Infectious Disease

1. Infectious Disease

2. Pathogens are microorganisms that cause disease. • A host is any organism that is capable of supporting the nutritional and physical growth requirements of another organism. • Infection is the presence and multiplication of a parasitic organism in the host.

3. Pathology depends on: • Organism • Site of infection • Treatment depends on the microorganism • Prokaryote vs. eukaryote vs. virus • Resistance to antibiotics

4. Not all interactions between bacteria and humans are harmful – normal microbiotaprevents the growth of pathogens. • Most microorganisms can be opportunistic pathogens which can cause disease if the host is immunocompromised or if they can enter the body in a place where they are not normally found. ( E. coli urinary tract infections)

5. Prions • Infectious proteins • Improperly folded proteins that cause other proteins to take on that shape • Extremely difficult to destroy • Discussed later with transmissible spongiform encephalopathies (TSE’s)

6. Bacteria • Prokaryotes • Lack a nucleus and membrane-bound organelles • Structurally simple but metabolically complex • Contain both DNA and RNA • Single circular chromosome • Plasmids : extrachromosomal DNA that provides information (antibiotic resistance) that can be shared with other bacteria.

7. Bacteria • Cytoplasmic membrane • Cell wall – peptidoglycan • May also produce a capsule of protein or carbohydrate – protects from the host immune system.

8. Virulence factors • Exotoxins – proteins released from a bacterial cell – enzymes that lead to cell death or dysfunction • Endotoxins- complex molecules made of lipid and polysaccharides found in the cell wall of gram-negative bacteria. Usually released when the cell is killed, can cause clotting, bleeding, inflammation, hypotension and fever.

9. Virulence factors • Adhesion factors – allow bacteria and viruses to attach to the host. • Receptor • Ligand or adhesin

10. Virulence factors • Evasive factors – • capsules, and slime layers evade phagocytes • Leukocidin C • Some survive and reproduce inside phagocytes • Coagulase • Enzymes that break up antibodies • Alter surface antigens during the disease course • Urea splitters raise environmental pH

11. Virulence factors • Invasive Factors- products that facilitate the penetration of anatomic barriers and host tissue. These can destroy cell membranes, connective tissue, intercellular matrices, and structural protein complexes.

12. Viral Infection • Viruses extremely small – can infect bacteria • Usually just composed of DNA (or RNA) + protein “coat” or capsid • Can’t reproduce on their own – need to use a host cell

13. Infection • Adsorbed to host cell receptor • Penetration • Coat removal • Uses host enzymes to replicate nucleic acid and proteins • New viruses are assembled • Virus is released • Lytic cycle

16. Cellular effects • Decreased synthesis of host proteins • Disruption of lysosomal membranes • Changes in host cell membrane proteins • Transform into cancer cell • Tissue damage may promote bacterial infection