Chain of Infection Flashcards
What are viruses and new viruses
- A pathogen or disease causing agent
- Not living, cannot reproduce on its own (viable host)
- Obligate intracellular pathogens
- No metabolism, <1nm in size
- New viruses have no existing herd immunity, unknown mechanism of transmission, reservoirs, pathogenicity, virulence properties, vaccines and therapeutic interventions
What is the chain of infection and its characteristics
- Development of an infection dependent upon uninterrupted process
- Infection may occur when a person is exposed to a reservoir of a potential pathogen, pathogen may entry human body
- Can be broken by infection control measures implemented by healthcare workers
- Characteristics: Reservoir for growth, portal of exit, mode of transmission and portal of entry to susceptible host
What are bacteria
- Single celled organisms
- Commonly spiral, rod or spherically shaped
- Multiply rapidly by division and require moisture and nutrients to grow
- Infections include gastroenteritis / salmonellosis
What are fungi
- Large diverse organisms, ranging from microscopic to easily visible
- Have spores which can move them to new locations via air currents
- Infections include oral thrush
What are protozoan / helminths
- Singled celled organisms transmitted via direct / indirect contact or an arthropod vector, infections include malaria / toxoplasmosis
- Worm parasites, due to injection of worm eggs, infections include tapeworm
What is a reservoir
- Any person, animal, arthropod, plant, soil or substance (any combination) in which an infectious agent normally lives and multiplies
- The pathogen depends primarily on a reservoir for its survival
- It is where a pathogen reproduces itself to allow transmission to a susceptible host
- Animate or inanimate
What are examples of reservoirs
- Human: Blood (hep B/C, HIV), respiratory (flu), GI (hep A), reproductive (STIs) tracts
- Animals: rodents (typhus), deer (lyme), cats (toxoplasmosis) and sheep / cattle (anthrax)
- Inanimate: Bedpans (wound infections), instruments (UTIs) horizontal surface (gastroenteritis), water (cholera), soil (tetanus)
What is a susceptible host and what increases susceptibility
- Person who is lacking immunity / resistance to the causative agent,
- Deficient immune system due to HIV, AIDS, chemotherapy
- Organ transplants, age, sex, ethnicity, lifestyle, occupation, nutritional / immunisation status
- Family medical history, medication, pregnancy, injury and post surgery
What are nosocomial infections
- Compromised hosts
- Chain of transmission and microorganisms in hospital environments
- Healthcare workers presenting with symptoms of infection should not expose themselves to patients who are at risk
What are the 3 defence mechanisms in humans
First:
- Mechanical barriers (skin, mucous membranes)
- Bodily secretions (saliva, tears, sweat, gastric juices, bile, mucous)
- Lymphoid tissue
- Normal flora
Second:
- Inflammatory response
- Localised redness, heat, swelling, pain and impaired function
- Systemic effects include fever, malaise, leucocytosis, increased circulating leucocytes, lymph node enlargement
- Nausea / vomiting
Third:
- Specific immunity
- Antibodies (immunoglobulins) produced in response to the presence of foreign proteins (pathogens)
- Immunity is body’s ability to resist disease by producing specific antibodies against specific antigens
List the portals of entry and mechanisms different pathogens utilise
- Natural openings (fungi, bacteria)
- Injuries (fungi, bacteria, nematodes)
- Direct penetration (fungi, nematodes)
- Insects (virus, phytoplasma)
- Mechanical (virus, phytoplasma)
- Grafting (virus)
How do pathogens enter via the skin
- Outer layer of packed, dead, skin cells usually acts as a barrier to pathogens
- Some pathogens enter through openings or cuts or by burrowing into / digesting outer layers of skin
How do pathogens enter via the mucous membranes
- Line body cavities that are open to environment
- Provide a moist, warm environment that is hospitable to pathogens
- Respiratory: S. pneumoniae, H. influenzae, L. pneumophila
- GI: Carried by vehicles / faecal-contamination, C. jejuni, E. coli, H. pylori, V. cholerae
- Genitourinary: Treponema pallidum, Neisseria gonorrhoeae, Chlamydia trachomatis, HPV, HIV
- Nosocomial: Such as UTIs caused by Proteus mirabilis, P. vulgaris and E. coli
How do pathogens enter via the parenteral route
- Pathogen deposited directly into tissue beneath skin / mucous membranes
- Break in skin (cuts, bites, burns, scrapes)
- Rabies, staph aureus
- Via an insect (plasmodium, trypansoma)
pHow can we break the chain of infection
- Elimination of sources of infection (reservoirs)
- Appropriate handling and disposal of body secretions (vomitus, faeces, sputum, blood and body fluids)
- Appropriate handling of contaminated items
- Segregation of waste categories and disposal
- Hand washing
- Wearing protective masks
- Wearing protective goggles
- Discarding needles
- Washing linen
- Social distancing >1.5m apart
- Quarantine
