Module 1: Infectious Disease Epidemiology Flashcards
Of 1,415 known Human pathogens:
61% are Zoonotic
75% of emerging pathogens are Zoonotic
Five major types of Infectious Agents:
- Bacteria
- Viruses
- Fungi
- Protozoa
- Helminths
Diseases that are they transmissible between vertebrate animals and humans under natural conditions
Zoonoses
Diseases that are transmissible between Humans
Anthroponoses
- Diseases that are transmissible from the ABIOTIC environment (e.g. soil, water) to humans
- Infectious agents must survive and grow in such an environment
- May also be zoonotic (saprozoonoses)
Sapronoses
- Diseases transmitted from humans to animals
- Often “zoonoses” is used
Zooanthroponosis
an organism (“pathogen”) that is capable of producing infection or infectious disease
Infectious Agents
What are NOT a zoonotic diseases?
- Toxins or Venom
- Animal infectious diseases that are transmitted experimentally but not naturally
- Human (only) infectious diseases transmitted by contamination of animal products
- Human infectious diseases transmitted by arthropods without an animal in the pathogen’s lifecycle
The ability of organism to penetrate and reproduce in a host; does not imply disease
- Proportion of individuals exposed to the agent that become infected (infected/exposed)
Infectivity
Ability of organism to cause disease
- proportion of infected individuals that develop clinical disease (diseased/infected)
Pathogenicity
Ability of organism to cause severe disease or death
- Proportion of diseased individuals that develop severe disease (severely diseased/all diseased)
- Proportion of infected cases that die from the condition (cause-specific deaths/all diseased)
Virulence
- Capable of becoming infected with the agent under natural conditions and diseases may occur
- Survival and/or development/replication of the agent can occur in the host
- Infected host can serve as a reservoir
Host (“susceptible host”)
Maintains the infection in the endemic state
- e.g., mice - hantaviruses
Natural Host
Does not normally transmit the agent
- e.g., horses - West Nile virus
Dead-end host
Supports rapid multiplication of the agent
- e.g., pigs - Nipah virus
Amplifier host
Chain of infection
- Agent must have a port of exit from the infected reservoir into susceptible host (portal of entry)
- Aerosol —>
- Feces —>
- Urine —>
- Blood —>
- Respiratory
- Gastrointestinal
- Broken skin
- Broken skin
Direct contact – spread through contact with open wounds, mucous membranes, or abraded skin contacting an infected animal or its tissues or fluids (e.g., blood, saliva, urine)
* Touching, biting, scratching
* Contaminated droplets
* Contaminated urine or body fluids
* Contaminated reproductive discharge
These are examples of:
Horizontal Transmission
Direct contact – spread through contact with open wounds, mucous membranes, or abraded skin contacting an infected animal or its tissues or fluids (e.g., blood, saliva, urine)
* Transplacental
* Transmammary
These are examples of:
Vertical transmission (mother-to-offspring)
spray with relatively LARGE, SHORT-RANGE aerosols by sneezing, coughing, or talking – classified as DIRECT TRANSMISSION
Droplet
Indirect contact – spread through an intermediary vehicle or vector
- the spread of pathogens through contact with inanimate objects, contaminated by an infected animal
Formite
Indirect contact – spread through an intermediary vehicle or vector
- Ingestion of disease-causing agents from contaminated food or water
Oral
transfer by an arthropod that acquires a disease agent from an animal and transmits it to a person
Vector-borne
Vector-borne
- NO multiplication or development of the agent
Mechanical vector
Vector-borne
- multiplication or development of the agent occurs
Biological vector
(SMALL PARTICLES) – classified as INDIRECT transmission
* Travel large distance (>3 meters)
* Can remain suspended in the air for an extended period
* Enter the respiratory tract
* Infrequent route of zoonotic disease transmission
Airborne
Multiple Modes of Transmission
* Vector-borne (fleas)
* Aerosol (humans)
Plague
Multiple Modes of Transmission
* Food-borne (milk)
* Direct contact with infected animals
Brucellosis
Multiple Modes of Transmission
* Vector-borne (ticks)
* Airborne
* Direct contact with infected animals
Tularemia
Multiple Modes of Transmission
* Food-borne (intestinal)
* Direct contact (cutaneous)
* Airborne (respiratory)
Anthrax
When is it difficult to identify source?
If there are multiple risk factors/transmission pathways
What are the risk factors for infectious disease?
- Age (young, elderly)
- Pregnant
- Immune-compromised
(YOPI)
A mosquito that acquires an infectious agent from an animal, further develops the agent, and then transmits it to a person by taking a blood meal is an example of?
Biological vector
This statement “Proportion of diseased individuals that develop severe disease” best characterizes the:
virulence of an infectious agent
