5M
5 Marks –
Define Communicable Disease
A communicable disease is a disease that can be transmitted from one person to another.
Transmission may be direct or indirect.
The causative agent may be bacteria, virus, parasite, or fungus.
Transmission occurs through air, water, food, contact, or vectors.
These diseases are common in the community.
They can spread rapidly if not controlled.
They cause outbreaks and epidemics.
They are a major public health problem.
Early diagnosis helps in control.
Prevention is essential.
Modes of Transmission of Communicable Diseases
Transmission may be direct or indirect.
Direct contact occurs by touching or close contact.
Droplet infection occurs by coughing or sneezing.
Vertical transmission occurs from mother to child.
Airborne transmission occurs through air.
Vehicle-borne transmission occurs through food and water.
Vector-borne transmission occurs through mosquitoes and flies.
Fomite-borne transmission occurs through articles.
Understanding modes helps in prevention.
Breaking transmission stops disease spread.
Chain of Infection
Chain of infection explains the spread of disease.
It consists of six links.
Infectious agent causes disease.
Reservoir is where agent lives.
Portal of exit allows agent to leave host.
Mode of transmission spreads agent.
Portal of entry allows agent to enter host.
Susceptible host gets disease.
Breaking any link prevents disease.
Important for control measures.
Host Factors in Communicable Diseases
Host is a person who harbors disease.
Age influences susceptibility.
Sex affects occurrence of disease.
Immunity protects against infection.
Nutritional status affects resistance.
Genetic factors play a role.
Occupation increases exposure.
Habits influence risk.
Socioeconomic status affects health.
Host factors decide severity.
Agent Factors in Communicable Diseases
Agent is the organism causing disease.
Includes bacteria, viruses, parasites, and fungi.
Infectivity is ability to enter host.
Pathogenicity is ability to cause disease.
Virulence is severity of disease.
Toxicity is toxin production.
Antigenicity helps immunity formation.
Survival outside host is important.
Dose affects disease occurrence.
Agent factors affect spread.
Reservoir of Infection
Reservoir is where agent normally lives.
It may be human, animal, or environment.
Human reservoir includes cases and carriers.
Animal reservoir causes zoonotic diseases.
Environmental reservoir includes soil and water.
Reservoir maintains disease in nature.
Source of infection comes from reservoir.
Identification helps in control.
Removal reduces transmission.
Important in epidemiology.
Incubation Period
Incubation period is time between infection and symptoms.
It varies with disease.
Short in food poisoning.
Long in diseases like rabies.
It helps in diagnosis.
It helps in quarantine decisions.
It indicates disease spread.
Useful in epidemiological studies.
Depends on agent and host.
Important for control.
Period of Communicability
Period of communicability is time during which disease can spread.
It varies for different diseases.
It may begin before symptoms.
It may continue after recovery.
Important for isolation decisions.
Helps in control programs.
Determines duration of precautions.
Used in outbreak control.
Depends on agent.
Essential in public health.
Isolation and Quarantine
Isolation separates sick persons.
Quarantine restricts movement of exposed persons.
Isolation is for diseased individuals.
Quarantine is for healthy contacts.
Both prevent disease spread.
Used in communicable diseases.
Important in epidemics.
Requires legal support.
Protects community.
Essential control measure.
Herd Immunity
Herd immunity is resistance of community to disease.
Occurs due to high level of immunity.
Protects susceptible individuals.
Seen after vaccination programs.
Important in disease elimination.
Depends on proportion immune.
Breaks transmission chain.
Reduces outbreaks.
Important for public health.
Used in immunization planning.
Secondary Attack Rate
Secondary attack rate measures spread among contacts.
It is proportion of contacts who develop disease.
Used in communicable diseases.
Helps in outbreak investigation.
Measures infectivity.
Useful in household studies.
Helps evaluate control measures.
Important epidemiological tool.
Expressed in percentage.
Guides prevention strategies.
10M
Epidemiology of Communicable Diseases – 10 Marks
Definition
Epidemiology of communicable diseases deals with the study of distribution and determinants of infectious diseases in the community.
