Infection and Response

Pathogens are microorganismsthat cause communicable diseases. Pathogens may infect plants or animals. They can spread by: direct contact, water or air, vectors (organisms that carry and pass on the pathogen without getting the disease).

The spread of infectious diseases can be reduced by: 

• simple hygiene measures, e.g. washing hands after using the restroom.
• destroying vectors (e.g. mosquitoes)
• isolating infected individuals, so that they can not pass on the pathogens.
• giving people at risk a vaccination

There are 4 types of communicable diseases:

• Viruses
• Bacteria
• Protists 
• Fungi

Viruses reproduce in body cells rapidly so they cause a lot of damage inside the body.

Measles is a disease caused by a virus:

• The symptoms are fever and a red skin rash.
• It is spread by breathing in droplets from sneezes or coughs.
• Although most people recover well from measles, it can be fatal if any complications occur. This is why most children are vaccinated against it at a young age. 

HIV (human immunodeficiency virus) causes AIDS: 

• It is spread by sexual contact or exchange or body fluids (e.g. when drug users share needles, it can transfer throught blood from one person to the other). 
• At first HIV causes flu-like symtoms.
• If remains untreated, it can start attacking the body's immune cells.
• Taking antiviral drugs can delay this happening. 
• Late stage HIV, or AIDS, is when the body's immune system has become so damaged that it cannot fight off infections or cancers so they become deadly. 

Bacteria may damage cells directly or produce toxins that damage tissues.