Week 1 Flashcards
What are the 3 disease prevention levels?
- Primary Prevention
- Secondary Prevention
- Tertiary Prevention
Primary Prevention
Stop disease from occurring e.g Vaccination
Secondary Prevention
Early detection of disease states (can prevent progression and severe symptoms of diseases)
- early intervention can lead to improved prognosis (routine blood pressure measurement)
- screening (disease testing) when disease is present but not detected
Tertiary Prevention
Reduce impact of disease when disease is symptomatic
- e.g rehabilitation, medication to manage symptoms
What is the number used for measuring effectiveness of disease prevention in society
Burden of disease (measure in years of healthy life lost)
Burden of disease
- DALY(Disability-Adjusted Life Years) = Life expectancy - each year of life “lost” (YLL)
- YLL = years lost to mortality, morbidity (weight by impact of disease on life)
- Expressed as a rate in the population
What does it mean to be healthy?
- a state characterised by integrity (anatomic, physiologic, psychological)
- ability to deal with stress (physical, biological, physiological, social)
- ability to perform personally valued roles (family, work, community)
The 3 Determinants of Health
- Individual characteristics and behaviours
- Social and economic environment
- Physical environment
Individual characteristics and behaviours
- genetics
- personal behaviours
- e.g smoking tobacco products
Social and economic environment
- education
- income and social status
- access to health services
- discrimination based on race, gender, sexuality, religion, culture
Physical environment
- safe water and clean air
- safe transportation
- safe housing
What are the components of the Ottawa Charter for Health Promotion?
- Strengthen Community Action = empowering communities and encouraging their ownership and control
- Develop Personal Skills = Increase the options for individuals to exercise more control over their own health and environments to make choices conducive to health
- Create Supportive Environments = safe stimulating provision of facilities that support healthy lifestyles
- Reorient Health Services = Create a health care system that contributes to the pursuit of health
- Legislation, fiscal measures, taxation and organizational change leading to greater equity
WHO focus Areas of Health Promotion
- Creating healthy cities
- Improving health literacy
- Promoting health and wellbeing
- Promoting health through good governance
Creating Healthy Spaces
• to create a health-supportive environment
• to achieve a good quality of life,
• to provide basic sanitation & hygiene needs
• to supply access to health care
Social Mobilisation
- Call to action: make bold political choices for health
- Ensures that health promotion priorities are determined by the communities which are affected
- Visibility and actioning alternative ideas and concepts about the forms health promotion takes
Factors constituting what makes something alive
- Composed of one or more cells
- Homeostasis
- Reproduction
- Respond to environment and communication between cells
- Metabolism
- Evolution over time
Taxonomy
The science of biological classification
- groups organisms on basis of similarity
- phylogeny = based on shared evolutionary history
- DNA analysis provides further evidence for relatedness (genomic typing)
- Genus and species names are italicised
Virulence factor
Disease causing capacity
Unique bacterial cell structures
- capsule
- pili
- flagella
- plasma membrane
- rigid cell wall
Unique bacterial cell structures : capsule
Thick, regular shell-like structure made from glycocalyx
- helps with bacterial adherence
- protection from immune response
Unique bacterial cell structures: Pili/ Fimbrae
Short protein fibres that protrude from cell wall
- role in adhesion
Unique bacterial cell structures: Flagella
Thin protein tubes much longer than pili
- used for locomotion, spins like boat propeller
Unique bacterial cell structures: cell membrane
Composed of lipids
- prone to damage and lysis
Unique bacterial cell structures: rigid cell wall
- determines where bacteria can live, kind of disease they cause, and treatment options
Gram stain process
- Unstained cells on microscope slide
- Apply crystal violet
- Add iodine
- Decolonize
- Apply carbol fuchsin
Why do species turn purple from Gram dyeing?
Gram positive cell wall is composed of lots of peptidoglycan and so traps crystal violet stain
• Gram-positive bacteria with thicker layers of peptidoglycan can survive in harsher environments
• Peptidoglycan provides protection to plasma membrane
• Gram-positive bacteria are particularly good
colonisers of skin e.g. Staphylococcus,Streptococcus
Why do species turn pink from Gram dyeing?
