Module 4: Communicable diseases. Flashcards
What is a disease?
It is a condition that impairs the normal functioning of an organism.
What is a pathogen? Give examples.
It is an organism that causes disease.
E.g. Bacteria, viruses, fungi and Protoctista.
What is a communicable disease?
It is a disease that can spread between organisms.
What 3 diseases are fungus responsible for? Who do they affect?
Black sigatoka - affects banana plants.
Ringworm - affects cattle
Athletes foot - affects Humans
What 3 diseases are Bacterium responsible for? Who do they affect?
Tuberculosis (TB) - affects animals (humans) and cattle.
Bacterial meningitis - affects Humans.
Ring tot - affects Potatoes + tomatoes.
What 3 diseases are virus responsible for? Who do they affect?
HIV/AIDS - affects humans.
Influenza - affects animals including humans
Tobacco mosaic virus (TMV) - affects plants
What 2 diseases are protoctist responsible for? Who do they affect?
Potato/tomato late blight - affects tomatoes/potatoes.
Malaria - affects animals including humans.
What is Direct transmission?
This is when a disease is transmitted directly from one organism to another.
E.g. Droplet infection - coughing and sneezing onto someone, sexual intercourse or touching an infected organism.
Give examples of diseases that spread through direct transmission.
- HIV is transmitted directly through sexual intercourse.
- HIV virus can be transmitted directly from a mother to her unborn child through the placenta.
- Athletes foot can be spread via touch.
What is indirect transmission?
When a disease is transmitted from one organism to another via an intermediate - e.g. air, water food of other organisms, known as a vector.
(A vector is an organism that spreads disease by carrying pathogens from one host to another)
Give examples of diseases that spread through indirect transmission.
- Potato/tomato late blight is spread when spores are carried between plants - first in air, then in water.
- Malaria is spread between humans via mosquitoes - insects that feed on blood. The mosquitoes act as vectors - they do not cause the malaria themselves, they just spread the protoctist that cause it.
What are the 3 main factors that affect disease transmission?
- Living conditions
- Social factors
- Climate
How does living conditions affect disease transmission?
Overcrowded living conditions increase disease transmission.
For example, TB is spread directly via droplet infection and indirectly as 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.
How does social factors affect disease transmission?
In humans social factors - income, occupation + the area where someone lives can increase the disease transmission.
For example, The risk of HIV is high in places where there is limited access to:
- Good healthcare = less likely to be diagnosed and treated for HIV. Most effective anti HIV drugs are less likely to be available - so the virus is more likely to be passed onto 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.
How does climate affect disease transmission?
- Can increase disease transmission.
For example Potato/tomato late blight is especially common during wet summers as spores need water to spread.
Malaria is most common in tropical countries - humid/hot conditions. This is because these are the ideal conditions for mosquitoes to breed (malaria vectors)
What are primary defences?
Give examples.
They aim to stop entry of pathogens into the body - can be physical or chemical.
They are non-specific, which means they work in the same way for all pathogens.
E.g. The skin, mucous membranes, blood clotting.
How does the skin act as a primary defence?
- It acts as a physical barrier by blocking pathogens entering the body.
- Also acts as a chemical defence by producing chemicals that are antimicrobial (which destroy or slow the growth of microorganisms) and can lower pH, inhibiting the growth of pathogens.
Give examples of the skin acting as a primary defence.
- Skin cells secrete fatty acids (oleic acid) that can kill some bacteria. - Fatty acids lower the Ph of the skin, creating an acidic environment that is difficult for pathogen to colonise.
- Skin cells secrete lysozyme - catalyses the breakdown of carbohydrates in the cell walls of some bacteria.
How do mucous membranes act as a primary defence?
- These protect body openings that are exposed to the environment - e.g. mouth, nostrils, ears, genitals and anus. (physical defence)
- Some membranes secrete mucus that traps pathogens and contains antimicrobial enzymes. (chemical defence)
Give examples of mucous membranes acting as a primary defence.
- The gas-exchange system - breathe in air that contains pathogens, most will be trapped in mucus lining the lung epithelium.
- Ciliated epithelium have hair-like structures that beat and move the mucus up the trachea to the throat and mouth, where it is removed.
How does blood clotting act as a primary defence?
Blood clots (a mesh of protein fibrin/fibres) plug wounds to prevent pathogen entry and blood loss.
They are formed by a series of chemical reactions that take place when platelets (fragments of cells in the blood) are exposed to damaged blood vessels.
How does inflammation act as a primary defence?
- Can be triggered by tissue damage - the damaged tissue releases molecules which increase the permeability of the blood vessels, so they start to leak fluid into surrounding area.
This causes swelling and helps to isolate any pathogens that may have entered the damaged tissue.
The molecules also cause vasodilation (widening of the blood vessels), which increases blood flow to the affected area. This makes the area hot and brings white blood cells to the area to fight off any pathogens that may be present.
Signs include swelling, pain, heat and redness.
How does wound repair act as a primary defence to pathogens?
The skin is able to repair itself and reform a barrier against pathogen entry (injury).
The surface is repaired by the outer layer of skin cells dividing and migrating to the edges of the wound.
The tissue below the wound then contracts to bring the edges of the wound closer together.
It is repaired using collagen fibres - too many collagen fibres = forms a scar.
How do expulsive reflexes act as a primary defence against pathogens?
This includes coughing and sneezing. Both are an attempt to expel foreign objects, including pathogens from the body. They happen automatically.
Sneeze - happens when the mucous membranes in the nostrils are irritated by things such as dust or dirt.
Cough - stems from irritation in the respiratory tract.
