Pathology, Disease Transmission, and Epidemiology: Key Concepts and Definitions

what does disease study?

Pathology

how is pathology informed

Pathogenesis

what does pathogenesis develop?

Diseases

sisease

abnormal state in which the body is not performing normal functions.

symptoms

Subjective characteristics of disease felt by the patient as a result of the disease(ie. pain)

signs

objective changes that can be observed and measured as a result of the disease (ie. fever, edema)

syndrome

characterization of a disease: determined by specific signs&symptoms of a disease (confirmed with lab tests; like a diagnoses)

communical Disease

classification of disease within a pop: spread from host to host (flu, chicken pox)

noncommunicable disease

classification of disease within a pop: not spread from host to host (includes microbes that live outside the body and when introduced they cause disease. tetnus)

reservoir

habitat of an infectious agent (not necessarily where its located, just where it can survive)

carriers

living organism w/ the pathogen reproducing in them & shedding into environment

carrier symptoms?

can range from NO symptoms at all to very prominent/obvious symptoms

what is direct transmission

contact person-person:

physical contact, no intermediate (rhinovirus & flu, ghonorrhea (sexually transmitted))

what is droplet transmission?

contact person-person:

microbes spread from respiratory droplets over SHORT distances <1m (sneezing/coughing, rhinovirus, flu)

what is indirect transmission

contact person-person:

transmission via non-living organism (fomite)

what is a fomite? what type of transmission is it involved in?

inanimate objects that become contaminated (bedding, toys, surgical instr. money...). involved in indirect contact transmission

what is airborne transmission?

vehicle transmission:

respiratory agents are dispersed into the air via dust particles (>1m long distances)

what is water/food borne transmission?

vehicle transmission:

waterborne: untreated water allows pathogens to replicate

food borne: undercooked, poorly refrigerated, unsanitary preparation

what are vectors

living organisms that transfer a pathogen from one person to another (anthropods: fleas, ticks, mosquitos, vertebraes: dogs, rodents) classified as vector transmission

what is mechanical transmission

type of vector transmission: (passive transport) antrhopod carried pathogen on is feet and makes contact w/ food. transmission occurs when human consumes food

what is biological transmission?

type of vehicle transmission: (active transport) anthropod bites an infected person and picks of pathogen in blood. injects into next host when feeding.

what is the end result of all routes of transmission?

infection! a susceptible host become infected

what is epidemiology?

study of the occurrence, distribution, and determinants of health and disease in a population

descriptive epidemiology

COLLECTION and analysis of data (general)

analytical epidemiology

analyzes a SPECIFIC disease, determines probable cause

experimental epidemiology

includes and hypothesis and controlled experiments (clinical trials with a test & control group

what is an outbreak?

numerous cases over a SHORT period of time (where cases are minimal)

non-outbreak cases vs. outbreak cases

non outbreak cases are considered the baselines of cases

endemic

a disease constantly present at LOW INCIDENCE in a population (common cold; viral)

epidemic

a disease the infects an unusually HIGH number of individuals in a population (influenza; viral)

pandemic

widespread, WORLDWIDE. a type of epidemic

human host-host epidemic

begins with one infected person: slow and steady progression followed by gradual decline (due to variable incubation times) cases are reported over LONGER time period (chicken pox, influenza)

common source epidemic

originates from a contaminated "common source" rapic increase in infected individuals due to many getting sick over a SHORT time period (common result is cholera/intestinal diseases)

incidence

number of NEW cases of a disease during paticular time (indicates SPREAD)

prevalence

number of NEW and EXISTING cases at a particular time (regardless of first appearance) (indicated HOW LONG a disease can persist in a pop)

mortality

deaths in a population , calculated as mortality rate (death/population)*100

disease progression: stage (1)

infection: organism invades, colonizes, and grows in host (host becomes infected!)

primary vs. secondary infection

primary: causes initial illness

secondary: opportunistic infection after primary

local infection

pathogens limited to small area of body

systemic infection (generalized)

infection throughout the body

disease progression: stage (2)

incubation: duration b/w infection & appearance of symptoms

disease progression: stage (3)

prodromal period: SHORT period after incubation; early, mild symptoms

disease progression: stage (4)

acute period: disease is most active, most severe symptoms

disease progression: stage (5)

decline period: symptoms subside

disease progression: stage (6)

convalescent period: patient regains strength and returns to normal

hospital environments

- diseased patients are pathogen reservoirs & carriers

- often patients share rooms

- healthcare workers move from patient to patient

- surgical procedures expose organs to contaminants

healthcare-associated infection (HAI)

an infection acquired while receiving treatment in a healthcare facility

predisposing factors

factors that make the body more susceptible to disease (gender, age, inheritance, climate/weather, vaccination, lifestyle, chemotherapy, fatigue...)

acute disease

symptoms develop rapidly but the disease lasts only a short time (influenza)

latent disease

causative agent is inactive for a time but then activates and produces symptoms

chronic disease

a disease that develops gradually and continues over a long period of time (tuberculosis, mononucleosis)

escherichia coli

part of normal intestinal microbiota, mostly harmless, main cause of diarrheal diseases and UTI's

enterohemorrhagic e. coli

causes food borne illness

- transmission: contaminated food/water (undercooked beef)

- incubation: 2-5 days

- symptoms last: >8 days

- shiga toxins

what are shiga toxins?

