Epidemiology - Final 2

drraythe's version from 2016-02-14 23:03

Epi. of infectious Dzs + Herd Immunity

Question Answer
Infectious dz Epidemiology involves the relationship of 3 factors, which are...Host (Who)
Enviro (Where)
Agent (What)
Reservoirs, (aka?) are what? How are they relevant to a dz? What are the 2 kinds of reservoirs?Aka "Essential Hosts." This is the usual habitat where the agent multiplies & is maintained [lives]. W/o the reservoirs, the agent CANNOT SURVIVE!!
The 2 types are:
(1) Animate - 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 2 horizontal modes of xmission? Explain themDirect Horizontal Xmission: 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)

Indirect Horizontal Xmission: When there is no direct contact, but the agent is transferred from objects, such as fomites, through xfusions/injxns, food borne, water borne, airborne (AEROSOL)... Small particles that can remain suspended in the air & 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 xmission? Explain the 2 types of vector borne xmissionINDIRECT XMISSION!
(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 Xmission"Xmission of infxn from 1 generation to the next by:
(1) Infxn of the embryo or fetus while in-utero (mammals) or In-ovo (birds, reptiles, fish, etc)
(3) Xmission by colostrum to offspring
What is a Susceptible Host?An animal or person that is capable of becoming infected w/ an infectious agent.
Define Reservoir or Essential HostsThe habitat, either animate or inanimate, in which the infectious agent resides (is maintained) &/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 xmission to other hosts via the mosquito)
Explain the relationship btwn Amplifier Hosts & Essential HostsNot all Amplifier Hosts are Essential Hosts,
BUT All Essential Hosts are Amplifier Hosts
What is an Accidental Host?Not reqd for maintenance but can become infected w/ 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 infxn to other susceptible hosts under natural conditions
What is infxn? (How is it diff from dz?) What is dz?Infxn is defined as the encounter of a potentially pathogenic agent w/ a susceptible human/animal host & the host shows an immunologic response to infxn. Infxn doesnt necessarily lead to dz!!
Dz is defined as a clinically apparent infxn - infxn accompanied by overt illness. Dz is only 1 possible outcome of infxn
What is the Incubation Period?Defined as the time period btwn exposure to an agent (infxn) & onset of CS/symptoms of dz.
What is the Latent Period?Time period btwn the initiation of infxn in the host & when the host becomes infectious to others (1st shedding of the agent)
What is Period of Xmission?Time during which the host is infectious to others (when the agent is being shed)
What is a Carrier State & what type of infxns are part of Carrier States?This can happen w/ a clinical OR subclinical infxn. A carrier state usually happens due to Incomplete or inappropriate Tx or poor immune response. The infectious agent is not completely eliminated leading to a carrier state...which means they are not showing CSs but shed the infectious agent to infect others...this can last months or years!!
What is the equation for Infectivity?
**What is Attack Rate? When do we use attack rate & how do you calculate it?The attack rate is the number of new cases in a population. Typically used for acute dzs, often in an outbreak situation. Infectivity may be defined by the Attack rate.
The equation is:
What is a 2° Attack Rate? How do you calculate it?In animal-animal xmitted infxn, quantifies infectivity. It is the probability that infxn occurs among susceptible animals following known contact w/ an index case (primary case)
The equation for it is (# new cases (got sick from contact w/ the index case) ) / (All those that came into contact w/ the index case that remained healthy)
How do you calculate Pathogenicity?
How do you calculate Virulence?
What is the Case-Fatality Rate & how do you calculate it?“The proportion of cases who eventually die from the dz.” or, reworded, "The incidence of death among individuals who develop the dz."
The calculation is:
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 dz.
It's calculated by:

ENTIRE POPULATION!! Not just those w/ 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 who have acquired immunity is so great, that under natural conditions a contagious agent cannot enter & spread w/in the herd.
What are the 3 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 & shift [H1N1]
(2) Duration of shedding by infected animals & degree of contact btwn members of the herd
(3) Ease w/ which the agent is xmitted: Airborne FMD rapid spread vs Rabies [bites]
(4) ↑ population density/movement/travel

Outbreak Investigation

Question Answer
What is an Outbreak?Outbreak synonymous w/ Epidemic/Epizootic, Where observed # of cases exceeds the expected #:
(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) Descriptive phase
(2) Herd Hx
(3) Case definition
(4) Generate epidemic curve
(5) Analytical phase
(6) Intervention & control
What 3 major phases compose the other phases in an investigation?(1) Descriptive
(2) Analytical
(3) Intervention+control
What are the 3 things you're doing in the Descriptive Phase of the investigation?You are describing dz parameters in terms of:
(1) CS/post mortem findings
(2) Incubation period
(3) Temporal, Spatial, Semographic
Read through the exampleFMD sucks. Yay.
What are the trade implications associated w/ the Vxs made of FMD?Unless it is a molecular Vx, where you can tell the diff. btwn the Abs produced from the Vx vs exposure, the Abs CANT be differentiated, so there will be trade restrictions btwn countries that do & don't Vx, since they wont know if it's safe or not.
What were some of the problems/weaknesses associated w/ 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 public health?)
Psychological effects - vets, farmers
Outbreaks continue
Division amongst vets & the government/farmers - Vets supported Vx to limit spread but not larger farmers/government (carrier status, damage to trade)
Need for ‘participatory epidemiology’
Small # farmers Vxd to protect herds they had created over decades
UK Vets involved in inspection at entry ports kept poor records & were inadequately trained to detect Foreign Animal dzs
Registration Procedures for shipments did not fulfill EU regulations
What were some of the strengths associated w/ the way they handled the FMD outbreak of 2001?Slaughter
Carcasses burned
Serosurveillance in sheep
The 3rd step in the phases of an investigation is forming the Case Definition. The 3 components of a case are..(1) CS
(2) Immune response (are there abs?)
(3) Detection of the agent (analytical phase) reqd to confirm it as a case

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