Epi- Final- 2

kelseyfmeyer's version from 2015-09-08 16:54

Epi. of infectious diseases + Herd Immunity

Question Answer
Infectious Disease Epidemiology involves the relationship of three factors, which (who), enviro (where), agent (what)
Reservoirs, (aka?) are what? how are they relevant to a disease? what are the two kinds of reservoirs?aka "essential hosts." This is The usual habitat where the agent multiplies and is maintained [lives]. Without the reservoiers, the agent CANNOT SURVIVE!! The two types are: (1) Animate reservoirs-animals or humans (2) Inanimate –soil, water
what is a portal of exit?the path by which a pathogen leaves its host. (Ex: resp. tract for influenza virus)
what are the two horizontal modes of transmission? explain them(1) Direct horizontal transmission: This is person-to-person, animal-to-animal, or animal-human. This contact could by via skin, sexual contact, or a short-distance aerosol (like mycobacterium TB, which is propelled short distances). (2) INDIRECT horizontal transmission is when there is no direct contact, but the agent is transferred from objects, such as fomites, through transfusions/injections, food borne, water borne, airborne (AEROSOL)... Small particles that can remain suspended in the air and travel for considerable distances in wind. (ex: Q fever which is coxiella burnetti). Another form of indirect is VECTOR BORNE (See other card)
is a vector a direct or indirect horizontal form of transmission? explain the two types of vector borne transmissionINDIRECT TRANSMISSION! (1) Mechanical vectors- survival: no replication or development of pathogen in insect vector (2) biological vectors: Replication or development of pathogen in the vector (such as borrelia burgdorferi in ticks or yersinia pestis in fleas)
explain "vertical transmission"Transmission of infection from one generation to the next by: (1) infection of the embryo or fetus while in-utero (mammals) (2) or in-ovo (birds, reptiles, fish, etc.). (3) transmission by colostrum to offspring
what is a Susceptible Host?An animal or person that is capable of becoming infected with an infectious agent.
Reservoir or Essential Hosts...define thisthe habitat, either animate or inanimate, in which the infectious agent resides [is maintained] and/or multiplies. The Agent is dependent upon this reservoir for survival in nature
what is an amplifier host?Host in which infectious agent multiplies to high levels sufficient to spread to other hosts. (EX: Venezuelan equine encephalitis (VEE) virus produces a high-titer viremia in horses sufficient for transmission to other hosts via the mosquito)
explain the relationship between amplifier hosts and essential hostsNot all amplifier hosts are essential hosts, BUT All Essential hosts are amplifier hosts
what is an accidental host?Not required for maintenance but can become infected with the agent. Does not provide an environment for the agent to multiply/replicate. (ex: rabies in humans)
what is a dead end host?Host that cannot spread the infection to other susceptible hosts under natural conditions
what is infection? (how is it diff from dz) What is disease?Defined as the encounter of a potentially pathogenic agent. With a susceptible human / animal host and the host shows an immunologic response to infection. Infection doesnt necessarily lead to disease!! DZ: Defined as a clinically apparent infection — infection accompanied by overt illness. Disease is only one possible outcome of infection.
what is the incubation period?Defined as the time period between exposure to an agent (Infection) and onset of clinical signs/symptoms of disease.
what is the latent period?Time period between the initiation of infection in the host and when the host becomes infectious to others (first shedding of the agent)
what is period of transmission?Agent being shed: Time during which the host is infectious to others
what is a carrier state, and what type of infections are part of carrier states?This can happen with a clinical OR subclinical infection. A carrier state usually happens due to Incomplete or inappropriate treatment or poor immune response. The infectious agent is not completely eliminated leading to a carrier state...which means they are notshowing CSs but shed the infectious agent to infect others...this can last months or years!!
what is the equation for infectivity?(Animals who become infected) / (Exposed animals in the population)
**What is attack rate/when do we use attack rate and how do you calculate it?In an Outbreak, infectivity may be defined by the Attack rate. The attack rate is typically used for acute diseases, often in an outbreak situation. The equation is (# new cases for epidemic period) / (population at risk (entire population))
What is a secondary attack rate? how do you calculate it?In animal-animal transmitted infection, quantifies infectivity. It is the probability that infection occurs among susceptible animals following known contact with an index case (primary case). The equation for it is (# new cases (derived from index case) ) / (All those that came into contact with the index case that remained healthy)
how do you calculate pathogenicity?(number of infected and exhibiting disease) / (total number infected)
how do you calculate virulence?(number with severe dz) / (total number with dz) ....OR.... (fatal cases) / (total cases)
what is the case fatality rate, and how do you calculate it?“The proportion of cases who eventually die from the disease.” or, reworded, "The incidence of death among individuals who develop the disease." The calculation is: [# Fatal cases(No. Of deaths)] / [# Total cases(all with disease)]
what is the mortality rate? How do you calculate it?Mortality rate refers to the incidence of death among all individuals in the population at risk of developing the disease. It's calculated by: (No. of deaths in the population) / (No. of individuals in the total population) <--not just those with the dz.(that's case fatality)
what is immunogenicity?The ability of an agent to induce an immune response, as measured by antibody production
What is herd immunity?The resistance TO an infectious agent of an entire group as a result of a substantial proportion of the group being immune to the agent.
When is herd immunity accomplished?It is accomplished when the number of animals in a given population that have acquired immunity is so great, that under natural conditions a contagious agent cannot enter and spread within the herd.
what are the three major factors which determine the duration of immunity in a herd setting?(1) Introduction of susceptible animals to the herd (2) Departure of immune animals from herd (3) Infectivity of the agent
infectivity of an agent can affect the duration of immunity in a herd. what are 4 factors which influence the infectivity?(1) Spontaneous mutations [Antigenic drift and shift [H1N1] (2) Duration of shedding by infected animals and degree of contact between members of the herd (3) Ease with which the agent is transmitted: Airborne FMD rapid spread vs rabies [bites] (4) Increased population density/movement/travel

