Infectious disease & transmission Flashcards
infectious disease
disease caused by pathogenic agent
pathogenic agent
organism that impairs normal funtioning and is typically manifested by distinguishing signs and symptoms
infectious
communicable aka infectious, transmittable, contagious (can be passed on to others)
types of pathogenic agents (aka germs)
smallest -> largest (prions, viruses, bacteria, fungi, protozoa, multicellular parasites)
- most are microscopic in size
- important to understand pathogenic agents to prevent and manage infectious diseases in animals
pathogenic agents
prions
consist primarily of proteins, cause neurodegenerative diseases, always fatal
- when identified, usually too late
- ex: bovine spongiform encephalopathy (BSE) aka mad cow disease
- feed on other neurological tissues in other cows
- preventative approach
viruses
have a core of genetic material and can only replicate inside a living cell of an organism
- ex: avian influenza - respiratory disease affecting poultry
bacteria
simple single celled microbes, different types can be helpful and harmful
- ex: mastitis - causes inflammation of the mammary gland in udders
- treated w/ antibiotics
fungus
multicellular microbes, may form parasitic or mutually beneficial relationships w/ animals and plants
- ex: ringworm - skin fungal infection found in cattle, sheep, dogs cats
protozoa
single celled microbe, free living or parasitic
- ex: coccidiosis in chickens
- parasite that damages intestinal systems
- most economically important disease in poultry
- ingest => GI damage => can be fatal
multicellular parasites
helminths (worms) and arthropods (attach to skin like fleas, ticks, lice etc)
- ex: roundworms
- bed and dairy cattle, sheep, goats, dogs, cats
- prevalent in environment
Agent characteristics
infectivity: ability to invade a host
- how does it infect host? how good is it?
- age, immune system, living environment
pathogenicity: ability to cause disease
- clinical/subclinical
- has to cause enough damage to see clinical signs
virulence: degree of disease severity
- high: pathogens get in host and kill animal quickly = reduced change of transmission
- low: longer to infect host = increase chance of transmission
epidemiological triad - who, what, where
host
- species: can’t infect all species
- immune system function
- age, sex, breed
- nutritional status
environment
- facility, system management, biosecurity
- contact w/ wildlife, water runoffs
- where food/water comes from
- climate => seasonality
- housing
agent
- type, how they infect
- life cycle, food/water/air
- secondary host?
- how to kill it
agent transmission
for an agent to move around in a population, it must escape from an infected host, and find a new susceptible host
transmission: movement of pathogen from one infected animal to a susceptible animal or a group of susceptible animals in the infected population; many levels of transmission
- direct and indirect
direct transmission
vertical: dam to offspring in utero or after birth
horizontal: direct contact
indirect transmission
vector: mechanical
- organisms carry agent from one host to another without being infected itself
- carriers usually arthropods
ex: pink eye
- bacterial agent transmitted by flies (face fly) => eat eye secretions and go from animal to animal
- common disease, difficult to control
- painful, may cause ulcers and blindness
- treatment: vaccines, preventative measures to control fly populations, fly tags
vector: biological
- organisms carry the agent w/n their body from one host to another
- fleas, ticks, mosquitoes common vectors
- vector may or may not be harmed by agent
ex: heartworm
- small larvae (microfilaria) in infected dog’s bloodstream, picked up by mosquito, larvae develops, mosquito infects new dog through bite
- adult worms live in dog’s heart, lungs and blood vessels
- treatment and prevention: anti-parasitic drugs => can cause heart problems if given when they’re already infected
fomite (very common)
- inanimate object carries agent from one animal to another
ex: avian influenza type A viruses - shed into bird’s droppings
- poultry vet wears boots on an infected farm w/ avian influenza then visits another farm w/ the same boots
- fecal droppings on the boots transmits virus
- prevention: biosecurity measures, management practices
- treatment: anti-viral medications, depopulation for severe strains of the virus
zoonoses
diseases in nature that are shared by vertebrate animals and humans
- more than 75% of emerging diseases are zoonotic
ex: US salmonella outbreaks (1.35M illnesses, 26,500 hospitalizations, 420 deaths/yr in US)
- 2021 backyard poultry: illnesses - 1,135, hospitalizations - 273, deaths - 32
- droppings in beddings get into feathers
- 2021 pet turtles (droppings): illness - 87, hospitalizations - 32, deaths - 1
- wear gloves
- 2019 pig ear dog treats: illness- 154, hospitalizations - 35, deaths - 0
- wash hands!
natural history of disease
- stage of susceptibiltiy
- stage of pre-symptomatic disease => been infected but sub-clinical
- stage of clinical disease => observing changes in animal
- stage of disability or recovery
What is the difference b/twn clinical signs and symptoms?
clinical: where we focus animals on, observable changes due to illness
symptoms: subjective => assessing behavior => doses of meds
screening vs. diagnostic testing
screening: detect disease when it’s subclinical
-both are needed for reducing disease transmission
levels of prevention
primary prevention (prevention)
- interventions occur before infection
- health promotion and protection
- ex: vaccine programs, routine screening/examinations, biosecurity practices
Aim: increase host resistance/decrease susceptibility
secondary prevention (screening)
- early detection/screening
- before clinical signs (ideally): subclinical happening
- known serious diseases
Aim: early detection, reduced transmission, increased chance of treatment success (early detection)
tertiary prevention (treatment)
- disease established: clinical signs and symptoms
- treatment and rehabilitation
- most expensive & resource intensive
Aim: stop/reduce disease progressions, minimize risk of transmission
temporal patterns of disease
sporadic
occurs only occasionally in a population
endemic
disease is habitually present w/n given geographic area, at an expected level
epidemic
disease appears at an increased level, during given period, at a rate that substantially EXCEEDS WHAT IS ‘EXPECTED’
pandemic
widespread over a large area, wordwide epidemic/crosses international boundaries
