Topic 1 - Definition of infectious diseases, sources of infection, factors influencing infectious diseases (pathogen-host relationship, protection of the host, environmental factors) Flashcards
What is epidemiology?
It is the study of diseases in populations and of factors that determine their occurrence.
With which steps do we investigate a disease?
- Occurrence
- Aetiology: Which pathogen is responsible?
- Epidemiology: What are the circumstances, how the disease evolves, how is it spread
- Pathogenesis
- Clinical signs
- Post mortem lesions: pathology
- Diagnosis
- Treatment
- Prevention: vaccines
- Control
- Eradication
- Public health
What is the Epidemiologic triangle?
Used to investigating how a disease spreads and how to combat it
What is included in the Epidemiologic triangle?
- Agent
- Host
- Environment
What is the “agent” in the Epidemiologic triangle?
The agent is the microorganism that actually causes the disease
Name the 4 main classes of infectious agents:
Bacteria, virus, fungi, parasites
What is the “host” in the Epidemiologic triangle?
The agent infects the host, which is the organism that carries the disease.
A host doesn’t necessarily get sick; hosts can act as carriers for an agent without displaying any outward symptoms of the disease.
Hosts get sick or carry an agent because some part of their physiology is hospitable or attractive to the agent
What is the “environment” in the Epidemiologic triangle?
Outside factors can affect an epidemiologic outbreak as well.
The environment includes any factors that affect the spread of the disease but are not directly a part of the agent or the host. For example: temperature, feed, management
Name the PHASES of infection:
- Entry
- Colonisation
- Replication
- Host damage
- Transmission
What is the “entry” phase of infection?
The entry is where the organism enter the body. It need to be optimal for the infection to be effective. Entry can be natural orifices or per cutaneous
What is the “colonisation” phase of infection?
Pathogens are present on the body site, but cause no harm - they cause no symptoms of infection
What is the “replication” phase of infection?
Create new infectious virons that are able to infect other cells of the body
What is the “transmission” phase of infection?
The spreading of the disease.
What are the sources of disease?
Direct of indirect route
What is “direct” route of infection?
Animal to animal, through contact
Give example of direct route of infection:
- Teeth of rabid animal get in contact with the animal of the susceptible host
- Sexual transmitted diseases
What is “indirect” route of infection?
No direct contact between the animals
Give example of direct route of infection:
- Excretions/secretion
- Artropods
- Water/food
- Soil/environment
- Animal products
What are the main directions of transmission of a disease?
Vertical
Horizontal
What is the horizontal direction of transmission of a disease?
Transmission between same generation. adult to adult
What is the vertical direction of transmission of a disease?
Transmission between to generation.
What are the different vertical direction of transmission of a disease?
- Germinative = birds
- Intrauterine = inhertied
- Galactogen = through milk
What is zoonosis?
A disease or infection that is naturally transmissible from vertebrate animals to humans
Name the different types of zoonosis:
- Ortho zoonosis
- Cyclo zoonosis
- Meta zoonosis
- Sapronoses
What is Orthozoonosis?
Direct and indirect transmission, animal to host
What is Cyclozoonosis?
Require more than one vertebrate host for development.
What is Metazoonosis?
require both vertebrates and invertebrates for the completion of their infectious cycle
What is Saprosonoses?
the infection happens from the environment
Name the different forms of infection:
- Simple
- Repeated
- Multiple agents
What is the repeated form of infection?
The same pathogen returns.
What are some complication of repeated form of infection?
We can have exacerbation or a superinfection
What is exacerbation?
A worsening of the disease. The body and immune system is weak, so pathogen will cause a severe infection
What is superinfection?
The infection last for a long time, and the animal will get infected with the same or with another disease.
Name some influencing factors for the ability of a pathogen to infect a host:
- Spectrum
- Pathogenicity
- Virulence
- Invasiveness
- Way of entry
- Environment
Which type of spectrum can an infection have?
Euryxen
Stenoxen
What is euryxen?
The host is wide ranged
What is stenoxen?
The host is narrow range
What is the pathogenicity?
The ability to cause a disease
What is virulence?
ability of an organism to infect the host and cause a disease.
The virulence can change:
Increase: Passaging in animals
Decreased: passaging in tissue culture or genetics
LD50 and MLD
What is invasivness?
Passing the defence lines/immune system.
There are some intracellular and extracellular agents, the intracellular is harder to fight for the immune system.
Name the influencing factors of the disease in the host:
Resistance
Environment
What are the different resistance factors of a host?
Non-specific resistance
Specific resistance
What is Non-specific resistance?
can be provided by the barriers of the immune system, such as the skin, mucous membranes.
Non-specific = innate immunity
What is specific resistance?
Specific resistance = passive imunity
Can be either natural or induced. The body produce anitbodies/the body is given antiboides to target the specific pathogens.
Name environmental factors that inluence the infectious disease:
- Nutrition
- Management/technology
- Weather
