Public Health and Immunology Quiz

General Epidemiology

• Epidemiology is the study of the frequency, distribution, determinants, and dynamics of diseases or conditions in a defined population.
• The word "epidemiology" comes from Greek words:
  • "epi" meaning "on or upon"
  • "demos" meaning "people"
  • "logos" meaning "the study of"
• Epidemiology involves investigating the occurrence distribution of health related events in relation to person, time, and place characteristics. (Distribution Triad)

Describing the Disease Under Study

• Time: Year, Season, Month, Week, Day, Hour of onset, Duration
• Place: Climatic zone, Country, Urban/rural, Local community, Towns, Cities, Institutions
• Person: Age, Sex, Birth order, Family size, Marital state, Occupation, Weight, Height, Social status, Physical activity, Education, Diet, Life style

Determinants

• Mean etiology & risk factors of the disease.
• Includes: agent factors, host factors and environmental factors (Epidemiological Triad = Ecological Triad)

Dynamics

• Mean chain of infection of the disease

  • Infectious Agent- Reservoir (source of infection) - Portal of exit - Mode of transmission - Portal of entry - Susceptible host

• Ecology means equilibrium from dynamic interaction between host, agent and environmental factors that help in maintaining disease presence in the community.

• The epidemiological triad is a conceptual model that portrays disease occurrence. It includes agent factors, host susceptibility, and environmental elements.

Patterns of Spread of Infectious Diseases

• Sporadic: Infrequent, scattered cases not related.
• Endemic: Disease constantly present in a community due to ecological factors.
• Hyperendemic: Endemic disease with high incidence and prevalence rates.
• Epidemic: Sudden increase in number of cases.
• Outbreak: Epidemic occurring in a confined group.
• Pandemic: Epidemic affecting countries globally.
• Enzootic: Disease constantly present in animals.
• Epizootic: Disease outbreak in animals.

Infectious Process Chain

• Process through which infectious agent is transmitted from source of infection to a susceptible host.
• Key steps: infectious agent, reservoir (source of infection), portal of exit, mode of transmission, portal of entry, susceptible host.

Reservoir

• In which the organism lives and multiplies.
• Includes
  • Human reservoir (cases or carriers)
  • Animal reservoir (zoonosis)
  • Non-living reservoir (soil, water, food)

Cases and Carriers

• Cases: Infected people exhibiting infection symptoms & signs
• Carrier: Infected individuals without symptoms or signs. Carriers can be Incubatory, Convalescent or Healthy

Types of Carriers

• Incubatory carrier: Becomes infective in the last few days of the incubation period before symptoms start.
• Convalescent carrier: Continues to excrete the infectious agent during the convalescent period.
• Contact carrier: Having high immunity can get infected and transmits within two weeks.
• Healthy carrier: Contacts contaminated environments such as contaminated food/water.

Another Classifications of Carriers

• By Period of infectivity (transient, temporary, chronic)
  • Transient: For a few days (last days of the incubation period, e.g., cholera)
  • Temporary: For a few weeks or months (e.g., viral hepatitis A & B)
  • Chronic (permanent): For years (e.g., incubatory carrier of AIDS)
• By foci of infection (respiratory, gastrointestinal, urinary, skin)
• By flow of organisms (regular, intermittent)

Animal Reservoir (Zoonoses)

• Zoonosis: Diseases primarily harming animals that can spread to humans Examples: Brucellosis (cattle), Rabies (dogs/cats), Salmonellosis(Poultry), Avian flu (Poultry).

Non-Living Reservoirs

• Non-living reservoirs of infection include water, food, and soil.
• Water is the most dangerous as it can contaminate and spread easily in areas without good sanitation.

Mode of Transmission

• Droplet (airborne) infection
• Foodborne infection
• Contact infection
• Arthropod-borne infection (vector-borne diseases)
• Occasional modes of transmission

I. General (innate) defense mechanism

• Natural barriers: Skin, eyes, gastrointestinal tract (GIT), and respiratory system.

