![Levels of infection
• Colonization : it denotes presence of an organism
in specific part of body with or without causing a
disease.
e.g. S.aureus in skin and normal nasopharynx.
• Subclinical [inapparent] infection :refers to an
inapparent, asymptomatic infection, or an infection
that has such a mild course that it does not alert
the patient enough to consult with a physician.
e.g. common cold; urinary tract infection
particularly in women.](https://image.slidesharecdn.com/dynamicsandmodeoftransmissionofdisease-240213051249-cb41828e/85/dynamics-and-mode-of-transmissionof-disease-ppt-3-320.jpg)
dynamics and mode of transmissionof disease.ppt
- 2. INFECTION • The entry and multiplication of an infectious agent in the body of man or animals. • It elicits a response in body either in the form of an immune response or a disease. • It may or may not result in a disease.
- 3. Levels of infection • Colonization : it denotes presence of an organism in specific part of body with or without causing a disease. e.g. S.aureus in skin and normal nasopharynx. • Subclinical [inapparent] infection :refers to an inapparent, asymptomatic infection, or an infection that has such a mild course that it does not alert the patient enough to consult with a physician. e.g. common cold; urinary tract infection particularly in women.
- 4. • Latent infection :A latent infection is inactive though continuing to infect, and which remains capable of producing symptoms. e.g. virus of herpes simplex. • Clinical or symptomatic infection: An infection by a microorganism which results in some sort of expression of lack of health (i.e., disease) may be described as a symptomatic infection e.g. malaria, typhoid, etc.
- 5. CONTAMINATION • The presence of an infectious agent on the surface of the body ; on or in clothes, bedding, toys, surgical instruments, or other inanimate things or substances including water, milk and food. • Contamination on a body surface doesnot imply a carrier state.
- 6. POLLUTION • Presence of offensive but not necessarily infectious matter in the environment.
- 7. INFESTATION • For persons or animals-the lodgment, development and reproduction of arthropods on the surface of body or in clothing. e.g., lice, itchmite, etc. • The term may also be applied to describe invasion of the gut by parasitic worms. e.g., ascariasis
- 8. HOST A person or animal, including birds and arthropods, that affords subsistence or lodgment to an infectious agent under natural conditions is considered a ‘HOST’
- 9. TYPES OF HOSTS – Obligate host – the organism can survive in a specific host only e.g., man in measles and typhoid fever. Definitive host- the host in which parasite passes its sexual cycle is primary or definitive host. e.g.., mosquito in malaria.
- 10. • Intermediate host- the host in which the parasite is present in larval or asexual state is secondary or intermediate host. e.g., man in malaria • Transport host- the carrier in which the organism remains alive but does not undergo development.
- 11. DISEASE Any deviation from normal functioning or from state of complete physical or mental wellbeing.
- 12. Types of diseases- • Infectious disease- a clinically manifest disease of man animals due to infection • Contagious disease- a disease that is transmitted through contact. e.g., scabies,cholera,leprosy. • Communicable disease- an illness due to a specific infectious agent or its toxic products capable of being directly or indirectly transmitted from man to man, animal to animal, or from environment to man or animal.
- 13. EPIDEMIC • epi-upon; demos-people • Unusual occurrence in a community or region of a disease, specific health related events clearly in excess of ‘expected frequency’ • Expected frequency - amount of disease occurring in the past in the absence of an epidemic.
- 14. • Slow epidemics – non communicable diseases. • Time scale of epidemics is shifted from days or weeks to years. • Excess of expected occurrence- the status of epidemic for a disease differs in different countries based on the expected occurrence of that disease in that country. e.g., cholera in developed and developing countries.
- 15. • Outbreak – this term is usually used to denote a small, usually localized epidemic in the interest of minimizing public alarm.
- 16. ENDEMIC • En – in ; demos – people • Refers to constant presence of a disease or an infectious agent within a geographical area or population group without importation from outside. • It denotes the expected / usual frequency of the disease within such area or population group. • An endemic disease may burst into epidemic when conditions favour. e.g., hepatitis A , typhoid fever.
- 17. • Hyper endemic – the disease is constantly present at a high incidence and/or prevalence rate and affects all age groups equally. • Holo endemic – a high level of infection beginning early in life and affecting most of the child population, leading to a state of equilibrium such that the adult population shows evidence of disease much less commonly than the children. e.g., malaria
- 18. SPORADIC • Scattered about. • The cases occur irregularly, haphazardly from time to time, and generally infrequently. • They show little or no connection with each other, nor a recognizable common source of infection. e.g., polio, tetanus, herpes zoster, many zoonotic diseases, etc.
