Emerging Infectious Diseases: Understanding, Prevention, and Treatment

Posted on Nov 1, 2024 in Biology

Emerging Infectious Diseases

Emerging infectious diseases are those that have appeared in the population over the last two decades or threaten to increase in the near future. Some of these germs have been long confined to their place of origin before abruptly coming into contact with people. For example, Ebola, whose agents have been responsible for contact with people following the invasion and destruction of forests. Other cases are due to mutations that have made the agents dangerous.

Persistent Infectious Diseases

The major infectious diseases of the past are still with us, hitting regions of the planet where they were believed to be eradicated. All these known infectious diseases are believed to constitute a health problem that often appears, reaching epidemic proportions.

Well-known examples include:

  • Dengue
  • Malaria
  • Cholera
  • Tuberculosis

Germ Theory of Disease

Several renowned researchers established the relationship between certain diseases and the presence of microorganisms in the patient. Although this did not confirm causality, a young German doctor, Koch, experimentally tested the germ theory. His conclusion was: every disease is caused by a microorganism that can be identified and generates a different disease.

Miasma Theory of Disease

For much of history, the origins and causes of infectious diseases were a mystery. The first rational explanations invoked air pollution and miasma emissions from the decomposition of organic matter.

Infective Agents

Viruses

Viruses are cellular parasites that need to enter cells to reproduce and are difficult to remove without destroying the host cells. Examples include the flu and AIDS.

Bacteria

Bacteria are prokaryotic unicellular organisms that can reproduce without invading other cells. Examples include tuberculosis and cholera.

Protozoa and Fungi

Protozoa are eukaryotic unicellular organisms, while fungi can be unicellular or multicellular. Examples include malaria and candidiasis.

Mechanism of Immune Response

  1. A germ is phagocytosed by a macrophage.
  2. Parts of the germ are exposed on the macrophage’s surface and presented to lymphocytes.
  3. Lymphocytes search for an effective antibody against the germ.
  4. If an antibody is found, the lymphocyte multiplies and produces specific antibodies against the germ.
  5. Other lymphocytes detect and destroy infected cells.

Antigens

Antigens are organisms or molecules that are recognized by and stimulate the immune system.

Antibodies

Antibodies are proteins produced by lymphocytes (white blood cells) and circulate in the blood plasma, where they attach to specific antigens and initiate their destruction.

Antibiotics

Antibiotics are chemicals of biological or synthetic origin that kill bacteria or prevent their multiplication. Dr. Fleming observed that contaminated lab cultures with a fungus had an uninfected area surrounding the fungus. After years of research, penicillin was isolated. Since then, other antibiotics have been discovered from living organisms and synthesized in laboratories.

Antivirals

Antivirals act on viruses. However, it is not easy to create a drug that can end a viral infection because viruses are not cells and reproduce inside cells. The few existing antiviral drugs aim to prevent the virus from entering the cell or spreading to other cells.

Drug Resistance

One factor influencing the emergence and re-emergence of infectious diseases is bacterial resistance to antibiotics. Resistance occurs through:

  • Mutation: Spontaneous changes in genetic makeup can confer resistance.
  • Gene Exchange: Bacteria can exchange genetic information, spreading resistance.

The selection and spread of resistant bacteria are facilitated by:

  • Incorrect treatments (overuse or insufficient use of antibiotics)
  • Use of antibiotics in plants and other animals

New Drugs

Preclinical Research and Development

Natural substances are selected, or new molecules are designed and tested for activity and toxicity.

Clinical Stage

Testing is done in three phases with volunteers:

  1. Phase 1: Small groups of healthy volunteers to check for harmful effects.
  2. Phase 2: Small group of untreated patients to assess efficacy and dosage.
  3. Phase 3: Larger group of patients if previous requirements are met.

How Does the Flu Virus Work and Multiply?

The flu virus is characterized by:

  • Genetic information distributed in 8 small RNA molecules.
  • An envelope carrying two types of molecules that define virus types.

Multiplication:

  1. The virus attaches to a cell membrane.
  2. The virus enters the cell by endocytosis.
  3. Viral and cell membranes fuse, releasing viral RNA.
  4. The cell makes copies of the viral genetic information and builds new viruses.

Why Does the Flu Vaccine Change?

Influenza viruses constantly change due to mutations in their genes. These mutations can alter the envelope molecules, rendering previous antibodies ineffective.

Surveillance Networks

To track the evolution and detect new disease germs, worldwide surveillance systems have been implemented. The WHO has developed the GOARN alert system, which centralizes information from public authorities, researchers, and NGOs.

Prevention of Bioterrorism

To prevent possible attacks, many countries have implemented prevention programs ranging from laboratory surveillance to vaccine storage to address germs before they affect an unimmunized population. However, the risks are limited by the difficulty of such attacks.