Epidemiological Triad
Agent factors
Includes bacteria, virus, parasite, fungi
Infectivity, pathogenicity, virulence
Dose of agent
Survival outside host
Host factors
Age and sex
Immunity status
Nutritional status
Genetic factors
Occupation and habits
Socioeconomic status
Environmental factors
Physical environment like climate and housing
Biological environment like vectors
Social environment like overcrowding and sanitation
Modes of Transmission
Direct transmission through contact and droplets
Indirect transmission through air, food, water, vectors
Natural History
Exposure to agent
Subclinical or clinical disease
Recovery, disability, or death
Importance
Helps in disease prevention
Guides control measures
Useful for planning health programs
Important in outbreak investigation
Conclusion
Understanding epidemiology helps in effective prevention and control of communicable diseases.
Chain of Infection and Its Prevention – 10 Marks
Definition
Chain of infection explains the sequence through which an infectious disease spreads from one person to another.
Components of Chain of Infection
Infectious agent
Organism that causes disease
Bacteria, virus, parasite, fungi
Reservoir
Place where agent lives and multiplies
Human, animal, or environment
Portal of exit
Path through which agent leaves reservoir
Respiratory tract, blood, feces, urine
Mode of transmission
Direct contact and droplet infection
Indirect transmission through air, water, food, vectors
Portal of entry
Path through which agent enters new host
Respiratory tract, skin, mucosa, digestive tract
Susceptible host
Person who lacks immunity
Affected by age, nutrition, immunity, health status
Methods to Break Chain of Infection
Control of agent
Early diagnosis and treatment
Use of antibiotics and antivirals
Control of reservoir
Isolation of cases
Treatment of carriers
Control of animal reservoirs
Blocking portal of exit
Use of masks
Safe disposal of excreta and sputum
Interrupting transmission
Safe water and food
Vector control
Hand hygiene
Protecting portal of entry
Use of protective equipment
Wound care
Protecting susceptible host
Immunization
Improving nutrition
Health education
Importance
Prevents spread of disease
Forms basis of control measures
Important in public health practice
Essential in outbreak control
Modes of Transmission of Communicable Diseases – 10 Marks
Definition
Mode of transmission is the method by which an infectious agent spreads from reservoir to a susceptible host.
Direct Transmission
Direct contact
Skin to skin contact
Sexual contact
Examples: scabies, sexually transmitted diseases
Droplet infection
Spread through coughing, sneezing, talking
Short distance spread
Examples: influenza, diphtheria
Vertical transmission
Transmission from mother to child
Occurs during pregnancy, delivery, or breastfeeding
Examples: HIV, hepatitis B
Indirect Transmission
Airborne transmission
Spread through droplet nuclei and dust
Long distance spread
Examples: tuberculosis, measles
Vehicle-borne transmission
Spread through food, water, milk, blood
Examples: cholera, typhoid, hepatitis A
Vector-borne transmission
Mechanical transmission by flies
Biological transmission by mosquitoes
Examples: malaria, dengue, plague
Fomite-borne transmission
Spread through articles like clothes, towels, utensils
Examples: conjunctivitis, skin infections
Importance
Helps in planning preventive measures
Essential for breaking chain of infection
Important in outbreak controlv
Host, Agent and Environmental Factors – 10 Marks
Agent Factors
Type of organism
Infectivity
Pathogenicity
Virulence
Toxicity
Antigenicity
Dose of agent
Survival outside host
Host Factors
Age
Sex
Immunity
Nutritional status
Genetic factors
Occupation
Personal habits
Socioeconomic status
Environmental Factors
Physical environment
Climate
Temperature
Housing
Ventilation
Biological environment
Vectors
Animals
Social environment
Overcrowding
Sanitation
Water supply
Education
Poverty
Importance
Interaction of these factors determines disease occurrence
Basis of epidemiological triad
Useful for prevention and control
Natural History of Communicable Diseases – 10 Marks
Definition
Natural history describes progression of disease in absence of intervention.
