Understanding Disease Classification and Immune Response

Disease Classification and Types

Specific Disease Categories

3. Diseases of Specific Organ Systems

   These affect different organs and body systems, including diseases of the respiratory, circulatory, and peripheral systems.

4. Autoimmune Diseases

   Autoimmune diseases are caused by a failure of the immune system, resulting in the production of molecules that harm the organism.

5. Diseases Caused by Accidents

   This category includes diseases resulting from traffic accidents, domestic incidents, work-related injuries, etc.

Infectious Diseases: Definitions and Dynamics

Prevalence vs. Incidence

Prevalence is defined as the total number of patients with a disease at a given time, while incidence refers to the new cases of disease appearing in populations over a specific period.

Pathogen-Host Relationship Dynamics

Infection is transmitted from the source of infection to a susceptible host—a healthy individual who may become ill after contact with the infectious agent. Key factors defining the relationship between the pathogen and the host include:

1. Infectivity

   The transmission capacity of the organism.

2. Invasiveness

   The ability of the infectious agent to install itself and multiply within the host.

3. Pathogenicity

   The ability of the pathogen to produce disease.

4. Virulence

   The degree or severity of pathogenicity.

Reservoirs of Infection

Prior to infecting humans, all pathogens utilize specific locations, known as reservoirs of infection, where they are produced and/or maintained, and from which they are transmitted to humans. The reservoir is normally an animal.

Phases of Infectious Diseases

Every infectious disease can be divided into three distinct phases:

• Incubation Period

  The time elapsed from the entry of the infectious agent until the onset of the first symptoms.

• Prodromal Period

  Characterized by the appearance of nonspecific general signs that occur in many processes. The pathogen has begun to act on the body but has not yet caused specific infection symptoms.

• Clinical Period

  Marked by the onset of specific symptoms and signs indicative of the disease. These clinical manifestations, combined with analytical data, enable an accurate diagnosis.

Prevention of Infectious Diseases

Infectious disease prevention focuses on two main strategies: acting on the reservoir/source of infection, or acting on the susceptible host. When focusing on the source, key actions include:

• Early diagnosis and treatment.
• Monitoring the distribution of the disease within the community.
• Finding and isolating carriers.
• Implementing health education programs.

Defenses Against Infection: The Immune System

Immunity is the resistance organisms possess against infections caused by pathogens or foreign substances. The immune system's reaction against an antigen is known as the immune response.

Types of Immunity

There are two primary types of immunity:

• Innate (Nonspecific) Immunity

  This immunity is present in the body before it is first exposed to pathogens. It is capable of destroying many pathogens during the initial contact. The inflammatory reaction is a prime example of a nonspecific immune response.

• Adaptive (Acquired or Specific) Immunity

  This immunity is acquired after contact with a specific pathogen. It involves lymphocytes and the molecules they release, such as antibodies.