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Dynamics of disease transmission

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    • 1. DYNAMICS OF DISEASE TRANSMISSION Dr. Sanat Rathod Assistant Professor GMERS Medical College Gotri Vadodara
    • 2. 2
    • 3. 1st - The Infectious Agent -any disease-causing microorganism (pathogen) Infectivity Pathogenicity Virulence 3
    • 4. 2nd: Source or Reservoir • 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 normally lives and multiplies, on which it depends primarily for survival, and where it reproduces itself in such a manner that it can be transmitted to a susceptible host. It is the natural habitat of the infectious agent.” 4
    • 5. Types of Reservoirs Human reservoir Animal reservoir Non-living reservoir •5
    • 6. cases •Primary case •Index case •Secondary cases •Clinical cases (mild/severe-typical/atypical) •Sub-clinical cases •Latent infection cases :Type •Incubatory •Convalescent •healthy Duration: •Temporary •Chronic carriers :Portal of exit •Urinary •Intestinal •Respiratory •others 6
    • 7. “A person in the population or study group Identified as having particular disease, health disorder or condition Under investigation” 7
    • 8. The clinical illness maybe mild or moderate, typical or atypical, severe or fatal. Epidemiologicall y, mild cases may be mor e impor tant sour ces of infection than severe cases because they are ambulant and spread the infection wherever they go, whereas severe cases usually confined to bed. 8
    • 9. Subclinical cases Inapparent, Covert, Missed or Abortive Cases • disease agent multiply in the host but does not manifest by S/S. • But contaminates the environment in the same way as clinical cases. • Subclinical cases play a dominant role in maintaining the chain of infection in the community. 9
    • 10. detected only by laboratory tests subclinical cases occurs in most infectious disease. Eg       Rubella, Mumps, Polio, Hepatitis A and B, Influenza, Diphtheria 10
    • 11. Latent infection • infectious agent lies in a non-infectious formdormant within the host without symptoms with no shedding (and often without demonstrable presence in blood, tissues or bodily secretions of the host)  eg.  HSV and VZV: nerve ganglia cells, CMV: kidney and salivary glands cells,  EBV: lymphocytes 11
    • 12.  Index Case ◦ Person that comes to the attention of public health authorities  Primary Case ◦ First case of a communicable disease introduced into the population unit bring studied ◦ Attack rate  Secondary Case ◦ Person who acquires the disease from an exposure to the primary case ◦ Secondary attack rate 12
    • 13. Carriers  An infected person or animal that harbors a An infected person or animal that harbors a specific infectious agent in the absence of specific infectious agent in the absence of discernible (visible) clinical disease and discernible (visible) clinical disease and serves as a potential source of infection to serves as a potential source of infection to others others Reason : due to inadequate treatment or immune response the disease agent is not completely eliminated leading to a carrier state. 13
    • 14. Three elements in a carrier state: 14
    • 15. CARRIERS As a rule carriers are less infectious than cases, but epidemiologically, they are more dangerous than cases because ◦ escape recognition ◦ continuing to live a normal life among population or community ◦ readily infect the susceptible individuals ◦ over a wider area and longer period of time under favorable conditions. 15
    • 16. Classification of Carrier Incubatory Carriers: those who shed the infectious agent during the incubation period. This usually occurs during last few days of IP  Measlesthe period of communicability is 4 days before the rash.  Mumpsusually 4-6 days before onset of symptoms  Polio7-10 days before onset of symptoms  Hepatitis Bfor a month before jaundice  Pertusis  Influenza  Diphtheria 16
    • 17. Carrier May Be Classified : By Type Convalescent Carriers:  those who continue to shed the disease agent during the period of convalescence  In the disease, clinical recovery does not coincide with bacteriological recovery.  Serious threat to HH members  Highlights importance of bacteriological surveillance of carriere state after recovery ◦ ◦ ◦ ◦ ◦ typhoid fever cholera, diphtheria, bacillary dysentery pertusis 17
