Week 2: Host-microbe interactions Flashcards
Describe a Prion
Non-living, protein only
Describe a eukaryotic infectious agent
Living, membrane-bound organelles
Describe bacteria
Living, single-celled
Describe a virus
Non-living, obligate intracellular parasite
What features create a susceptible host?
Age, nutrition, illness, immunosuppression, genetics, anatomical defects
How does age make you a susceptible host?
The very young have immature Immune systems
The elderly have an ageing immune system
The extremities of age result in an impaired ability to mount an effective immune response
How does nutrition create a susceptible host
Inadequate levels of protein and micronutrients including vitamins A,B,C, D and E; as well as minerals iron, selenium and zinc
All leading to impaired immune function and delayed wound healing
How can illness create a susceptible host
Co-morbid conditions lead to increased host susceptibility due to disruption of physiological functions
How does immunosuppression create a susceptible host
Innate or acquired, resulting suppression of the innate and/or adaptive immune response. (Chemotherapy)
How do genetics affect host susceptibility
Heritable traits result in altered phenotypes can increase risk.
Some genetic mutations lead to changes in physiological functions associated with innate immune response
Some mutations result in disrupted or delayed recognition of infectious agents
How do anatomical defects create a susceptible host
Changes in normal physiological functions of organs or organ systems
What are the three basic elements required for transmission of infectious agents
Source of infectious agents
Susceptible host
Mode of transmission
How does horizontal transmission occur
Between individuals via direct contact or indirectly by contact with the reservoir or vehicle or vector.
What is contact transmission
Direct transferral between one host and another
Direct contact transmission
Transmission occurs when susceptible hosts come into contact with the skin or bodily secretions of an infected person
Indirect contact transmission
When susceptible host touches an inanimate object
What are the major portals of entry and exit of a human host
Natural openings related to physiological function
Breaches of barrier integrity
How does the skin protect against infectious agents
Physical barrier to protect against pathogens
How do mucous membranes protect against infectious agents
Physical barrier against pathogen entry from superficial openings to deeper tissues
What are the naturally existing portals of entry in the body
Skin, respiratory tract, gastrointestinal tract, urine ital tract, congenital infections
How is skin a portal of entry
Cracks or injury to the skin create portals of entry. Some agents can however burrow through intact skin.
How do infectious agents enter the respiratory tract
Via inhalation or aerosols, spores and particular matter
How do infectious agents enter the gastrointestinal tract
Contaminated food or drink
How do infectious agents infect the urogenital tract
Infectious agents can ascend the urinary tract
Sexually transmissible pathogens are inoculated directly during bodily contact
What are the naturally existing portals of exit
Skin, respiratory tract, gastrointestinal tract, urogenital tract, blood
How is skin a portal of exit
Superficial layers of skin shed leading to direct and indirect transmission
How is the respiratory tract a natural portal of exit
Infectious agents present in mucosal secretions including saliva, mucous and sputum.
Excreted by sneezing or coughing and talking
How is the gastrointestinal tract a portal of exit
Infectious agents cause irritation of interstitial mucosa. The shedding of large volumes of the agents in frequent or water stool.
How is the urogenital tract a portal of exit
Infectious agents causing sexually transmittable infections are shed in high numbers in seminal fluid or vaginal secretions
How is blood a portal of exit
Infections being transmitted haematogenously to distant body sites and to unborn babies
What is the definition of common vehicle transmission
Agents transmitted by a common inanimate vehicle, with multiple cases resulting from exposure
What is contact transmission
An infection spread via direct or indirect contact with an infected person
Immunocompromised
Having an impaired immune system making a person more susceptible to infectious agents
Source
The origin of an infectious agent
