types of pathogen

• • Communicable diseases can pass between organisms. 23% of deaths yearly are a direct result of communicable diseases.
  • Communicable diseases are caused by infective organisms. These are known as Pathogens.
  • A pathogen is a microorganism that has the ability to cause disease and can be a bacteria, virus, fungi or protoctista
• Most bacteria produce toxins that damage host cells.

  This is usually through disruption to the cell membrane or by altering the cell cycle to prevent replication and division.
• bacterial infection -

  • In humans, TB is caused by Mycobacterium tuberculosis
  • Another example of a bacterial infection is Bacterial Meningitis
• bacterial infection - plants

  • Ring rot is caused by Clavibacter michiganensis, Typically affects tomatoes, potatoes and aubergines.
• • Viruses are tiny non-living infectious agents.
  • Viruses can be described as the ultimate parasite as they can cause disease in any organism- some specifically attack bacteria.
  • They are essentially composed of genetic material surrounded by protein.
  • Viruses take over cell metabolism by inserting viral genetic information into the host DNA.
• An example of a virus that infects humans is HIV- Human Immunodeficiency Virus. HIV can lead to development of AIDS- Acquired Immunodeficiency Syndrome

  • HIV is a retrovirus with reverse RNA.
  • The virus targets T helper cells and essentially destroys the immune system so that the body is more susceptible to secondary infections.
• An example of a virus that affects humans and animals is Influenza- particularly strains A, B and C

  Affects ciliated epithelial cells of gas exchange system, leading to secondary infection (most deaths are from these secondary bacterial infections esp. pneumonia)
• An example of a virus that infects plants is TMV- Tobacco Mosaic Virus

  • damages leaves and stunts growth
• The fungi that cause communicable disease are those which are parasitic.

  Fungi cause more of an issue in plants than in animals- they typically affect the leaves of plants, preventing them from photosynthesising.

  Some can produce toxins which damage host cells.
• Athlete’s foot is an example of a fungal infection in humans. Tinia pedia- digests warm, moist skin cells. This can lead to secondary infection (particularly in the immunocompromised)
• Ringworm is an example of a fungal infection in animals.

  Tricophyton verrucosum- causes grey crusty circular areas of skin
• • Protoctista/Protists are eukaryotic organisms which can be single celled or colonied.
  • Most that are pathogenic are parasitic and use animals or humans as their host. In many cases they require a vector.
  • They digest and use cell contents as they reproduce.
• Malaria is an example of a pathogenic protist in humans. Female Anopheles mosquitoes spread the protoctista.

  Most cases are Plasmodium sp. i.e. Plasmodium malariae and Plasmodium falciparum