Presentation on theme: "Dynamics of infectious disease transmission"— Presentation transcript:
1 Dynamics of infectious disease transmission Dr Noreen ShahSenior LecturerDept of Community MedicineKGMC
2 Objectives: At the end of this session the students will be able to; Define concepts of infectious disease epidemiologyDescribe different modes of transmission of infectious diseasesExplain the chain of infectionDescribe the ways to break Chain of Infection
3 Epidemiologic TriadThe standard model of infectious disease causation.It has 3 corners (vertices).Agent: A microbe that causes disease.Host: An organism that harbors disease.Environment: External factors that allows disease transmission.
5 Dynamics of transmission I. Source/ReservoirII. ModesofTransmissionIII. SusceptibleHostCommunicable diseases are transmitted from the reservoir/source of infection to susceptible host through .
6 I. Source or reservoirThese are natural habitat of infectious agents in which an infectious agent normally lives and multiplies.Examples are;Human reservoirsAnimal reservoirs (zoonotic diseases)Reservoir in non-living things.
7 1. Human reservoirs Cases Carriers According to spectrum of disease:Clinical cases(Mild/severe-typical/atypical)Sub-clinical casesLatent infection casesPrimary caseIndex caseSecondary casesType:IncubatoryConvalescenthealthyDuration:TemporaryChronicPortal of exit:UrinaryIntestinalRespiratoryothers
8 Cases may be:Primary case: The first case of an infectious disease introduced into the population.Index case: The first case that come to attention of investigators.Secondary case: Cases that develop from primary cases.
9 Cont. Cases may be according to spectrum of disease; Clinical cases: may be mild/severe/typical or atypical depending upon the gradient of involvement.Subclinical cases: Asymptomatic or mildly infected that does not alert the patients.Latent cases: Asymptomatic infection capable of showing symptoms under some circumstances if activated.
10 Carriers:Carriers are infected persons that harbor specific infectious agent in the absence of visible clinical disease and serves as a potential source of infection to others.Carriers are less infectious than cases.They live a normal life but can infect other individuals.Epidemiologically they are more dangerous as these escape recognition.
11 Cont. Carriers may be classified by: Types:Incubatory Carrier: Person capable of transmitting an infectious agent during incubation period.Convalescent Carrier: Person who continue to shed the disease agent during the period of convalescence, e.g. typhoid fever, cholera, whooping cough, in these clinical recovery does not coincide with bacteriological recovery.Healthy Carrier: Emerge from subclinical cases.
12 Cont. 2. Temporary or chronic: Temporary carriers: Are those who shed infectious agent for short periods of time. All the three incubatory, convalescent and healthy are included.Chronic carriers: A carrier who excretes the infectious agent for indefinite period. E.g. typhoid fever, hepatitis B, dysentery, malaria, etc.
13 Cont.3. Portal of exit:Carriers may be classified according to portal of exit of infectious disease.UrinaryIntestinalRespiratoryOpen wounds andBlood.
14 2. Animal reservoirs (zoonotic diseases) Infection disease that are transmissible under natural conditions from vertebrate animals to man, e.g. rabies, plague, bovine tuberculosis etc.
15 3. Reservoir in non-living things Soil and inanimate matter can also act as reservoir of infection. E.g. soil may harbor agents that causes tetanus, anthrax etc.
16 II: MODES OF TRANSMISSION OF DISEASE Communicable diseases transmitted from the reservoir or source of infection to a susceptible host in many ways.
17 Mode of transmission Direct transmission Indirect Direct contactDroplet infectionContact with soilInoculation into skin or mucosaTrans-placental (vertical)Vehicle-borneVector-borne:MechanicalbiologicalAir-borneFomite-bornUnclean handsand fingerspropagativeCyclo-prop.Cyclo-develop.
19 1. Direct transmission:Direct physical contact: From source/ reservoir to a susceptible host, e.g. skin to skin contact, STDs AIDS, eye infections etc.Droplet infection: By saliva & nasopharyngealsecretions e.g. flu, diphtheria, whooping cough, tuberculosis, meningococcal meningitis etc.
20 3. Contact with soil: The disease agent is in soil e. g 3. Contact with soil: The disease agent is in soil e.g. hook worm infection, tetanus, mycosis etc. 4. Inoculation into skin or mucosa: The disease agent inoculated directly into skin or mucosa e. g. rabies, hepatitis B, etc. 5. Trans placental (vertical): e.g. Toxoplasmosis, others, rubella, cytomegalovirus, herpes simplex (TORCH)
21 2. Indirect transmission Vehicle borne transmission: The agents multiplies or develops in vehicle & transmits through agencies like water, vegetables, fruits, milk, milk products, ice, blood, serum, tissue or organs transplantation.E.g. diarrhea, typhoid, cholera, polio, hepatitis A, brucellosis, etc.
22 2. Vector-borne transmission: Living carriers that transports infectious agents to a susceptible individual. It may be;Mechanical transmission: When a vector simply carries pathogenic microorganisms on their body and transfers them to food. E.g. flies and cockroaches.
23 ii. Biological transmission: the agent multiplies and develops in a vector. E.g. Propagative transmission: Multiplication without cyclic change such as DHF, yellow fever, etc. Cyclo-development transmission: No multiplication but cyclic change such as filariasis, etc. Cyclo propagative transmission: Multiplication and change in form such as malaria, etc.
