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What host cannot spread the infection to other susceptible hosts under natural conditions?
dead end host
What is defined as encounter of a potentially pathogenic agent with susceptible animal host and host shows IMMUNE RESPONSE to infection?
What is time period between exposure to agent (infection) and onset of clinical signs?
What is time between initiation of infection in host and when host becomes infectious to others (sheds agent)?
What is time during which host is infectious to others; from 1st shed to end of disease?
period of transmission/communicability
What is clinically apparent infection/overt illness?
disease (one possible outcome of infection)
What are 4 possible outcomes to exposure to infectious agent?
What are 3 criteria for defining a case?
- clinical syndrome (symptoms)
- immune response (info on time of exposure)
- agent detection (by lab confirmation)
What is an infection in susceptible host without clinical signs? What would be required to show presence of infection?
- subclinical infection
- antibody response
Does a carrier have clinical signs? Can they shed to others?
- no symptoms
- yes, shed to others
What refers to small gradual changes that occur through point mutations? These minor changes account for annual epidemics.
What is an abrupt, major change to produce novel subtypes via genetic reassortment?
What is the ability of an organism to cause infection in susceptible host? How would you calculate this?
infectivity = infected people / exposed people
What is the infectivity during an outbreak called? how do you calculate? Is this typically for acute or chronic disease?
- attack rate = # new cases for epidemic period/ entire pop at risk
- acute disease
What provides a measure of a disease's ability to spread?
secondary attack rate (primary cases spread to cause secondary ones)
What is proportion of infected people that develop clinical signs? How to calculate?
pathogenicity = # infected and exhibiting signs / total number infected
What is number of persons that develop severe disease?
What is the proportion of cases that eventually die from disease? How to calculate?
case fatality ratio = # fatal cases/ # of cases with disease
What is incidence of death among all individuals in population? Calculate?
mortality rate = # fatal cases / total population
What is the ability of agent to induce immune response, and how do you measure if there is a response?
- evaluate antibody production