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123 Cards in this Set
- Front
- Back
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Infectious Disease Epidemiology: Major Differences
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A case can also be an exposure
Subclinical infections influence epidemiology Contact patterns play major role Immunity There is sometimes a need for urgency |
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Epidemiology
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Deals with one population
Risk case Identifies causes |
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Infectious disease epidemiology
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Two or more populations
A case is a risk factor The cause often known |
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HLA-
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human lymphocytic antigen- used in transplantation of organs
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Epidemiologist-
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control and match organs- study genetics of organs – match HLA
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Two or more populations
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Humans
Infectious agents Helminths, bacteria, fungi, protozoa, viruses, prions Vectors- help to transfer agent from one place to another Mosquito (protozoa-malaria), snails (helminths-schistosomiasis) Blackfly (microfilaria-onchocerciasis) – bacteria? Animals Dogs and sheep/goats – Echinococcus Mice and ticks – Borrelia (bacteria) |
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Helminth
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- parasites
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Prions- is
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nfectious protein particle
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The cause often known
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An infectious agent is a necessary cause
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What is infectious disease epidemiology then used for?
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Identification of causes of new, emerging infections, e.g. HIV, vCJD, SARS
Surveillence of infectious disease Identification of source of outbreaks Studies of routes of transmission and natural history of infections Identification of new interventions |
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acute disease
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symptoms develop rapidly and runs course quickly
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chronic disease
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usually mild symptoms that develop slowly and last a long time
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subacute disease
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disease with time course and symptoms bw acute and chronic
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asymptomatic disease
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disease without symptoms
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latent disease
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appears a long time after infection
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communicable disease
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transmitted from one host to another
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contagious disease
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communicable disease that is easily spread
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noncommunicable disease
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disease arising from outside of hosts or from opportunistic pathogen
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local infection
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infection confined to a small region of the body
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systemic infection
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widespread in many body systems- travel in blood or lymph
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focal infection
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serves as a source of pathogens for infections at other sites in body
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primary infection
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initial infection within a given patient
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secondary infection
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follow a primary- often by opportunistic pathogens
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Direct
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Skin-skin
Herpes type 1 Mucous-mucous STI Across placenta toxoplasmosis Through breast milk HIV (WBC) Sneeze-cough Influenza (comman cold) |
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Indirect
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Food-borne
Salmonell (bacterial) Water-borne Hepatitis A (viral) Vector-borne Malaria Air-borne Chickenpox Ting-borne (bite) Scarlatina |
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Exposure
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A relevant contact – depends on the agent
Skin, sexual intercourse, water contact, etc |
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toxoplasma gondii
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toxoplasmosis- abortion, mental retardeation, blindness, anemia, diarrhea
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treponema pallidum
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syphilis- abortion, multiorgan birth defects
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listeria monocytogenes
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listeriosis- granulomatosis infantiseptica, death
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granulomatosis infantiseptica
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nodular inflammatory lesions and infant blood poisening
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cytomegalovirus
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usually asymptomatic-deafness, microphaly, mental retardation
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parvovirus B19
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erythema infectiosum- abortion
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lentivirus (HIV)
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AIDS- immunosuppression
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rubivirus rubella
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german measions- severe birth defects/ death
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direct contact
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cutaneous, anthrax, genital warts, gonorrhea, herpes, rabies, syphilis, staphylococcus infections
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indirect contact
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common cold, enterovirus, influenza, measles, tetanus, whooping cough
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airborne
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dust particles- chickenpox, coccidiomycosis, histoplasmosis, influenza, measles, pulmonary anthrax, TB
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waterborne
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streams, swimming pools- compylobacter infections, cholera, giardia diarrhea
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food borne
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poultry, seafood- food poisoning (botulism staphylococcal) hep A, listeriosis, tapeworm, toxoplasmosis, typhoid fever
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mechanical vector transmission
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on insect bodies
flies roaches E.Coli salmonellosis |
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biological vector transmission
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lice, mice flies
chagas's disease lyme disease malaria plague |
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clinical
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death
carrier immunity no imm |
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sub-clinical
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carrier
immunity no imm |
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carrier
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when one has infection but no symptoms
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dynamics of infection
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latent period, infectious perios, non- infections
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dynamics of disease
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incubation period, symptomatic period, non-diseased
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Index –
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the first case identified
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Primary –
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the case that brings the infection into a population
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Secondary –
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infected by a primary case
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Tertiary
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– infected by a secondary case
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attack rate
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ill
exposed |
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Epidemiologic Triad
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agent of infection
host environment |
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Agent
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Infectivity
Pathogenicity Virulence- how dangerous Immunogenicity Antigenic stability Survival |
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Environment
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Weather
Housing Geography Occupational setting Air quality Food |
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HOST
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Age
Sex Genotype Behaviour Nutritional status Health status |
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Infectivity (
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ability to infect)
(number infected / number susceptible) x 100 |
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Pathogenicity
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(ability to cause disease)
(number with clinical disease / number infected) x 100 |
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Virulence (
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ability to cause death)
(number of deaths / number with disease) x 100 |
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Predisposition to Infections
(Host Factors) |
Gender
Genetics Climate and Weather Nutrition, Stress, Sleep Smoking Stomach Acidity Hygiene |
