This lecture is about the basics of communicable diseases,like definitions,chain of infection or dynamics of diseases transmission and prevention and control measures about infectious diseases .

1. AB RAJAR
ASSOCIATE PROFESSOR
COMMUNITY HEALTH SCIENCES.

2. LEARNING OBJECTIVES:
• Definition of terminology related with communicable diseases.
• Classifications of communicable diseases.
• Surveillance and its types.
• Mechanism of disease transmission.
• Prevention and control of communicable diseases.
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3. COMMUNICABLE DISEASE
It may be defined as an:-
 “illness due to a specific infectious agent as its toxic products &
effects capable of being directly or indirectly transmitted from man to
man, animal to animal or from the environment” i.e.(from
air,dust,soil,water,food etc)
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4. DISEASE:
o It is a physiological/psychological dysfunction. It is a condition in which body
health is impaired. This is an objective pathology of the body, such as an
infection.
ILLNESS:
oA condition in which the equilibrium of the body is distrubed.The subjective
sense; the individual does not feel well & can not function as usual.
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•IMPORTANT DEFINITIONS

5. FOLK ILLNESS:
o Syndromes from which members of a particular group claim to suffer;& for
which their culture provide their etiology, a diagnosis, preventive measures,&
regimens of healing.
SICKNESS:
oIt is a state of social dysfuntion.It is the condition of those who are socially
recognized as unwell.
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•IMPORTANT DEFINITIONS

6. •IMPORTANT DEFINITIONS
INFECTION:
oThe process of introduction of microorganisms into human host followed by
their multiplication within the body at the expense of the host is called
infection.
INFESTATION:
oIt is a state of having a parasite in or on the body which includes arthropods
or animal parasites.
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7. IMPORTANT DEFINITIONS
SUSCEPTIBLE:
oA person in whom the defensive power against infections is less is called
susceptible.
IMMUNE:
oA person who possess power to resist infection.
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8. IMPORTANT DEFINITIONS(cont…)
EPIDEMIC: (epi=upon ,demos=people)
oAny disease injury or other health related events occurring suddenly in
members clearly in excess of normal expectancy
• E.g. cholera.
ENDEMIC:(en=in, demos=people).
oIt refers to the constant presence of a disease or infectious agent within
a geographic area or population group without importation from
outside.
• E.g. common cold
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9. IMPORTANT DEFINITIONS(cont…)
SPORADIC: (means scattered about).
oThe cases occur irregurally,haphazardly from time to time & generally
infrequently showing little or no connection with each other nor a
recognizable common source of infection.
• e.g.polio,tatnus,herpes zooster & meningococcal meningitis etc.
PANDEMIC:
oAn epidemic usually affecting a large proportion of the population &
occurring over a wide geographic area such as a section of a nation, the entire
nation, a continent or the world.
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10. IMPORTANT DEFINITIONS(cont..)
EXOTIC:
• Diseases which are imported into a country in which they do not otherwise occur.
• E.g. Rabies in UK.
ZOONOSIS:
• An infection or infectious disease transmissible under natural condition from
vertebrate animals to man.
• E.g. Rabies,Plague,Hydatid diseases,Anthrax etc.
Anthropozoonosois:
• Infections transmitted to man from vertebrate animals.
• (Rabies,Plague,Hydatid disease, Anthrax etc).
Zooanthroponoses:
• Infections transmitted from man to vertebrate animals.
• (Human TB in cattle).
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11. IMPORTANT DEFINITIONS(cont..)
HOST:
• A person or other animal including birds & arthropods, that affords logement to
an infectious agent under natural condition is called Host.
Primary (or) Definitive Host:
• Host in which parasite attains maturity or passes its sexual stage.
• E.g. mosquito in malaria, man in Filariasis.
Secondary(or)Intermediate Host:
• Host in which parasite is in a larval or asexual state.
• E.g. man in malaria, mosquito in Filariasis.
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12. Obligate Host:
• It means the only host.
• E.g. man in measles & Typhoid fever.
Dead End Host:
• The host is infected, but does not become functionally infectious,& thus does
not transmit on the infection.
• E.g. Rabies, Bubonic Plague, Tetanus.
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IMPORTANT DEFINITIONS(cont..)

13. IMPORTANT DEFINITIONS(cont..)
INCUBATION PERIOD:
• The time interval b/w invasion by an infectious agent & appearance of the
first sign or symptom of the disease.
INFECTIVE PERIOD:
• The time interval during which an infectious agent can be transmitted from a
reservoir (patient) to the susceptible host.
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14. WINDOW PERIOD:
• The time b/w initial infection & the development of detectable antibodies
against the infection.
LATENCY PERIOD:
• The time from receiving the infection to the onset of infectiousness,i.e.the
ability to transmit infection.
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IMPORTANT DEFINITIONS(cont..)