found in e.coli; targets blood vessels in intestinal lining

- the body responds by sending platelets to stop bleeding (forms clotts)

- decreased blood flow to organs can cause organ failure

*key symptom is bloody diarrhea (5-10% lead to kidney failure

infection vs. disease

infection: growth of microbes in host

disease: when those pathogens affect normal functioning of host

pathogenicity

potential ability of a pathogen to causes disease in host

virulence

ACTUAL ability of a pathogen to infect or damage a host

ID 50

expression of virulence: number of microbes required to produce an infection in 50% of healthy humans (lower the number the easier is is for infection to occur)

O-antigen

in contact w/ environment:

advantage: varies among bacterial strains (unique)

disadvantage: target for human immune response (antigen) location for viral attachment

portal of entry: mucous membrane

penetrates mucous linings of respiratory tract(inhalation), GI tract, urinary tract

portal of entry: skin

entry via hair follicles (unbroken skin is impermeable to microbes)

portal of entry: parenteral routes

if barriers are penetrated (cuts, bites, injections) microbes can be deposited directly into tissues

Mechanism of bacterial entry

"lock & key" mechanism

- bacteria = ADHESIN

- host = RECEPTOR

adherance

process of pathogens adhering to a host cell

adhesins

located on glycocalyx of pathogen (polysaccharide layer on the outside of the cell wall)

can also be on pathogenic pili (adhere to host) or flagella (mobility)

phagocytosis

once inside the cell, hosts tries to detroy microbe via this process.

lysozyme

digestive enzyme that break down peptidoglycan

lysosome

cell vesicle that contains numerous digestive enzymes

capsule formation

evade host: glycocalyx released by a bacterium can form a capsule around cell wall (reduces phagocytosis effectiveness increasing survival)

two microbes that use capsules

Streptococcus pneumonieae (causes pneumonia disease)

Bacillus anthracis (causes antrax disease)

enzyme release

evade host: coagulases, enzyme that forms clots when contacts fibrinogen (used by some staphylococcus).

kinases excreted when microbe is ready for release (used by some streptococcus)

antigenic variation

evade host: some microbes can change surface antigens resulting in the inability for host antibodies to bind and destroy the microbe

siderophores

direct damage: microbial proteins secreted iinto the environment and binds to IRON (affects host by using host nutrients and increases microbial growth) (

exotoxins

produced internally then secreted OUT (gram pos AND gram neg bacteria)

endotoxins

part of lipopolysaccharide layer (LPS) which can be released (gram neg ONLY)

exotoxin details

production is coupled to growth/metabolism during exponential phase, easily diffusible into blood, enzymes that destroy host cells

treatment: anti-toxin injections (specific antibodies for a specific exotoxin)

A-B exotoxins

A - enzymatic component - Attacks cell

B - binding component - Binds toxin to host cell receptor (glycoprotein or glycolipid).

After binding (B); A is transported into cell

botulinum toxin

clostridium botulinum

tetanus toxin

clostridium tetani

anthrax toxin

bacillus anthracis

endotoxin detail

part of LPS:

lipid A = portion of LPS secretes toxins when cell wall lyses during binary fission (ONLY gram neg like salmonella of e. coli

reaction = chills, fever, aches, weakness, death

portals of exit

The same as portals of entry (allows for movement from one host to another)

resp - coughing/sneezing, GI - feces, blood - anthropods, needles/syringes

immune system

bodys defense system against disease causing organisms, malfuntioning cells, and foreign particles

innate immunity

defenses gained from birth

adaptive imunity

response to a specific causative agent; defenses target a specific pathogen inside and outside host

first line of defense: physical

innate: physical factors

- skin: epidermis is constantly shed, extreme dryness inhibits growth

- mucous membranes: secretes mucus/glycoproteins that prevent desiccation of cilia, also traps microbes preventing further entry into body

first line of defense: chemical

innate chemical factors - perspiration, lysozyme (breaks down peptidoglycan=lysis), earwax (pH 3-5), saliva, gastric juice (pH 1-3), vaginal secretions (pH 3-5)

low pH inhibits microbial growth

second line of defense

phagocyte production (white blood cells), fever.

infection attracts WBC's

white blood cell count

high count in blod may indicate bacterial infection (normally found throughout blood, but will enter tissues if invaders are detected)

neutrophils

phagocytic 70%: early stages of an infection

eosinophils

phagocytic 0.5-1%: produce toxic proteins that target parasites

monocytes

phagocytic 2-4%: mature into macrophages in tissues

dendritic cells

phagocytic 3-8%: located in skin and mucous membranes

free macrophages

wandering, roam tissues and gather at sites of infection

fixed macrophages

residents in tissues and organs (liver, lings...)

mechanism of phagocytosis

1) chemotaxis: chem signals from damages cells attract phagocytes

2) adherance: TLR's bind to PAMP's releasing cytokines and initiating phagocytosis

3) ingestion: phagosome

4) digestion: lysosome fuse with phagosome (release lysoZYME to breakdown)

5) exocytosis: fragments released

Host defensive cells

macrophages and dendritic cells

host cell receptors

toll-like receptors (TLRs)

what do TLRs bind to?

pathogen-associated molecular patterns (PAMPs)

PAMPs

in bacteria - lipopolysaccharide (gram neg), flagella (all), peptidoglycan (gram pos), DNA (all)

in viruses - genetic info