Disease definition

any condition which interferes with normal functioning of the body and impairs the health, opposite of health

Types of diseases

Congenital diseases (inborn and genetically inherited) and Aquired diseases (after birth and non-inheritable)

Congenital diseases two types and examples

Due to genetic mutation (e.g. haemophilia, sickle cell anemia), due to chromosomal or genomic mutations (Down’s Syndrome, Turner’s Syndrome)

Aquired diseases two types & many subtypes

Communicable or infectious diseases- air, water, food, physical contact; produced by bacteria, viruses, protists, fungi, parasites (e.g. ticks)
Non-communicable or non-infectious diseases- deficiency disease (diabetes), degenerative disease (arthritis), cancer, mental disease, allergy and autoimmune diseases, occupational diseases, due to enviornment (like UV, radiation)

WHO definition of health

Health is the state of complete physical, mental, social well-being and not merely the absence of disease, the ability to lead a socially and economically productive life

Biomedical concept of health

absence of disease, based on the “germ theory of disease”

Ecological concept of health

Dynamic equilibrium between human being and enviornment- disease is a maladjustment of the human organism to enviornment

Psychosocial concept of health

Also influenced by social, psychological, cultural, economic and political factors of the people concerned

Holistic concept of health

synthesis of all other concepts, recognizes strength of social, economic, political, and enviornmental influences on health; health as a unified/multi dimensional process involving the wellbeing of whole person in context of his enviornment

Disease vs illness vs sickness

Disease- when something is wrong with bodily function, physiological/psychological dysfunction
Illness- presense of a specific disease, subjective state of the person who feels aware of not being well
Sickness- state of social disfunction, role that the individual assumes when ill

Different responsibilities for health

Individual- self care for maintaining own health,
Community- health care to the people by the people
State- constitutional rights
International- Health for All through PHC

Epidemiology definition

The study of factors affecting the health and illness of populations. Serves as the foundation and logic for interventions made in the interest of public health and preventative medicine

Epidemic definition

The occurence of more cases of a disease than expected in a given area or among a given group of people over a particular period of time

Pandemic definition

An epidemic occuring over a very wide area (usually multi country) and usually affecting a large proportion of the population

What is a mathematical model? (3 aspects)

Mathematical description of the real world, focuses on specific quantitative features of the scenario and ignores others (simplification), involved hypotheses that can be tested against real data

Why study epidemic models? (3 things)

To supplement statistical extrapolation, to learn more about the qualitative dynamics of a disease, to test hypotheses about e.g. prevention strategies, disease transmission, etc.

Why use SIR models?

new diseases emerge suddenly and spread quickly, effective an fast control measures are needed, allow you to predict when you don’t know

SIR meaning

Fractions of: susceptibles, infecteds and recovereds in a population

Simple SIR model, description of each

Susceptibles have no immunity, Infecteds have the disease and can spread it to others, Recoverds have recovered and are immune

β (beta) meaning in epidemiology

The infection rate- an infected individual comes into contact with βN other individuals per unit time (of which the fraction that are susceptible to contracting the disease is S/N)

γ (gamma) meaning in epidemiology

Removal/recovery rate- 1/γ is the mean period of time during which an infected individual can pass it on

Basic reproduction number definition

The average number of secondary cases caused by an infectious individual in a totally susceptible population, tells us how easy/difficult it is to eradicate an infection (easier to eradicate one that is low), R₀

Basic reproduction number formula

R₀ = infection rate/removal rate

What has to be the case for an epidemic to occur?

R₀>1

Individualistic definition for R₀

The number of infections an infected person would generate over the course of their infections if everyone they encountered were susceptible

Population definition for R₀

The average force for growth of infection in a population where everyone is susceptible

What is it when R₀<1

The infection cannot invade a population, infection control mechanisms are unnecessary, it will eventually die out by itself

What is it when R₀>1

(On average), the pathogen will invade that population, control measures necessary for prevent/delay an epidemic, every increasing the number of infected

What is it when R₀=1

Approximately the same number of individuals are infected with each new generation causing endemicity

