Understanding Key Concepts in Immunology and Infectious Diseases

Immunological Terms

• Vector Transmission: A DNA molecule used to transfer a particular gene or a specific DNA sequence to another cell.
• Reservoir: A deposit, such as a straight one developed by surgeons, once the rectum has been removed due to disease.
• Phagocyte: A cell capable of surrounding, engulfing, and digesting microorganisms, foreign matter, old cells, and cellular debris, which it covers with its pseudopodia and then digests in the cytoplasm.
• Lymphocyte: A type of leukocyte (white blood cell) included within the agranulocytes.
• Antigen: Antigens are usually proteins or polysaccharides.
• Antibody: Antibodies are glycoproteins of the gamma globulin type. The soluble form can be found in the blood or other bodily fluids of vertebrates.

Infectious vs. Non-Infectious Diseases

• Infectious Disease: The manifestation resulting from an infection caused by a microorganism such as bacteria, fungi, viruses, and occasionally, protozoa or prions.
• Non-Infectious Diseases: Diseases affecting the normal operation of the body, such as:
  • Cardiac or vascular disease
  • Cancer

Disease Classification and Germ Theory

• Emerging Diseases: A class of infectious diseases that arise in specific times and places and become, or threaten to become, new epidemics. Their emergence is the origin of much of the legislation restricting traffic in samples or biological specimens across borders.
• Reemerging Diseases: Diseases that reappear in regions of the world where they were thought to have been eradicated. Examples include cholera, tuberculosis, and dengue fever.
• Epidemic: Occurs when a disease affects a greater number of individuals than expected in a population during a given time.
• Pandemic: The involvement of an infectious disease of humans over a wide geographical area.
• Endemic: A pathological process that is maintained over a long period in a population or geographical area. They are usually infectious diseases.
• Germ Theory: A theory that proposes that microorganisms are the cause of many diseases.
• Harmless Microorganisms and Pathogens: Harmless microorganisms do not produce infectious diseases, unlike pathogens.

Koch's Postulates

Koch's postulates are a set of criteria used to establish a causal relationship between a microorganism and a disease:

1. The pathological agent must be present in every case of the disease under appropriate conditions and absent in healthy people.
2. The agent must not appear in other diseases or as a harmless bacterium.
3. The agent must be isolated from the body in pure culture from lesions of the disease.
4. The agent must cause the disease in a susceptible animal upon inoculation.
5. The agent must be isolated again from the lesions produced in experimental animals.