1 / 55

Dynamics of disease transmission

Dynamics of disease transmission

Adeel3
Download Presentation

Dynamics of disease transmission

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. DYNAMICS OF DISEASE TRANSMISSION Dr. Adeel Ahmed Khan MBBS, FCPS (Community Medicine) Trainer, Saudi Board Program of Preventive Medicine Makkah, KSA

  2. 2

  3. 1st - The InfectiousAgent -anydisease-causing microorganism (pathogen) Infectivity Pathogenicity Virulence 3

  4. 2nd: Source orReservoir • The starting point for the occurrence of a communicable disease • • Source of infection: the person, animal, object or substance from which an infectious agent passes or is disseminated to the host (immediate source) • RESERVOIR: • “any person, animal, arthropod, plant, soil, or substance, or a combination of these, in which an infectious agent normallylives and multiplies, on which itdepends primarily for survival, and where itreproducesitself in such a manner that it can be transmitted to a susceptiblehost. • It is the natural habitat of the infectiousagent.”

  5. Types ofReservoirs Animal reservoir Human reservoir Non-living reservoir • 5

  6. :Type • Incubatory • Convalescen • healthy • Primarycase • Index case • Secondarycases cases • Duration: • Temporary • Chronic • :Portal ofexit • Urinary • Intestinal • Respiratory • others • Clinicalcases • (mild/severe-typical/atypical) • Sub-clinicalcases • Latent infectioncases 6

  7. “Apersoninthe populationor studygroupIdentifiedashavingparticular disease, healthdisorderor ConditionUnderinvestigation”

  8. The clinical illness maybe mild ormoderate, typical or atypical, severe or fatal. Epidemiologically, mild cases may be moreimportant sourcesof infection than severe cases because they are ambulant and spread the infection wherever they go, whereas severe cases usually confined tobed.

  9. Subclinicalcases • Inapparent, Covert, Missed or AbortiveCases • disease agent multiply in the host but does not manifest byS/S. • But contaminates the environment in the same way as clinicalcases. • Subclinical cases play a dominant role in maintaining the chain of infection in thecommunity.

  10. Subclinicalcases detected onlyby laboratory tests • occurs in most infectiousdisease. • Eg • Rubella, • Mumps, • Polio, • Hepatitis A andB, • Influenza, • Diphtheria

  11. Latentinfection • Infectious agent lies in a non-infectious form • Dormant within the host without symptoms with no shedding (and often without demonstrable presence in blood, tissues or bodily secretions of the host) • E.g., • HSV and VZV: nerve gangliacells, • CMV: kidney and salivary glandscells, • EBV: lymphocytes

  12. Latentinfection • infectious agent lies iinnaa nonon-n-iinfnfectectiiooususffoorm-rm- ddormormantant within the host without sysymmptptoommsswith no shshededdidinngg (and often without demonstrable presence in blood, tissues or bodily secretions of thehost) egeg.. HSV and VZV: nerve gangliacells, CMV: kidney and salivary glandscells, EBV: lymphocytes

  13. Index Case • Person that comes to the attention of public health authorities • Primary Case • Firstcase of a communicable disease introduced into the population unit bring studied • Attack rate • Secondary Case • Personwhoacquiresthe disease from an exposure to the primary case • Secondary attack rate 12

  14. Carriers An infected person or animal that harbors a specific infectious agent in the absence of discernible (visible) clinical disease and serves as a potential source of infection to others Reason:  due to inadequate treatment or immuneresponse the disease agent is not completelyeliminated leading to a carrierstate. 13

  15. Three elements in a carrierstate:

  16. CARRIERS • As a rule carriers are less infectious than cases, but epidemiologically, they are more dangerous thancases • because • escaperecognition • continuing to live a normal life among population or community • readily infect the susceptibleindividuals • over a wider area and longer period of time under favorableconditions.

  17. Classification ofCarrier IncuIncubatbatoorryyCCaarrrrieierrs:s: those who shed the infectious agent during the incubation period. This usually occurs during last few days ofIP Measles- the period of communicability is 4 days before therash. Mumps- usually 4-6 days before onset ofsymptoms Polio- 7-10 days before onset ofsymptoms HepatitisB- for a month beforejaundice Pertusis Influenza Diphtheria 16

  18. Carrier Classification: ByType • ConvalescentCarriers: • those who continue to shed the disease agent during the period of convalescence • In the disease,clinical recovery does not coincide with bacteriologicalrecovery. • Serious threat to HHmembers • Highlights importance of bacteriological surveillance of carriere state afterrecovery • typhoidfever • cholera, • diphtheria, • bacillarydysentery • pertusis

  19. Healthy Carriers: • victims of subclinical infection who havedeveloped carrier state without suffering from overt disease, but are nevertheless shedding the disease agent • poliomyelitis, • cholera, • meningococcal meningitis, • salmonellosis, • diphtheria. • Note:- Person whose infection remains subclinical may or may not act as carrier (eg.- in polio inf may remain subclinical but person act as temp carrier due to shedding of virus in stool..while TB most of us with +ve Mt, donot disseminate bacillie- so not labelled ascarrier.

  20. Temporary carriers are those who shed the infectious agent for short period of time. Chronic carriers are thosewhoexcretes the infectious agent for indefiniteperiods

  21. Chroniccarriers • Chronic carriers are far more important sources of infection thancases. • The longer the carrier state, the greater the risk of community-- reintroduce disease into areas which are otherwise free ofinfection • The duration of the carrier state varies with the disease. • In typhoid fever and hepatitis B, the chronic carrier state may last for severalyears. • In chronic dysentery it may last for year orlonger. • In diphtheria, the carrier state is associated with infected tonsils, in typhoid fever with gall bladder disease.