- 19. PANDEMIC • An epidemic usually affecting a large proportion of population , occurring over a wide geographic area. e.g., Influenza- 1918 & 1957 Cholera eltor – 1962 Acute hemorrhagic – 1971 & conjunctivitis 1981
- 20. EXOTIC • Diseases which are imported into a country in which they usually do not otherwise occur. e.g., Rabies in UK, Epidemic polyarthritis in visitors to Fiji
- 21. ZOONOSIS • An infection or infectious disease transmissible under natural conditions from vertebrate animals to man. enzootic • Zoonosis epizootic
- 22. • Enzootic – an endemic occurring in animals e.g., anthrax, rabies, brucellosis, bovine TB, endemic typhus and tick typhus. • Epizootic – an outbreak of a disease in an animal population. e.g., anthrax,
- 23. • Anthroponoses – vertebrate animal man e.g., Rabies, plague, hydatid diseases • Zooanthroponoses – man vertebrate animal e.g., human TB in cattle • Amphixenoses – man lower vertebrates e.g., T.cruzi & S.japonicum
- 24. NOSOCOMIAL INFECTION • It denotes the disease or infection acquired by a person as a result of being in a hospital. • The disease is not present or not in the incubation period at the time of admission or is not residual of an infection acquired during a previous admission. • It includes infections which are acquired in the hospital but appearing after discharge, and also such infections among staff and facility. e.g., infection of surgical wounds, hepatitis B and urinary tract infections.
- 25. OPPORTUNISTIC INFECTIONS • It denotes the infection caused due to reduction in host immunity by an organism that is not normally pathogenic to the body. • It occurs in immuno-compromised conditions. • Organisms – cytomegalovirus, herpes simplex, toxoplasma, M.tuberculosis, M.avium complex, pneumocystis, etc. • Conditions – AIDS, carcinomas, long term use of steroids.
- 26. IATROGENIC INFECTIONS • Any untoward or adverse consequence of a preventive, diagnostic or therapeutic regimen or procedure, that causes impairment, handicap, disability or death resulting from a physicians professional activity or from the activity of other health professionals which is preventable. e.g. reaction to penicillin and other immunizing agents, aplastic anemia following chloramphenicol, etc.
- 27. SURVEILLANCE • ‘Continuous scrutiny’ of the factors that determine the occurrence and distribution of the disease and other conditions of ill health. • It is essential for effective control and prevention. • Includes the collection, analysis interpretation and distribution of relevant data for action. • Its main purpose is to detect changes in trend or distribution in order to initiate investigative or control measures.
- 28. • Types of surveillance – Epidemiological surveillance, Nutritional surveillance, Demographic surveillance , Serological surveillance, etc. • It also connotes exercise of continuous scrutiny of health indices, nutritional status, environmental hazards, health practices and other factors that may affect health.
- 29. ERADICATION • Termination of all transmission of infection by extermination of the infectious agent through surveillance and containment. • It is an ‘all or none phenomenon’ and denotes termination of disease in whole world. • Only one disease has been eradicated till now - smallpox
- 30. ELIMINATION • Denotes eradication of a disease from a specific geographic region or political jurisdiction • In our present state, diseases which are amenable for eradication are measles, polio, diphtheria and guinea worm.
- 32. DEFINITION IT IS THE SEQUENCE OF EVENTS WHEREIN INFECTION IS TRANSMITTED FROM AN AGENT TO A SUSCEPTIBLE HOST THROUGH VARIOUS MODES OF TRANSMISSION.
- 33. LINKS IN THE CHAIN
- 35. SOURCE : A PERSON, ANIMAL, OBJECT OR SUBSTANCE FROM WHICH AN INFECTIOUS AGENT IS DISSEMINATED TO THE HOST.
- 36. RESERVOIR : ANY PERSON, ANIMAL,SOIL ARTHROPOD,PLANT OR SUBSTANCE IN WHICH AN AGENT LIVES , MULTIPLIES & SURVIVES IN SUCH MANNER THAT IT CAN BE TRANSMITTED TO A SUSCEPTIBLE HOST. 1. HOMOLOGOUS : EX- VIBRIO 2. HETEROLOGOUS : EX- SALMONELLA
- 37. TYPES OF RESERVOIR 1. HUMAN 2. ANIMAL 3. NON LIVING THINGS
- 38. 1.HUMAN RESERVOIR : IT MAY BE A CASE OR CARRIER. a.Case : a person in the population identified as having the particular disease. B.carrier: A person or an animal that harbours a the infectious agent in the absence of discernible clinical disease and serves as a source of infection for others.
