Disease Reservoirs & Transmission Flashcards
Who is considered one of the early founders of epidemiology?
Which disease was he investigating?
- John Snow
- Cholera
Disease transmission is the result of interaction between what 3 components?
Host, agent, environment
In the 1854 outbreak of cholera in London, how many fatalities were there?
616, up to 12.8% of the people living in the most heavily affected areas
What was found at the center of the cholera outbreak in London?
A well
When are the earliest reports of anthrax?
1491 BC
Who was responsible for the beginning of the modern “germ theory”?
Which bacteria did he work with?
- Robert Koch
- B. anthracis
In 1881, Pasteur was developing and testing what in sheep, goats and cattle?
An early vaccine
Typhoid Mary was an asymptomatic carrier of typhoid fever which is caused by what bacteria?
Salmonella typhi
In 1897, Ronald Ross discovered that malaria was transmitted by what vector?
Mosquitoes
In 1900, Walter Reed discovered that mosquitoes transmitted what disease?
Yellow fever
T/F: In disease prevention, knowing the mode of transmission is generally more important than identifying the specific agent.
True
T/F: Disease transmission can be represented as a chain of events.
True
What are 6 possible links in a chain of infection?
- Pathogen/microorganism
- Reservoir
- Means of escape/portal of exit
- Mode of transmission
- Means of entry/exposure
- Host susceptibility
What is a reservoir?
What are some examples of reservoirs?
- A habitat in which an infectious agent normally lives, grows and multiplies.
- Humans, animals, environment
What is one way pathogens are maintained over time, from year to year or generation to generation?
Reservoirs
Answering yes to which three questions will help to determine if something is a reservoir?
- Is it naturally infected with the pathogen?
- Can that species of animals (human, soil) maintain the pathogen over time?
- Can this source transmit the disease to a new, susceptible host?
Name 4 diseases/pathogens that humans are a reservoir for.
- Smallpox
- Measles
- Mumps
- Taenia solium
Name 4 disease/pathogens that animals are a reservoir for.
- Salmonella spp.
- Toxoplasma gondii
- Feline leukemia virus
- Foot and Mouth disease virus
Name 2 diseases/pathogens for which the reservoir is in the environment.
- Legionella
- Coccidioides
T/F: Pathogens use the same strategy to survive, over time, in the reservoir as a population.
False - They used different strategies to survive.
What are 3 examples of survival strategies used by pathogens?
- Mutate to escape immunity, so that animals become susceptible again over time.
- Evade immunity, allowing reinfection to occur after a short period of time.
- Cause chronic infections with minimal symptoms (balanced pathogenicity).
Does infection = disease = infectivity?
No
T/F: Clinically ill animals that are reservoir competent are probably infectious.
True
Can asymptomatic animals be carriers?
Yes
Are all sick animals reservoirs?
No
What are 2 examples of direct horizontal transmission?
Projection and contact
What are 2 examples of indirect horizontal transmission?
What are 2 examples of both of these?
- Vehicle: common vehicle and fomite
- Vector: biological vector and mechanical vector
What is vertical transmission?
From a reservoir host to its offspring.
What is congenital transmission?
When pathogen can cross the placenta, infect eggs, etc.
What is perinatal transmission?
When transmission occurs during parturition or via the colostrum.
What is horizontal transmission?
From the reservoir to a new host.
What is direct horizontal transmission?
Direct from the reservoir to a susceptible host.
What is indirect horizontal transmission?
Via any sort of intermediary, animate or inanimate.
What are 3 forms of direct, horizontal transmission?
Direct contact, direct projection (droplet spread) and airborne.
What are five examples of direct horizontal contact?
- Skin-to-skin contact
- Mucous membrane contact (including sexual transmission)
- Direct contact with soil reservoir
- Bite
- Scratch
What are examples of direct projection (droplet spread)?
Wet, large and short range aerosols (sneezing, coughing, talking).
Why is airborne transmission considered to be a form of direct transmission?
What is an exception to this?
- Disease agents do not generally survive for extended periods within aerosolized particles.
- Foot and Mouth disease
What is a vehicle?
An inanimate object which serves to communicate disease.
What is a vector?
A living organism that serves to communicate disease.
What are 3 examples of common vehicles?
- Food
- Water
- Contaminated IV drugs
What are fomites?
Objects that can be contaminated and transmit disease on a limited scale.
Are vectors live organisms?
Yes
Most vectors are what?
Arthropods
What defines a mechanical vector?
The agent does not multiply or undergo part of its life cycle while in/on the arthropod.
What defines a biological vector?
The agent undergoes changes or multiplies while in the vector; these activities are required for transmission.
Is Lyme disease transmitted directly or indirectly?
How is it transmitted?
- Indirectly
- Ticks
Is West Nile virus direct or indirect?
How is it transmitted?
- Indirect
- Mosquitoes
In December of 2005 there was an outbreak of this disease in Germany as the result of a hare hunt that took place the end of October that same year.
What was the causative agent of the disease?
- Tularemia
- Francisella tularensis
What was the source of the disease in the 2005 Germany outbreak?
The hare carcasses.
