Module 9: Interaction Between Host & Microbe Flashcards
The Human Microbiome
- the sum total of all microbes found on and in a normal human
- these microbes are critically important to the health and normal functioning of humans
- collect genetic sequences in different parts of the body to determine which microbes are there
- enzymes help humans digest food and metabolize all kinds of substances
Initial Colonization of a Newborn
- first exposure to microbes: breaking of fetal membranes
- baby becomes colonized with mother’s vaginal biota
- baby’s born by caesarean section are colonized by adult skin biota
Pathogen
any agent which causes disease
True Pathogen
capable of causing disease in healthy persons with normal immune defences
Opportunistic Pathogen
cause disease when the host’s defences are compromised or when the pathogen becomes established in a part of the body that is not natural to them
Progression of an infection
- the relative severity of the disease caused by a particular microorganism depends on the virulence of the microbe
Virulence is determined by:
its ability to establish itself in the host and cause damage
Step One: Becoming Established - Portals of Entry
- inoculating dose: infection will only proceed if a minimum number of microbes is present -> infectious dose
- microbes with a small infectious dose, have greater virulence
Step Two: Becoming Established - Attaching to the Host
- Adhesion: process by which microbes gain a more stable foothold on host tissues
- firm attachment: is always a prerequisite for causing disease
Step Three: Becoming Established - Surviving the Host Defences
- avoiding phagocytosis
- avoiding death inside phagocyte
- absence of specific immunity
Step Four: Causing Disease - 3 ways that microorganisms damage their host
- directly through the action of enzymes
- directly through the action of toxins (exotoxins + endotoxins)
- indirectly by inducing host’s defences to respond excessively or inappropriately
Step Four: Causing Disease
- accumulated damage can lead to cell and tissue death -> necrosis
- viruses destroy by multiplying in and lysing cells
Step Five: Exiting Host
- portals of exit: respiratory tract, salivary glands, skin cells, fecal matter, urogenital tract, blood
Sign
is any objective evidence of disease as noted by an observer
Symptom
is the subjective evidence of disease as sensed by the patient
Asymptomatic Infection
when an infection produces no noticeable symptoms, even though the microbe is active
latency
in certain chronic infectious diseases the infectious agent retreats into a dormant state
Course of an Infection: 4 main phases
- incubation period
- prodromal
- acute
- convalescence
- (continuation)
Incubation Period
- time from initial contact with infectious agent to the appearance of the first signs and symptoms
- agent is multiplying at the portal of entry but has not yet caused enough damage for signs and symptoms to appear
Prodromal Stage
- early signs and symptoms
Acute Phase
- infectious agent is well established
- multiplying at high levels
- exhibits its greatest virulence
Convalescence
- patient’s strength and heath gradually return
Continuation Period
- the organism lingers for month, years, or indefinitely after patient is well
- the organism is gone but symptoms continue
Reservoir
primary habitat in the natural world from which a pathogen originates
Transmitter
the individual or object from which the pathogen is actually acquired
Living Reservoirs - Carriers
individual who inconspicuously shelters a pathogen and can spread it to others without knowing
Carrier States (5)
- asymptomatic
- incubating
- convalescent
- chronic
- passive
Asymptomatic
infected but show no symptoms of disease
Incubating
spread the infectious agent during the incubation period
Convalescent
recuperating patients without symptoms: they continue to shed viable microbes and convey the infection to others
Chronic
individuals who shelter the infectious agent for a long period after recovery because of the latency of the infectious agent
Passive
risk of picking up pathogens mechanically and accidentally transferring them to other patients
Living Reservoirs - Animals
vectors = a live animal that transits an infectious agent from one host to another
Zoonosis
an infectious disease indigenous to animals that humans can acquire through direct or indirect contact with infected animal
Living Reservoirs - Biological Vector
- actively participates in pathogen’s life cycle
- communicates the infectious agent to human host by biting, aerosol, touch
Living Reservoirs - Mechanical Vector
transport pathogen without being infected
Non-Living Reservoirs
- soil, air, water
Communicable
when an infected host can transmit the infectious agent to another host and establish infection in that host
Non-Communicable
- occurs primarily when a compromised person is invaded by his/her own microbiota
- when an individual has accidental contact with a microbe that exists in a nonliving reservoir
- doesn’t arise through transmission of the infectious agent from host to host
