This document discusses the epidemic process and characteristics of infectious diseases. It defines the epidemic process as the rise and spread of infectious diseases among people. Infectious diseases are caused by the interaction between an infectious agent and susceptible host. They have an incubation period and cause immunity after infection in most cases. The document outlines the components of the epidemic process including infectious agents, transmission factors, and susceptible hosts. It also describes characteristics of infectious agents such as infectivity, pathogenicity, and virulence. Carriers are defined as those who spread infectious organisms without showing symptoms. The classification of diseases as acute, chronic, or subacute is also explained.

1. KURSK STATE MEDICAL UNIVERSITY
DEPARTMENT OF INFECTIOUS DISEASE AND
EPIDEMIOLOGY
Epidemic processEpidemic process
Teacher: Titareva Ludmila VictorovnaTeacher: Titareva Ludmila Victorovna

2. Epidemic process is theEpidemic process is the
process of the rise and theprocess of the rise and the
spreading of the infectiousspreading of the infectious
diseases among the people.diseases among the people.

3. The characteristics ofThe characteristics of
the infectious diseases:the infectious diseases:
• Presence of the infectiousPresence of the infectious
agentagent
• The incubation period inThe incubation period in
generalgeneral
• The acute caurseThe acute caurse
• The immunity afterThe immunity after
majority of infectiousmajority of infectious
diseasesdiseases
The characteristics ofThe characteristics of
the noninfectiousthe noninfectious
diseases:diseases:
• The absence of theThe absence of the
infectious agentinfectious agent
• The incubation period isThe incubation period is
unknownunknown
• It is a chronic disease.It is a chronic disease.

4. • InfectiousInfectious disease is the result of thedisease is the result of the
interaction between an infection agent andinteraction between an infection agent and
a susceptible person.a susceptible person.
• NoninfectionNoninfection disease is thedisease is the
disadaptation of the organism indisadaptation of the organism in
consequence of the influence of differentconsequence of the influence of different
factors of environment.factors of environment.

5. Components of the epidemicComponents of the epidemic
processprocess
Infectious agents
Transmission factors
Susceptible
macroorganism

6. Source of infectiousSource of infectious
• --agent is infected (sick or carrier)agent is infected (sick or carrier)
organism - human or animalorganism - human or animal
(object which is the site of natural(object which is the site of natural
habitation and multiplication of pathogenichabitation and multiplication of pathogenic
organisms, from where they can infectorganisms, from where they can infect
healthy people)healthy people)

7. Infectious agent’sInfectious agent’s localization in thelocalization in the
organism and mechanism of it’sorganism and mechanism of it’s
transmission from one individual totransmission from one individual to
another form persistent connection, whichanother form persistent connection, which
provide pathogenic species preservationprovide pathogenic species preservation
in the environment andin the environment and continuitycontinuity ofof
epidemic process of infectious disease.epidemic process of infectious disease.

8. A case is a risk factor …A case is a risk factor …
Infection in one person can be transmitted to othersInfection in one person can be transmitted to others

9. Characteristics of infectious agentsCharacteristics of infectious agents
• Morphology, size, chemical character,Morphology, size, chemical character,
antigenic make up…antigenic make up…
• InfectivityInfectivity
• PathogenicityPathogenicity
• VirulenceVirulence
• ImmunogenicityImmunogenicity

10. Infectivity (ability to infect)Infectivity (ability to infect)
(number infected / number susceptible) x 100(number infected / number susceptible) x 100
Pathogenicity (ability to cause disease)Pathogenicity (ability to cause disease)
(number with clinical disease / number infected) x(number with clinical disease / number infected) x
100100
Virulence (ability to cause death)Virulence (ability to cause death)
(number of deaths / number with disease) x 100(number of deaths / number with disease) x 100
All are dependent on host factorsAll are dependent on host factors

11. Mechanisms of the pathogenicMechanisms of the pathogenic
effectseffects
• Direct tissue invasionDirect tissue invasion
• The production of a toxinThe production of a toxin
• Persistent infectionPersistent infection
• Immunologic enhancementImmunologic enhancement
• Immune suppressionImmune suppression

12. Forms of infectious diseasesForms of infectious diseases
-MANIFESTED FORM:-MANIFESTED FORM:
acuteacute
chronicchronic
-ASYMPTOMATIC CARRIER:-ASYMPTOMATIC CARRIER:
acuteacute
ChronicChronic
-Etiological agent.-Etiological agent.