    • 18. Carrier may be classified : BY TYPE Healthy Carriers:  victims of subclinical infection who have developed 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, do not disseminate bacillie- so not labelled as carrier. 18
    • 19. Temporary carriers are those who shed the infectious agent for short period of time. Chronic carriers are those who excretes the infectious agent for indefinite periods 19
    • 20. Chronic carriers Chronic carriers are far more important sources of infection than cases. The longer the carrier state, the greater the risk of community-- reintroduce disease into areas which are otherwise free of infection The duration of the carrier state varies with the disease.  In typhoid fever and hepatitis B, the chronic carrier state may last for several years.  In chronic dysentery it may last for year or longer.  In diphtheria, the carrier state is associated with infected tonsils, in typhoid fever with gall bladder disease. 20
    • 21.    Mary Mallon (1869 –1938), better known as Typhoid Mary, was the first person in the US identified as an asymptomatic carrier of the pathogen associated with typhoid fever. She was presumed to have infected some 50 people, three of whom died, over the course of her career as a cook. She was forcibly isolated twice by public health authorities and died after a total of nearly three decades in isolation. 21
    • 22. Carrier classified : By Portal Of Exit of Infectious Agent  Respiratory carrier: e.g. influenza  Fecal (intestinal) carrier: e.g. typhoid, cholera  Blood carrier: e.g. hepatitis B and HIV  Urinary : e.g. Typhoid  sexual Carrier: gonococcus and HIV 22
    • 23. Animal reservoirs • infection that is transmissible under natural conditions from animals to man. • e.g. – – – – – Bacterial: Leptospira, plague from Rat. Viral : Rabies from dog. Protozoa: Leishmaniasis from dog. Helminths : Hydatid disease from dog Tape worms : Cattle , Pig. •23
    • 24. Reservoir in non-living things Some organisms are able to survive and multiply in nonliving environments such as soil and water Clostridium that causes tetanus and botulism can survive many years in the soil Hookworms deposit their eggs into the soil Water contaminated by human or animal feces cause GI tract disease (list includes bacteria, viruses, protozoa) •24
    • 25. 3rd - The Portal of Exit • Route of escape of the pathogen from the reservoir-IA enters into surrounding reservoir env-transfer to host at their portal of entry Examples: respiratory secretions, GI blood exposure, breaks in skin 25
    • 26. 4th –Mode of Transmission Direct transmission Direct contact Droplet infection Contact with soil Inoculation into skin or mucosa vertical Indirect transmission Vehicle-borne :Vector-borne • Air-borne Fomite-born Unclean hands and fingers 26
    • 27. Direct Transmission •27
    • 28. Direct Contact •Inf spread by direct contact of skin-skin, skin mucosa, mucosamucosa of same or other person •by touching, kissing,, bites, or sexual intercourse •Direct & immediate transfer of IA from reserviour –host (no intermediate agency) •So it introduces larger dose of IA •No time interval of survival in environment.. •Overcrowded place or where place with lack of ventilation Scabies Pediculosis STD’s Skin/eye inf leprosy •28
    • 29. Droplet spread: • Direct projection of droplets of saliva/nasopharynge al secretion by Sneezing, Speaking, Coughing • Droplets directly impinge on conjunctiva, nasal mucosa or skin •29
    • 30. • • • • H1N1 Tubercle bacilli Measles •30 Chickenpox
    • 31. Inoculation: Pathogen injected into tissues. • – – Tetanus spores Arboviruses (Insects). •31
    • 32. Vertical transmission Transplacental  To R C H  HIV  HBV 15 •32
    • 33. Indirect Transmission 5 ‘F’ food, flies, fomite, finger, fluid 33
    • 34. Vehicle transmission • • Water: Cholera, H A V , H E V, Typhoid etc. FOOD: Staphylococci, Cl. Botulinum. • • Blood/serum-HIV, HBV,HCV Organ-cmv    Clustering of cases Distance bw secondary cases more Common source can be traced 34
