Lecture 4: Disease and Epidemiology Flashcards
What is pathology?
Study of disease
What does aetiology mean?
The cause of disease
Pathogenesis
development of disease
Infection
invasion or colonization of the body by pathogens
Define disease
an abnormal state in which the body is not performing normal functions, example: E. coli- present in healthy intestine, but pathogenic in UTI
What is the difference between normal microbiota and pathogenic?
Microbiota are specifically adapted for different systems. What may be normal and healthy in one system can become pathogenic if it enters a different system.
Human Microbiome Project
analyzes relationships between microbial communities on the body and human health
Transient microbiota
may be present for days, weeks or months and then disappear
Normal microbiota or normal flora…
permanently colonize the host and do not cause disease under normal conditions
Normal microbiota make colonies in certain region of body
Distribution and composition of normal microbiota are determined by what factors?
- Nutrients
- Physical and chemical factors
- Host defences
- Mechanical factors
What is microbial antagonism?
Also known as competitive exclusion, this is competition between microbes such that normal microbiota protect the host.
How do normal microbiota antagonize other microbiota?
- Compete for nutrients
- Produce substances that are harmful to invading microbes
- Affect pH and available oxygen
Give an example of microbial antagonism.
E.coli inhibit the growth of Salmonella and Shigella
Commensalism
one organism benefits and the other is unaffected. Eg. S epidermis inhabit the skin
Mutualism
both organisms benefit eg. E. coli synthesizes vitamin K
Parasitism
one organism benefits at the expense of the other. Many disease causing bacteria are parasitic.
Symbiosis
the relationship between normal microbiota and the host, one organism is dependent on the other.
Some normal microbiota are _______ ________
opportunistic pathogens
The same pathogen must be present in every case of the disease.
Koch’s first postulate
Koch’s second postulate
The pathogen must be isolated from the diseased host and grown in pure culture.
Pathogen from the pure culture must cause the same disease when inoculated into a healthy, susceptible lab animal.
Koch’s third postulate
Koch’s 4th postulate
The pathogen must be isolated from the inoculated animal and must be shown to be the original organism.
What are the three exceptions to Koch’s postulate?
- Some pathogens can cause several disease conditions
- Some pathogens cause diseases only in humans
- Some microbes have never been cultured.
What are infectious diseases?
Disorders caused by a microorganism which can be passed from person to person.
Syndrome
a specific group of signs and symptoms that accompany a disease
Communicable disease
a disease that is spread from one host to another
Contagious disease
disease that are easily and rapidly spread from one host to another
Noncommunicable disease
a disease that is not spread from one host to another
Incidence rate
the number of new cases per population at risk in a given time period. These are all new outbreaks.
Prevalence
number of people who develop a disease at a specified time, regardless of where it first appeared (includes both old and new cases).
Sporadic disease
a disease that occurs only occasionally
Endemic disease
disease constantly present in a population
Epidemic disease
disease acquired by many people in a given area in a short time
Pandemic
worldwide epidemic
Acute disease
symptoms develop rapidly but the disease lasts only a short time, e.g. 2-4 weeks
Chronic disease
symptoms develop slowly and last for a long time, eg. more than three months
Subacute
intermediate between acute and chronic 2 weeks to 3 months
Latent disease
causative agent is inactive for time but then activates and produces symptoms
Herd immunity
immunity in most of a population or when many immune people are present in a community
Local infection
pathogens are limited to a small area of the body
Systemic (generalized) infection
an infection throughout the body
Focal infection
systemic infection that began as a local infection
Sepsis
toxic inflammatory condition arising from the spread of microbes, especially bacteria or their toxins, from a focal infection
Bacteremia
bacteria in the blood
Septicemia
also known as blood poisoning, growth of bacteria in the blood
Toxemia
toxins in the blood
Primary infection
acute infection that causes the initial illness
Secondary infection
opportunistic infection after a primary (predisposing) infection
Subclinical disease
no noticeable signs or symptoms
What are some predisposing factors that make the body more susceptible to disease?
Climate and weather Lifestyle (eg. exercise level) Age Nutrition Gender (eg. anemia more common in women) Inherited traits, eg. sickle cell Fatigue
Incubation period
interval between initial infection and first signs and symptoms
Prodromal period
short period after incubation, early, mild symptoms
Period of illness
disease is most severe
Period of decline
signs and symptoms subside
Period of convalescence
body returns to its prediseased state
What are some reservoirs of infection?
