Transmission of Disease (BMS Learning Outcomes)

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Questions and Answers

What is the first step of Koch's postulates?

The pure culture must reproduce the disease in animals

Microorganisms must be observed in every case of the disease (correct)

Microorganisms must be recovered from the diseased animal

Microorganisms must be isolated and grown in pure culture

Which mechanism is NOT part of the chain of transmission of infection?

Mode of transmission

Immune response (correct)

Susceptible host

Agent

Which type of transmission involves a mother passing a disease to her child?

Horizontal transmission

Vector transmission

Indirect transmission

Vertical transmission (correct)

How does saliva contribute to preventing disease?

It has antibacterial agents and a lavage effect Signup and view all the answers

What is the primary role of B lymphocytes in the immune response?

They produce antibodies and memory cells Signup and view all the answers

Which statement best describes the blood-brain barrier?

It acts as a filter, restricting most microbes and toxins Signup and view all the answers

What does the mucociliary escalator do?

Removes mucus and trapped microbes from the respiratory tract Signup and view all the answers

What is a common mode of indirect transmission?

Through air or water Signup and view all the answers

Which of the following components serves as the mechanical barrier of the skin?

Keratin Signup and view all the answers

What is the main function of Killer T-lymphocytes?

Destroy virus-infected or cancer cells Signup and view all the answers

What is phagocytosis primarily responsible for?

Eating and destroying invading micro-organisms Signup and view all the answers

Which type of immunity is present from birth?

Natural immunity Signup and view all the answers

Which type of immunity is characterized by the injection of ready-made antibodies?

Passive or artificial immunity Signup and view all the answers

Which type of T-lymphocytes is responsible for activating B-lymphocytes?

Helper cells Signup and view all the answers

What is the role of Suppressor T-lymphocytes in the immune response?

Turn off immune responses Signup and view all the answers

What occurs when micro-organisms invade the body?

Activation of phagocytosis Signup and view all the answers

Which of the following diseases can provide permanent immunity when contracted?

Measles Signup and view all the answers

What is a characteristic of Active immunity?

Developed through subclinical infections or vaccination Signup and view all the answers

What is the role of polymorphonuclear leucocytes in the immune system?

Carrying out phagocytosis Signup and view all the answers

Study Notes

Koch's Postulates

Koch's postulates are criteria used to establish a causal link between a microorganism and a specific disease.
Postulate 1: The microorganism must be present in every case of the disease but absent in healthy individuals.
Postulate 2: The microorganism must be isolated from the diseased host and grown in pure culture.
Postulate 3: Introducing the pure culture into a healthy susceptible host must reproduce the disease.
Postulate 4: The identical microorganism must be reisolated from the experimentally infected host.

Chain of Transmission

The spread of infection requires several linked elements:
- Agent: The infectious microorganism
- Reservoir: The source of the agent (e.g., human, animal, environment).
- Exit: The method by which the agent leaves the reservoir (e.g., coughing, sneezing, feces).
- Mode of transmission: How the agent moves from the reservoir to a new host (e.g., direct contact, airborne).
- Portal of entry: The route by which the infectious agent enters the new host (e.g., respiratory tract, skin wound).
- Susceptible host: A host who is vulnerable to the agent's effects.

Transmission Mechanisms

Horizontal transmission: Person-to-person spread
Vertical transmission: Mother-to-child spread
Direct transmission: Immediate contact with infectious substance (e.g., sexual contact, kissing, touching).
Indirect transmission: Transmission through an intermediary like a contaminated surface or vector (e.g., vehicle-borne pathogens via food, water, or contaminated objects, vector-borne diseases via insects, animals).

Host Defense Mechanisms

Mucociliary escalator: The respiratory tract's lining with mucus and cilia (tiny hairs) removes inhaled particles, trapping and clearing them out.
Skin: The tough keratinized outer layer provides a mechanical barrier. Unkeratinized areas (mouth, eyes, respiratory tract) are more susceptible.
Fatty acids and salts: Skin glands produce antibacterial agents like fatty acids and lysozyme.
Saliva: Contains protective antibacterial agents and a cleansing effect.
Gingival crevicular fluid: Antibacterial exudate in the gum area, containing immune defenses.
Blood: Blood flow flushes out pathogens, and clotting mechanisms trap them.
Blood-brain barrier: This filters out harmful substances, preventing infection entry into the brain and spinal cord.

Host Immune Response

Immune system: Recognizes and destroys foreign invaders (antigens). Differentiates between body tissues and antigens.
Lymphocytes: White blood cells, developing in bone marrow and circulating in lymphatic system.
- B lymphocytes: Mature into plasma cells, producing antibodies targeted at specific antigens. Memory B cells provide long-term immunity.
- T lymphocytes: Assist with immune response and directly destroy pathogens:
  - Killer T cells: Destroy virus-infected or cancerous cells.
  - Helper T cells: Activate B cells for antibody production.
  - Suppressor T cells: Control immune response, stopping reactions as needed.
Phagocytosis: ("cell eating") is carried out by polymorphonuclear leucocytes (a type of white blood cell), which engulf invading micro-organisms.

Immunity

Natural Immunity: Existing at birth; inherited from mother.
Acquired Immunity: Develops throughout life, responding and creating immunity to a disease. Can be short-term (e.g., influenza) or long-term (e.g., measles).
Active immunity (natural or artificial): The body produces its own antibodies in response to exposure to antigens through illness or vaccination. Long-lasting immunity.
Passive immunity (artificial): Receiving antibodies from an external source (e.g., antibodies given after exposure to a disease, mothers antibodies given to the child). Temporary protection.

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Description

This quiz covers Koch's postulates, which establish the criteria for linking microorganisms to diseases, as well as the chain of infection transmission involving agents, reservoirs, exits, and modes. Test your understanding of these crucial concepts in microbiology and infectious diseases.