15. IMPORTANT DEFINITIONS(cont..)
EXPOSURE PERIOD:
• The time during which an individual or a group is exposed to a source of
infection.
GENERATION TIME:
• The interval of time b/w receipt of infection by a host & maximal
infectivity/communicability of that host.
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16. INFECTIVITY:
• Capacity of organisms to multiply in or around the host.
PATHOGENICITY:
• Capacity to cause disease in an infected host.
VIRULENCE:
• The ability of a microorganism to produce disease in a shorter period of time
with a very low dose even.
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IMPORTANT DEFINITIONS(cont..)

17. COMMUNICABLE DISEASE(cont…)
 INFECTIOUS DISEASE:
• A clinically manifest disease of man or animals resulting from an infection
• E.g.cholera,measles,T.B,chickenpox etc.
 CONTAGIOUS DISEASE:
• A disease that is transmitted through contact.
• E.g. Scabies,Leprosy,STDs,Trachoma.
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18. COMMUNICABLE DISEASE(cont…)
IATROGENIC DISEASE:
• Any untoward or adverse consequence of a preventive, diagnostic or
therapeutic regimen or procedure, that comes imairment,handicap,disability
or death resulting from a physician’s professional activity or from the activity
of other health professionals.
• E.g.
I. Reactions to penicillin & immunizing agents.
II. Hepatitis B following blood transfusion.
III. Childhood leukemia due to prenatal X-Rays.
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19. COMMUNICABLE DISEASE(cont…)
NOSOCOMIAL INFECTION:
• It is a hospital acquired infection originating in a pt. while in a
hospital denoting a new disorder (unrelated to the pt’s primary
condition).
• E.g.=Infection of surgical wounds,Hep:B & UTI .
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20. CROSS INFECTION:
• When pts suffering from a particular disease are admitted in
hospital, they may acquire fresh infection from their neighbors
who may suffering from other disease.
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COMMUNICABLE DISEASE(cont…)

21. OPPORTUNISTIC INFECTION:
 This is infection by an organism(s) that takes the opportunity
provided by low resistance in host defense(e.g AIDS) to infect the
host &hence cause disease.
• E.g. Herpes simplex,CMV,Toxoplasma,TB.etc
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COMMUNICABLE DISEASE(cont…)

22. CLASSIFICATION OF C.D
CLASSIFICATION:1
• Arthropod-born infections{insects}.
• Respiratory infections.
• Intestinal infections.
• Zoonosis.
• Surface infections.
CLASSIFICATION:2
• Water washed Diseases.
• Feco-oral diseases.
• Soil mediated infections.
• Water contact diseases.
• Skin infections
• Respiratory Infections.
• Diseases via body fluids.
• Insect-Born Diseases.
• Ectoparasite Zoonosis.
• Domestic Zoonosis.
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23. CLASSIFICATION OF C.D
Communicable diseases may be divided into two broad categories viz:
CLASSIFICATION:1
(A ) ARTHROPOD-BORN INFECTIONS{INSECTS}.
• Malaria,
• Filariasis,
• Dengue syndrome,
• Yellow fever,
• Sleeping sickness,etc.
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24. CLASSIFICATION=1
(B) RESPIRATORY INFECTIONS:
• Samllpox,Chickenpox,
• Measles, Rubella,
• Mumps, Influenza,
• Diphtheria, Whooping cough,
• Tuberculosis.
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CLASSIFICATION OF C.D

25. CLASSIFICATION=1
(C) INTESTINAL INFECTIONS:
• Poliomyelitis,
• Viral hepatitis,
• Cholera,
• Acute diarrheal diseases,
• Typhoid fever,
• Food poisoning,
• Amoebiasis,
• Ascariasis,
• Hookworm infection etc.
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CLASSIFICATION OF C.D

26. CLASSIFICATION OF C.D(cont…)
CLASSIFICATION=1
(D) ZOONOSIS:
 Viral:
• Rabies, Yellow fever.
Bacterial:
• Plague,Brucellosis,Human salmonellosis.
Parasitic Zoonosis:
 Taeniasis,Hydatid disease,Leishmaniasis.
Rickettsial Diseases:
 (a genus of bacteria, transmitted by lice,fleas,ticks & mites to humans & other animals)
• Scrub typhus, Maurine typhus, Tick typhus Q Fever
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27. CLASSIFICATION=1
(E) SURFACE INFECTIONS:
oTrachoma,
oLeprosy,
oSTD,AIDS,
oTetanus.
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CLASSIFICATION OF C.D