- 39. case A case may be clinical, sub clinical,or latent. These variations in manifestation Of disease are referred to as – “spectrum of disease” 1.Clinical :signs & symptoms are apparent it may be mild,moderate,typical or atypical. 2.Subclinical :signs & symptoms are not apparent. 3.Latent :the host doesnot shed the agent which lies dormant with out symptoms. Ex- herpes simplex.
- 40. Epidemiological terminology 1.Primary case : first case of an infectious disease introduced into the population unit under study. 2.Index case : it is first case to come to the attention of the investigator. 3.Secondary case: it is the case developing from contact with primary case
- 41. carriers Classification a.Type : 1. incubatory 2. convalescent 3. healthy b.Duration : 1. temporary 2. chronic c.Portal of exit : 1. urinary 2. intestinal 3. respiratory 4. others
- 42. a.Type 1.Incubatory : infectious agent shed during incubation period of disease ex-measles ,mumps ,polio 2.Convalescent : disease agent shed during period of convalescence. ex- dysentery ,typhoid 3.Healthy : victims of sub clinical infection developing carrier state with- out suffering from disease but shedding the infectious agent ex: cholera ,diptheria
- 43. b. Duration 1.Temporary : those who shed infectious agent for a short period 2.Chronic : those who shed the infectious agent for indefinite periods ex- typhoid ,hepatitis-b. c. Portal of exit may be urinary ,intestinal ,respiratory. ex-typhoid , cholera, diptheria
- 44. 2.Animal reservoir : sometimes animals and birds act as source of infection. They may be cases or carriers. ex: rabies , influenza “zoonoses” 3.Reservoir in non-living things : soil,fomite & other inanimate objects may also act as source of infection. the ability of an agent to cause infection can be described by 1.pathogenicity 2.virulence
- 45. Modes of disease transmission
- 46. Disease…… • a condition in which body health is impaired, a departure from a state of health, an alteration of human body interrupting the performance of vital functions. • Communicable / non-communicable
- 47. Communicable disease • An illness due to a specific infectious agent or its toxic products and is capable of being directly or indirectly transmitted from man to man , animal to animal , or from environment to man or animal. • e.g.,: AIDS ,Hepatitis B
- 48. Non-communicable disease • An impairment of bodily structure and / or function that necessitates a modification of the person’s normal life. • Do not get transmitted from one to the other. • e.g.,: hypertension , road traffic accidents
- 49. Modes of transmission of a communicable disease • The road taken by the causative agent to reach the susceptible host from its reservoir or source.
- 50. • Source….. a person , animal , object or substance from which an infectious agent passes or is disseminated to host. • Reservoir…. the natural habitat in which the organism metabolizes and replicates.
- 51. Chain of Infection Reservoir Or source Mode of transmission Susceptible host
- 52. • Mode depends upon 1. Infectious agent 2. Portal of entry 3. Local ecological conditions • Rule … one disease ……… one route e.g., filariasis by culex mosquito • Break the rules e.g., AIDS , salmonellosis
- 53. Classification • Direct transmission 1. Direct contact 2. Droplet infection 3. Contact with soil 4. Inoculation into skin or mucosa 5. Transplacental transmission • Indirect transmission 1. Vehicle- borne 2. Vector-borne 3. Air-borne 4. Fomite - borne 5. Unclean hands and fingers
- 54. Direct transmission • Direct contact skin to skin mucosa to mucosa mucosa to skin • Direct and essentially immediate transfer • No intermediate agency
- 55. • Reduces the period for which the organism will have to survive outside the human host • Ensures larger dose of infection. • E.g., STD, AIDS, leprosy leptospirosis ,skin &eye infections.
- 56. • Droplet infection • Direct projection of spray of droplets of saliva and nasopharyngeal secretions. • Direct impingement upon conjunctiva , skin or inhalation onto the oro - respiratory mucosa. • Limited to a distance of 30-60 cm between source and host.
- 57. • Potentiality increases with 1. Close proximity 2. Over crowding 3. Lack of ventilation • E.g., respiratory infections , eruptive fevers like measles , diphtheria , tuberculosis , meningococcal meningitis.
