Infection

1. Colonisation - Infection transmitted via direct contact, vectors, exposure, etc. 

2. Invasion - Infectious agent invades surrounding tissues - penetrate tissues and avoid host's nonspecific + specific defense

3. Multiplication- Warm, nutrient filled host environment = rapid multiplication. May replicated within cells (viral) or in macrophages (bacterial).

4. Spread- Produce localised infections which spread to other areas of the body, may remaind localised if strong immune systems or rapdily spread if immune system is compromised. 

1. Incubation period - Microorganism entered individual (colonisation and multiplication) but insufficient in numbers for appearance of symptoms

2. Prodromal stage - Pathogen continues to multiply + host begins to feel intial symptoms e.g., fever, swelling, inflammation, soreness.

3. Invasion period - Immune + inflammatory response being triggered, development of symptoms related to specific pathogen and signs and symptoms are most severe. Height of infection.

4. Convalescene period - Symtpoms may decline as host may recover, disese may enter a latency phase or become fatal. 

Prokaryotic - no mitochondria or membrane bound organelles, reproduce via division, may be spherical (cocci), rod-like (bacilli), comma shaped (vibrios), spiral (spiralla) or corkshrew shaped (spirochete).

Surival and growth of bacteria is dependant on effectiveness of body's defense and the bacteria's capacity to resist the defences. Can rapidly divide and has protection against phagocytosis due to a thick coat.

Can produce exotoxins to injure cells or endotoxins to cause fever (pyrexia). Can change antigens to become resistant. 

Bacteremia- Bacteria being transported in blood due to failure of body's defense mechanisms. 

Capable of replication but only within living cells. Does not possess metabolic organelles but contains nucleic acid protected by capsid. 

Life cycle:

Attachment to target cell -> Penetration -> uncoating/release of viral nucleic acid -> Replication -> Assembly -> Release. 

Antibodies defend against virus by preventing viral entrance into cells however virons can sometimes divide quicker than body can produce antibodies. 

Virus can have antigenic variation and appear as a new virus to the body, e.g. flu. = Body has to produce new antibodies. 

Eukaryotic - can form complex structures e.g. mould or can be single celled, e.g. yeast. 

Can invade external body (dermatophytes) or have deep infection involving internal organs. Infection with fungus = mycosis. 

Can readily adapt to host environment and can block recognition from macrophages and inhibit migration of leukocytes. 

Secrete enzymes to damage host tissues. Can also stimulate production of immunosuppressive cytokines reducing some aspects of host's immune system. 

Parasite = any living thing that lives on another living organism

Protozoa = single celled parasite.

Some protozoas can become parasites, e.g. worms.

Risk factors include unclean drinking water, weakened immunity, contact with infected soil, subtropical regions, etc.

Rarely transmitted human to human and usually through vectors, e.g. malaria via mosquitos.