Principles of Infection Flashcards
(46 cards)
What are the 2 types of parasites?
Commensal - can be opportunistic
Pathogen - conditional
Name the sterile parts of the body
Lower respiratory tract
Blood, joint and subcutaneous connective tissue
Female upper genital tract
Urinary tract 9 (not distal urethrae)
CNS including CSF & eye
Other viscera e.g. liver, spleen and pancreas
What is the result of infections?
Infections cause harm to the host causing disease
What are the 4 Koch’s postulates?
Gene theory states that a microorganism must be:
- Present in every case of the infection
- Cultured from cases in vitro
- Reproduce disease in animals
- Isolated from infected animal
Describe a chronic infection
Slower onset / post acute
May still have major locally / systemic symptoms
Has a chronic inflammatory response when host doesn’t succumb immediately to infection
but can’t clear the infection
e.g. Tuberculosis or chronic osteomyelitis
What are pathogens?
Microbes that cause disease often with small numbers ia natural routes, despite natural barriers and immune defences
Describe the key features of an Acute infection
Rapid onset
Major local & systemic symptoms
Acute inflammatory response
e,g. streptococcus polygenes or straphylococccus aureus
What are the host’s defences?
Innate and adaptive immune system
What is a full pathogen?
Initiates infection via neutral route despite immune defences
What microbial and host mechanisms are kept in balance?
Pathogenic mechanisms
- adhesion, toxins, capsule
Host defensive mechanisms
- natural barriers, defensive cells, complement
What are strict pathogens?
Microbes that will always cause disease e.g Bacillus anthracis (anthrax)
What are the body’s natural barriers?
- skin
- eyes
- GI tract
- lungs
- Gut
Give an example of a toxin mediated acute infection
Diphteria (cornyebacterium diphtheriae Tetanus - gram +ve rods - terminal drumstick spores - anaerobe , soil dweller - opisthotorius = severe hyperextension
What is saprophyte?
Saprophyte is a free living organism living on decaying organic matter
How is inflammation regulated?
Inflammation is an ordered process that is regulated via
- Vasodilation
- Oedema
- Complement activation
- Clotting
- PMNs recruitment
- Mast cell degradation
How do host cells respond to pathogens and commensals?
Normally the host cell will manifest an inflammatory response to a pathogen, but not to a coloniser at a normal non sterile site
What is asymptomatic infection?
Pathogenic microbe infection (not commensal or normal flora)
- mild / no inflammatory response
- damage to host is mild / not at all
e.g. chlamydia trachornitis (urethral in males, cervical in women)
50% men asymptomatic
80% women symptomatic
What is inflammation?
Response to tissue injury
Brings serum molecules and cells to infection sites
What are latent infections?
A virus that never leaves the body and can be reactivated
e.g. chocken pox in children causes shingles in adults (varicella zoster -> herpes zoster)
What are conditional pathogens?
Pathogens causing disease only under certain conditions
What is parasitism?
Pathogens that actually cause disease
What is the role of inflammation?
Increases blood supply
Increases capillary permeability
Cell (polymorphs/macrophage) migration from blood to tissue
What are the symptoms of infection?
Local
- redness, swelling, warmth, pain, loss of functions
- pus (pyogenic infection)
Systemic
- Fever, rigors, chills, tachycardia, tachypnoea (increased breathing rate)
What are virulence factors?
Molecules produced by pathogens which add to the effectiveness of the pathogen to:
- evade immune responses
- enter / exit host cell
- immunosuppression
- colonisation
- obtaining nutrients from host
