Disease Reservoirs and Transmission Flashcards
Disease transmission is a result of the interaction between what 3 things?
- The host
- The agent
- The environment
Who is considered the Father of Epidemiology?
John Snow
What did John Snow publish in 1849?
Evidence that cholera is transmitted by fecal-oral route and by the water supply.
What is this?
A spot map: with most of it’s concentration at the center.
John Snow created it to show that a well pump was the source of cholera in London.
Robert Koch first isolated which bacterium to prove what?
Bacillus anthracis to prove that it really causes anthrax.
This was the beginning of the modern germ theory.
Louis Pasteur developed and tested early ______ in sheep, goats and cattle.
Vaccines
Who was Typhoid Mary?
She was an asymptomatic carrier of Salmonella typhi that caused outbreaks of Salmonella wherever she went/cooked. She was forcibly quarantined for most of her life.
In 1897 Ronald Ross discovered what?
That mosquitoes transmitted malaria.
In 1900, Walter Reed discovered what?
That mosquitoes transmit Yellow Fever.
Disease transmission can be represented by a _______ ____ ______.
Chain of events.
Chain of Infection
What is a reservoir?
Habitat in which an infectious agent normally lives, grows and multiplies (humans, animals or the environment.)
Reservoirs maintain pathogens over time, from year to year ot generation to generation.
When trying to recognize a reservoir, what 3 questions should you be asking yourself?
- Is it naturally infected with the pathogen?
- Can the species of animal maintain the pathogen over time?
- Can this source transmit the disease to a new susceptible host?
With regard to Trichninella, pigs and bears are considered to be what type of host?
People are considered what type of host?
- Pigs and bears* are reservoir hosts.
- People* are accidental hosts.
Pathogens mutate to escape immunity so that animals become _______ again over time.
Susceptible
Pathogens can evade immunity, allowing _________ to occur after a short period of time.
Reinfection
Pathogens can cause chronic infections with minimal symptoms called what?
Balanced pathogenicity
Infection does not equal ______ which does not equal ________.
Infection does not equal disease which does not equal infectivity.
Clinically ill animals that are reservoir competent are probably what?
Infectious
- But so are asymptomatic carriers…*
- However not all ill animals are reservoirs.*
What are the 2 major types of transmission?
Horizontal and Vertical
What is vertical transmission?
From reservoir host to offspring.
Can be congenital: some pathogens can cross the placenta, infect eggs, etc.
Can also be perinatal: during parturition or via colostrum/milk.
What is horizontal transmission?
From the reservoir to a new host.
Can be direct: directly from the reservoir to a susceptible host.
Can also be indirect: via any sort of intermediary, animate or inanimate.
Horizon/Direct Transmission can occur 1 of 3 ways which are what?
- Direct contact
- Direct projection
- Airborne
What is direct contact?
Skin-skin contact, mucous membrane contact (including sexual transmission), direct contact with a soil reservoir (bite, scratch, etc…)
What is direct projection?
Droplet spread.
Wet, large and short range aerosols (sneezing, coughing, or talking.)
What is airborne transmission?
This is considered to be a form of direct transmission because disease agents do not generally survive for extended periods within aerosolized particles.
What is a vehicle?
An inanimate object that can indirectly spread disease.
ex: Food, water, contaminated IV drugs, fomites: farm boots, surgical tools, or an actual vehicle (such as a tractor).
What is a vector?
A living organism (mostly arthropods) that serves to communicate disease indirectly.
2 types: mechanical or biological
- Mechanical= the agent DOES NOT multiply or undergo part of it’s life cycle while in/on the arthropod.*
- Biological= the agent undergoes changes or multiplies while in the vector; these activities are required for transmission.*
What type of disease transmission is Lyme Disease?
West Nile Virus?
Horizontal indirect transmission
same as Lyme Disease for WNV.
