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Sandra Romain
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Deconstructing Epidemics
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Deconstructing Epidemics
- through anthropological methods, using several interpretive frameworks
- biomedical quantitative perspective
What is an Epidemic?
-endemic - when an infectious/non-infectious disease is present in a population at a relatively
constant (usually low) level at all times (little change in incidence over time)
-epidemic - when infectious/non-infectious disease rate (# of new cases or incidence) suddenly
increases above the expected or normal level for a short time in a localized area
-pandemic - when number of diseases cases occurring worldwide suddenly increases
-causes, manifestations, distributions and consequences… and the application of this study to
the control of health problems (public health)
-biological discipline
-germ theory
-host, agent and environment (reservoirs?)
Major Causes of Human Disease and Examples of Each Type
Cause (non-infectious disease):
-nutrition (cirrhosis of the liver, rickets, scurvy, obesity)
-poisons (carbon monoxide, ergotism, arsenic, lead)
-allergens (hay fever, sinusitis, poison ivy)
-metabolic disorders (neonatal jaundice, parkinson’s)
-hormonal disorders (hypothyroidism, diabetes, giantism)
-genetic disease (tay-sachs, sickle cell anemia)
-psychological factors (posttraumatic stress syndrome, anorexia nervosa)
-physical factors (UV radiation, altitude sickness, bends)
Cause (infectious disease):
-bacteria (strep throat, TB, syphilis, ulcers)
-rickettsiae (typhus, rocky mountain spotted fever)
-viruses (measles, herpes, warts, some cancers)
-prions (kuru, creutzfeldt-jakob disease)
-protozoa (giardia, trypanosomiasis, malaria)
-fungi (histoplasmosis, athlete’s foot, ringworm, yeast)
-metazoa (schistosomiasis, hookworm, tapeworm)
Epidemiological Questions
-who is prone to a particular disease?
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Deconstructing Epidemics
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-when is the disease most likely to occur (including trends over time)
-where is the risk of disease highest/lowest?
-what exposure (factor) do the victims have in common?
-how much is the risk increased through exposure?
-how many cases of the disease could be avoided by eliminating the exposure?
What is Needed to Answer These Questions?
-subject to bias, error
-require record keepers and infrastructure
-subject to disruption in times of crises and civil unrest
-ongoing systems
Case Definitions
-specificity - how accurately a test identifies people who have the disease
-sensitivity - how accurately a test identifies people who don’t have the disease
-laboratory/diagnostic facilities and resources
-challenges to epidemiological statistics: bias, disruption and capacity
Basic Epidemiology Descriptive Statistics
-incidence = # of new cases of a disease occurring during a specific time period/place !
# of persons at risk for developing the disease during that time period
-prevalence = # of cases of a disease present in a population at a specific time !
# of persons in the population at that time (including new and existing cases)
-prevalence usually for chronic and endemic diseases
-case fatality rate = # of deaths due to a particular disease in a given time interval !
# of cases of the disease
Modes of Transmission of Human Infectious Diseases
Mode (direct transmission):
-respiratory (influenza, chicken pox, measles)
-fecal-oral (giardia, hep A, rotavirus, pinworm)
-sexual (syphilis, gonorrhea, HIV, genital herpes)
-vertical (congenital) (rubella, syphilis, HIV, toxoplasmosis)
-direct physical contact (yaws, diphtheria, chickenpox, herpes simplex)
Mode (indirect transmission):
Vehicle Borne
-water borne (cholera, hepatitis, typhoid fever)
-food borne (botulism, salmonellosis, tapeworm)
-soil borne (hookworm, tetanus, histoplasmosis)
-needle sharing (hep B, HIV, HTLV-1)
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Deconstructing Epidemics
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Vector Borne
-mosquitoes (malaria, yellow fever, dengue fever)
-ticks (rocky mountain spotted fever, lyme disease)
-fleas (bubonic plague, murine typhus fever)
-lice (louse borne typhus fever, trench fever)
-flies (trypanosomiasis, leishmaniasis, onchocerciasis)
-other (chagas disease)
Mode (complex cycles): (schistosomiasis, guinea worm, hydatid disease)
-nosocomial - hospital acquired disease
Disease Progress
-active (natural or vaccine-induced)
-passive (mother to baby)
-become infectious after latent period
-symptoms start to show after incubation period
-can become infectious before showing symptoms/without showing symptoms
Reproductive Rates
-R0 = basic reproductive rate
-reproductive rate - the number of secondary infections produced by one primary infection
-if R0 > 1, epidemic can occur
-if R0 < 1, disease will die out
Disease Ecology is a Dynamic Equilibrium
-disease is a selection force in human evolution
-humans are a selection force in disease evolution
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