What are pathogens?
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Pathogens are microorganisms including viruses, bacteria, protists and fungi that cause infectious disease.
Viruses:
- Very small
- Move into cells and make many copies of itself
- This leads to the cell bursting and releasing all of the copies into the bloodstream
- The damage and destruction of the cell makes the individual feel ill
Bacteria:
- Small
- Multiply very quickly through binary fission (a dividing process)
- Produce toxins- damage cells
Protisits:
- Some are parasitic - use humans and animals as their hosts (live on and inside, causing damage)
Fungi:
- Can either be single celled or have hyphae (thread-like structures)
- Produce spores- can spread to other organisms
What are the ways pathogens can be spread?
- Direct contact- touching contaminated surfaces
- By water
- By air- pathogens can be carried in the air, the breathed in (droplet infection)
How can the damage the disease causes be reduced?
By limiting the spread of pathogens:
* Improving hygiene
* Reducing contact with infected individuals (isolation)
* Removing vectors- the organisms that spread the disease (using pesticides)
* Vaccination (allows fpor immunity against pathogen)
Viral diseases- measles:
- Symptoms- fever, red skin rash, can lead to pneumonia and blindness
- How it’s spread- droplet infection
- How it’s prevented- vaccination for children to reduce transmission
HIV:
- Symptoms- intially flu-like symptoms, but virus attacks the immune system and leads to AIDS
- How it’s spread- by sexual contact
How it’s prevented:
* The spread- using condoms, not sharing needles
* The development to AIDS- use of antiretroviral drugs (stop the virus replicating in the body)
Viral diseases- tobacco mosaic virus:
- Symptoms- discolouration of leaves, affected part of leaf cannot photosynthesise (less chloroplpats)
- How it’s spread- contact between diseased plants and healthy plants, insects as vectors
How it’s prevented- pest control (pesticides), TMV-resistant strains
Bacterial diseases- salmonella:
- Symptoms- fever, stomach cramps, vomitting and diarrhoea (caused by the toxins they excrete)
- How it’ spread- raw meat and eggs, unhygeinic conditions
- How it’s prevented- poultry are vaccinated against salmonella, avoid washing meat and cook thoroughly
Batcterial ddiseases- gonorrhea:
- Symptoms- thick yellow orgreen discharge from the vagina or penis, pain when urinating
- How it’s sread- sexually transmitted disease spread through unprotected sexual contact
- How it’s prevented- using contraception (e.g. condoms) and antibiotics (but many resistant strains are developing)
Fungal diseases- rose black spot:
- Symptoms- purple or black spots on leaves of rose plants, leaves turn yellow and drop early
- How it’s spread- the spores of the fungus are spread in water (rain) by wind
- How it’s prevented- by using fungicides or burning the plant of affected leaves
Protist diseases- malaria:
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Caused by protist pathogens that enter the red blood cells and damage them
* Symptoms- fevers and shaking
* How it’s spread- the vector is the female Anopheles mosquito, in which the protist reproduce sexually. When the mosquito punctuures the skin to feed on blood, the protist enters the bloodtream via saliva
* How it’s prevented- using insecticide coated insect nets while sleeping, travellers taking anti-malarial drugs to kill parasites that enter their blood.
Human defence system:
- Works by preventing pathogens from enetring the body
HDS- the skin:
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- Acts as a physical barrier
- Produces antimicrobial secretions to kill bacteria
HDS- the nose:
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- Has hairs and mucus- traps particles to prevent them from entering the lungs
HDS- the trachea and bronchi:
- Secrete mucus in order to trap pathogens
- Cilia (hair-like structures on cells) - beat to waft mucus upwards so it can be swallowed
HDS- the stomach:
- Produces hydrochloric acid- kills pathogens in mucus, food and drink
HDS- phagocytosis:
- Engulfs and consumes pathogens
- This destroys them- you can no longer feel ill
HDS- producing antibodies:
- Each pathogen has an antigen on their surface
- The shape of antigen is complimentary to an antibody
- Once antibody binds to pathogen, pathogens clump together
- This makes it easier for white blood cells to find them
If you become infected again with the same pathogen, the specific complementary antibodies would be produced at a faster rate, making the individual immune.
HDS- producing antitoxins:
Neutralise toxins released by pathogen by binding to them
Vaccinations:
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Makes an individual immune to a certain disease
* The vaccination contains a dead or weakened pathogen
* This stimulates the white blood cells to produce antibodies complimentary to the antigens on the pathogen
Advantages of vaccinations:
- They have eradicated many diseases so far (e.g. smallpox)
- Epidemics (lots of cases in an area) can be prevented through herd immunity
