Infection and Response


Pathogens and Disease

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
1 of 3


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. 
2 of 3


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

3 of 3


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Medicine and drugs resources »