    • 35. Vectorinsects Mechanical Hf Biological Diarrhea Dysentery Typhoid Trachoma Propagative Only multiplication No developmental Plague bacilli in rat flea Cyclo propagative Multiplication developmental Malaria parasites in mosquito Cyclodevelopmental No multiplication developmental Filaria parasite In mosquito 35
    • 36. Trans-ovarian transmission  Inf agent vertical transmitted from female mosquito to her progeny ◦ ◦ ◦ ◦ ◦ Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF Trans-stadial transmission Lyme disease, infects tick vector as a larva, and the infection is maintained when it molts to a nymph and later develops as an adult 36
    • 37.  host feeding preference  infectivity-ability to transmit disease agent  susceptibility – ability to become infected  survival rate of vectors in environment  Domesticity  Seasonal factors… 37
    • 38. Fomites : Contaminated Nonliving Objects like Cup, towel, napkin, linen, Clothing, glass, Toys, Pencils, door handle, surgical instruments, syringes, dressing materials… Ex: Diphtheria, Trachoma influenza scabies 38
    • 39. 5th - The Portal of Entry -route through which the pathogen enters its new host •39
    • 40. Respiratory System io t la a h n in  Upper respiratory tract Diphtheria  Lower respiratory tract Tuberculosis •40
    • 41. Gastrointestinal System Infectious agent excreted in faeces & transmitted to the oral portal of entry through 􀂃 contaminated food, water, milk, drinks 􀂃 hands • • • • • • 􀁺 Typhoid fever 􀁺 Shigella 􀁺 Cholera 􀁺 Polio 􀁺 Rotavirus 􀁺 Hepatitis A, Hepatitis E ingestion Feco-Oral Route •41
    • 42. Se co x nt ua ac l t Urinary & Reproductive Tracts Gonorrhea Syphilis HIV •42
    • 43. Breaks in Protective Skin Barrier  Percutaneous Leptospirosis  Percutaneous (bite of arthropod) Yellow fever •43
    • 44. 6th - The Susceptible Host A person or an animal that afford lodgment to an infectious agent under natural conditions. •Accepts the pathogen 44 •The support of pathogen life & its reproduction depend on the degree of the host’s resistance.
    • 45. •Cancer Patients •HIV-AIDS Patients •Transplant Patients •On steroids.. •Infant & Elderly Patients 45
    • 46. HOST Obligate host : hos the only host Eg: Man in measles & typhoid Primary /definitive host: in which parasite attains maturity or passes its sexual stage Secondary or intermediate hosts: the parasite is in a larval or asexual state •46
    • 47. Life cycle Sporozoits Liver Mature Salivary Gland Marozoits RBC Schizont Oocyte Mature Ring Trophozoits Ookinete Zygote Mosquito Exflagellation Gametocyte Male / Female
    • 48. THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
    • 49.  DOSE OF INOCULUM  SITE OF MULTIFICATION  RATE OF MULTIFICATION  HOST DEFENCE MECHANISM
    • 50. No of cases Median incubation time 15 2 3 10 5 0 1 2 3 4 5 6 7 8 9 10 11 12 1314 15 16 17 18 19 20 21 22 Probable exposure 50% 1 50% Time
    • 51. Period From Disease Initiation To Disease Detection For NCDs
    • 52. GENERATION TIME INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTIVITY OF THAT HOST No of cases 10 Generation time 5 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Zeit
    • 53. THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
    • 54. It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person, from an infected animal to man , or from an infected person to an animal, including arthropods
    • 55. Ate the food (exposed) Did not eat the food (not exposed) Ill Well Total Well Total Attack Ill Attack Rate Rate 10 3 13 76% 7 4 Attack Rate = Ill / (Ill + Well) x 100 during a time period Attack rate = (10/13) x 100 = 76% ( 7/11) x 100 = 64% 11 64%
    • 56. It is defined as the number of exposed persons developing the disease within the range of the incubation period, following exposure to the primary case
    • 57. Total number of cases – initial case(s) SAR (%) = Number of susceptible persons in the group – initial case(s) x 100  Used to estimate to the spread of disease in a family, household or other group environment.  Measures the infectivity of the agent and the effects of prophylactic agents (e.g. vaccine) 58
    • 58. Thank You