7.1

What is a pathogen?

A disease causing organism

What are infectious/communicable diseases?

Diseases that arespread from one person to another

also called transmissible diseases

What happens when we are exposed to pathogens?

Don’t realise that we’re exposed to it

But body has number of defences that protect us from them

Pathogens are prevented frome ntering the body or, if they do, are dealt with before they can cause symptoms of disease

Become ill → body’s immune system enables recovery without any medical intervention

What the types of pathogens?

Bacteria

Virus

What is bacteria?

Unicellular, prokaryote organisms with a cell wall but lacking membrane bound organelles and organised nucleus

AKA as prokaryote

unicellular organisms with simple internal structure

lack a nucleus

DNA floats freely in cytoplasm or is in the form of circular plasmids

Majority are non-pathogenic

Bacteria affect body differently, depending on the species. effects may include producing toxins or inducing allergic response

Structures within bacteria

Role of bacteria?

Essential to life on earth

• role in decomposition of organic material

• cycling of elements

• used in industrial processes (lactobacilli is used to make yoghurt and sauerkraut, flabours of cheese depends on the types of bacteria used in production)

Where are bacterial located?

Large number on skin

alimentary canal

armpit of adult male → two million bacteria per square centimetre of skin surface

intestines → so numerous that they are a major part of digestion process

no effect on ill health, but others can cause illness or death when present in relatively small numbers

What are the types of bacteria?

How can bacteria be identified?

To identify a bacterium, it is first grown on an agar plate or growth medium in specific conditions.

Then it can be stained and viewed under a microscope.

What are viruses?

• An infectious agent, too small to be seen with a light microscope, consisting of protein sheath surrounding a core of nucleic acid; viruses are totally dependent on living cells for reproduction

• Contain genetic material in the form of either DNA or RNA but not both

• molecule of DNA or RNA is surrounded by a coat of protein

• some have external lipid envelope

What do viruses do?

No in living things because they can’t reproduce by themselves - infect a living cell and it’s DNA or RNA induces the cell to manufacture more virus particles

New virus particles are then able to leave the host cell to infect others

in this process, cells become damaged or changed, or die

Differ in the type of cell they invade, so symptoms shown relate to the tissue that is affected

some multiply in bacterial cells, causing death of bacterium (such viruses are called bacteriophages)

Example of process of viral replication illustrated by HIV

How are communicable diseases by spread

By transmission of pathogenic organism from one person to another

such diseases are said to be contagious

directly passed from one person to another

may be spread by vectors → intermediate hosts of the pathogen such as mosquitoes or fleas

Types of transfer

Transmission by direct contact

Ingestion of contaminated food or Drink

Transfer of body fluids

Infection by droplets

Airborne transmission

Transmissinon by vectors

Transmission by direct contact

Spread of pathogen by actual physical contact

contact may be direct → actually touching infected person

indirect → touching object that has been touched by infectious person

e.g. skin infections, STI’s

Ingestion of pathogen contaminated food or drink

Can result in disease

dysentery, typhoid fever, salmonella

Transfer of body fluids?

from one person to another can result in the transmission of a number of infections.

When blood or other body fluids from an infected person comes into contact with the mucous membranes, such as in the nose, mouth, throat and genitals, or the bloodstream of an uninfected person, such as through a needle stick or a break in the skin, t pathogens may enter the body of that person.

The human immunodeficiency virus, and hepatitis B and C, are spread in this way.

Infection by droplets

tiny droplets of moisture containing pathogenic organisms are emitted when breathing, talking, sneezing or coughing.

droplets may be breathed in by others, or may settle on food or utensils to be later ingested with food.

Many viral infections, such as those causing Ebola, COVID-19, mumps, colds and influenza, can be spread by droplets

Airbone transmission

When the moisture in exhaled droplets evaporates, many bacteria are killed, but viruses and some bacteria remain viable and can cause infection when inhaled.

As these particles are lighter, they remain viable for a greater distance than those transmitted by droplets.

Measles and chickenpox are spread by this method

Transmission by vectors

transfer of pathogens by other animals, such as insects, ticks or mites.

Some vectors transfer the pathogen directly; others, such as house flies, may spread the pathogen to food or water, which is then ingested.

Many vector-borne diseases are spread by a specific vector. For example, malaria and dengue fever are spread by mosquitoes, trypanosomiasis (African sleeping sickness) is spread by the tsetse fly, Lyme disease is spread by ticks, and bubonic plague is spread by fleas from rats and mice.