- 58. • Contact with soil direct exposure to contaminated soil or soil with saprophytic organisms. e.g., hookworm larvae , tetanus , mycosis.
- 59. • Inoculation into skin or mucosa Hepatitis B through contaminated rabies virus needles and syringes by dog-bite
- 60. • Transplacental transmission From the mother to the child e.g., TORCH agents , varicella , Syphilis ,hepatitis B, Coxsackie B AIDS Non-living agents like thalidomide, diethylstilbestrol cause embryonic malformations.
- 61. Indirect transmission • Requires an intermediate agent or an in-animate object. 5F ‘s :,food , flies , fingers , fomites ,fluid Additional requirement : capability to survive outside the host in the external environment and retain its basic properties of pathogenesis & virulence till it finds a new host. Depends upon 1. Characteristics of the agent 2. Inanimate object 3. Influence of environmental factors
- 62. • Vehicle-borne Intermediate agent: water , food , ice , blood , serum, plasma or other biological products such as tissues & organs. Organisms may multiply (Staph. aureus in food ) or develop or just get passively transmitted (Hepatitis A virus in water)
- 63. • Through water and food: infections of alimentary tract • Through blood :Hepatitis B , malaria , syphilis , brucellosis ,trypanosomiasis , infectious mononucleosis , cytomegalovirus infection • Organ transplantation: CMV infection through kidney transplants
- 64. Epidemiological features: • Heavy dose of contamination out break of disease. • Initial confinement to the exposed to contaminated vehicle. • Primary case may be obscured by the time secondary cases appear. • Not always possible to isolate the infectious agent from incriminated vehicle. • Epidemic subsides on control or withdrawal of vehicle. • Great distances may be travelled by the infectious agents. • Common source is often traceable.
- 65. • Vector-borne Vector….an arthropod or any living carrier that transports an infectious agent to a susceptible individual. cyclops bat mice
- 66. Epidemiological classification: BY VECTOR :- a) Invertebrate type : 1)Diptera – flies & mosquitoes 2)Siphonaptera – fleas 3)Orthoptera – cockroaches 4)Anoplura –sucking lice 5)Hemiptera –bugs 6)Acarina – ticks &mites 7)Copepoda – cyclops b) Vertebrate type : mice , rodents , bats
- 67. • BY TRANSMISSION CHAIN :- a) man & a non-vertebrate host 1) man – arthropod – man (malaria) 2) man – snail –man (schistomiasis) b) man , another vertebrate host & a non-vertebrate host 1) mammal – arthropod – man (plague) 2) bird – arthropod – man (encephalitis) c) man & 2 intermediate hosts 1) man – cyclops-fish-man (fish tapeworm) 2) man – snail – crab – man (paragonimiasis)
- 68. • BY METHODS IN WHICH VECTORS TRANSMIT AGENT :- a) biting b) regurgitation c) scratching-in of faeces d) contamination of host with body fluids of vectors. • BY METHODS IN WHICH VECTORS ARE INVOLVED IN TRANSMISSION & PROPAGATION OF PARASITES :- a) mechanical b) biological
- 69. • Mechanical transmission soiling of feet or proboscis or by passage of organism through its GIT and passively excreted e.g., houseflies typhoid
- 70. • Biological transmission replication or development or both may take place a) Propagative : e.g., plague bacilli in rat fleas b) Cyclo-propagative : e.g., malaria parasites in mosquito c) Cyclo-developmental : e.g., microfilaria in mosquito
- 71. Influential factors : • Host feeding preferences • Infectivity • Susceptibility • Survival rate of vectors • Domesticity • Suitable environmental factors.
- 72. 1. Air borne a. droplet nuclei : they are tiny particles 1- 10 microns that represent dried residue of droplets. They are formed by evaporation of droplets coughed or sneezed or generated by aerosols. ex : tb, influenza, chicken pox, measles b. dust : larger droplets settled on the floor and other objects in the immediate environment and become a part of the dust. During the act of sweeping, dusting dust is released & becomes air borne ex : staph, streptococcus, coccidioido mycosis
- 73. • Fomite-borne Fomite…. inanimate objects or substances other than water or food contaminated by the infectious discharges from a patient and capable of harboring &transferring the infectious agent to a healthy person. e.g., diphtheria , typhoid , bacillary dysentery
- 74. • Unclean hands and fingers • Imply lack of personal hygiene • 1984 dysentery epidemic in India e.g., intestinal parasites , typhoid , dysentery.