- Human reservoirs, eg. Carriers may have inapparent infections or latent diseases
- Animal reservoirs, eg. Zoonoses are diseases transmitted from animals to humans
- Nonliving reservoirs eg. soil and water
Direct contact transmission
requires close association between the infected and susceptible host
Indirect contact transmission
spread to a host by a nonliving object called a fomite
Droplet transmission
transmission via airborne droplets less than 1 meter
What is vehicle transmission?
Transmission by a medium, a non-living reservoir
Waterborne transmission
disease spread by contaminated water, for example cholera, shegalinosis
Food borne transmission
transmitted by food that are incomplete cooked, poorly refrigerated. Food born pathogen are food poisoning and tapeworm infestation
Airborne transmission (on exam)
spread of infection by droplet nuclei in dust that travell more than one meter from reservoir to host by coughing, sneezing. Measles and tuberculosis can be transmitted by air born droplets. Staphylococci and Streptococci can survive in dust and transmitted by air born rout
What is a vector?
is any agent (person, animal or microorganism) that carries and transmits an infectious pathogen into another living organism
Give some examples of vectors
Arthropods, especially fleas, ticks and mosquitos
What are the two general methods my which arthropods transmit disease?
1) Mechanical transmission eg. arthropod carries pathogen on its feet
2) Biological transmission: complex mechanism; pathogen reproduces in the vector, transmitted via bites or feces
Nosocomial infections
Infection acquired while receiving treatment in any healthcare facility.
How common are nosocomial infections?
1 in 25 hospital patients. 2 million per year, 20,000 deaths per year
What are the causes of nosocomial infections?
- Microorganisms in the hospital environment
- Weakened stasis of the host
- Chain of transmission in a hospital
Compromised host
An individual whose resistance to infection is impaired by disease, therapy or burns
What are the two principal routes of transmission? (chain of transmission)
- Direct contact
2. Indirect contact, by fomites
What are some ways to reduce the number of pathogens that can spread?
- Handwashing
- Disinfecting tubs used to bathe patients
- Cleaning instruments scrupulously
- Using disposable bandages and intubation
What are the characteristics of emerging infectious diseases?
- Disease that are new
- Increasing in incidence or potential to increase soon
- Usually zoonotic, viral and vector-borne
Contributing factors to EID’s?
- Genetic recombination (eg. E. Col O157 and H5N1)
- Evolution of new strains (eg. vibrio cholerae)
- Widespread use of antibiotics and pesticides
- Changes in weather patterns (eg. Hantavirus)
- Modern transportation (eg. West Nile Virus)
- Ecological disaster, war and expanding human settlement (Coccidioidomycosis)
- Animal control measures (Lyme disease)
- Public health failure (diphtheria)
Epidemiology
The study of where and when diseases occur and how they are transmitted in populations
What do epidemiologists do?
Determine etiology of a disease
Identify other important factors concerning the spread of disease
Develop methods for controlling a disease
Assemble data and graphs to outline incidence of disease
What did John Snow (1848-1849) do?
Mapped the occurrence of Cholera in London
What did Ignaz Semmelweis do (1846-1848)?
Showed that hand washing decreased the incidence of puerperal (postpartum) sepsis?
What did Florence Nightingale do (1858)?
Showed that improved sanitation decreased the incidence of epidemic typhus.
Descriptive epidemiology (person)
collection and analysis of data (John Snow)
Analytical epidemiology (person)
analyzes a particular disease to determine its probable cause (Nightingale)
Experimental epidemiology
involves a hypothesis and controlled experiments (Semmelweis)
What is the CDC and what does it do?
Centers for Disease Control and Prevention; collects and analyzes epidemiological information in the U.S.
MMWR
Morbidity and Mortality Weekly Report
Morbidity
incidence of a specific notifiable disease in a certain geographical location
Mortality
deaths from notifiable disease
Notifiable infectious diseases
diseases in which physicians are required to report occurrence
Morbidity rate
number of people affected in relation to the total population in a given time period
Mortality rate
number of deaths from a disease in relation to the population in a given time