Gram negative bacteria have two membranes
• The outer membrane contains lipopolysaccharides (LPS) = endotoxin
• When Gram negative bacteria die, they liberate LPS which triggers an immune reaction
• Thin peptidoglycan layer, between plasma and outer membranes
Bacterial endospermes permit survival during times of environmental adversity
• Form (some species) in response to nutritional deprivation or other unfavourable environmental condition
• Can persist dormant in harsh environments and resume growth should conditions improve in future
• e.g. Bacillus anthracis = anthrax
- Biological weapon
- Aersolised spores
- Tiny,cheap,transportable
Fungi
Have one of two body plans and can be unicellular or multicellular
• Fungi are eukaryotic microorganisms
- much larger and complex
- includes yeasts and molds, as well as more familiar mushrooms
Protozoa
Many protozoa are free living, others parasitic and have complex life cycles
• Protozoa = eukaryotes that are generally unicellular and lack a cell wall (“one-celled animals”)
- Trypanosoma brucei (RIGHT – a flagellate) – causative agent of vector-borne (tsetse fly) sleeping sickness – unicellular parasitic protozoa
• Flagellates have one or more flagella for locomotion.
• Amoebae move by extending portions of their cytoplasm.
• Ciliates have cilia, like little hairs, that beat for motion. Most are free-living.
• Apicomplexa - generally not motile, most are intracellular parasites.
Toxoplasma Gondii life cycle
• An active feeding/reproducing stage in definitive host
(cat)
• Cyst like eggs (oocysts) released from host (cat faeces) -
initially metabolically inactive protective structures
• Become infective in the environment
• Ingestion by intermediate host results in formation of cysts in neural or muscle tissue
• Can be transmitted from pregnant woman to her unborn infant causing severe defects
Viruses
Acellular parasites requiring host cell in which to replicate
• Virion=anindividual viral particle
- Genetic material surrounded by protein coat = capsid
- Many also surrounded by an envelope
- Determines host range or specificity
• Bacteriophages are viruses that infects bacteria (so specific hence considered as an alternative to antibiotics)
Prions
Misfolded proteins that have the ability to transmit their misfolded shape onto normal variants of same protein
• Infections include: Kuru, Creutzfeld-Jakob disease (CJD), bovine spongiform encephalitis (BSE; mad cow disease)
- Associated with eating contaminated animal products and cannibalism
Define contamination
Unwanted presence of microorganism = not sterile
Define colonisation
Presence and replication of microorganism on a body surface without causing disease
Define infection
Presence and replication of a disease - causing microorganism
Define infectious disease
Infection that causes damage to host cells and/or interferes with normal host function
- mild to severe
- localised to severe
- temporary to permanent
Define commensalism
Two organisms of different species living in close association - one benefit, the other is neither benefitted nor harmed
Define pathogen
A disease-causing microorganism
Define carriage
Colonisation with a pathogen without disease
- Asymptotic carriers may serve as a source of infection for others
Define opportunistic infection
Disease caused by a microbe that does not usually cause disease
- sudden access to accustomed site
- often associated with immunocompromised host
Commensals
- hundreds of bacterial species, small number of other microbes (fungi, yeasts)
- provide protection from infection
• contribute to nutrient absorption
• obstruct and inhibit pathogen invasion
• aid development and function of immune response
Requirements for infectious disease
- Maintenance in reservoir
- Transmission to host
- Invasion through a portal of entry
- Adherence to host tissue
- Infection: Multiplication within host
- Temporary evasion of host défenses
- Disease: interference with normal host function
- Exit via portal of exit and transmission
Reservoirs
Place for pathogens to persist before and after an infection, generally without causing disease
• Some pathogens can survive indefinitely in soil, water, or other environmental reservoirs
Zoonosis = human disease for which an animal is a reservoir
• Animal reservoirs do not succumb to disease, they are adapted for survival with pathogen
Type of reservoir has implications for disease control
• Mosquito (vector) control for arthropod-borne (arbo)viruses
• Complete elimination of only one human pathogen – smallpox virus – has been achieved
Transmission
Pathogens must reach a new host via one or more modes of transmission
Vertical transmission
• From pregnant woman to fetus across placenta
• From mother to infant via breastmilk
Contact transmission
