Host-Microbe Relationship Flashcards
Three types of host-organism relationships:
- Mutualism
- Commensalism
- Parasitism
Mutualism: both organisms benefit
Commensalism: one benefits, other neither benefits NOR is harmed
Parasitism: one benefits, other is harmed
Definitions! Contamination Colonization Infection Disease Infectious Disease
Contamination: the presence of microbes on a surface or tissue = PRESENT
Colonization: the patient has a sufficiently high concentration of organisms at a site that they can be detected, yet the organism is causing NO signs or symptoms
Infection: the INVASION of a host organism’s bodily tissues by pathogenic organisms with or without the manifestation of disease (INVASION, with or without disease)
Disease: abnormal condition of body function(s) or structure that is considered to be harmful to the affected individual (host) (INVASION –> TISSUE IMPAIRMENT)
Infectious Disease: pathological consequences of being infected
Stages of Pathogenesis
After patient has been exposed to a pathogen (contact), to cause disease, a pathogen must successfully achieve the following steps/stages:
- Gain entry to the host (adhesion, invasion)
- Travel to the location where is can establish an infection and multiply
- Evade or overcome the host’s immune response
- Cause damage (i.e. disease) to the host
3 Components of Disease Triad
Host, Environment, Pathogen
Host
Risk factors; e.g. occupation, behaviour, hygiene, genetic composition, nutrition & immunological status
Environment
Geology and climate, biologic factors, socioeconomic status
Pathogen
Pathogenicity (virulence, dose, etc).
Factors influencing the development of disease
a) Characteristics of the microbe
- Dose (# of organisms, duration of exposure)
- Virulence of the organism (strength of the pathology)
b) Immune status of host (ability to resist, host general physical health & nutritional status)
Course of Infectious Disease
Incubation Period Prodromal Period Illness Decline Convalescence
Incubation Period
Period where there are NO signs and symptoms detected while the virus is incubating
Time elapsed b/w exposure to a pathogenic organism & when the symptoms and signs are first apparent
Prodromal Period
Stage where there are vague and general symptoms
Illness Period
Stage which has the most severe signs and symptoms
Interval when patient manifests signs and symptoms SPECIFIC to type of infection
Decline Period
When there is declining signs and symptoms
Convalescence Stage
NO signs and symptoms at all!
Gradual recovery of health and strength after an illness
Latent Period
Period of replication before shedding
Communicable Period
Follows latency, and begins with shedding of the agent
Frequently – the communicable period begins before symptoms are present
Carriers
- Asymptomatic
- Incubatory
- Convalescent
- Chronic
Carries: a person with inapparent infection who is capable of transmitting the pathogen to others. Carriers often transmit disease b/c they do not realize they are infected, and consequently take no special precautions to prevent transmission
Asymptomatic Carriers: those who never experience symptoms despite being infected
Incubatory Carriers: those who can transmit the agent during the incubation period before clinical illness begins
Convalescent Carriers: those who have recovered from their illness but remain capable of transmitting to others
Chronic Carriers: those who continue to harbour a pathogen for months or even years after their initial infection
SUMMARY of Patterns of Infection
- Acute self limiting
- Persistent with shedding
- Persistent latent
- Persistent slow following acute
- Persistent slow with no acute stage
- Acute self limiting: resolution (ex. common cold)
- Persistent with shedding (may be asymptomatic, but infective)
- Persistent latent: asymptomatic, NOT infective during latency!
- Persistent slow following acute: infective (e. HIV/AIDS)
- Persistent slow with no acute stage (infective)
