Infectious disease & transmission

Question 1

infectious disease

Answer 1

disease caused by pathogenic agent

Question 2

pathogenic agent

Answer 2

organism that impairs normal funtioning and is typically manifested by distinguishing signs and symptoms

Question 3

infectious

Answer 3

communicable aka infectious, transmittable, contagious (can be passed on to others)

Question 4

types of pathogenic agents (aka germs)

Answer 4

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

Question 5

pathogenic agents

Question 6

prions

Answer 6

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

Question 7

viruses

Answer 7

have a core of genetic material and can only replicate inside a living cell of an organism
- ex: avian influenza - respiratory disease affecting poultry

Question 8

bacteria

Answer 8

simple single celled microbes, different types can be helpful and harmful
- ex: mastitis - causes inflammation of the mammary gland in udders
- treated w/ antibiotics

Question 9

fungus

Answer 9

multicellular microbes, may form parasitic or mutually beneficial relationships w/ animals and plants
- ex: ringworm - skin fungal infection found in cattle, sheep, dogs cats

Question 10

protozoa

Answer 10

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

Question 11

multicellular parasites

Answer 11

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

Question 12

Agent characteristics

Answer 12

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

Question 13

epidemiological triad - who, what, where

Answer 13

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

Question 14

agent transmission

Answer 14

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

Question 15

direct transmission

Answer 15

vertical: dam to offspring in utero or after birth
horizontal: direct contact

Question 16

indirect transmission

Question 17

vector: mechanical

Answer 17

• 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

Question 18

vector: biological

Answer 18

• 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

Question 19

fomite (very common)

Answer 19

• 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

Question 20

zoonoses

Answer 20

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!

Question 21

natural history of disease

Answer 21

1. stage of susceptibiltiy
2. stage of pre-symptomatic disease => been infected but sub-clinical
3. stage of clinical disease => observing changes in animal
4. stage of disability or recovery

Question 22

What is the difference b/twn clinical signs and symptoms?

Answer 22

clinical: where we focus animals on, observable changes due to illness
symptoms: subjective => assessing behavior => doses of meds

Question 23

screening vs. diagnostic testing

Answer 23

screening: detect disease when it’s subclinical

-both are needed for reducing disease transmission

Question 24

levels of prevention

Question 25

primary prevention (prevention)

Answer 25

• interventions occur before infection
• health promotion and protection
• ex: vaccine programs, routine screening/examinations, biosecurity practices

Aim: increase host resistance/decrease susceptibility

Question 26

secondary prevention (screening)

Answer 26

• early detection/screening
• before clinical signs (ideally): subclinical happening
• known serious diseases

Aim: early detection, reduced transmission, increased chance of treatment success (early detection)

Question 27

tertiary prevention (treatment)

Answer 27

• disease established: clinical signs and symptoms
• treatment and rehabilitation
• most expensive & resource intensive

Aim: stop/reduce disease progressions, minimize risk of transmission

Question 28

temporal patterns of disease

Question 29

sporadic

Answer 29

occurs only occasionally in a population

Question 30

endemic

Answer 30

disease is habitually present w/n given geographic area, at an expected level

Question 31

epidemic

Answer 31

disease appears at an increased level, during given period, at a rate that substantially EXCEEDS WHAT IS ‘EXPECTED’

Question 32

pandemic

Answer 32

widespread over a large area, wordwide epidemic/crosses international boundaries