May be direct or indirect
• Direct = physical contact between infected and non-infected individuals
- kissing, hand-shaking, sexual
contact
• Indirect = an inanimate object = fomite, acts as intermediary between infected and non-infected individuals
- drinking from same glass, sharing a towel
Airborne transmission
- Droplet transmission: coughs and sneezes can spread droplets of saliva and mucus
- Airborne transmission: tiny particles, possibly produced by talking, are suspended in the air for longer and travel further
Vector-borne transmission
(Relies on insects or invertebrates)
• Biological vectors essential for • lifecycle of pathogen
– Pathogen undergoes replication or important stage of development within vector
– (a) tick = vector for Lyme disease. Infection of tick essential part of pathogen’s lifecycle (bacterium)
• Mechanical vectors = vehicle
– No pathogen replication,
incidental carriage of pathogen
– (b) fly picks up norovirus particles on its legs at public toilet and transmits to picnic food
Food/Water-borne transmission
• Intestinal pathogens commonly rely on food- or water-borne transmission
• Microorganisms released through faeces of infected individual make contact with food or water = faecal-oral contamination
Portals of entry
Pathogen must invade host through a barrier at an appropriate portal of entry
• A cut, burn, breach can enhance entry – particularly for opportunistic pathogens
• Pathogens transmitted by biological vectors - usually introduced directly into circulatory system as vector feeds
• A pathogen must then breach skin or mucosal barriers of respiratory, gastrointestinal or urogenital tracts
• Tight junctions between epithelial cells maintain barrier function
• Sweat, oil bathes skin with antimicrobial substances
• Anatomical/mechanical barriers- mucous membrane, skin, urine flow
• Chemical barriers – acid produced by stomach, antimicrobials in tears, other secretions
• Microbial barriers – commensal microbiota and secreted antimicrobial compounds
• Genetic barriers - Inter-species susceptibilities, Receptor profiles
Adherence to host tissue
Once they have entered, pathogens must adhere to host
• Multiple mechanisms
• Must resist being swept away by host defences and body fluids
• Bacterial pathogens may adhere in several ways
(a) Glycocalyx
(b) Fimbrae
(c) Viral pathogens often use envelope glycoproteins to adhere to membrane proteins on host cells
(d) Protozoan parasite Giardia intestinalis uses ventral adhesive disc to adhere tightly to cells lining host’s intestine
Infection - Replication in host
• Most pathogens must increase in number to cause disease
• Time between exposure and onset of symptoms = incubation period
• As host fights off infection, or patient receives treatment, number of microorganisms decreases
Evade host defenses
Host response to infection has two main components:
• Plan A = block invasion = Barrier protection
• Plan B = destroy invaders
= innate immunity – containment
= adaptive immunity – specific killing and development of memory
Disease - interference with host function
• Pathogens cause disease in several ways; how is species dependent
• Pathogenicity = capacity of an organism to cause disease
• Virulence factors = microbial features that contribute to pathogenesis
• Some pathogenic bacteria produce toxins
• Bacterial exotoxins–one or more bacterial proteins secreted into surroundings
• Interfere with host cellular process; vary in specificity–someonly act on certain cell types
• LPS is component of outer membranes of Gram-negative bacteria - provides structural strength and negative cell charge
• When Gram-negative bacteria die, LPS is released as an
endotoxin
• Also considered a pyrogen, or fever causing agent
• Some phagocytic immune cells (scavengers) have receptors
specific for LPS
• Binding of LPS to receptor sends signals to cell for production and secretion of chemical messenger proteins > inflammation
• Immune benefits, but also make individual feel pretty sick
Several possible outcomes of viral infection depend on type of virus and host cell type
• Acute viral infection – virus replicates rapidly and may kill cell (Influenza)
• Chronic infection – slower viral replication (Hepatitis)
• Latent infection – persistence with no viral replication; may reactivate (Herpes simplex)
• Oncogenic viruses disrupt normal cell control leading to cancer (cervical cancer)
• Once inside cells, most viruses have specific cytopathic effects (CPE)
Pathogens leave host through portal of exit
• Portals of exit are often same as portals of entry
- Respiratory air-borne pathogens, sexually transmitted infections,
• For pathogens of intestinal tract – portal of exit is usually anus
• In some cases, no portal of exit exists – host is dead-end