28. CLASSIFICATION (cont…)
CLASSIFICATION=2
I. Water washed Diseases.
II. Feco-oral diseases.
III. Soil mediated infections.
IV. Water contact diseases.
V. Skin infections
VI. Respiratory Infections.
VII. Diseases via body fluids.
VIII.Insect-Born Diseases.
IX. Ectoparasite Zoonosis.
X. Domestic Zoonosis.
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29. CLASSIFICATION=2
1.Warer washed Diseases:
• Scabies,
• Trachoma,
• Ophthalmia neonatorum,
• Lice(louse),
• Dermatomycosis.
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CLASSIFICATION (cont…)

30. CLASSIFICATION=2
2.Feco-oral diseases:
• Gastroenteritis,
• Amoebiasis,
• Giardiasis,
• Bacillary Dysentery,
• Cholera,
• Typhoid,
• Hep:A &E,Poliomylitis,
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CLASSIFICATION (cont…)

31. CLASSIFICATION=2
3.Soil mediated infections:
• Whipworm,
• Ascariasis,
• Hookworm,
• Tetanus,
• Stronglyoides
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CLASSIFICATION (cont…)

32. CLASSIFICATION=2
4.Water contact diseases:
• Schistosomiasis,
• Guinea worm.
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CLASSIFICATION (cont…)

33. CLASSIFICATION=2
5.Skin infections:
• Chickenpox.
• Herpes zoster,
• Small pox.
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CLASSIFICATION (cont…)

34. CLASSIFICATION=2
6.Respiratory Infections:
• ARI,
• Influenza,
• Measles,
• Rubella,
• Mumps,
• Pertusis,
• Diphtheria,TB
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CLASSIFICATION (cont…)

35. CLASSIFICATION=2
7.Diseases via body fluids:
• Gonorrhea,
• Venereal Syphilis,
• HIV/AIDS,
• Chancroid,
• Hep:B,C,D.
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CLASSIFICATION (cont…)

36. CLASSIFICATION=2
8.Insect-Born Diseases:
• Malaria,
• Filariasis,
• Yellow fever,
• Dengue fever(DHF),
• Sleeping sickness,
• Leishmaniosis.
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CLASSIFICATION (cont…)

37. CLASSIFICATION=2
9.Ectoparasite Zoonosis:
• Plague,
• Typhus
• Relapsing fever.
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CLASSIFICATION (cont…)

38. CLASSIFICATION=2
10.Domestic Zoonosis:
• Hydatid Disease,
• Toxoplasmosis,
• Rabies,
• Leptospirosis,
• Brucellosis,
• Anthrax.
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CLASSIFICATION (cont…)

