Lecture 6 - Infectious Dz & Pathogenesis Flashcards
What are saprophytes
microbes that feed off of dead/decaying tissues
not a true ‘pathogen’ since host/tissue already deadWh
What are pathogenic heterotrophs?
feed off of living cells/tissues
feeding will cause host damage (to cells so they release nutr.)
pathogen lives in/on host - can be outside/inside host cell
Intracellular pathogens exist inside the host cell - all viruses are intracellular pathogens, only some bacteria are IC pathogens
How much damage can a pathogen cause?
pathogens have a neg relationship with their hose - host is being damaged while pathogen benefits
most successful pathogens evolved to cause limited amount of damage to host - if host dies, it no benefits
exception is pathogens can easily spread/infect other hosts - kill current host and move on
What are primary pathogens
disease-causing microbes w/ means to breach defences of healthy host
can survive natural defense barriers and initial immune attack and begin replicating
What are oppertunistic pathogens?
only cause dz in immunocomp host
have ability to cause dz but req,
1. lrg # of bact
2. immunocomp system
Part of normal flora - immunocomp cannot regular microbes
Also acquired thru enviro/others
What are the steps to microbial dz?
- transmission
- infection - entry, attachment colonization
3, replication - tissue damage
- spread within host
- spread outside host
Explain transmission in steps of microbial dz
SPREAD OF DISEASE
- normal flora no need to be transmitted
all others are acquired via transmission
What is direct transmission?
anim-anim
req physical contact btw infect-suspectible
microbe does not spend significant time in enviro
same household, herdWha
tWhat are types of direct transmission
touching, kissing, sex, contact with body lesions/fluids
Aerosol transmission - respiratory droplets
What is indirect transmission
microbe acquired from surface/enviro
microbe spent time in enviro
types:
fomites, waterborn, airborne, vectorborn
What are fomites? examples?
inanimate objects
Household - water/food bowls, bedding
clinic/vet - stethoscopes, weigh scales
enviro - dirt, wood, straw bedding
What are airborn trasmissions
pathogens carried in evaporated droplets or dust from one loc to another
can travel far, land on fomite, very sm, very resist to drying
ex anthrax
What are vector-borne transmission
vector = sml anim capable of transmit dz
usually insects - mosquito, ticks, fleas, flies
vector no pathology, but carries to susceptible animal
What is fecal-oral transmission
organisms in feces are ingested
direct or indirect (grooming, eat contam food/water/soil)
Parvovirus, salmonella
How to reduce fecal-oral transmission
cook ur food, handwashing, protect water supplies, feed away from feces, pick up dog poop
What is verticle transmission
Mother-child
ex FIV, hepatitis B
In utero - from mom blood to placenta to fetus
Trans-vaginally - neonate exposed in birthing canals, enters via swallowing thru MM
Via nursing - pathogens enter mam glands into colostrum - drank by neonate
What is horizontal transmission
other routes than mom-child
indirect/direct
EX. feedlot
What are nosocomial infection/
dz acquired in hospital/clinic
direct/indirect
aerosols from another patients, fomites, contam fluid (saline squirt bottle, reuse IV fluids)
Always concerning bc microbes have inc change of drug resist + inc chance that suspectible animal is immunocomp
Zoonosis
anim-human
indirect or direct
contact w/ blood, urine, feces, bitten by tick/mosquito(vector), eat/drink unsafely - unpasteruized milk
What are some important zoonoses?
rabies, salmonella, e. coli, campylobacter
What is endemic dz?
always present in popul. at expected, low lvl
Seasonal flu, common cold
What is an epidemic dz
sudden inc in # of cases in period of time within a popul.
rapid spreading, stays WITHIN community
ex ebola
What is a pandemic dz?
widespread epidemic
more cases/short period, spread within community - adjacent communities
due to new infectious dz (new strain/species), popul lack prior exposure
Ex. covid 19
Explain infection in steps of microbial dz
3 parts
Entry - disruption of barriers in entry/adhesion. minimum # must enter to cause DZ (Minimun infectious dose)
attachment - attach to cells before replication, attach vai fimbriae, pilli, lipopolysacc, slime layers, receptors on surface of bact recognize and bind to specific host cell receptors
establishment - multiply, if immune attacks/eliminate faster than replication rate, animal no sick. If received MID, immune not quick enough
What is the minimum infectious dose?
minimum # of microbes to enter to cause dz
inhale 5 cold virus no work but 10,000 will
MID req; pathogenicity + immune state of host
What is pathogenicity?
measure of how much dissue damage a microbe can cause
What is direct damage?
due to an action of the microbe
bact/fungi prod damaging toxins to release nutr. + spread to other tissues (hemolysin causes RBC break down)
Virus’ use host cells as “factories for multiplication” and will kill cell to release new viruses
What is indirect damage?
occures when immune reacts to presences of infectious microbe
activates - some degree of inflamm
inflame always non-specific and damages host tissues in process of destroying bact
Describe the disease course
specific to pathogen/host
follow same pattern
infection (entry, attach, multi)
incubation
prodromal
Clinical (symptomatic)
resolution -> convalescence
What does the ability to cause dz depend on?
infectiouse dose
pathogenicity of microbe
immune status of anim
Describe the incubation period
time btw exposure to pathogen when clinical signs first appear
hrs, dys, wks, mo, yrs
NO clinical signs
pathogen is establishing/multiplying
microbes shed during incube
What is the prodromal period
when there are non-specific signs
pathogen established, numbers still low
What is the clinical period
symptomatic period
highst #’s of infectious organisms
clin signs specific to pathogen
easiest diagnosable stage
What is resolutiong in dz?
period of dec #’s of pathogen + dec of severity of clin signs
What is convalescnece?
period when specific symptoms are Gone - infectious organisms still present at low numbers
body return to normal state - inc risk of other dz/re-infection
infectious organisms still present so anim can shed infectious organisms
What is reinfection, reccurent and resistant alt endings?
Reinfect - infection completely resolves but started again from transmission stage. Underlying issue
Reccurent
Resistant - issue never completely resolves, still present
What are chronic infections - chronic symptomatic/asymp?
chronic symp - persists with continued sympto dz
chronic asymp - infection @ low lvls, low lvls of replication, no clin signs, may/may not transmit
What is latent infection
chronic asymp infection
organisms remians in host, not actively repli or prod pathogenic factors, no transmission
IF its reactivated, returns to clin stage and transmissable
What is remission/relapse?
remission - clin signs temporaryily absent, stay in remission for long/short period, was never cured
Relapse - when clin signs present
infectious organism start to replicate again if latent or prod pathogenic factors
