Infectious agents

Question 1

List the main types of infectious agents causing disease in humans, recall examples of each type and the disease it causes

Answer 1

Infectious agents

1. Viruses ; not cells in their own right
2. Bacteria; prokaryotes
3. Fungi; eukaryotes (single cell)
4. Protozoa; eukaryotes
5. Helminth parasites; eukaryotes (multicellular)

Question 2

Viruses

Answer 2

1. not cells in their own right- OBLIGATE PARASITES
2. Contain RNA or DNA genetic material
3. Make use of a host cell nuclear synthetic machinery to replicate
4. Show host specificity but infect almost all other life forms, including bacteria
5. Divide by budding out of host cell
6. Various routes of infection

ex HIV-retrovirus

Question 3

Bacteria

Answer 3

1. Fundamentally different from all other living things in being PROKARYOTES (cell wall composition)
   
   • Contain a chromosome of DNA but no nucleus, but in condensations called Nucleoids
2. Widely distributed in nature
3. Some are pathogenic
   
   • eg. Neisseria and Shigella
4. Divide by binary fission
5. Various routes of infection
6. ex Bacteria Shigella spp.
   
   • Infectious dose 10-100 bacteria
   • Faecal-Oral transmission

Septicaemic disease

is characterised by:

• rapid progression
• septic shock
• severe inflammatory response

Question 4

Fungi

Answer 4

1. Eukaryotic
   
   1. occur as yeasts, filaments or both
   2. yeasts bud or divide; filaments (hyphae) which have cross walls or septa
   3. cause cutaneous, mucosal and/or systemic mycoses

ex .Candida albicans

Question 5

Protozoa

Answer 5

1. Unicellular eukaryotic organisms

• include intestinal, blood and tissue parasites
• replicate in the host by binary fission or by formation of trophozoites inside a cell
• many have a complicated life cycle involving two hosts
• infection is acquired by ingestion or through a vector
• eg insect or invertebrate vector

ex Malaria and Leishmaniasis

Question 6

Helminth parasites

Answer 6

1. Roundworms
2. Flatworms (flukes)
3. Tapeworms
4. Metazoa with eukaryotic cell structure
5. Multi-cellular
6. Visible to the naked eye
7. Have life cycles outside the human host
8. Life cycle complexity varies from simple embryonation to alternation of generations in different hosts

Question 7

I AM BOREDDD AS WELL

(PLEASE SPARE SOME TIME TO LOOK AT PICTURES OF THE EXAMPLES)