Process of Infection

• Infection microorganisms exist in reserviors 

- Environment (contaminated water, soil)

- Animals

-Infected human

• Transmitted via direct contact or indirectly by vectors

Direct- faecal oral transmission via food/water or soil

Indirect- insect bites, stings, passive transfer

• After deposit in a receptive environment, microorganism stabalises adherence to the tissue through surface receptors

• Infectious agent can invade surrounding tissues

1. Attachment; Virus becomes attached to a target epitheliall cell

2. Penetration; The cell engulfs the virus by endocytosis

3. Uncoating; Viral contents are released

4. Release; New viral particles are made and released into the extra cellular fluid

5. Assembly; New phage particles are assembled

6. Biosynthesis; Viral RNA enters the nucleus, where is is replicated by the viral RNA polymerase

• Cells have developed mechanisms to penetrate tissues and avoid the hosts' nonspecific and specific defences

- Inflammation, Immunituy

• Warm, nutrient filled host environment promotes multiplication

• Cells undergo rapid multiplication

- replicate within infected cells (viral pathogens)

- replicate in macrophages and other cells (bacterial pathogens)

• This multiplication process happens via binary fission

- One bacterium becomes 2, 2 becomes 4, 4 becomes 8 and so on

• The localised infections spread to other regions of the body
• Highly invasion infections may enter the lymphatics, blood and internal organs

• Successful spread relies on virulence factors;

- Adhesion molecules, toxins and protection against host's inflammatory and immune system

• If host has;

- Intact immune system, microorganism remains localised

-Immune or inflammatory system is compromised, infection may spread rapidly