Common Infections

Common Infections

Infections caused by bacteria

• Myobacterium 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

Exam Tip

Know the symptoms and how the pathogen causing each disease is spread. Typically, this topic appears as data analysis questions in the exam where you may be given a graph to analyse and interpret.