The document provides a comprehensive overview of communicable diseases, including definitions, classifications, and mechanisms of transmission. It distinguishes between various types of diseases such as infectious, contagious, nosocomial, and zoonotic diseases, along with their respective transmission modes like direct and indirect contact. Additionally, it describes surveillance methods and the importance of understanding the dynamics of disease transmission for effective prevention and control.

1. Introduction To Communicable Diseases
Lecturer: Mr. Osman H. Ali

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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.

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

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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.
• 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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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.

8. IMPORTANT Definitions(cont…)
EPIDEMIC: (epi=upon ,demos=people)
o Any 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).
o It 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).
o The 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:
o An 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.
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Conti….
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).

12. 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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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.
IMPORTANT Definitions(cont..)

14. 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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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.
Important Definitions(cont..)

16. 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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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.
Important Definitions(cont..)

18. 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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19. 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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20. 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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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.
Communicable Disease(cont…)

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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
Communicable Disease(cont…)

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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.

24. 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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CLASSIFICATION=1
(B) RESPIRATORY INFECTIONS:
• Samllpox,Chickenpox,
• Measles, Rubella,
• Mumps, Influenza,
• Diphtheria, Whooping cough,
• Tuberculosis.
Classification Of C.D

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CLASSIFICATION=1
(C) INTESTINAL INFECTIONS:
• Poliomyelitis,
• Viral hepatitis,
• Cholera,
• Acute diarrheal diseases,
• Typhoid fever,
• Food poisoning,
• Amoebiasis,
• Ascariasis,
Classification Of C.D

27. 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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CLASSIFICATION=1
(E) SURFACE INFECTIONS:
oTrachoma,
oLeprosy,
oSTD,AIDS,
oTetanus.
Classification Of C.D

29. 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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CLASSIFICATION=2
1.Warer washed Diseases:
• Scabies,
• Trachoma,
• Ophthalmia neonatorum,
• Lice(louse),
• Dermatomycosis.
Classification (Cont…)

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

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

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

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

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

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

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

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

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

40. Surveillance
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. 40

41. 41
Conti….
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.

42. Mechanism of transmission
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43. Transmission Of Infectious Disease
Dynamics
of
disease
transmission:
1.Sourece &
Reservoir
2.Modes of
Transmission
3.Susceptible
host.
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44. 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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1.SOURCE AND RESERVOIR

46. 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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47. 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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48. 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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49. 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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50. 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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51. 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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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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2.MODES OF TRANSMISSION

54. 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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55. 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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56. 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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57. 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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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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Direct transmission
• Contact With Soil:
• The disease agent may be in soil, compost or decaying vegetable matter.
• Examples of diseases, hook worm, tetanus, mycosis.

60. 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.
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Conti….
• 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

62. 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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• 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.
Indirect Transmission

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Conti…
• 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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• 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.
Indirect transmission

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Conti…
• 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

67. • Infectivity
• Pathogenicityy
• Virulence
•Immunogenicityy
• Antigenicstability
• Survival
• Weather
• Housing
• Geography
• Occupationnel setting
• Air quality
• Food
Environment
• Age
• Sex
• Genotype
• Behaviour
• Nnutritional status
• Heath status
Host
Agent
Factors Influencing Disease transmission

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3.SUSCEPTIBLE HOST.

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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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Preventation And Control Of The Communicable Diseases

71. 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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72. 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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73. 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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74. 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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75. THANK YOU
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