3: Infectious diseases and outbreak

Zoonosis

Infectious disease from non-human hosts that has spread to humans

The 3 mechanisms infectious agents cause damage / injury

1. Damage cells via contact or invasion

2. Release toxins for distanced cell death or enzymes for local damage

3. Provoke an immune response that causes tissue damage

Different inflammatory cells associated with different infectious agents:

viruses = lymphocyte, monocyte

fungi = lymphocyte, monocyte, granulomas

mycobacteria = lymphocyte, monocyte, granulomas

bacteria = neutrophils

helminths = eosinophils

Pathogens

infectious hosts that survive through a cost to the host (i.e. sickness)

Commensal relationship

microbes that are considered normal flora due to being mostly beneficial

• crowding out harmful microbes

• assist in food breakdown in the gut

• resists pathogens and educated the immune system

  ** some normal flora can become pathogens under certain conditions – immunocompromisation, overgrowth, etc.

Pathogenicity

the ability of a microbial agent to cause disease

Virulence

the degree to which an organism is pathogenic

Viruses are composed of…

nucleic acid (DNA/RNA) and protein (capsid), with no cell wall or nucleus

Surface protein: attach to specific host cell surface protein receptors to gain entry into cells

Viruses work by…

1. invading cells to use their machinery for replication; cannot multiple on their own – they have no metabolism

2. inciting an immune reaction to kill the cell or surrounding cells OR making the cell cancerous

Transient virus infections

acute, short-term

Persistent virus infections

chronic

Bacteria are composed of…

Simple, single-cell that contains DNA

Lacks a true nucleus and most cell organelles; prokaryotic

Bacteria work by…

1. Binding to cells or fibers through glue-like adhesins OR binding to tissue proteins with pili (hair-like protein projections)

2. Damage cells through enzyme or toxin release

3. Cause suppurative inflammation (pus)

Fungus work by…

1. absorbed organic matter using enzymes

2. reproduce by spreading single-cell spores

Mycoses

fungal infection

Parasites work by…

1. live on / in a host to get food at the expense of the host

2. grow, reproduce, and invade organ systems

3. cause chronic infectious disease; can co-exist for a long time

The 3 types of parasites

1. ectoparasites (insect-like, attach to skin)

2. protozoa (motile, single cell)

3. helminths (worms, dracunculiasis)

Prions

a type of protein that triggers normal brain proteins to fold abnormally, clump together, and accumulate – leads to brain damage

Scientific name for prion diseases

transmissible spongiform encephalopathies (TSEs)

Features of TSEs

• rare, progressive neurodegenerative disorders

• rapid progression

• always fatal

• caused by eating infected meat

The chain of infection

1. HOST – individual prone to acquiring infection

2. RESERVOIR – where infectious agent lives and multiplies; the source of infection to others

3. CARRIER – where the pathogen is harboured without causing symptoms

4. CONTAGION – the spread of infection

the 3 types of ways to diagnose infection

1. laboratory tests

2. imaging scans

3. biopsies

Active immunity

antibodies are produced due to expose to a disease, slowly developing long-term immunity

Natural: infection with actual disease

Artificial: vaccination

Passive immunity

antibodies are produced externally, quickly developing short-term immunity

Natural: maternal breastfeeding

Artificial: eg blood infusion

Antigens

molecules capable of stimulating an immune response

Antibodies (immunogloins)

Y-shaped proteins produced by B-cells in response to antigen exposre

Vaccine

biological product that safely induces an immune response to an antigen

The 3 types of classification of bacteria

Classification is according to shape and arrangement

1. Cocci (spheres)

2. Bacilli (rods)

3. Spirals