13. Diseases have a range of seriousness, effect, duration,Diseases have a range of seriousness, effect, duration,
severity, and extentseverity, and extent
Classified into 3 levelsClassified into 3 levels
AcuteAcute relatively severe, of short duration and oftenrelatively severe, of short duration and often
treatabletreatable
 usually the patient either recovers or diesusually the patient either recovers or dies
SubacuteSubacute intermediate in severity and duration, havingintermediate in severity and duration, having
some acute aspects to the disease but of longer durationsome acute aspects to the disease but of longer duration
and with a degree of severity that detracts from aand with a degree of severity that detracts from a
complete state of healthcomplete state of health
 Patient expected to eventually healPatient expected to eventually heal
ChronicChronic less severe but of long and continuousless severe but of long and continuous
duration, lasting over a long time periods, if not a lifetimeduration, lasting over a long time periods, if not a lifetime
 Patient may not fully recover and the disease can get worsePatient may not fully recover and the disease can get worse
overtimeovertime
 Life not immediately threatened, but may be over long termLife not immediately threatened, but may be over long term

14. Carrier:Carrier: one that spreads or harbors anone that spreads or harbors an
infectious organisminfectious organism
– Some carriers may be infected and not be sick. e.g. TyphoidSome carriers may be infected and not be sick. e.g. Typhoid
MaryMary
– Mary MallonMary Mallon (1869 – 1938) was the first person in the United(1869 – 1938) was the first person in the United
States to be identified as a healthy carrier of typhoid fever. OverStates to be identified as a healthy carrier of typhoid fever. Over
the course of her career as a cook, she infected 47 people, threethe course of her career as a cook, she infected 47 people, three
of whom died from the disease.of whom died from the disease.
– Her notoriety is in part due to her vehement denial of her ownHer notoriety is in part due to her vehement denial of her own
role in spreading the disease, together with her refusal to ceaserole in spreading the disease, together with her refusal to cease
working as a cook.working as a cook.
– She was forcibly quarantined twice by public health authoritiesShe was forcibly quarantined twice by public health authorities
and died in quarantine. It is possible that she was born with theand died in quarantine. It is possible that she was born with the
disease, as her mother had typhoid fever during her pregnancydisease, as her mother had typhoid fever during her pregnancy

15. Active carrierActive carrier: individual exposed to: individual exposed to
and harbors a disease-causing organism.and harbors a disease-causing organism.
May have recovered from the diseaseMay have recovered from the disease
Convalescent carrier:Convalescent carrier: exposed toexposed to
and harbors disease-causing organismand harbors disease-causing organism
(pathogen) and is in the recovery phase(pathogen) and is in the recovery phase
but is still infectiousbut is still infectious
Healthy carrier:Healthy carrier: exposed to anexposed to an
harbors pathogen, has not shown anyharbors pathogen, has not shown any
symptomssymptoms

16. Incubatory carrier:Incubatory carrier: exposed to andexposed to and
harbors a disease and is in the beginningharbors a disease and is in the beginning
stages of the disease, showing symptoms,stages of the disease, showing symptoms,
and has the ability to transmit the diseaseand has the ability to transmit the disease
Intermittent carrier:Intermittent carrier: exposed to andexposed to and
harbors disease and can intermittentlyharbors disease and can intermittently
spread the diseasespread the disease
Passive carrier:Passive carrier: exposed to andexposed to and
harbors disease causing organism, butharbors disease causing organism, but
has no signs or symptomshas no signs or symptoms

