteria, like those found in the intestines, are useful. All bacteria are prokaryotes, and do not have a nucleus. Unlike viruses, bacteria are cells and so are larger but cannot be seen without a microscope.

diarrhoea

feeling and being sick (vomiting)

stomach cramps

Having diarrhoea and vomiting mean infected people quickly become dehydrated and can go into shock. Large outbreaks of cholera are often found shortly after natural disasters or during armed conflict. Thousands of people currently die each year of cholera.

A vaccine prevents cholera infection. If infected, treatment involves taking oral rehydration solutions to prevent dehydration and shock. The solutions have salts and glucose in them to help replace those lost in diarrhoea and vomiting. Antibiotics are also used.

a bad cough often resulting in coughing up blood

loss of appetite leading to weight loss

high temperature

tiredness and fatigue

Tuberculosis is caused by the bacterium Mycobacterium tuberculosis. Many healthy people have an immune system that is strong enough to kill any infecting bacteria. If patients have other diseases or a weakened immune system they are more likely to catch TB.

The BCG vaccine prevents infection with TB. If infected, antibiotics are prescribed.

Helicobacter pylori is a bacterium which can cause stomach ulcers. It is a common infection and many people who are infected show no symptoms. The bacteria simply live in the stomach lining without causing ulcers. Transmission from an infected person is through saliva.

For some people, infection by H. pylori starts to irritate the lining of the stomach which then stops protecting them from the hydrochloric acid in their stomach. This irritation forms an ulcer. We don't yet know why some people are more likely to develop ulcers.

Some lifestyle factors such as spicy food, stress, excessive alcohol and smoking can increase the risk of stomach ulcers.

Symptoms of stomach ulcers include:

indigestion

heartburn

loss of appetite and weight loss

Antibiotics can be used to treat stomach ulcers shown to be caused by Heliobacter pylori.

Protists are a group of small organisms that have features that belong to animals, plants and fungi. They are a diverse group of organisms. Some are more like animals, others more like plants and some, called moulds, are closest to fungi. They are all eukaryotic, which means they have a nucleus.

Malaria is spread by mosquitos, which carry the Plasmodium protist. These are often found in areas with higher temperatures like Africa, Asia, and South and Central America, but not the UK because of our lower temperatures. Mosquitos suck blood containing the protists from an infected person. They pass the protist, to other people they suck blood from. The mosquitos do not become ill and are called 'vectors' because they transmit the disease.

The symptoms of malaria include a fever, sweats and chills, headaches, vomiting and diarrhoea. Damage is also caused to the blood and liver. Of the 200 million people infected each year, up to half die from this disease. There is no vaccination for malaria. Infection can only be prevented by stopping individuals from being bitten. People sleep under mosquito nets and wear insect repellent to avoid bites. Antimalarial drugs are also taken, which treat the symptoms and can prevent infection.

Not all fungi cause disease. Yeast is a single-celled fungus that is economically important because we use it to make things like bread and beer. Not all fungi are single-celled. Some such as mushrooms are multicellular and so much larger. These are still made of tiny cells like yeast, but have many more of them. Fungal cells have a nucleus and so are eukaryotic.

Athlete's foot is a rash caused by a fungus that is usually found between people's toes. It causes dry, red and flaky or white, wet and cracked skin. It is often found in communal areas like swimming pool changing rooms or gyms. It is transmitted by touching infected skin or surfaces that have been previous contaminated. It is treated by antifungal medication.

A species of fungus called Hymenoscyphus fraxineus infects ash trees. Infected plants suffer the following symptoms:

leaf loss

die back of new shoots

bark lesions.

This species of pathogenic fungus is relatively new to the UK. It was first found in 2012. The fungus spreads through the air, so we call it an airborne infection. Since 2012 it has spread to about one third of all large woodlands in the UK.

Scientists are not yet sure how quickly this fungus will spread of what its full impact will be on our ash population. They are trying to identify the genetic factors that mean that some ash trees are naturally resistant to the fungus.

Method: suitable food hygiene

Example of disease: Salmonella

How it works: Cooking foods thoroughly and preparing them in hygienic conditions kills pathogens.

Method: Suitable personal hygiene

Example of disease: Athlete's foot

How it works: Washing surfaces with disinfectants kills pathogens. Treating existing cases of infection kills pathogens.

Method: Vaccination

Example of disease: Tuberculosis

How it works: Immunisations introduce a small or weakened version of a pathogen into your body, and the immune system learns how to defend itself.

Method: Contraception

Example of disease: HIV/AIDS

How it works: By using barrier contraception like condoms, it stops the transfer of bodily fluids and sexually transmitted diseases.

Method: Sterilising water

| How it works: Chemicals or UV light kill pathogens in unclean water.

Method: Suitable food hygiene

| How it works: Cooking foods thoroughly and preparing them in hygienic conditions kills pathogens.

Method: Suitable personal hygiene

| How it works: Washing surfaces with disinfectants kills pathogens. Treating existing cases of infection kills pathogens.

Method: Vaccination

How it works: Immunisations introduce a small or weakened version of a pathogen into your body, and the immune system learns how to defend itself.

Method: Contraception

How it works: By using barrier contraception like condoms, it stops the transfer of bodily fluids and sexually transmitted diseases.

Sexually transmitted infections (STIs) are passed from one person to another through sexual contact. This includes anal, oral or vaginal sex. There are more than 30 different pathogens that cause STIs. These include bacteria like Chlamydia and viruses like HIV. To reduce the spread of STIs people can abstain from sexual activity or use a barrier-type of contraception like a condom.

Chlamydia is a sexually transmitted infection caused by a bacterium. It is a common infection, especially amongst people under 25. The NHS recommends that people who are under 25 and sexually active have a Chlamydia test every year or if they change partner.

Chlamydia causes a burning pain when urinating and often forms a thick yellow or green discharge from an infected person's penis or vagina. In women it can also cause bleeding between periods and men can develop swollen testicles.

If untreated, infection with Chlamydia can result in infertility. Like other bacterial infections, Chlamydia is treated by antibiotics.

Infect a host

Bacterium

Bacterium