  22. Mary Mallon (1869 –1938), better known as Typhoid Mary, was the first person in the US identified as an asymptomatic carrier of the pathogen associatedwithtyphoidfever.  She was presumed to have infected some 50 people, three of whom died, over the course of her career as acook. She was forcibly isolated twice by public health authorities and died after a total of nearly three decades in isolation. 

  23. Carrier classified: By Portal Of Exit of InfectiousAgent • Respiratory carrier: e.g.influenza • Fecal (intestinal) carrier:e.g.typhoid, cholera • Blood carrier: e.g. hepatitis B andHIV • Urinary :e.g.Typhoid • sexual Carrier: gonococcus andHIV

  24. Animalreservoirs • infection that is transmissible under natural conditions from animals to man. • e.g., • Bacterial: Leptospira, plague fromRat. • Viral : Rabies from dog. • Protozoa: Leishmaniasis fromdog. • Helminths : Hydatid disease from dog • Tapeworms: Cattle ,Pig. •23

  25. Reservoir innon-living things Some organisms are ableto survive and multiply in nonliving environments such as soil andwater Clostridium that causestetanus and botulism can survive many years in thesoil Hookworms deposit theireggs into thesoil Water contaminated byhuman or animal feces cause GI tract disease (list includes bacteria, viruses, protozoa) • 24

  26. 3rd - The Portal ofExit • Route of escape of the pathogenfrom the reservoir-IA enters intosurrounding env-transfer to host at their portal ofentry Examples: respiratory secretions, GI blood exposure, breaks inskin 25

  27. 4th –Mode ofTransmission Direct transmission Indirect transmission Vehicle-borne :Vector-borne• Directcontact Dropletinfection Contact withsoil Air-borne Fomite-born Uncleanhands Inoculation into skin ormucosa vertical andfingers

  28. DirectTransmission

  29. DirectContact • Inf spread by direct contact of skin-skin, skin mucosa, mucosa- mucosa of same or otherperson • by touching, kissing,, bites, or sexualintercourse • Direct & immediate transfer of IA from reserviour –host (nointermediate Scabies Pediculosis STD’s Skin/eyeinfLeprosy COVID-19 agency) • So it introduces larger dose ofIA • No time interval of survival in environment.. • Overcrowded place orwhere place with lack ofventilation

  30. Directprojectionof droplets of • saliva/nasopharynge al secretion by • Sneezing, Speaking, • Coughing • Dropletsdirectly impinge on • conjunctiva, nasal Dropletspread: • mucosa orskin

  31. • • • • COVID-19,H1N1 Tubercle bacilli Measles Chickenpox

  32. Transplacental Vertical transmission • To R C H • HIV • HBV

  33. IndirectTransmission 5‘F’ food, flies, fomite, finger,fluid

  34. Vehicletransmission • • Water:Cholera,HA V,HE V,Typhoid etc. FOOD:Staphylococci, Cl.Botulinum. • • Blood/serum-HIV,HBV,HCV Organ-cmv    Clustering ofcases Distance bw secondary cases more Common source can betraced

  35. Vector- insects Mechanical Hf Diarrhea Dysentery Typhoid Trachoma Biological Propagative Only multiplication No developmental Plague bacilli inrat flea Cyclo propagative Multiplication developmental Malaria parasitesin mosquito Cyclodevelopmental No multiplication developmental Filariaparasite Inmosquito

  36. host feedingpreference infectivity-ability to transmit diseaseagent • susceptibility – ability to becomeinfected • survival rate of vectors inenvironment • Domesticity • Seasonalfactors…

  37. Fomites: Contaminated Nonliving Objects likeCup, towel, napkin, linen, Clothing, glass, Toys, Pencils, door handle, surgical instruments, syringes, dressingmaterials… Diphtheria, Trachoma influenza scabies Ex:

  38. 5th - The Portal ofEntry -route through whichthe pathogen enters its new host

  39. RespiratorySystem inhalatio Upper respiratorytract Diphtheria Lower respiratorytract Tuberculosis n

  40. GastrointestinalSystem Feco-Oral Route Infectious agent excreted in faeces & transmitted to theoral portal of entrythrough contaminated food, water, milk, drinks hands ingestion • Typhoid fever • Shigella • Cholera • Polio • Rotavirus • Hepatitis A, HepatitisE

  41. Urinary &Reproductive Tracts Gonorrhea Syphilis HIV Sexual contact

  42. Breaks in ProtectiveSkin Barrier Percutaneous Leptospirosis Percutaneous (bite ofarthropod) Yellow fever

  43. 6th - The SusceptibleHost A person or an animal thatafford lodgment to an infectious agent under naturalconditions. • Accepts thepathogen • The support of pathogen life & its reproduction depend on the degree of the host’sresistance.

  44. CancerPatients • HIV-AIDSPatients • Transplant Patients • Onsteroids.. • Infant &Elderly Patients 45

  45. HOST Obligate host : the onlyhost Eg: Man in measles &typhoid Primary /definitive host: inwhich parasite attains maturity or passes its sexualstage Secondary or intermediate hosts: the parasite is in a larval or asexual state

  46. THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT ANDAPPEARANCE OF THE FIRST SIGN OR SYMPTOM OFTHE DISEASE INQUESTION

  47. DOSE OFINOCULUM SITE OFMULTIFICATION RATE OFMULTIFICATION HOST DEFENCEMECHANISM

  48. No ofcases Median incubationtime 2 3 15 10 5 0 1 2 3 4 5 6 7 8 9 10 11 12 1314 15 16 17 18 19 20 2122 Time 1 Probableexposure 50% 50% Median onsettime

  49. PeriodFrom Disease InitiationTo Disease Detection ForNCDs

More Related