17. Infectious diseases can be rationallyInfectious diseases can be rationally
classified according to specificclassified according to specific
localization of infectious agent inlocalization of infectious agent in
the organism, correspondingthe organism, corresponding
mechanism of transmission andmechanism of transmission and
main biological properties ofmain biological properties of
causative agent:causative agent:
 intestinal infectionsintestinal infections
 respiratory infectionsrespiratory infections
 blood infectionsblood infections
 infections ofinfections of external coversexternal covers

18. Host FactorsHost Factors
• Genetic endowmentGenetic endowment
• Immunologic statusImmunologic status
• Personal characteristicsPersonal characteristics
• Personal behaviorPersonal behavior
• Definitive versus intermediate (inDefinitive versus intermediate (in
vector-borne diseases)vector-borne diseases)

19. Phases of transmissionPhases of transmission
• Secretion of infection agent from anSecretion of infection agent from an
infected organisminfected organism
• Presence of infection agent in thePresence of infection agent in the
environmentenvironment
• Penetration of infection agent into the newPenetration of infection agent into the new
healthy organismhealthy organism

21. Close association between the triangle ofClose association between the triangle of
epidemiology and theepidemiology and the chain ofchain of
transmissiontransmission
Disease transmission occurs when theDisease transmission occurs when the
pathogenpathogen or agent leaves theor agent leaves the reservoirreservoir
through athrough a portal or exitportal or exit and is spread byand is spread by
one of severalone of several modes of transmission.modes of transmission.
Breaks in the chain of transmission willBreaks in the chain of transmission will
stop the spread of diseasestop the spread of disease

22. MECHANISMS OFMECHANISMS OF
TRANSMISSIONTRANSMISSION
Direct transmissionDirect transmission
-contact-contact
Indirect transmissionIndirect transmission
-faecal-oral-faecal-oral
-air-borne-air-borne
-transmissive:-transmissive:
VectorborneVectorborne
Vertical transmissionVertical transmission
Artificial transmissionArtificial transmission

23. Direct transmissionDirect transmission
or person to personor person to person
Immediate transfer of the pathogen or agent from aImmediate transfer of the pathogen or agent from a
host/reservoir to a susceptible hosthost/reservoir to a susceptible host
Can occur through direct physical contact or directCan occur through direct physical contact or direct
personal contact such as touching contaminatedpersonal contact such as touching contaminated
hands, kissing or sexhands, kissing or sex

24. Direct transmission – without anyDirect transmission – without any
factors of transmission.factors of transmission.

25. Indirect transmissionIndirect transmission
pathogens or agents are transferred orpathogens or agents are transferred or
carried by some intermediate item orcarried by some intermediate item or
organism, means or process to a susceptibleorganism, means or process to a susceptible
hosthost
done in one or more following ways:done in one or more following ways:
airborne, waterborne, vectorborneairborne, waterborne, vectorborne

26.  Indirect transmissionIndirect transmission
 AirborneAirborne
Droplets or dust particles carry the pathogen to the host andDroplets or dust particles carry the pathogen to the host and
infect itinfect it
Sneezing, coughing, talking all spray microscopic droplets inSneezing, coughing, talking all spray microscopic droplets in
the airthe air
 faecal-oralfaecal-oral
Carried in drinking water, swimming pool, streams orCarried in drinking water, swimming pool, streams or
lakes used for swimming. Examples: choleralakes used for swimming. Examples: cholera
 VectorborneVectorborne
A pathogen uses a host (fly, flea, louse, or rat) as aA pathogen uses a host (fly, flea, louse, or rat) as a
mechanism for a ride or nourishment this ismechanism for a ride or nourishment this is mechanicalmechanical
transmissiontransmission
biological transmissionbiological transmission when the pathogen undergoeswhen the pathogen undergoes
changes as part of its life cycle, while within the host/vectorchanges as part of its life cycle, while within the host/vector
and before being transmitted to the new hostand before being transmitted to the new host