II. Specific (acquired) immunity

• Natural:

  • Passive: Maternal immunity, colostrum, breast milk
  • Active: Clinical and sub-clinical disease

• Artificial:

  • Passive: Seroprophylaxis
    • Active: Vaccines and toxoids

General Defense Mechanism

• Skin, eyes, respiratory tract, GIT mechanisms.
• Skin: intact surface and bactericidal effect of sweat
• Eyes: Blinking reflex, tears as protective mechanisms
• Respiratory system: Sneezing, coughing for expelling pathogens
• GIT: Saliva and bacteria flora in the mouth inhibit growth; gastric acidity (HCl) and intestinal flora of the colon destroy microorganisms

Vaccines

• Preparations of one or more types of organisms

• Types:

  • Live
  • Live attenuated
  • Killed/inactivated

• Live vaccine: e.g., Smallpox (from cowpox virus), Measles, mumps, rubella (MMR), Sabin (OPV)

• Live attenuated vaccines: More potent than killed vaccines

• Killed/inactivated vaccines: Killed by heat or chemicals; Require more doses and boosters. e.g. Typhoid vaccine

Route of administration of vaccines & toxoid

• Subcutaneous (SC) or intramuscular (IM) for most immunizations.
• ID (intradermal)
• Orally (e.g., Sabin polio vaccine)
• Intranasal

System of Active Immunization

• Primary dose is typically a single or multiple doses and is needed initially then booster doses may be required

Protective period of active immunization

• The period of immunity given by a vaccine.
• Periods vary by vaccine. e.g., Cholera vaccine = 6 months

Control of Cases, Contacts & Carriers

• Early case finding
• Treatment
• Isolation
• Release
• Health education
• Notification
• Surveillance

Control of Carriers

• Recognize by bacteriologic diagnosis during pre-employment exams
• Examine contacts
• Treat the source of infections
• Periodic investigations after release

Epidemic Measures (for disease outbreaks)

• Mass immunization of children (e.g., Sabin vaccine)
• Epidemiologic studies
• Postpone active immunization by injection (e.g., Salk vaccine)
• Postpone throat or nose surgery
• Active Surveillance

Viral Hepatitis

• Inflammation of the liver from viral infection
• Three main types of viruses (A, B, C)

HBV

• DNA virus, man; only reservoir.
• Infective for weeks, chronic carrier for years and lifetime
• Exits via blood and body fluids
• Incubation period= 6 weeks- 6 months
• Horizontal & Vertical transmission

Modes of Transmission

• Horizontal: Exposure to infected blood (e.g., through contaminated needles).
• Vertical: Maternal transmission to fetus
• Other routes: Sexual contact, Organ transplantation/dialysis

Clinical Outcomes of HBV Infections

• Acute hepatitis B (90% resolution, 1% fulminant)
• HBsAg for > 6 months (50% Asymptomatic carrier state, 9% Chronic persistent hepatitis, Chronic active hepatitis)
• Extrahepatic disease (polyarteritis nodosum, glomerulonephritis), Cirrhosis, Hepatoma

Complications

• Development of chronic carriers - Fulminate hepatitis - Chronic hepatitis - Liver cirrhosis, Liver malignancy

Diagnosis

• Clinically: usually non-diagnostic
• Laboratory: Detection of HBV markers (HBsAg indicates active or past infection, Anti HBcAg)
• PCR HBV DNA

Susceptibility & Immunity

• All ages susceptible
• No specific seasonal incidence.
• Immunity follows disease attack or immunization.

Prevention and control

• General preventive measures (Precautions against exposure to infected blood, Use of disposable syringes, blood product sterilization)
• Prevent sexual transmission (Health education)

Combined Vaccine

• Twinrix®, hepatitis A & B combination vaccine (for people 18 years of age and older).

Seroprophylaxis

• Passive immunization by injecting human specific hepatitis immunoglobulin.

Poliovirus

• Acute viral infectious, food-borne disease causing Acute flaccid paralysis.
• Three antigenic types
• Reservoir: Man only-Cases: all clinical cases, carriers: All types (incubatory, convalescent & healthy)
• Exits via throat secretions (pharyngeal focus) and stools (intestinal focus).
• Bimodal transmission (droplets or feco-oral)

Clinical pictures

• Inapparent Infection (non-manifested)
• Clinical polio(minor, major, paralytic and non-paralytic)

Complications of Poliomyelitis

• Soft tissue (muscle) and bone deformities
• Infection: Respiratory, Myocarditis and Urinary
• Fatality rate 2-10% (Bulbar form)

Diagnosis

• Clinically: Not diagnostic (except for paralytic & non-paralytic)
• Laboratory: Isolation of virus from throat washing/stools and serological testing

Immunity to Polio

• Naturally acquired (after clinical and subclinical infections)
• Artificially acquired (from mother, seroprophylaxis & active immunization)

Prevention and control (Polio)

• General: Environmental sanitation; Health education, Health promotion & Community development
• Specific: seroprophylaxis (Human immunoglobulin) & vaccination (Sabin & Salk)

Test your knowledge on convalescent carriers and vaccination practices in public health. This quiz covers important concepts such as passive immunity, vaccination coverage, and diseases associated with convalescent carriers, along with key public health measures. Sharpen your understanding of immunity and disease prevention strategies.