Infectious Disease - Mechanism of Transmission Flashcards
Koch’s postulates to determine the causality of disease (4)
1) microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms
2) microorganism must be isolated from a diseased organism and grown in pure culture
3) cultured microorganisms should cause disease when introduced into a healthy organism
4) microorganisms must be preisolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent
-CORRECT***
Problems with the postulates
1) microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms
-organisms like Staph, enterococcus found in both healthy and diseased organisms
2) microorganism must be isolated from a diseased organism and grown in pure culture
-not all organisms can be cultured, you can also isolate from a healthy individual
3) cultured microorganisms should cause disease when introduced into a healthy organism
-doesn’t always happen, can be asymptomatic
Disease process stages (5)
1) Incubation period
2) Prodromal period
3) Illness
4) Decline
5) Convalescence
Which stage determines how effective a pathogen is at spreading?
incubation period length
longer incubation periods = better at transmitting
short incubation period = host feels ill and take themselves out
Incubation period
interval between the introduction of an organism and the onset of the illness
asymptomatic
don’t know you’re sick
not taking steps to prevent spread
when you’re infectious
days: influenza (1 to 3), COVID (3 to 5)
weeks: varicella
years: myobacterium tuberculosis
Prodromal period
organisms actively multiplying and causing damage to host
vague, non-specific
general symptoms
fever, malaise, myalgia, loss of appetite, runny nose, conjunctivitis
infection has amplified in the host, taking over
e.g. tingling sensation before a cold sore
Illness
most severe signs and symptoms
organisms are actively multiplying in the host
clinical presentations at its peak
host is still infectious but typically less likely to transmit
feeling unwell, likely remove themselves from environment
Decline
declining signs and symptoms
Convalescence
no signs or symptoms/minimal
back to normal
period that follows active illness
patients may still be contagious (not always)
pathogen load tends to be lower than during active infection
can be fairly prolonged, with pathogen still detectable
T or F: Diseases will exhibit all 5 stages.
FALSE
Natural History of an Infectious Disease - Phases (2)
1) Pre-clinical
2) Clinical
Pre-clinical phase
A - biologic onset of disease
P - pathological evidence of
Between pre-clinical and clinical phase
S - signs and symptoms
Clinical phase
M - medical care sought
D - diagnosis
T - treatment
T or F: Diagnoses tend to be sought early on in the disease course.
FALSE
usually well into your illness when you seek care
diagnosis is late
Carrier state
someone that harbours an infectious agent for prolonged periods of time
WITOUT showing any overt clinical symptoms / signs
able to spread the pathogen
plays a major role in maintaining the chain of infection within a population
e.g. Chlamydia trachomatis, Mumps, HSV-1, HSV-2.
Famous example of a carrier
QUIZ/EXAM Q***
Mary Mallon “typhoid Mary”
food handler in the early 1900 in NY state
infected: Salmonella Typhi (typhoid), SUBCLINICAL disease
kept cooking and spread outbreaks, killing many people
typhoid caused by a specific type of salmonella
S. Typhi leads to typhoid fever but also can seed an individuals gall bladder and result in the establishment of a carrier state (sometimes life long without Tx)
form of salmonella that is extra intestinal
goes from gut to blood, can go into gallbladder
if in gallbladder - stays there and is continuously shed in urine
Following symptom onset - types of infections (3)
1) Acute
2) Chronic
3) Latent
Acute infection
rapid onset and usually lasts a short period of time
often highest pathogen burden.
Chronic infection
disease develops and established a steady state and lasts a long time
for life
e.g Mycobacterium tuberculosis, HIV, herpes family
Latent infection
typically sub-clinical
may reactivate from time to time
infection is never really eliminated
latent phenotype
3 opportunistic infections you can get with HIV
EXAM Q**
1) aspergillus
2) candida
3) salmonella
HIV stages following symptom onset
virus replicates in CD4 cells
usually use CD4 as a way of assessing immunocompromised
lower=more immunocompromised
initially - huge drop in CD4 count
recovers, but then depletes over time in a chronic fashion
CD4 count of 200 = AIDS, at risk for opportunistic infections like aspergillus
Reservoirs of Infectious Diseases (3)
1) Human
2) Animal
3) Non-living