27. air-borneair-borne MECHANISMS OFMECHANISMS OF
TRANSMISSIONTRANSMISSION

28. faecal-oralfaecal-oral
MECHANISMS OF TRANSMISSIONMECHANISMS OF TRANSMISSION

29. Vector-borne MECHANISMS OFMECHANISMS OF
TRANSMISSIONTRANSMISSION

30. Pathogen - VectorPathogen - Vector
Viruses (Arbovirus) - MosquitoesViruses (Arbovirus) - Mosquitoes
Bacteria (Yersinia) - FleasBacteria (Yersinia) - Fleas
Bacteria (Borrelia) - TicksBacteria (Borrelia) - Ticks
Rickettsias (R. prowazeki) - Lice, ticksRickettsias (R. prowazeki) - Lice, ticks
Protozoa (Plasmodium) - MosquitoesProtozoa (Plasmodium) - Mosquitoes
Protozoa (Trypanozoma) -Tsetse fliesProtozoa (Trypanozoma) -Tsetse flies
Helminths (Onchocerca) - Simulium fliesHelminths (Onchocerca) - Simulium flies

31. Groups of arthropods:Groups of arthropods:
• Mechanic vectors ( fly ) - intestinalMechanic vectors ( fly ) - intestinal
infectionsinfections
• Intermediate hosts ( mosquito ) - malariaIntermediate hosts ( mosquito ) - malaria
• Reservoir of the infection ( tick ) – tick-Reservoir of the infection ( tick ) – tick-
borne encephalitis, relapsing fever )borne encephalitis, relapsing fever )

32. Vertical transmissionVertical transmission

33. Artificial transmissionArtificial transmission

34. Categories of parasities:Categories of parasities:
• ObligatoryObligatory--always connected with their host. Theyalways connected with their host. They
haven't stage in environment, but they may transmit tohaven't stage in environment, but they may transmit to
their host not only during bloodsucking, but also duringtheir host not only during bloodsucking, but also during
sexual contact, transplacentally.sexual contact, transplacentally.
• Optional – capable to leave their host some time and goOptional – capable to leave their host some time and go
out into the environment.out into the environment.
• Accidental- environment is normal and compulsory ofAccidental- environment is normal and compulsory of
their inhabitance. They may autonomously inhabitancetheir inhabitance. They may autonomously inhabitance
and some times accumulate in the soil, water, plants.and some times accumulate in the soil, water, plants.

36. Susceptible organismSusceptible organism
• Nonspecific resistanceNonspecific resistance
• Specific resistanceSpecific resistance

37. Natural and social factorsNatural and social factors stipulatestipulate
quantitativequantitative and qualitative changesand qualitative changes
in the epidemic process (in the epidemic process (increase orincrease or
decreasedecrease), thus they are), thus they are
secondary motive forcessecondary motive forces
of epidemic processof epidemic process

38. Epidemic process originates andEpidemic process originates and
maintained only due to combinedmaintained only due to combined
action of three main motive forcesaction of three main motive forces::
• Presence of infectious agent’sPresence of infectious agent’s
sourcesource;;
• Realization of transmissionRealization of transmission
mechanismmechanism;;
• Population susceptibility to thePopulation susceptibility to the
infection.infection.
If any of these factors is excluded,If any of these factors is excluded,
epidemic process stopepidemic process stop

39. Factors which influence epidemic process:Factors which influence epidemic process:
• SocialSocial
• NaturalNatural
Natural center – territory, where favorableNatural center – territory, where favorable
conditions of have appeared for theconditions of have appeared for the
interaction of infectious agents, factors ofinteraction of infectious agents, factors of
transmission and susceptible organisms.transmission and susceptible organisms.

40. • Endemic occurrence is defined as the constant presenceEndemic occurrence is defined as the constant presence
of a diseases or infectious agent within a givenof a diseases or infectious agent within a given
geographic area or the usual prevalence of a givengeographic area or the usual prevalence of a given
diseases within such area.diseases within such area.
• Epidemic haven’t any specification of geographic area.Epidemic haven’t any specification of geographic area.
Then an epidemic may encompass any time periods.Then an epidemic may encompass any time periods.
• Pandemic is the occurrence in a community or region ofPandemic is the occurrence in a community or region of
a group illnesses of normal expectancy.a group illnesses of normal expectancy.
• Exotic diseases which are not characteristic for givenExotic diseases which are not characteristic for given
territory.territory.