Pre-pathogenesis Phase
Agent is present in environment
Host is susceptible
No disease yet
Pathogenesis Phase
Subclinical stage
Incubation period
No symptoms
Disease detectable by screening
Clinical stage
Signs and symptoms appear
Mild, moderate, or severe disease
Outcome stage
Recovery
Disability
Carrier state
Death
Importance
Helps in identifying intervention points
Useful for prevention strategies
Basis of levels of prevention
Herd Immunity – 10 Marks
Definition
Herd immunity is resistance of a community to spread of disease due to immunity in large proportion of population.
Mechanism
Immune individuals block transmission
Protects susceptible persons
Reduces outbreak occurrence
Factors affecting herd immunity
Proportion immune
Effectiveness of vaccine
Type of disease
Population density
Importance
Protects non-immunized individuals
Essential for disease elimination
Basis of mass immunization programs
Examples
Measles
Polio
Diphtheria
Public health significance
Reduces epidemics
Controls communicable diseases
Important in planning immunization
Isolation and Quarantine – 10 Marks
Isolation
Separation of sick persons
Prevents spread of infection
Applied to confirmed cases
Types of isolation
Strict isolation
Contact isolation
Respiratory isolation
Quarantine
Restriction of movement of exposed persons
Applied to healthy contacts
Observed for incubation period
Types of quarantine
Absolute quarantine
Modified quarantine
Surveillance
Importance
Prevents disease transmission
Used during outbreaks and epidemics
Legal and administrative support required
Difference
Isolation is for sick persons
Quarantine is for exposed healthy persons
Isolation and Quarantine – 10 Marks
Isolation
Separation of sick persons
Prevents spread of infection
Applied to confirmed cases
Types of isolation
Strict isolation
Contact isolation
Respiratory isolation
Quarantine
Restriction of movement of exposed persons
Applied to healthy contacts
Observed for incubation period
Types of quarantine
Absolute quarantine
Modified quarantine
Surveillance
Importance
Prevents disease transmission
Used during outbreaks and epidemics
Legal and administrative support required
Difference
Isolation is for sick persons
Quarantine is for exposed healthy persons
Surveillance of Communicable Diseases – 10 Marks
Definition
Surveillance is continuous systematic collection and analysis of health data.
Types
Passive surveillance
Active surveillance
Sentinel surveillance
Components
Data collection
Data analysis
Interpretation
Feedback
Uses
Early detection of outbreaks
Monitoring disease trends
Planning control measures
Evaluation of health programs
Importance
Foundation of disease control
Supports public health decision making
Control Measures of Communicable Diseases – 10 Marks
Control of source
Early diagnosis
Treatment
Isolation
Carrier detection
Control of transmission
Safe water and food
Vector control
Environmental sanitation
Disinfection
Protection of host
Immunization
Chemoprophylaxis
Nutrition improvement
Health education
Importance
Reduces morbidity and mortality
Prevents epidemics
Strengthens public health system
Role of Health Education in Control of Communicable Diseases – 10 Marks
Meaning
Health education helps people adopt healthy behaviors.
Role
Promotes personal hygiene
Encourages immunization
Improves sanitation practices
Reduces risky behaviors
Methods
Individual education
Group education
Mass media
Importance
Community participation
Sustainable disease control
Cost-effective strategy
Improves health awareness
Conclusion
Health education is essential for long-term control of communicable diseases.
20M
20 Marks Question 1
Communicable Diseases – Definition, Epidemiological Factors, Modes of Transmission, and Control Measures
Definition
A communicable disease is a disease that can be transmitted from an infected person, animal, or reservoir to a susceptible host.
Transmission may occur directly or indirectly.
These diseases are caused by living infectious agents.
They are an important cause of morbidity and mortality.
They can lead to outbreaks and epidemics.