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infectious agent
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bacteria
virus fungi protozoa helminths |
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resevior
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people
equipment water |
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portals of exit
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excretions
secretions droplets skin |
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means of transmission
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direct contact/formite
injection ingestion airborne/aerosols |
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portal of entry
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broken skin
mucous membrane gastrointerstrinal/ respiratory/urinary tract |
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susceptible host
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neonates
diabetics immunosuppressed cardiopulmonary disease |
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infectious agents
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Bacteria
Viruses Fungi Protoctists / Protozoa Helminths |
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Mycoplasma-
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don’t have cell wall
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Chlamydiae-
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can enter cell like virus but is a bacteria
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Enterobacteriacease-
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cause diahrea
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vCJD
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injestion of BSE-contaminated food
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sporadic creutzfeldt jalcob disease
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somatic mutation or spontaneous conversion
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latrogenic creutzfeldt jalcob disease
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accidental medical exposure to CJD contaminated tissues
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familial creutzfeldt jalcob disease
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germline mutation in PRNP gene
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gerstmann straussler sheinker syndrome
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germline mutation in PRNP gene
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fatal familial insomnia
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germline mutation in PRNP gene
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kuru
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ritualistic cannibalism
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scrapie
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aquired, horizontal transmission, vertical trans
unclease |
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bovine spongform encephalopathy BSE
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ingestion of BSE- contaminated meat and bonemeal
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chronic wasting disease
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same as scrapie
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feline spongiform encephalopathy
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ingestion of BSE contaminated food
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transmissible mink encephalopathy
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aquired (ingestion) but source unknown
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exotic ungulate encephalopathy
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ingestion of BSE good
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resevoirs
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a host that carries a pathogen without injury to itself and serves as a source of infection for other host organisms (asymptomatic infective carriers)
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vectors
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a host that carries a pathogen without injury to itself and spreads the pathogen to suscrptible organisms (asymptomatic carriers of pathogens)
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MYPANOSOMIASIS
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protozoan blood parasite that causes sleeping sickness, uses tsetse fly as vector
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trypanosomiasis
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The protozoan blood parasite that causes sleeping sickness,
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Viruses
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(Arbovirus) - Mosquitoes
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Bacteria
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(Yersinia) - Fleas
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Bacteria
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(Borrelia) - Ticks
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Rickettsias
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(R. prowazeki) - Lice, ticks
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Protozoa (Plasmodium) -
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Mosquitoes
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Protozoa (Trypanozoma) -
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Tsetse flies (sleeping sickness)
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Helminths (Onchocerca) -
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Simulium flies
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Koch’s Postulates
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The same organism is present in every case
It is isolated or grown in pure culture The disease can be reproduced in healthy animals after infection with pure culture The identical pathogen is reisolated from the experimental animals |
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Infectious Disease Process
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Direct tissue invasion
Toxins Persistent or latent infection Altered susceptibility to drugs Immune suppression Immune activation (cytokine storm) |
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Endemic
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Transmission occur, but the number of cases remains constant
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Epidemic
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The number of cases increases
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Pandemic
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When epidemics occur at several continents – global epidemic
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Sporadic level
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: occasional cases occurring at irregular intervals
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Endemic level:
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persistent occurrence with a low to moderate level
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Hyperendemic level:
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persistently high level of occurrence
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Epidemic or outbreak:
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occurrence clearly in excess of the expected level for a given time period
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Pandemic:
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epidemic spread over several countries or continents, affecting a large number of people
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Attack rate =
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ill
exposed |
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Epidemiologic Triad
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agent of infection
host environment |
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Agent
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Infectivity
Pathogenicity Virulence- how dangerous Immunogenicity Antigenic stability Survival |
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Host
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Age
Sex Genotype Behaviour Nutritional status Health status |
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env't
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Weather
Housing Geography Occupational setting Air quality Food |
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Infectivity
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(ability to infect)
(number infected / number susceptible) x 100 |
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Pathogenicity (
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ability to cause disease)
(number with clinical disease / number infected) x 100 |
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Virulence (
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ability to cause death)
(number of deaths / number with disease) x 100 All are dependent on host factors |
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Predisposition to Infections
(Host Factors) |
Gender
Genetics Climate and Weather Nutrition, Stress, Sleep Smoking Stomach Acidity Hygiene |
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infectious agent
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bacteria
virus fungi protozoa helminths |
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reservoir
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people
equipment water |
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portals of exit
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excretions
secretions droplets skin |
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means of transmission
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direct contact/formite
injection ingestion airborne/aerosols |
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portal of entry
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broken akin
mucous membrane gastrointestrinal respirtatory urinary tract |
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susceptible host
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neonates
diabetics immunosuppressed cardiopulmonary disease |
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Infectious Agents
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Bacteria
Viruses Fungi Protoctists / Protozoa Helminths |
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Mycoplasma-
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don’t have cell wall
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Chlamydiae-
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can enter cell like virus but is a bacteria
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Enterobacteriacease-
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cause diahrea
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variant cruetzfeldt jakob disease
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injestion of BSE contaminated fppd
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