pathogens and communicable diseases

• Disease 


  a condition that impairs the normal functioning of an organism. Both plants and animals can get diseases.
• pathogen

  an organism that causes disease. Types of pathogen include bacteria, viruses, fungi and protoctists (a type of single-celled eukaryotic organism).
• communicable disease 


  a disease that can spread between organisms.
• tuberculosis:

  • affects animals typically humans and cattle
  • pathogen responsible- bacterium called mycobacterium tuberculosis and M.boris
  • transmitted through air- coughing, sneezing, laughing and talking
  • damages and destroys young tissue
  • suppresses immune system so the body is less able to fight off disease
  • treated by antibiotics
  • prevented by improving living standards and getting vaccinated
• bacterial meningitis:

  • affects very young children and teenagers
  • pathogen responsible- bacterium called streptococcus pneumoniae or Neisseria meningitidis
  • transmitted through sneezing, coughing, kissing
  • can be spread by people who carry this bacteria in their nose or throat but not ill
  • it infects the membranes which surround the brain called the meninges which can then spread to the rest of the body and cause septicaemia and rapid death
  • treated by antibiotics
  • vaccines can protect against some forms of bacterial meningitis
• ring rot

  • affects potatoes and tomatoes
  • pathogen responsible- bacterium called claribacter michiganensis
  • vascular infection in daughter tubes divide from infection seeds
  • it affects potatoes infecting leaves, tubers and fruit
  • no cure
• HIV/AIDS


  Affects humans
• Pathogen responsible


  Virus called human immunodeficiency virus (Lentivirus)
• Transmission of HIV/AIDS


  1. Unprotected sex

  2. Shared needles

  3. Contaminated blood products

  4. Mother to baby during pregnancy or breastfeeding
• HIV/AIDS


  • The virus attacks the T helper cells needed to set up an immune response to infections
  • These cells get destroyed so people are open to more infections e.g TB, pneumonia and some types of cancer
• Anti-retroviral drugs


  Slow the progress of the HIV/AIDS infection
• influenza:

  • affects animals including humans
  • pathogen responsible: virus called orthomyxovirus
  • transmitted through tiny droplets made when people cough sneeze or talk
  • infects the ciliated epithelial cells and kills them
  • three strains A, B and C
  • can be fatal to young children, elderly and people who suffer from chronic illness
  • no cure but can be prevented by vaccine if the flu hasn't mutated
• tobacco mosaic virus

  • affects plants
  • pathogen responsible- virus tobamovirus
  • infected leaves rubbing against healthy plants, or contaminated tools or workers hands
  • damages leaves and fruit
  • leaves have a mosaic appearance
  • no cure
  • some resistant crops
• black Sigatoka

  • affects banana plants
  • pathogen responsible- fungus called mycosphaerella figiensis
  • spread through rain splashes, wind born and spores
  • fungus that attacks and destroys the leaves
  • hyphae penetrate and digest cells
  • no cure but use of fungicides and strict monitoring of plants help prevent transmission
  • resistant strains of plant being developed
• ringworm

  • affects cattle
  • pathogen responsible- fungus called trichophyton
  • transmitted by by contact with objects or surfaces that an infected person or animal has recently touched or rubbed against
  • creates grey white crusty areas on skin
  • treated by anti fungal cream
• athletes foot

  • affects humans
  • pathogen responsible- fungus called Tina pedia
  • transmitted by areas of damp fungus
  • form of human ring worm that grows on and digests the warm moist skin between the toes
  • causes cracking and scaling which is itchy between the toes and may become sore
  • treated by anti fungal creams
• potato/tomato blight

  • pathogen responsible- protoctist called phytophthora
  • transmitted by pores on infected plant materials
  • hyphae penetrates host cells destroying tubers and fruit
  • no cure
  • some resistant crops
  • careful management and chemical treatment reduces transmission
• malaria

  • affects animals including humans
  • pathogen responsible- protist called plasomdium
  • transmitted by mosquitos
  • reduces in the gut of anopheles mosquitoes and in the red blood cells of humans
  • prevented by mosquito nets and long sleeved clothing
• Direct transmission 


  when a disease is transmitted directly from one organism to another.
• Direct transmission can happen in several ways, including: droplet infection (coughing or sneezing tiny droplets of mucus or saliva directly onto someone), sexual intercourse, or touching an infected organism.
• Indirect transmission 


  when a disease is transmitted from one organism to another via an intermediate.
• Intermediates include air, water, food or another organism (known as a vector).
• Overcrowded living conditions increase the transmission of many communicable diseases. e.g Tuberculosis (TB) is spread directly via droplet infection. It's also spread indirectly because the bacteria can remain in the air for long periods of time and infect new people. The risk of TB infection is increased when lots of people live crowded together in a small space.
• In humans, social factors (such as income, occupation and the area where a person lives) can also increase the transmission of communicable diseases.

  e.g the risk of HIV infection is high in places where there's limited access to:

  • good healthcare - people are less likely to be diagnosed and treated for HIV, and the most effective anti-HIV drugs are less likely to be available, so the virus is more likely to be passed on to others.
  • good health education - to inform people about how HIV is transmitted and how it can be avoided, e.g. through safe-sex practices like using condoms.
• Climate can also affect the spread of communicable diseases.

  e.g

  • Potato/tomato late blight is especially common during wet summers because the spores need water to spread.
  • Malaria is most common in tropical countries, which are humid and hot. This is because these are the ideal conditions for mosquitoes (the malaria vectors) to breed.