Common Infections (Edexcel GCSE Biology)

Common Infections

Infections caused by bacteria

• Mycobacterium tuberculosis causes tuberculosis (TB) in humans

  • The bacteria infect the lungs, causing a chronic cough and bloody mucus

  • It is a disease often associated with poor hygiene and sanitation

  • M. bovine in cows can also transmit to humans to cause TB

• Vibrio cholerae causes Cholera

  • Bacteria infect the intestines causing diarrhoea, vomiting and leg cramps

  • Cholera can lead to death if not treated quickly

  • It is a disease often associated with poor hygiene and sanitation

• Helicobacter pylori causes stomach ulcers

  • Infection of the stomach commonly occurring during childhood

  • H. pylori infection often gives no symptoms, but can lead to leads to pains in the abdomen, loss of appetite, bloating and nausea

• Chlamydia trachomatis causes chlamydia

  • This is a sexually transmitted infection

  • There may be no symptoms in some patients, others may have pain when they urinate, unusual discharge or bleeding after sex

  • Chlamydia can cause infertility if left untreated

Infections caused by fungi

• Chalara Ash Dieback

  • This fungal infection originated in Asia and affects ash trees of all ages with devastating effects

  • It causes dark patches on the leaves, early leaf loss and bark lesions

  • Spores travel large distances in the wind

Infections caused by protists

• Plasmodium falciparum is a protist that causes severe forms of malaria in humans

  • The parasite is spread by mosquitoes

  • It cases damage to the blood and the liver

  • Infected individuals experience fever, chills and fatigue

  • Malaria can progress with more serious symptoms eventually leading to death

Infections caused by viruses

• Ebola Virus infects and kills body cells

  • Symptoms are flu-like initially

    • This includes headaches, high temperature, joint and muscle pains

  • Serious cases will also show diarrhoea, sickness, rashes and may lead to haemorrhagic fever (fever and internal bleeding)

• Human Immunodeficiency Virus (HIV) destroys white blood cells in the immune system

  • Initial symptoms are flu-like

    • This includes headaches, high temperature, joint and muscle pains

  • If untreated, the virus compromises the immune system leading to the onset of Acquired Immune Deficiency Syndrome (AIDS)

    • AIDS is used to refer to several life-threatening illnesses which may result from having a compromised immune system

More about HIV

• The virus infects a certain type of lymphocyte of the body's immune system

• Normally lymphocytes seek out and destroy pathogens that enter the body, producing antibodies that attach to pathogens, enhancing phagocytic activity

• However, HIV avoids being recognised and destroyed by lymphocytes by repeatedly changing its protein coat

• It then infects a certain type of lymphocyte and uses the cells’ machinery to multiply

• This reduces the number of lymphocytes of the immune system, and also the number of antibodies that can be made

• This decreases the body’s ability to fight off infections, eventually leading to AIDS (Acquired immunodeficiency)

How HIV affects lymphocytes

The Spread of Common Infections

• Diseases that are caused by pathogens that pass from one host to another are described as transmissible diseases

• Transmission can occur through several different mechanisms:

• Airborne - droplets travelling in the air (maybe as a result of wind or sneezing/coughing) lead to infection

  • e.g. Colds, influenza, tuberculosis, Chalara ash dieback

  • These types of infection in animals can be prevented by:

    • Avoiding crowded areas

    • Good hygiene generally

    • Ventilation of homes or workspaces

  • These types of infection in plants can be prevented by:

    • Preventing imports of trees from countries known to carry the disease

    • Cutting down infected trees as soon as possible and replacing with an alternative species which is unaffected

• Waterborne - pathogens that live in dirty water are transmitted to organisms that come into contact with it

  • e.g. Cholera

  • This can be prevented by avoiding poor quality water and making sure that people have access to clean water

• Oral transmission - pathogens are ingested and transmitted to the host

  • e.g. Stomach ulcers

  • This can be prevented by having access to clean water and good hygiene standards

• Body fluids and sexual transmission - Exchange of saliva, blood or semen can carry pathogens from one host to another

  • e.g. HIV, Chlamydia, Ebola

  • Generally, body fluid transmission is prevented by:

    • Isolating infected individuals

    • Cleaning and sterilising contaminated areas

  • Sexual transmission of chlamydia and HIV can be reduced by:

    • Wearing condoms

    • Screening to detect cases and particularly after unprotected sex

    • Medications

    • Drug users with HIV should also avoid sharing needles

    • Limiting the number of sexual partners

    • Raising awareness by education programmes

• Animal vectors - Animals carry pathogens between hosts

  • e.g. Malaria

  • Animal vectors can be prevented by

    • Using insect repellent

    • Mosquito nets

    • Preventing the vector from reproducing

Transmission of Common Infections Table