Communicable Diseases

Question 1

Define the term ‘communicable disease’.

Answer 1

A communicable disease is a disease caused by a pathogen, that can be directly or indirectly transmitted from one living thing to another, either through the environment, or between people.

Question 2

Explain the two types of infectious disease.

Answer 2

Emerging diseases
- newly discovered diseases that are appearing for the first time, e.g., COVID-19. Also includes diseases that are emerging for the first time within a population/geographical location.

Re-emerging diseases
- diseases that were previously under control or eradicated, e.g., due to vaccination, which are gaining new footholds in the community and increasing in number, e.g., due to antibiotic resistance.

Question 3

Explain the two main modes of transmission for infectious diseases.

Answer 3

Direct contact
- transmission occurs from direct contact with an infected person, e.g., kissing, sex, mother to unborn baby.

Indirect contact
- transmission occurs without being in direct, close contact with an infected person, e.g., inhaling respiratory droplets, touching contaminated object.

Question 4

Describe a virus and how a virus causes a viral infection.

Give an example of a viral infection.

Answer 4

A virus is a piece of genetic material enclosed within a protein coat.

A virus infects its host by attaching to a host cell membrane. The virus inserts its genetic material into the host cell, and hijacks the cells inner machinery to produce more viral proteins.
Eventually the host cell burst and dies, releasing the viruses into the body to repeat the cycle.

Example of a viral infection: COVID-19 caused by the SARS-CoV-2 virus.

Question 5

Describe bacteria and how a bacteria causes a bacterial infection.
Give an example of a bacterial infection.

Answer 5

A bacteria is a single celled organism. They come in three forms: bacilli (rod shaped), cocci (spherical), and spiral (helix).

A bacterial infection is the proliferation of a pathogenic (harmful) bacterial on the skin, or inside the body.

Example of a bacterial infection: food poisoning caused by Salmonella.

Question 6

Describe fungi and how a fungi causes a fungal infection.

Give an example of a fungal infection.

Answer 6

Fungi are plant-like organisms that cause diseases of the skin, lungs and mucosal membranes.
Proliferation of a fungi is known as mycosis.

Example of a fungal infection: Athlete’s foot caused by Tinea Pedis

Question 7

Describe protozoa including their characteristics.

Give an example of a protozoan infection.

Answer 7

A protozoa is a single celled organism - a parasite that is infectious to humans.

Protozoa can come in many different shapes/forms, e.g., Amoeba can change shape, however, other protozoa have fixed structure.

Example of a protozoan infection is Malaria caused by Plasmodium.

Question 8

Describe the 4 stages of disease, including the response of the pathogen and immune system at each stage.

Answer 8

Incubation stage:
The period of time between the pathogen entering the body and the onset of the symptoms. Usually lasts between 2-14 days.
Pathogen
- hiding and trying to replicate
Body
- recognises that infection has occurred
- recruits the immune system to scout out the pathogen & report back with info

Prodromal stage:
Most infectious stage - the infected person not unwell enough to isolate.
Onset of first symptoms e.g., sore throat, runny nose, tiredness.
Pathogen
- rapidly increasing in strength and number
- starting to take over cells and tissues
Body
- has received information about the pathogen
- recruits WBC to fight the pathogen
- antibody production begins

Illness stage
Peak of the infection - person feels most unwell and extremely tired due to increased WBC and decreased RBC count.
Can identify which pathogen has infected based on symptoms e.g., loss of taste/smell in COVID-19.
Pathogen
- decreasing in number as the immune system overcomes the pathogen
Body
- all components of the immune system are in use
- winning the fight against the pathogen

Recovery stage
Extremely vulnerable stage as if re-infection occurs at this stage, can be fatal. Important to continue course of antibiotics even if feeling better!
Body is in a weakened state and immune system is exhausted.
Symptoms begin to relieve.
Pathogen
- mostly overcome by the immune system
- strongest pathogens can re-infect in the prodromal stage = fatal
Body
- mostly won the fight against the pathogen
- rebuilding WBC defence and increasing RBC count