Outbreak Investigation

Question Answer
What is an outbreak?Outbreak synonymous with epidemic/epizootic, Where observed no. of cases exceeds the expected no.: (1) In a specified area (spatial) (2) Among a specific gp. of animals/people (demographic) (3) Over a particular time period (temporal)
what are the 6 phases of the epidemiological workup (phases of the investigation)?(1) decriptive phase (2) herd history (3) case definition (4) generate epidemic curve (5) analytical phase (6) intervention+control
what three major phases compose the other phases in an investigation?(1) Descriptive (2) analytical (3) intervention+control
during the descriptive phase of the investigation ,what are the 4 things theyre doing?describe dz parameters, case definition, generate epidemic curve, review herd history
what are the three things you're doing in the descriptive phase of the investigation?You are describing disease parameters in terms of.... (1) clinical signs/post mortem findings (2) incubation period (3) Temporal, spatial, demographic
read through the exampleFMD sucks. yay.
what are the trade implications associated with the vaccines made of FMD?unless it is a molecular vaccine, where you can tell the diff. between the Abs produced from the vx vs exposure, the Abs CANT be differentiated, so there will be trande restrictions between countries that do and don't vx, since they wont know if it's safe or not.
what were some of the problems/weaknesses associated with the way they handled the FMD outbreak of 2001?Difficult to employ slaughter policy quickly, 1200 overseas vets recruited to assist. Epidemic spread resulting from lack of implementation in certain areas. Public objections to slaughter of infected carcasses near residential areas. Smoke - ( pollution threat to health?). Psychological effects-vets, farmers. Outbreaks continue-Division amongst vets + the government/farmers. Need for ‘participatory epidemiology’.Vets supported vaccination to limit spread but not larger farmers/government re: carrier status + damage to trade. Small farmers for vaccination to protect herds they had created over decades. Also, UK Vets involved in inspection at entry ports kept poor records + were inadequately trained to detect Foreign Animal diseases. Registration Procedures for shipments > not fulfill EU regulations.
what were some of the strengths associated with the way they handled the FMD outbreak of 2001?Slaughter, carcasses burned, serosurveillance in sheep, biosecurity
the third step in the phases of an investigation is forming the case definition. The three components of a case are..(1) clinical signs (2) immuno response (are there abs?) (3) Detection of the agent (analytical phase) required to confirm it as a case

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