Introduction to Infection Flashcards
Why do we need to know the cause of infection?
- need to be able to measure infection with the correct tests
- need to give the correct treatment
- need to know the appropriate biosecurity measures to stop it spreading
- need to know what vaccines will be effective
- need to understand the disease progression
What is the definition of infection?
- colonisation of an individual by an infectious agent
What is the definition of a disease?
- when normal bodily functions are impaired, reducing performance and leading to clinical signs
What is a carrier?
- any animal that can spread the pathogen
What is aetiology?
- the cause, or causes of a disease or condition
- not all disease have a single aetiology some have multiple
What is an incubation period?
- the time period between infection and when clinical signs are observed
can be a few days - months/years
What is an infectious period?
- the time interval during which a host is infectious
Why is incubation period important?
- helps with diagnosis
- helps with treatment
- important for biosecurity
What are 4 ways we can categorise infectious agents?
- By size
- by location
- by evolutionary classification
- by transmission
Size - what are microparasites?
- parasitic organisms you can see by the eye
- multicellular
- fleas, mites, ticks, worms (nematode, tapeworm, trematode)
Microorganism lifestyles can be what?
- parasitic
- opportunistic
- mutualism/commensal
- symbiosis
- saprophyte
Describe a parasitic lifestyle
- can cause a disease by themselves
- can infect healthy individuals
- commonly require a host to reproduce
Describe a opportunistic lifestyle
- infection caused by an infectious agent due to an opportunity that has occurred allowing the infection to occur
- weakened immune system
- removal of a microbiome
- breached barrier
- current infection
Describe a commensal/mutualism lifecycle
- a relationship where one or both benefit, but without detriment affect to either party
- commensals can become opportunistic
Describe a symbiosis lifecycle
- a relationship where both organism benefit and are dependent on each other
- e.g., microbiome in cattle/ horse GI tract
Describe a saprophyte lifecycle
- microorganism that lives on dead or decaying organic matter
- impact of saprophytic bacteria on post-mortems of animals
How do we classify infectious agents by location?
- extracellular or intracellular
- localised or disseminated
What can location be split into for parasitology?
- endoparasites (helminths, protozoans)
- ectoparasites (fleas, ticks, lice, mites, monogeneans)
where are most ectoparasites found?
- skin
where are most helminths found?
- alimentary
- cardiorespiratory
where are most protozoan parasites found?
- blood-borne
How can pathogens be divided based on evolution?
- organisms are either prokaryotic or eukaryote
Why are viruses an exception to evolution categories?
- viruses are neither prokaryotic or eukaryote
- they don’t fully meet definition of an organism
- no virus can replicate independently
What are prions and why don’t they fit into the evolution category?
- they don’t fit into prokaryote or eukaryote
- just proteins but transmissible
- can misfold host prion proteins
- cause Bovine Spongiform Encephalopathy
What is a Eukaryotic cell?
- eukaryotic cells have a nucleus and other organelles that are surrounded by a membrane
- they are found in multicellular organisms
What are the components of a eukaryote?
- plasma membrane
- cilia
- cytoplasm
- cytoskeleton
- centriole
- lysosomes
- peroxisome
- mitochondria
- ER
- Golgi apparatus
- nucleolus
- nucleus
- nuclear envelope
- ribosomes
What is a prokaryotic cell?
- prokaryotic cells from single-celled organisms such as bacteria
- they do a membrane bound nucleus or organelles
What are the components of a prokaryote?
- nucleoid area containing DNA
- capsule
- plasma membrane
- cytoplasm
- flagellum
- plasmid - small circles of DNA
- ribosomes
Why does it matter whether an infectious agent is prokaryotic or eukaryotic?
- immune recognition varies between the two
- treatments are designed to interact with unique molecules in the pathogen
- different structures are found in prokaryotic/eukaryotic organisms
What are Toll-like receptors?
- they are receptors in key immune cells that can recognise specific pathogen-associated molecular patterns (PAMPs)
What routes do pathogen have to transmit?
- ingestion
- aerial transmission
- direct contact
- indirect contact - e.g., fomites
- inoculation - vector bone bites
- iatrogenic transmission - creates by doctor
- across placenta
What can transmission be subdivided into what?
- Horizontal
- Vertical
- transmission can be both
What is horizontal transmission?
- transmitted from any individual to another of the same generation
what is vertical transmission?
- transmission from one generation to the next by infection of embryo/foetus/newborn by parent
What is a direct lifecycle?
- a lifecycle in which a parasite is transmitted directly from one host to the next without an intermediate host or vector
What is an indirect lifecycle?
- where one or more intermediate hosts are required