24 iii. Air borne: Transmission is carried in air in form of droplets and dust e.g. tuberculosis, influenza, chicken pox, measles, viruses, spores of fungi etc.iv. Fomite borne: These are inanimate substances other than water or food contaminated by the infectious discharge, e.g: diphtheria, typhoid bacillary dysentery, hepatitis A, eye and skin infections.
25 Diseases may be transmitted as: Horizontal transmission: From one individual to another in the same generation.Direct contact (licking, touching, biting)Indirect contact (cough, sneeze, vectors, fomites, fomites, allow the transmission of disease without physical contact.
27 iii. Susceptible host:The person who is at risk for developing an infectious disease.Factors making person susceptible are,age (young and elderly are more at risk)underlying chronic diseases such as diabetesImmuno suppression conditions like HIV chemotherapy, and malnutrition.
29 Chain of InfectionDefinition: Chain of infection is a model (a circle of links) used to understand the infection process.Each circle represents a component in the cycle.Each link must be present and in the sequential order for an infection to occur.Breaking any link in the chain can disrupt the infection.
31 Different Ways to break Chain Diseases have certain weak pointsThe basic approach in controlling the disease is toIdentify these weak points andBreak the weakest links in chain of transmission
32 Chain of Infection: An infectious agent leaves its It is the process that begins when,An infectious agent leaves itsReservoir or host through aPortal of exit and thenIs conveyed by some mode of transmission toEnter through an appropriate portal of entry toInfect a susceptible host
33 1. Infectious agent:Infectious agent is the pathogen (germ) that causes diseases
34 Breaking the Chain Infectious agent Early diagnoses and treatment Cleaning, disinfection and sterilizationInfection prevention policiesPest control
35 2. Reservoir or hostPrincipal habitat where infectious agents live and multiplyFrom there they may spread to cause infection.Reservoirs may be humans, animals or environmental.
36 Breaking the Chain2. Reservoir of infection Cleaning, disinfection and sterilizationInfection prevention policiesPest control
37 3. Portal of exit:It is the site from where micro-organisms leave the host to enter another host to cause infection. E.g.Upper respiratory tract: saliva, sneeze, coughGastrointestinal tract: feces, vomitBlood: infected bloodUro - genital tract: semen, vaginal secretions, urineSkin and mucous membranes: discharges
38 Breaking the Chain 3. Portal of exit Hand hygiene Personal protective equipmentControl of aerosols and splatter (aerosols can transmit respiratory infections like tuberculosis, splashing of mucosa is also a potential risk)Respiratory etiquetteWaste disposal
39 4. Modes of transmission Modes of transmission are, The route by which an infectious agent is transmitted from a reservoir to another host.6 Fs, food, fluid, fingers, fomites, feces, flies.Modes of transmission are,Direct transmission.Person to person: Touching, kissing, sexual intercourse, coughing, sneezing, talking etcTrans – placental: Transfer of infectious agents from pregnant woman to fetus via placenta.
40 Indirect transmission. Air borne transmission: The infectious agent is present in air as dried secretions from respiratory tract, e.g. tuberculosis.Vehicle borne transmission: any non-living substance that can be contaminated by an infectious agent, which then transmits it to a new host. Vector borne transmission: An organism, usually an arthropod, which transmits an infectious agent to a new host. E.g. houseflies, mosquitoes, lice and ticks.
41 Breaking the Chain 4. Mode of transmission Hand hygiene Personal protective equipmentFood safetyCleaning, disinfection, sterilizationIsolation
42 5. Portal of entry:The site through which micro-organisms enter the susceptible host.Inhalation: influenzaIngestion: gastro enteritisNeedle prick: hepatitis BSexual contact: HIV/AIDS,Open wound or punctures: tetanus
43 Breaking the Chain 5. Portal of entry: Hand hygiene Personal protective equipmentPersonal hygieneFirst aid
44 6. Susceptible Host: A organism that can be infected by pathogens. Vulnerable Populations:Very young and the very old,Immune suppressed (due to genetics, transplant drugs, malnutrition, or viral infection like HIV).Occupational exposure.Non-immune.
45 Breaking the Chain 6. Susceptible Host: Immunization Treatment of under laying diseasePatient education
46 Quiz;1. Identify the part(s) of chain of infection that has been eliminated by the following action. Catheter care.Mode of transmissionPortal of exitPortal of entry2. Identify the part(s) of chain of infection that has been eliminated by the following action. Food handlingInfectious agentSource /reservoir
47 3. Identify the part(s) of chain of infection that has been eliminated by the following action. Hand washing.Susceptible hostMode of transmissionPortal of entry4. Identify the part (s) of chain of infection that has been eliminated by the following action. Identification of organism.Portal of exitInfectious agent
48 5. Identify the part (s) of chain of infection that has been eliminated by the following action. Personal protective equipmentSource/ ReservoirPortal of exitPortal of entry6. Identify the part (s) of chain of infection that has been eliminated by the following action. SterilizationSource or reservoir/mode of transmissionPortal of entry/Portal of exitMode of transmission / Infectious agent
49 7. Identify the part (s) of chain of infection that has been eliminated by the following action. Employees healthSource/ ReservoirSusceptible hostInfectious agent8. Identify the part (s) of chain of infection that has been eliminated by the following action. Recognition of high risk patientsPortal of entrySource or reservoir
50 9. Identify the part (s) of chain of infection that has been eliminated by the following action. Recognition of high risk patientsSource reservoirSusceptible hostInfectious agent10. Identify the part (s) of chain of infection that has been eliminated by the following action. Early recognition of signs of infectionPortal of entrySource or reservoir