3.1 Communicable Diseases

3.1.1 Communicable (Infectious) Diseases

Keywords: Communicable Disease, Health, Pathogen
FSL: GCSE Biology Revision "Communicable and Non-Communicable Diseases"

Health: Not just an absence of disease, but a state of physical and mental wellbeing.
Communicable Disease: A disease that can be transmitted, caused by pathogens.
Pathogen: A disease-causing microorganism. Either directly damages your cells (like viruses) or via toxins (like bacteria).

There are four types of pathogens:

• Bacteria: e.g. UTI/STIs (humans)
• Viruses: HIV (humans); tobacco mosaic virus (plants)
• Fungal Spores: Ringworm (humans); potato blight (plants)
• Protists: Malaria (humans)

Viruses

- Viruses inject their DNA into the nucleus into a cell and hijack it to produce copies of itself. It eventually bursts open, spreading the viruses everywhere, making you feel ill.
- They are very small (much smaller than a cell) so it makes infection easier.
- Viruses aren't actually alive, as they cannot reproduce on their own and need a host. Therefore you cannot kill a virus, only destroy it.

Bacteria

- Bacteria are living organisms. They are cells themselves, and they reproduce via binary fission (a type of cell division). They are small, but not as small as viruses.
- Antibiotics kill bacteria, and they can get their own viruses.
- Not all cause bad diseases, plenty of bacteria are beneficial to you (e.g. some aid in digestion).

Bacteria vs Viruses

When bacteria and viruses are in the body, they reproduce rapidly. Bacteria produce poisons called toxins. These toxins damage body cells and result in negative symptoms.
In comparison, viruses invade the cells of the body. They live and reproduce inside the cells. These cells will burst, releasing copies of the virus to invade other body cells.
Symptoms include rashes, high temperature and headache: a response of the body.

Protists

- Protists are a living type of microorganism that are reliant on a host (they are parasites).

Modes of transmission