Communicable Diseases Overview

Communicable Diseases

• Communicable diseases are illnesses transmitted from one person to another, caused by infectious agents.
• These agents are spread from a source to a susceptible host, either directly or indirectly.
• They are also known as infectious diseases.

Infectious Disease Model

• Infectious diseases involve three key elements:
  • Host: The individual or organism affected by the disease
  • Pathogen: The infectious agent (e.g., bacteria, virus, parasite)
  • Environment: The surrounding conditions that contribute to the spread of infection

Human Pathogen Transmission

• Infectious transmission can occur via:
  • Airborne transmission
  • Contact and faeces
  • Contaminated water
  • Pathogens in blood stream and tissues

Transmission Modes

• Direct transmission:
  • Physical contact, droplets, aerosols
• Indirect transmission:
  • Inanimate vehicles (fomites, etc.)
  • Animate biological vehicles (vectors)
  • Mechanical
  • Biological (diseases with a cyclical life cycle)–cyclo-developmental (flarial worms), and cyclo-propagative (eg. malaria).

Types of Communicable Disease

• Respiratory infections
• Intestinal infections
• Arthropod-borne infections
• Surface infections
• Sexually transmitted diseases (STDs)

Infectious Agents and Associated Diseases

• Viruses: Common cold, influenza, measles, mumps, chicken pox, AIDS, hepatitis-B
• Bacteria: Cholera, typhoid, tuberculosis, tetanus, anthrax, food poisoning
• Fungi: Skin infections
• Protozoans: Malaria, kala-azar, amoebic dysentery, sleeping sickness
• Worms: Intestinal infections, elephantiasis

Respiratory Infections

• Caused by viruses, bacteria, or other pathogenic microbes in the respiratory system (lungs, throat, airways).
• Spread through respiratory secretions (mucus, saliva) expelled during coughing, sneezing, talking, or laughing.
• Some germs are spread via airborne droplets.

Tuberculosis

• A specific infectious disease affecting the lungs (pulmonary TB).
• Can also affect other vital organs (intestine, brain, bones, joints, lymph glands, skin).
• Incubation period varies from weeks to months or years depending on the dose of infection and patient immunity.
• Transmission typically occurs through droplet infection (containing sputum expelled from positive patients).

Chickenpox (Varicella)

• Common in children under 10.
• Uncommon in adults.
• Incubation period: 14-16 days.
• Spread via droplet infection and contact with contaminated surfaces (fomites).

Measles (Rubeola)

• Occurs commonly in children (3-5 yrs).
• Incubation period: 8-14 days.
• Transmitted via droplet infection and direct contact.

Arthropod-Borne Infections

• Illnesses caused by parasites, viruses, and bacteria transmitted by arthropods.
  • Includes mosquitoes, sandflies, bugs, blackflies, snails, and lice
• Leading causes of death worldwide.

Malaria

• Protozoan disease (parasitic disease).
• Infection is commonly transmitted by the bite of an anopheles female mosquito.
• Incubation period is about 9-30 days.
• Vector transmission: bite of a female mosquito.
• Other transmission: injection of infected blood or plasma, congenital (infected mother to newborn)

Plague

• Zoonotic or zoonotic disease: infection transmitted to man, typically by fleas infected from rats or rodents.
• Incubation period is about 9-30 days.

Surface Infections

• Infections of the skin caused by bacteria, fungus, viruses, or parasites.
• Examples include rabies, trachoma, tetanus, leprosy.

Rabies

• Caused by the rhabdovirus.
• Bullet-shaped virus, sensitive to sunlight and ultraviolet light.
• Incubation period varies with the site of infection; in humans it can take 10 days- 15 years.
• Transmitted via the saliva of an infected animal via bites.

Leprosy

• Chronic infection of humans, affecting superficial tissues (skin) and peripheral nerves.
• Incubation period is about 3-5 years
• Transmitted via prolonged close contact, or through airborne droplets.

Sexually Transmitted Diseases (STDs)

• Infections transmitted through sexual contact, caused by bacteria, viruses, or parasites.
• Examples include AIDS, Syphilis, Gonorrhea.

Acquired Immunodeficiency Syndrome (AIDS)

• Chronic infection caused by the human immunodeficiency virus (HIV).
• Reduces immunity, making the host susceptible to other infections.
• Incubation period: 8-10 years for adults, within 2 years for children below 5 years

Intestinal Infections

• Viral, bacterial, or parasitic infections causing gastroenteritis (inflammation of the GI tract).
• Examples: Poliomyelitis, cholera, typhoid fever, hepatitis, food poisoning, hookworm infections

Cholera

• Severe acute gastrointestinal (GIT) infection.
• Incubation period is a few hours to 5 days.
• Transmitted via contaminated food and water, or by person-to-person contact through contaminated hands.

Hookworm Infection

• Caused by small worms attaching to intestinal walls and causing bleeding and poisoning.
• Transmission is primarily via tiny worms penetrating the base of feet of those working in fields.

Control of Communicable Diseases

• National Tuberculosis Program (NTP)- Directly Observed Treatment, Short-Course (DOTS):
• Aims for early diagnosis and short-course treatment for efficient disease control
  • Focuses on political commitment, adequate funding, quality-assured bacteriology (diagnosis), standardized treatment, drug supply management, and monitoring.

Measles- Control and Prevention

• Active immunization with live attenuated measles virus, and passive immunization with human normal immunoglobulin.

Arthropod-Borne Infections- Control and Prevention

• Prevention via vector control (eg., prevention from mosquito bites), and larval measures.

Malaria- Control and Prevention

• Prevention against mosquito bites, control of adult mosquito reservoirs, anti-larval measures, through proper use of insecticide-treated mosquito nets and indoor residual spraying.

Rabies- Control and Prevention

• Vaccination, public/animal awareness programs, and proper animal bites/ rabies exposures management.

Dengue- Control and Prevention

• Health education, early detection and treatment, treating mosquito nets with insecticides, destroying breeding places of mosquitoes in and around the home, and avoid hanging clothes inside the home.

Schistosomiasis- Control and Prevention

• Stool examination & reduce snail density (clearing vegetation, constructing drainage system), diminish infection rate via proper hygiene practices, vaccination, and treatment.

Filariasis- Control and Prevention

• Health education (mode of transmission, personal hygiene), environmental sanitation, and medication (ivermectin, albendazole, diethylcarbamazine)

National Leprosy Control Program

• Focuses on providing adequate anti-leprosy drugs (MDT).
• Aims to prevent and reduce disabilities from leprosy by 35% (through rehabilitation, Prevention of Impairments and Disabilities (RPIO)).
• Aims to improve case detection and post-elimination surveillance.

Sexually Transmitted Diseases (STIs)/HIV- Control and Prevention

• Availability of free voluntary HIV counselling and testing
• 100% Condom Use Program, especially in entertainment establishments.
• Peer education and outreach, multi-sectoral coordination, and community empowerment.

General Notes

• Many programs (eg. NTP, NLCP) have specific programs, goals, missions, and visions.

This quiz explores the key aspects of communicable diseases and their transmission. Learn about the infectious agents, modes of transmission, and the role of hosts and environments in spreading these diseases. Test your knowledge on how infection occurs and the types of pathogens involved.