pathogensis - at risk populations_ prof bhisma murti.ppt
TRANSCRIPT
PathogenesisPopulations at Risk for Infection
or Disease
Prof. dr. Bhisma Murti, MPH, MSc, PhD
Department of Public Health, Faculty of Medicine, Universitas Sebelas Maret
Infectious disease epidemiology• Involves two populations
1. Animal2. Infectious agent
Has its own life cycle, immunology, and evolution• Involves additional considerations
Reservoir Transmission Contact and mixing patterns of infective and
susceptible hosts Degree and duration of infectiousness
1. Measurement of disease events2. Infectious disease epidemiology
Infectiousness• Time lines of infection
Time line of infectiousness Latent period
Time from infection to development of infectiousness Period of infectiousness
Time from development of infectiousness to end of time when the host can infect another host
Noninfectious periodRemoved from population - harvestedDeadRecovered
1. Measurement of disease events2. Infectious disease epidemiology
Infectiousness• Time lines of infection
Time line of infectiousness Time line of disease
1. Measurement of disease events2. Infectious disease epidemiology
Incubation periodTime from infection to development of symptomatic
disease
Infectiousness• Time lines of infection
Time line of infectiousness Time line of disease
Incubation period Symptomatic period
1. Measurement of disease events2. Infectious disease epidemiology
Infection without symptoms = inapparent case
Can be infectious
Pathogenicity = probability of developing symptoms after being infected
Infectiousness• Time lines of infection
Time line of infectiousness Time line of disease
Incubation period Symptomatic period Nondiseased
1. Measurement of disease events2. Infectious disease epidemiology
Recovery from symptomsRecoveredImmuneCarrier – recovers from symptoms but remains
infectiousDeath
• Time lines of infection
Time
Nondiseased• Dead• Recovered• Immune• Carrier
IncubationPeriod
Symptomatic Period
Time of infection
Susceptible
Development of Symptoms
End of Symptoms
Time Line of Disease
Latent Period
InfectiousPeriod
Noninfectious• Removed• Dead• RecoveredSusceptible
Time Line of Infectiousness
• Time lines of infection
Time
Latent Period
InfectiousPeriod
Noninfectious• Removed• Dead• RecoveredSusceptible
Time Line of Infectiousness
Nondiseased• Dead• Recovered• Immune• Carrier
IncubationPeriod
Symptomatic Period
Time of infection
Susceptible
Development of Symptoms
End of Symptoms
Time Line of Disease
• Time lines of infection
Time
Nondiseased• Dead• Recovered• Immune• Carrier
IncubationPeriod
Symptomatic Period
Time of infection
Susceptible
Development of Symptoms
End of Symptoms
Time Line of Disease
Important to Patient and ClinicianImportant to Patient and Clinician
• Time lines of infection
Time
Latent Period
InfectiousPeriod
Noninfectious• Removed• Dead• RecoveredSusceptible
Time Line of Infectiousness
Important to Infectious Agent and Important to Infectious Agent and Production Medicine VetProduction Medicine Vet
Transmission probability• The probability that, given contact
between an infective source and a susceptible host, successful transfer of the parasite will occur so that the susceptible host becomes infected Depends on:
The characteristics of the infective sourceThe parasiteThe susceptible hostThe type and definition of contact
1. Measurement of disease events2. Infectious disease epidemiology
Transmission probability• The probability that, given contact
between an infective source and a susceptible host, successful transfer of the parasite will occur so that the susceptible host becomes infected Depends on:
The characteristics of the infective source
1. Measurement of disease events2. Infectious disease epidemiology
Another animal Insect vectorInanimate object: water, feed, fomites
Transmission probability• The probability that, given contact
between an infective source and a susceptible host, successful transfer of the parasite will occur so that the susceptible host becomes infected Depends on:
The type and definition of contact
1. Measurement of disease events2. Infectious disease epidemiology
The mode of transmission determines what types of contact are potentially infectious
Contact pattern – contagious disease• Some diseases – contact pattern is determined
by density When confined in smaller areas, contacts are more
frequent Important for diseases spread by casual contact
Other diseases – contact pattern is determined by pathogen or animal characteristics Sexually transmitted diseases will only affect
sexually active adults, not calves, pregnant animals, or anestrous animals
1. Measurement of disease events2. Infectious disease epidemiology
Contact pattern – non-contagious disease• Vertically transmitted diseases
Dam to offspring in utero Vector borne diseases
Snail Biting insects / arthropods
1. Measurement of disease events2. Infectious disease epidemiology
Basic reproductive number (R0)
1. Measurement of disease events2. Infectious disease epidemiology
R0 =Number of
contacts per unit time
Transmission probability per
contact Duration of
infectiousness = cpd
R0 is a complex parameter that summarizes many of the important aspects of an infectious agent in a host population
1. Measurement of disease events2. Infectious disease epidemiology
Time
Num
ber o
f ind
ivid
uals
Epidemic, low R0
Susceptible
Immune
InfectedNew Cases
1. Measurement of disease events2. Infectious disease epidemiology
Time
Num
ber o
f ind
ivid
uals
Epidemic, high R0
Susceptible Immune
Infected
New Cases
1. Measurement of disease events2. Infectious disease epidemiology
Time
Num
ber o
f ind
ivid
uals
Endemic, low R0
Susceptible
Immune
InfectedNew Cases
1. Measurement of disease events2. Infectious disease epidemiology
Time
Num
ber o
f ind
ivid
uals
Endemic, high R0
Susceptible
Immune
Infected
New Cases
1. Measurement of disease events2. Infectious disease epidemiology
Epidemic, low R0 Epidemic, high R0
Endemic, low R0 Endemic, high R0