Epidemiological Factors
Agent factors
Type of agent – bacteria, virus, parasite, fungi
Infectivity – ability to enter and multiply in host
Pathogenicity – ability to cause disease
Virulence – severity of disease
Dose of agent
Survival outside host
Host factors
Age and sex
Immunity status
Nutritional status
Genetic factors
Occupation
Personal habits
Socioeconomic status
Environmental factors
Physical factors – climate, housing, ventilation
Biological factors – vectors, animals
Social factors – overcrowding, sanitation, water supply, poverty
Modes of Transmission
Direct transmission
Direct contact – touching, sexual contact
Droplet infection – coughing, sneezing
Vertical transmission – mother to child
Indirect transmission
Airborne – droplet nuclei, dust
Vehicle borne – food, water, milk, blood
Vector borne – mosquitoes, flies
Fomite borne – clothes, utensils, towels
Control Measures of Communicable Diseases
Control of source of infection
Early diagnosis and treatment
Isolation of cases
Detection and treatment of carriers
Notification of disease
Control of transmission
Safe water supply
Food hygiene
Environmental sanitation
Vector control
Disinfection and sterilization
Protection of susceptible host
Immunization
Chemoprophylaxis
Improvement of nutrition
Personal hygiene
Health education
Conclusion
Communicable diseases can be effectively controlled by understanding their epidemiology and applying comprehensive preventive and control measures at community level.
20 Marks Question 2
Chain of Infection – Components and Methods to Break the Chain
Introduction
Chain of infection explains the sequence by which infectious diseases spread.
It consists of interlinked components.
Breaking any one link can stop disease transmission.
Components of Chain of Infection
Infectious agent
Organism that causes disease
Includes bacteria, virus, parasite, fungi
Reservoir
Place where agent normally lives and multiplies
Human reservoir – cases and carriers
Animal reservoir – zoonotic diseases
Environmental reservoir – soil, water
Portal of exit
Path by which agent leaves reservoir
Respiratory secretions
Blood
Feces
Urine
Mode of transmission
Direct transmission – contact, droplets
Indirect transmission – air, food, water, vectors, fomites
Portal of entry
Respiratory tract
Gastrointestinal tract
Skin and mucosa
Blood
Susceptible host
Person lacking immunity
Affected by age, nutrition, immunity, health status
Methods to Break Chain of Infection
Control of agent
Early diagnosis and treatment
Use of antibiotics and antivirals
Control of reservoir
Isolation of cases
Treatment of carriers
Control of animal reservoirs
Blocking portal of exit
Use of masks
Safe disposal of excreta and sputum
Interrupting transmission
Safe water and food
Vector control
Environmental sanitation
Hand hygiene
Protecting portal of entry
Use of protective equipment
Wound care
Protecting susceptible host
Immunization
Chemoprophylaxis
Nutrition improvement
Health education
Importance
Forms basis of communicable disease control
Essential in outbreak and epidemic control
Important public health concept
Conclusion
Understanding and breaking the chain of infection is the most effective way to prevent and control communicable diseases.
20 Marks Question 3
Epidemiology and Prevention of Communicable Diseases with Examples
Introduction
Epidemiology of communicable diseases studies distribution and determinants of infectious diseases.
It helps in prevention and control at community level.
Epidemiological Triad
Agent
Type of organism
Infectivity
Pathogenicity
Virulence
Host
Age and sex
Immunity
Nutrition
Genetic factors
Occupation
Environment
Climate
Housing
Sanitation
Vectors
Socioeconomic conditions
Examples of Communicable Diseases
Tuberculosis
Airborne transmission
Controlled by early diagnosis, treatment, BCG vaccination
Malaria
Vector borne disease
Controlled by mosquito control and chemoprophylaxis
Cholera
Water borne disease
Controlled by safe water and sanitation
Prevention of Communicable Diseases
Primary prevention
Health promotion
Environmental sanitation
Safe water and food
Immunization
Secondary prevention
Early diagnosis
Screening
Prompt treatment
Isolation
Tertiary prevention
Treatment of complications
Rehabilitation
Disability limitation
Public Health Measures
Surveillance
Notification
Outbreak investigation
Health education
Conclusion
Epidemiology provides the scientific basis for prevention and control of communicable diseases and is essential for improving community health.