Microbial Pathogenesis

Definitions:

Disease is: 'any deviation from or interruption of the the normal structure and/or function of any part of the body'.

A pathogen is: 'a disease causing organism'.

Opportunistic pathogens: e.g. Escherichia coli is a normal, 'non-pathogenic' commensal organism in the human gut, but infection of the bladder can result in ascending infection of the ureters & eventually, the kidneys, resulting in renal failure. Most strains of E.coli are inefficient in establishing such infections, but some strains express particular adherence factors which allow them to ascend the ureter & reach the kidney.

Obligate pathogens display the most extreme adaptation to their host organisms.

What does a pathogen have to do?

Infect (infest) a host
Reproduce (replicate) itself
Ensure that its progeny are transmitted to another host

Mechanisms of Transmission:

Aerosols - inhalation of droplets, e.g. Rhinoviruses, the 'Common Cold Virus' or Adenoviruses.
Faecal-Oral - e.g. Astroviruses, Caliciviruses; these viruses cause acute gastroenteritis.
Vector-borne - e.g. in Arthropods such as mosquitos, ticks, fleas: Arboviruses.
Close personal contact - especially exchange of bodily fluids: Sex; Blood, e.g. Herpesviruses.

Sites of virus entry:

	Bestsellers - Music - DVDs - Videos - Electronics Search for ... (keywords):
	Search for ... (keywords): Bestsellers - Music - DVDs - Videos - Electronics

Transmission patterns:

Horizontal Transmission: Direct person-to-person spread.
Vertical Transmission: Relies on PERSISTENCE of the agent to transfer infection from parents to offspring. Several forms of vertical transmission can be distinguished:
Neonatal infection at birth, e.g. gonorrhorea, AIDS.
Infection in utero e.g. syphilis, CMV, Rubella (CRS), AIDS.
Germ line infection - via ovum or sperm.

The eventual outcome of any virus infection depends on a balance between two processes:

PERSISTENCE of the agent vs. CLEARANCE from the host

Host Responses

Mammals have a variety of defences against infection.

Non-specific mechanisms:

Skin
Enzymes
Fever

Specific mechanisms - the immune response:

Mucosal Immunity
Humoral Immunity
Cell Mediated Immunity

Microbiology
by L.M.Prescott et al.
A balanced, comprehensive introduction to all major areas of microbiology. The sixth edition has been updated extensively to reflect the latest discoveries in the field.
(Amazon.co.UK)

Search for more information on this topic