disease spread Flashcards
how does sickness result (2)?
- part of an organism’s body malfunctions (ex: heart attack, diabetes)
- when a pathogen invades an organism’s body and causes infection (virus, bacteria)
define pathogen
biological agent that produces disease in its host - they are usually microorganisms
define infection
when a pathogen invades and reproduces within its host, causing it damage
define epidemiology
study of distribution, cause and risk factors of health-related events (ex: infectious disease) in populations - goal is to control disease and maintain human health
what is important for assessing the impact of a disease (4)?
mode of infection transmission, how easily new hosts are infected, how well people can fight off disease/recover, environment in which the host lives
true or false - diseases are all the same
false - disease epidemics vary widely in severity and scale
true or false - pathogens are parasites?
true
define parasite
organism that lives in close association with a host and gains advantage from the relationship at the expense of the host
define host organism
organism on or in which a parasite lives and uses its ressources
define microorganism (microbes)
organism that is too small to be seen with the naked eye (requires a microscope) - most are benign, but some cause infectious diseases
what are 5 kinds of pathogens?
fungi, protozoans, helminths, bacteria, virus
what are fungi?
- eukaryotic organisms: can grow as single celled yeasts or multicellular branched weblike structures (mycelia)
- important sources of food and medicine (ex: mushrooms, penicillin)
- hundreds of species live on/in human body but are harmless
examples of fungal pathogens
candida albicans - causes yeast infections when population explodes
other: athlete’s foot, fungal pneumonia, ringworm
what are viruses?
- not really alive: mircroscopic parasites made of tiny packets of DNA and RNA wrapped in a protein coat
- hijack cellular machinery of their hosts
- not cell-based life form
- infect all life forms, including bacteria
examples of viruses
- influenza A (respiratory infection)
- rhinovirus (common cold)
what are bacteria?
- single celled prokaryotes without membrane bound nuclei
- between 500 and 1000 species are hosted by humans
- most don’t cause disease, and can even aid health
examples of bacteria disease
borrelia burgdorferi - lyme disease
escherichia coli - causes deadly food poisoning
what are protozoans
- single celled eukaryotes with a defined, membrane bound nucleus
- can be free living or parasitic, some parasitic ones cause disease
examples of protozoan pathogens?
- plasmodium (malaria)
- giardia lamblia (severe diarrhea)
what are helminths?
- parasitic worms (animals, therefore multicellular and eukaryotic)
- not all cause disease
examples of helminth pathogens
- schistosoma mansoni: infect digestive track which causes blockages and blood loss
- tichinosis: found in undercooked/raw meat, worm migrates from gut to muscles, including the heart
which type of pathogen is described as not being truly “alive”?
viruses
what type of pathogen causes malaria?
protozoan
what type of pathogen causes lyme disease?
bacteria
which microbes live in/on humans without necessarily causing disease?
c. albicans (fungi - yeast infections), e. coli (bacteria - food poisoning)
how does bacteria reproduce?
binary fission
what is binary fission?
a cell that replicates its DNA and splits in half, with one copy of DNA going to each of the two cells
how do bacteria take advantage of their host to grow/replicate?
use nutrients around the host cell to make new bacteria
can bacteria reproduce in a dead organism?
yes, it only needs nutrients from its host
can a virus reproduce in a dead organism?
no - must invade a functional host cell to produce new virus particles
how do viruses reproduce?
they hijack host cell’s reproduction machinery and force it to make new virus particles
what should you consider when deciding on the way to combat a disease?
consider the pathogen type (bacteria, virus, etc.)
how can you target bacteria?
antibiotics - they can:
- block synthesis of cell wall
- interfere with bacterial ribosomes
- inhibit RNA synthethis
- inhibit DNA replication
- increase permeability of cell membrane
what is used to combat fungi, protozoans and helmiths?
poisons (chemicals) toxic to the pathogen but not the host - antifugals, antiprotozoals and antihelmintics
what is used to combat viruses?
antivirals - disrupt function of viruses (ex: blocking receptors needed to enter host cell, disrupt viral replication) without affecting cellular function of the host
define immune system
an organism’s immune system helps protect it against invading pathogens
what is the innate immune response?
rapid, generic, relies on ability to identify broad classes of pathogens
examples of innate immune response?
barriers, internal defenses
acquired immune response
slower, specific, relies on ability to learn and remember specific pathogens
examples of acquired immune response?
first exposure, subsequent exposure
define barriers
physical/chemical barriers that block pathogen from entering the body
examples of barriers
skin, stomach acid, digestive enzymes, mucus lining
what is internal defense
white blood cells respond to pathogens that breach barriers
examples of internal defense
trauma stimulating inflammatory response, white blood cells attack pathogens, pathogens release chemicals that recruit/activate other parts of the immune system (including acquired)
what is first exposure?
system learns to identify pathogen - LEARNING
examples of first exposure
- immune system learns to identify specific pathogens
- slower response than innate
- special cells are trained to recognizen antigens of invading pathogens
- other cells learn to produce antibodies for specific pathogen
what is subsequent exposure
system remembers antigen, stimulating rapid response to infection - REMEMBERS
examples of subsequent exposure
- immune system remembers antigens
- stimulates a more rapid response
- specific antibodies are used swiftly
- healthy immune system distinguishes pathogen from host’s cells and molecules (doesn’t attack itself)
define immunity
immunity occurs when an organism is able to protect itself from an invading pathogen
true or false - pathogens are infectious agents that cause disease
true
true or false - all pathogens are parasidic
true
which pathogen uses the cellular machinery of its host to replicate?
viruses
what produces immunity to an infection
immune system identifies and remembers specific pathogens it has encountered
what is the SIR model?
3 compartments - susceptible, infected, recovered.
every individual in a population begins as susceptible. as they get sick, they move into the infected department. as they recover, they are moved into the recovered compartment. when an epidemic is over, everyone is susceptible or recovered. arrow from S to I is how quickly individuals are infected and arrow from I to R is how quickly they recover. this model can be represented on a graph.
three determinants of disease spread
population density (N), transmission rate (beta) and infectious period (L)
define population density
how often individuals contact each other
define transmission rate
rate of disease transmission between infected and susceptible individuals of population. depends on how often infected/susceptible come into contact, and the probability of a contact resulting in infection
define infectious period
average period of time an infectious person can transmit disease to susceptible person
what is the name of the line that shows infections over time?
epidemic curve
what factors will flatten an epidemic curve?
lower population density, lower transmission rate, short infectious period (fast recovery)
formula for infection
betaSI
formula for recovery
I/L
how do you calculate change in I
new infections - new recoveries
SIR model assumtions (3)
1- once infected and recovered, individual has permanent immunity
2- everyone has equal chance of contacting everyone in population
3- as soon as individuals are infected, they are immediately infectious
equation for basic reproductive number - R0
R0 = SbetaL
define birth rate
all newborns enter the population as susceptible, at a rate depending on population size
define death rate
individuals in each subpopulation die at a constant rate
define the basic reproductive number, R0
average number of infections caused by a sick individual in a susceptible population
how do you calculate critical immunization threshold (pc)
pc = (1 - 1/R0)
