Epidemiology & Host-parasite Relationships Flashcards
Attack rate
Number of persons who developed on this versus the number exposed to the agent during a disease outbreak
Incidence
Number of new occurrences of disease , injury, or desk in the study population during the time period being examined.
Indicates the frequency, rate of disease, ease of transition, and incubation period. It also indicates the attack rained and the secondary attack rate which is an indication of the ease of spread (transmission) of an agent.
Secondary attack rate
Number of individuals who contract the disease within the incubation period from the first person with it i.e primary or index case
seasonality
If the incidence rate is consistently higher during a specified time of year, the risk of developing the disease goes up at that time.
Prevalence
Incidence (new cases) + old cases;
Number of people who currently have the disease
Endemic
Disease of humans present in a particular region at an essentially constant level (expected incidents).
Epidemic
Is that an increase in the incidence of a particular disease above the expected incidence – 1 standard deviation above endemic
Pandemic
Applied to epidemics of unusually large proportions.
For example worldwide epidemic
Zoonosis
A disease of animals present in a particular region at an essentially constant level
Epizootic
A sudden increase in the incidence of a particular disease in the animal population
Carrier
A person or animal contains, spreads or harbors an infectious agent
(Inapparent carrier, immune carrier, transient carrier)
Inapparent (sub clinical) infection
No detectable clinical symptoms of infection but sero-conversion occurs
Dormant (latent) infection
Carrier state
Opportunistic infection
Infection caused by normal flora or transient bacteria when normal host offenses are compromised.
Example yeast infection after antibiotics
Primary infection
Clinically apparent invasion and multiplication of microbes and body tissues, causing local tissue injury
Secondary infection
Microbial invasion subsequent to primary infection.
Ex: bacterial infection after viral URI
Mixed infection
Two or more microbes infecting the same tissue.
Example abscesses
Acute infection
Rapid onset – hours or days ;
brief duration – days or weeks
Chronic infection
Prolonged duration – weeks months or years
Localized infection
Confined to a small area or to an organ
Generalized infection
Disseminated to many body regions
Pyogenic infection
Pus-forming
S. Aureus
Fulminant
Actions that occur suddenly and intensely and are rapidly progressive
Pathogenicity
The ability to produce disease and a host organism.
Virulence
Degree of pathogenicity
Determined by virulence factors
Frank pathogen
An organism which can cause disease any normal post; when identified in clinical specimens is considered to be the probable agent of disease
Opportunistic pathogen
Etiologic agent isolated from a patient whose host defense mechanisms have been compromised
Herd immunity
The spread of a communicable disease within a group based on the proportions of susceptible and immune individuals in the group.
Epidemics or outbreaks of disease occurs when the proportion of susceptible individuals is high and disappear as a proportion of immune individuals increase.
Diseases spread by the ________ ______ require a higher proportion of immune individuals to prevent an outbreak than disease spread by _______ ________
Airborne route
Direct contact
Portals of entry
Likelihood of infection increases the closer the proximity the POE is to the target tissue
Ex influenza virus
Dose
Virulence of an organism is usually expressed as the amount that will infect (ID50) or kill (LD50) 50% of susceptible animals.
The larger the dose received the greater the chance for disease.
If an organism is highly virulent then fewer organisms will be required to cause disease.
Adherence is a prerequisite for_______
Pathogenicity
Rapidly growing organism produces _______ disease which is characterized by ______ onset and _________ progression
Acute disease
Rapid
Rapid
In general a slow-growing organism produces a ________ disease which is characterized by a indolent or insidious onset and progression
Chronic
Endotoxin (LPS)
A. Pyrogenic B. Heat stable- survives autoclave C. Does not form toxoids D. Broad spectrum of activity ( affects many species) E. Produced by GRAM NEGATIVE organisms
Exotoxins
A. Polypeptides are proteins that are either secreted or sell associated
B. Can be chromosome, plasmid encoded or carried on temperate bacteriophages
C. Usually heat labile
D. Can form toxoids (highly immunogenic)
E. Generally do not induced fever
F. Produced by gram-positive and Graham negative bacteria
