AQA GCSE Communicable disease (Biology)

Communicable disease

A communicable disease is an infectious disease spread between organisms and it is caused by pathogens.

Pathogens are microorganisms that cause infectious disease. They can infect both plants and animals.

Examples of pathogens include

1.Bacteria

2.Viruses

3.Fungi

4.Protists.

Pathogen	How the pathogen makes us ill	Appearance
Bacteria	Bacteria may produce poisons (toxins) that damage tissues and make us feel ill. Bacteria reproduce rapidly inside the body
Virus	Viruses live and reproduce inside cells rapidly, causing cell damage.
Fungi	Some fungi grow on or inside the body, damaging tissues.
Protist	Protists make us ill by acting as parasites they live inside our body, feed on our cells

Transmission of disease

Communicable diseases can be spread by:

Transmission method	How the pathogen is transmitted	Examples of diseases that are transmitted this way
By air (droplet infection)	An infected individual such as a human will cough or sneeze to expel droplets that contain the pathogen. An uninfected individual will breathe in these droplets and become infected. Many plant pathogens such as bacteria, viruses and fungal spores are transferred from one plant to another by air.	Humans: Influenza Covid Plants: Rose black spot
Direct contact	An uninfected organism makes physical contact with either infected organism, or a surface that is contaminated with pathogens. In animals many sexually transmitted infections are transmitted this way by direct contact of skin or mucus membranes. Plant pathogens can be transmitted by diseased plant material making contact with uninfected plant material. Animals can act as vectors by transferring pathogens from an infected individual to an uninfected individual.	Sexually transmitted infections such as syphilis or chlamydia Plant diseases such as tobacco mosaic virus The female Anopheles mosquito transfers the protist Plasmodium between an individual infected with malaria and an uninfected individual. So, the mosquito acts as a vector.
By water	Animals consuming either water contaminated with pathogens, or food which contains water that is contaminated with pathogens. Consumption of raw or undercooked food can also cause transmission of disease as the cooking process kills the pathogens Plants can be covered by water that is contaminated with fungal spores	In animals this can cause diarrhoea based diseases, cholera, typhoid or salmonella food poisoning. In rose plants it can cause rose black spot

Reducing or Preventing the Spread of Disease.

There are several ways that communicable disease can be reduced, or prevented.

For Animals:

Means of transmission control	Method to control transmission	Why it works
Hygiene	Wash hands Using disinfectants on surfaces Cooking food properly Cleaning surfaces	Kills or removes pathogens
Isolation or quarantine	Keeps infected people away from unifected individuals	Stops direct contact and transmission by air.
Vaccination	Gives a weakened or dead form of the pathogen	White blood cells, which form part of the bodies immune system will produce antibodies against the pathogen, so if infection occurs at a later point, the person will be immune.
Destroying vectors	Killing mosquitoes or preventing breeding of mosquitoes	Stops the organism that transfers the pathogen from passing on the pathogens
Safe sexual health practices (STIs)	Use condoms and regular testing of STIs.	Reduces the transfer of pathogens through bodily fluids.

For Plants:

Means of transmission control	Method to control transmission	Why it works
Destroying infected plants	Removing and burning diseased plants Removing infected leaves or branches	Removes the source of the pathogen so it cannot infect neighbouring plants
Crop rotation	Avoid planting the same crop in the same soil each year	Many pathogens stay in the soil; rotating crops breaks their life cycle and stops them spreading into the next year’s crop.
Using disease-resistant varieties	Planting crops bred to resist certain fungi, bacteria or viruses.	Fewer plants become infected, so the disease has limited opportunity to spread.
Good hygiene in fields	Cleaning tools before moving to another field or plant bed. Washing machinery and boots to remove soil and spores.	Stops pathogens being carried by people, tools, or vehicles.
Controlling vectors	Common plant disease vectors include aphids, whitefliies	Killing or reducing the number of pests will prevent them from transferring pathogens from plant to plant
Healthy planting practices	Leaving space between plants Avoiding overcrowding	This reduces contact between plants, so less direct contact of pathogens
Using chemical controls	Using fungicides, bactericides or insecticides	Reduces the number of pathogens or their carriers