Contagious Diseases
What are Pathogens?
Pathogens are organisms that cause infectious diseases. Pathogens are also known as infectious agents and germs. When a pathogen enters and attacks a host, symptoms begin to appear. A host is a human who can carry a pathogen and become ill.
There are five main types of pathogens:
- Bacteria - Bacteria are microscopic, single-celled organisms having different shapes, such as rods, spirals, or spheres. Bacteria are usually larger than viruses and have a nucleus containing DNA. Most bacteria are harmless, but there are a few that can cause illness.
- Virus - Viruses are infectious agents that are smaller than bacteria and require a living host to replicate and thrive. Once a virus invades the host cells, it uses the host cell to replicate, producing many new viruses that infect other cells. This process usually damages or destroys the infected cells.
- Fungus - Fungi, which can be single-celled or multicellular organisms, can survive outside a host. Their cell contains a nucleus with cellular components enclosed within a thick cell wall.
- Protozoa - Protozoa are single-celled organisms that can move through water and prey on other microorganisms. They feed off their hosts parasitically and multiply causing infections and illnesses.
- Helminths - Helminths, or parasitic worms, are larger multicellular organisms that enter and inhabit many areas of the body, often causing illness by feeding on the host.
Knowledge Check Choose the best answer for the question.
2-1. Which of the following statements is true about pathogens?
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