39. SURVELLANCE
SURVELLANCE:
• “It is the continuous & systemic collection, analysis & interpretation of health data”
• “The continuous scrutiny of the factors that determine the occurrence & distribution of
the disease & other conditions of ill-health “
• It may be:
 1.ACTIVE SURVEILLANCE:
• A reporter is contacted at regular intervals to specifically ask about the occurrence of diseases under
surveillance.
 2.SENTINEL SURVEILLANCE:
• The reporting is from the sources(doctors ,hospitals ,etc) that are likely to see the cases of disease
under surveillance.
 3.PASSIVE SURVEILLANCE:
• This is routine reporting in which the reporter initiates the case reports.
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41. TRANSMISSION OF INFECTIOUS DISEASE
Dynamicsofdisease
transmission:
1.Sourece &
Reservoir
2.Modes of
Transmission
3.Susceptible
host.
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42. TRANSMISSION OF INFECTIOUS DISEASE
MECHANISM OF TRANMISSION/Dynamics of disease transmission:
• The mechanism of communicable disease transmission is mainly related to
“CHAIN OF INFECTION", it consist of;
1) Source & Reservoir,
2) Modes of Transmission,
3) Susceptible host.
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44. TRANSMISSION OF INFECTIOUS DISEASE(cont..)
SOURCE:
• Is defines as the person,animal,object or substance from which an infectious
agent passes or is disseminated to the host.
RESERVOIR:
• Is defined as” any person,animal,arthropod,plant,soil or substance (or
combination of these)” in which an infectious agent lives & multiplies.
Reservoir may be of three types:
A. Human reservoir
B. Animal reservoir
C. Reservoir in non-living things.
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45. TRANSMISSION OF INFECTIOUS DISEASE(cont..)
HUMAN RESERVOIR:
• The important source or reservoir of infection for humans is a man himself.
• In human reservoir 2 things should be noted:-
I. CASES:
 May be defined as a person in the population or study group identified as having the
particular disease, health disorder or condition.
II. CARRIERS:
 A carrier is defined as an infected person or animal that harbors a specific infectious agent in
the absence of discrbile clinical disease & serve as a potential source of infection for others.
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46. CLASSIFICATION OF CARRIERS
A. By TYPE:
I. Incubatory Carriers: are those who shed the infectious agent during the
incubation period of disease E.g,measles, mumps, polio.
II. Convalescent Carriers:-are those who continue to shed the disease agent
during the convalescent period. E.g. typhoid fever, dysentery, cholera,
whooping cough, diphtheria.
III. Healthy Carriers:-are those who emerges from subclinical cases .The are
victims of subclinical infection who have developed carriers state without
suffering from overt disease. E.g. poliomyelitis, meningitis, cholera, diphtheria
& salmonellosis.
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47. CLASSIFICATION OF CARRIERS (cont…)
B. By DURATION:
1.Temporary Carriers:
 Those who shed the infectious agent for short periods of time.
• It includes the incubatory, convalescent & healthy carriers.
2.Chronic Carriers:
 One who excretes the infectious agent for indefinite periods.
• E.g. typhoid fever, hepatitis B, gonorrhea, dysentery.
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48. CLASSIFICATION OF CARRIERS (cont…)
C. By PORTAL OF EXIT:
 They are also classified as urinary, intestinal, respiratory, nasal carriers etc.
 Skin eruptions open wounds and blood are also portals of exit.
i. Urinary: typhoid, gonorrhea.
ii. Intestinal: cholera, typhoid.
iii. Respiratory: staphylococcal infection.
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49. RESERVOIR (cont..)
2. ANIMAL RESERVOIR:
 The source of infection may some times be animals and birds.
 The diseases & infections which are transmissible to men from
vertebrates is called Zoonosis.
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50. RESERVOIR (cont..)
3. RESERVOIR IN NON-LIVING THINGS:
 Soils & inanimate matter can also act as a reservoirs of infection.
• E.g. soil may harbors agents that cause tetanus, anthrax.
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52. MODES OF TRANSMISSION
• Communicable diseases may be transmitted from the reservoir or
source of infection to a susceptible individual in many different ways.
• The mode of transmission on infectious diseases may be classified as :
A. DIRECT TRANSMISSION.
B. INDIRECT TRANSMISSION.
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53. MODES OF TRANSMISSION (cont…)
• DIRECT TRANSMISSION:
I. Direct contact
II. Droplet infection
III. Contact with soil
IV. Inoculation into skin or mucosa
V. Trans placental (vertical transmission)
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54. MODES OF TRANSMISSION (cont…)
• INDIRECT TRANSMISSION
I. Vehicle borne
II. Vector borne (mechanical, biological)
III. Air borne (droplet nuclei, dust)
IV. Fomite
V. Unclean hands and fingers
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55. DIRECT TRANSMISSION
• DIRECT CONTACT:
• Infection may be transmitted by direct contact from skin to skin of the source
or others person .e.g. by touching, kissing or sexual intercourse.
• Diseases transmitted includes STD, AIDS, leprosy, skin & eye infection.
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56. DIRECT TRANSMISSION
• DROPLET INFECTION:
• This is due to the direct projection of a spray of droplets of saliva & nose
pharyngeal secretion during coughing & sneezing.
• Diseases transmitted by droplet spread includes many respiratory
infections. E.g. common cold, whooping cough & T.B.
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57. DIRECT TRANSMISSION
• CONTACT WITH SOIL:
• The disease agent may be in soil, compost or decaying vegetable matter.
• Examples of diseases, hook worm, tetanus, mycosis.
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58. DIRECT TRANSMISSION
• IN OCCULATION INTO SKIN AND MUCOSA:
• The disease agent may be inoculated directly into the skin or mucosa.
• E.g. rabies virus by dog bite, hepatitis B & C virus through contaminated needles and
syringes.
• TRANSPLACENTAL OR VERTICAL TRANSMISSION:
• In this case the disease agents can be transmitted transplacentally & is
another form of direct transmission.
• Examples are (TORCH)
• To= toxoplasma gondii
• R=rubella virus
• C= cytomegalo virus
• H=herpes virus
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59. INDIRECT TRANSMISSION
• This transmission includes the traditional 5F’s “ Flies, Fingers, Fomites, Food &
Fluid’’.
• VEHICLE BORNE
• It implies the transmission of the infectious agent through the agency of water,
food (including raw vegetables, fruits, milk & milk products)
• E.g. acute diarrhea, typhoid fever, cholera, polio, hep: A.
• VECTOR BORNE
• Vector is defined as an arthropod or any living carrier that transports an
infectious agent.
• Transmission by a vector may be mechanical or biological.
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60. • AIR BORNE:
• Droplet Nuclei:
• Are a type of particles implicated in the spread of air borne infections.
• They may be formed by:
• Evaporation of droplets of coughed or sneezed into the air, diseases include T.B, Influenza,
chicken pox, measles.
• DUST:
• Some of larger droplets which are expelled during talking, coughing & sneezing settles down
by their sheer weights on the floor , carpets, furniture, cloths etc
• A Variety of pathogenic bacteria, virus and fungal spores have been found in the dust of hospital
wards.
• Examples of diseases are pneumonia, T.B etc.
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INDIRECT TRANSMISSION

