Principles of infection Flashcards
What does successful transmission of infection depend on?
-Pathogens being able to leave the body of the infected host. -Pathogens being transferred by direct/indirect contact. -Pathogens being able to enter the body of the new host through different ways e.g: inhalation
Define infection
The harmful colonisation of a host by a foreign microorganism
Define disease
The disorder of normal bodily functions which causes specific clinical symptoms
What is direct transmission?
Susceptible animal comes into contact with infected animal (body fluids, lesions) and Aerosol transmission where pathogen is contained in droplets. Close proximity is required.
What is indirect transmission?
Mechanical vectors i.e syringes, needles, bedding….Biological vectors i.e living organisms (insects) that may carry the pathogen to a susceptible host.
What are the 4 routes of entry for a pathogen?
Inoculation - skin/mm…Inhalation and infection- through the resp. tract….Ingestion and infection- through the digestive tract…Transplacental infection- If placenta damaged it could allow infection to pass to developing foetus.
What is virulence?
The quantitative measure of the pathogenicity (ability of pathogen to cause disease)
Some pathogens release tissue damaging substances called toxins, What are exotoxins?
Gram POSITIVE bacteria produce proteins called exotoxins which can damage tissues far removed from the sites at which the bacteria is multiplying.
What are endotoxins?
They’re produced by gram NEGATIVE bacteria (from their cell walls) These toxins are only released when the bacteria cell dies, the effects include fever, diarrhoea, and could progress to death
How can the host’s natural resistance be lowered?
Stress, infection, young animals, genetic factors i.e horses can’t contact foot and mouth disease.
What is a subclinical infection?
The host Is infected but does not show any clinical signs of it. They may carry the virus onto someone else
What is the physical barrier of the immune system?
The skin- the salt in sweat dehydrates bacteria, causing them to shrivel….MM- coats the openings which can trap viruses, dirt, bacteria
Describe the 3 pronged attack in innate immunity
1 Inflammation- More blood goes to the site of infection, bringing more WBCS 2- Phagocytes reach infected tissues and the neutrophils engulf pathogens (phagocytosis) 3- Interferon, a chemical is released by infected cells, healthy cells take this up to resist attack from the virus
What cells is Acquired immunity made up of?
B lymphocytes, T lymphocytes
What do B lymphocytes do?
They produce plasma and memory cells which create antibodies for if the pathogen occurs in the future