R₀ examples for known diseases

AIDS: 2-5, Smallpox: 3-5, Measles: 16-18, Malaria: >100

Factors affecting R₀ (3 things, their letters & ways to reduce them)

p- Transmission probability per exposure, can reduce by: screening blood, using gloves, condoms
c- number of contacts per time unit, can reduce by: isolation, sexual abstinence
d- duration of infectious period, can be reduced by medical interventions (e.g. TB)

Factors affecting R₀ formula

R₀ = p x c x d

Ways to enhance the SIR model (3 main ideas)

Consider additional populations of disease vectors (e.g. fleas, rats), consider an exposed but not yet infected class (SEIR model), can consider biased mixing, age differences, multiple types of transmission, geographic spread, etc.

What is sometimes used instead of an SIR model for sexually transmitted diseases, way to enhance it

SIRS, SIS, and double (gendered) models

Public health immunization program goal

Attain as close to 100% coverage as possible to prevent even one case from occuring

Herd immunity- what is it based on

The notion that if a population or group is mostly protected from a disease by immunization (>85%) then chance of a major epidemic occuring is limited

Herd immunity- what does it do, how does it work

Provides a barrier to direct transmission of infections through population, lack of susceptible people stops spread of a disease throughout the group

Reproduction number when you take into account vaccination and herd immunity, using V and S_0, what number does it have to be for an epidemic to occur

If only a fraction (S₀) is susceptible then the reproduction number is- R₀S₀ now this has to be >1 for an epidemic to occur,
If V = number of people vaccinated then- S₀=1-V
No epidemic can occur if: V>1 - 1/R₀

How to calculate R when a proportion (p) are immune (formula)

R = R₀ -(p x R₀)
That then needs to be >1 for an epidemic to happen

Example: if R is 2 then what does p need to be to prevent an epidemic?

P>0.5

European Center for Disease Prevention & Control (ECDC) brief description of function

Asseses and monitors emerging disease threats to coordinate responses

European Medicines Agency (EMA) brief description of function

Manages the scientific assessement of all EU medicines’ quality, safety and efficiency

Zoonosis definition

Any disease or infection that is naturally transmissible from vertebrate animals to humans

Pathogens definition

agents that cause disease, infect a wide range of animals, including humans

Which animals have innate immunity

All animals

Which animals have adaptive immunity

vertebrates

1st line of defense in body

skin, mucous membranes and their secretions

2nd line of defense in body (3 things)

antimicrobial substances, inflammation and fever, phagocytic white blood cells

3rd line of defense

Specialized lymphocytes (B cells and T cells)

which type of immunity is present before any exposure to pathogens and is effective from the time of birth?

Innate

What does innate immunity consist of? (2)

external barriers, internal cellular and chemical defenses

What immunity develops after exposure to agents such as microbes, toxins, or other foreign substances

Adaptive

In innate immunity what does recognition and response rely on?

Traits common to groups of pathogens

Is innate immunity present in vertebrates?

Yes

What do barrier defenses include? (what, of what tracts?)

Skin and mucous membranes of the respiratory, urinary and reproductive tracts

Examples of body fluids which are hostile to many microbes?

Saliva, mucous, tears

What feature of the pH of skin and the digestive system prevents growth of many bacteria?

It is low

TLRs definition

Toll-like receptors

What do cellular innate defences include? (3)

Phagocytic cells, (in verebrates) Natural Killer cells, Lymphatic system

How do phagocytic cells recognize groups of pathogens

By TLRs

4 types of Phagocytic cells

Neutrophils, Macrophages, Dendritic cells, Eosinophils

neutrophils description (where they are found, how they are activated, what they do)

Circulate in blood and are affected by signals from infected tissues, engulf and destroy pathogens

macrophages description (where they are found, alternative name)

Found throughout the body (especially lymphatic system and spleen), also called “big eaters”

Dendritic cells description (where they are found, what they do)

Found in the skin, stimulate the development of adaptive immunity

Eosinophils description (where they are found, what they do, who do they target)

Found beneath mucosal surfaces, discharge destructive enzymes against multicellular invaders (e.g. parasitic worms)

Natural Killer cells description (where they are found, what they do, who do they target?)

