Download host - microbe relationships and disease

HOST- MICROBE RELATIONSHIPS
AND DISEASE PROCESSES
CHAPTER 14
Copyright © 2012 John Wiley & Sons, Inc. All rights reserved.
Symbiotic Relationships



Mutualism
– Microbe benefits
– Host benefits
– E. coli in intestine
Parasitism
– Microbe benefits
– Host is damaged
– All pathogens
Commensalism
– Microbe benefits
– No effect on host
– Corynebacterium in eye
Copyright © 2012 John Wiley & Sons, Inc. All rights reserved.
Host Invasion

Contamination
– Presence of microbes

Infection
– Invasion or colonization
by microbes

Disease
– Change away from a
normal state of health
Copyright © 2012 John Wiley & Sons, Inc. All rights reserved.
Pathogenicity Determinants

Microbial count

Virulence / Avirulence

Attenuation

Virulence Transposition via infection of novel hosts
• Rabies vaccine
Copyright © 2012 John Wiley & Sons, Inc. All rights reserved.
Microflora

1014 microbes versus 1013
body cells
Colonization

Non-sterile areas

Sterile areas

Resident microflora

Transient microflora

Copyright © 2012 John Wiley & Sons, Inc. All rights reserved.
Opportunism

Host Defense failure
– Immune system
– Diabetes
– Burn victims

Microbes in unusual
locations

Microflora disturbances
Copyright © 2012 John Wiley & Sons, Inc. All rights reserved.
Koch’s Postulates

1. Same microbe in every case
of disease

2. The agent must be isolated
and grown in pure culture.

3. Healthy hosts must get the
same disease when
inoculated.

4. The agent must be reisolated and show to be the
same causative agent.
Copyright © 2012 John Wiley & Sons, Inc. All rights reserved.
Exceptions to Koch’s postulates

Microbes do not always cause the same disease
– Related to portal of entry
– e.g. Strep throat, septicemia, flesh eating disease

Microbes cannot be cultured in isolation
– Viruses, Chlamydia, Rickettsia

Many microbes cause the same disease
– UTIs, pneumonias, meningitis
Copyright © 2012 John Wiley & Sons, Inc. All rights reserved.
Disease Types

Infectious vs. non-infectious

Communicable vs. non-communicable

Contagious
Copyright © 2012 John Wiley & Sons, Inc. All rights reserved.
Bacterial Pathogenicity

Adherence factors permit
attachment – Adhesins

Damage to Tissues
1. Invasive process directly
2. Enzymes /Toxins
1. Hyaluronidase
2. Coagulase
3. Kinase
3. WBC mediated damage
Copyright © 2012 John Wiley & Sons, Inc. All rights reserved.
Bacterial Toxins
Endotoxins
Exotoxins

Gram negative

Gram positive

LPS cell wall component

Proteins, usually enzymes

Fever

Potent effects

Shock

Specialized tissue damage

•
•
•
•
Released at cell death

Hemolysins
Leukocidins
Neurotoxins
Enterotoxins
Secreted into bloodstream
Copyright © 2012 John Wiley & Sons, Inc. All rights reserved.
Exotoxin - Hemolysin
Copyright © 2012 John Wiley & Sons, Inc. All rights reserved.
Viral Pathogenicity

Cytopathic effects
– Cell rupture
– Inclusion bodies
– Giant cells

Latent infections

Persistent infections
– HBV
Copyright © 2012 John Wiley & Sons, Inc. All rights reserved.
Eukaryotic Pathogen Effects

Algae
– Toxins

Fungi
– Toxins/enzymes
– Direct damage

Protozoa
– Direct damage

Helminths
– Direct damage
– Obstruction
Copyright © 2012 John Wiley & Sons, Inc. All rights reserved.
Vocabulary Terms

Symptom

Subacute disease

Sign

Latent disease

Syndrome

Local

Sequelae

Focal

Acute disease

Systemic

Chronic Disease
Copyright © 2012 John Wiley & Sons, Inc. All rights reserved.
Disease Terminology



Bacteremia

Primary infection

Secondary infection

Superinfection

Mixed infection

Inapparent infection
Septicemia
Viremia
Copyright © 2012 John Wiley & Sons, Inc. All rights reserved.
Disease stages

Incubation

Prodromal

Invasive (Disease)

Decline

Convalescence
Copyright © 2012 John Wiley & Sons, Inc. All rights reserved.
Factors influencing Infectious Disease
Prevention

Health care availability
– Drugs
– Immunization
– Sanitization
– Community Health

Emergence of new
pathogens

Social migration/Change

Immigration
Copyright © 2012 John Wiley & Sons, Inc. All rights reserved.