61. • Fomite borne, unclean hands &fingers:
• FOMITES includes:
• syringes, surgical dressings, towels, drinking glasses, spoons, soiled clothes, books,
cups, pencils, instruments etc.
• Diseases transmitted = diphtheria, hepatitis A, skin infections.
• UNCLEAN HANDS:
• Hands are the most common medium by which pathogen agents are transferred to food
from the bowl etc as well as from other foods.
• Examples are :
• -Staphylococcal infection
• -Typhoid & Para typhoid fever
• -Gastroenteritis
• -Dysentery
• -Hepatitis A
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INDIRECT TRANSMISSION

62. • Infectivity
• Pathogenicity
• Virulence
•Immunogenicity
• Antigenicstability
• Survival
• Weather
• Housing
• Geography
• Occupational setting
• Air quality
• Food
Environment
• Age
• Sex
• Genotype
• Behaviour
• Nutritional status
• Health status
Host
Agent
Factors Influencing Disease Transmission

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64. 3.SUSCEPTIBLE HOST.
• Susceptibility means a likelihood of a person getting a disease, for successful
transmission, the Infectious agent must have following stages:
i. The infectious agent must find a portal of entry.
ii. The organism must reach the appropriate tissues for its multiplication & survival.
iii. The disease agent must find a way out of the body to reach a new host(if there is
no portal of exit, the infection becomes a dead-end infection as in Rabies,
Bubonic plague & Tetanus).
iv. The organism must survive in the external environment for sufficient period till a
new host is found.
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66. PREVENTATION AND CONTROL OF THE COMMUNICABLE DISEASES
• The principle of prevention & control of diseases comes under following
headings:-
1. NOTIFICATION:-
• The immediate notice of this infection by the health officer as an authority. So
that they take measures for preventing the further spread of diseases.
2. EARLY DIAGNOSIS:-
• The physician must take a tentative diagnosis & advises isolation measures.
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67. PREVENTATION AND CONTROL OF THE COMMUNICABLE DISEASES (cont
3. ISOLATION:
 It is meant the separation of person suffering from communicable disease
from the rest of the family to prevent the transmission from the sick to the
healthy.
• QUARANTINE:-
• Isolation of healthy travelers (who do not possess any certificate of having
been immunized) from an infected area for at least the longest incubation
period of disease.
• DISEASE PERIOD OF QUARANTINE
• Cholera, plague, yellow fever 5days,6days,6day
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68. PREVENTATION AND CONTROL OF THE COMMUNICABLE DISEASES (cont..)
4.DESTRUCTION OF INFECTING AGENTS:-
• The destruction of pathogenic micro-organisms called disinfection & those
substances which destroy pathogenic material are called disinfectants, germicides
& bactericides.
5. INCREASING THE RESISTANCE OF THE SUSCEPTIBLE BY IMMUNIZATION:-
• It is very powerful measure for the control of communicable diseases & the
infection.
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69. PREVENTATION AND CONTROL OF THE COMMUNICABLE DISEASES (cont..)
6. BEHAVIORAL CHANGE:- (Health Education)
• Its purpose is to inform the community, about the principle of preventive
medicine & public health.
7. INVESTIGATION OF AN ATTACK OF ILLNESS:-
Responsibility of an health officer .
• To learn exact date of illness.
• To search the source of infection
• To search the history of any recent illness in the family or neighbors.
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