Circulate throughout the body and detect abnormal cells, release chemicals leading the cell death, inhibiting the spread of virally infected or cancerous cells

What does the lymphatic system consist of? What are their functions? (2)

Lymphatic vessels through which lymph (fluid in the lymphatic system) travels, structures (nodes and organs) that trap foreign substances

Lymphoid organs (6)

Spleen, thymus, appendix, Peyler’s patches, adenoid, tonsils

Examples of peptides and proteins of the innate immune system (2)

Interferon and proteins of the immune system

How do peptides and proteins function in the innate immune system? (2)

By attacking pathogens or impeding their reproduction

Interferon- what is it, what types of organisms is it found in, function?

protein unique to vertebrates, induces nearby uninfected cells to produce substances that inhibit viral reproduction

What is interferon produced by?

Virus-infected body cells

How many proteins make up the complement system?

About 30

Where can you find proteins of the complement system and in what state?

They circulate in the blood plasma in an inactive state

Who are the proteins of the complement system activated by and what do they do?

Activated by microbes, cause lysis of invading cells and help trigger inflammation

What is a mast cell?

A type of cell of the connective tissue which releases histamine

What does histamine do?

triggers blood vessels to dilate and become more permeable

Local inflammatory response- what is it brought about by, what does it include (5 signs)? (general)

brought about by molecules released upon injury of infection, includes redness, swelling, heat, pain and loss of function

Cytokines in the inflammatory response- what are they released by, what are its effects, what do the effects cause?

Released by activated macrophages and neutrophils, it signals molecules that promote blood flow to the site of injury, causing redness and increase of skin temperature

Examples of what can trigger acute inflammation (2)

cell or tissue damage, presence of dead cells or noxious agents such as bacteria

What is the first phase of wound healing?

Acute inflammation

What does the acute immune response aim to do?

remove the injury causing agent and limiting the extent of tissue damage

Acute inflammatory response step 1 (2 things)

Mast cells release histamines, macrophages release cytokines that cause capillaries to dilate

Acute inflammatory response step 2 (2 things)

Capillaries are now more permeable and allow fluid containing antimicrobial peptides to enter the tissue, neutrophils are attracted.

Acute inflammatory response step 3 (1)

Neutrophils digest pathogens and cell debris

Pus definition

A fluid rich in white blood cells, dead pathogens, and cell debris from damaged tissues

Septic shock definition

A life-threatening condition caused by an overwhelming inflammatory response

Fever- what is it, what is it triggered by

Systemic inflammatory response triggered by pyrogens (e.g. interleukin 1)

What releases pyrogens

Macrophages and toxins from pathogens

Fever phase 1

Pathogen or toxin- most common cause is infection from bacteria/viruses, macrophage ingesting that will start the process

Fever phase 2 (4 ish sub-steps)

Macrophages respond- by ingesting, they destroy the pathogen, releasing endotoxins, which induce the production and release of interleukin-1 into the bloodstream

Fever phase 3- interleukin 1

Interleukin-1 travels to the brain, induces the hypothalamus to produce more prostaglandins which resets the bodys “thermostat” to a higher temperature, producing fever

Hypothalamus function

Controls the bodys temperature settings

Prostaglandins function

Resetting the bodys thermostat to a higher temperature, producing fever

Fever phase 4 (+ 3 results) (after interleukin 1 in brain)

Fever onset- body raises temperature resulting in: blood vessel constriction, increased metabolic rate, shivering

Fever phase 5 (after fever onset)

Chill phase- skin remains cold, shivering occurs, this stops once the body reaches the setting of the thermostat

Fever phase 6 (final phase)

Crisis phase- increased body temperature remains until the interleukin-1 is eliminated, heat reducing methods (sweating, vasolidation (widening of blood vessels)) cause the person to feel warm, it indicates the bodys temperature falling`

Examples of how some pathogens avoid destruction

Modifying their surface to prevent recognition, resisting breakdown following phagocytosis

Two types of aquired immunity

Naturally aquired, artificially aquired

Two types of naturally aquired immunity (+ brief explanations)

Active (getting the disease, even when no symptoms), passive (from mother to fetus through placenta or milk)