Infectious and Non-Infectious Diseases: An Overview

Posted on Nov 18, 2024 in Biology

Infectious Diseases

Infectious diseases originate from the colonization of the body by infectious agents or vermin infestation.

Routes of Transmission

Infectious agents can be transmitted from a sick individual through:

  • Direct Contagion: Occurs from person to person.
  • Indirect Contagion: Transmission through various mediums:
    • Air: Microorganisms from a sick person pass to a healthy person through coughing or sneezing, transmitting respiratory diseases like tuberculosis.
    • Water: A significant transmission route for pathogens, causing diseases like cholera.
    • Food: Contaminated food can cause serious diseases such as salmonellosis.
    • Vectors: Animals can transmit parasites, such as tapeworms, or diseases like sleeping sickness.

Infectious Agents

Infectious agents include microorganisms like bacteria, fungi, protozoa, and parasites (usually worms). Some acellular structures, primarily viruses and prions, are also infectious agents.

Infection Process

Infection results from the multiplication of microorganisms in the body, leading to symptoms that characterize the infectious disease. The infection process involves:

  1. Colonization of cell surfaces.
  2. Penetration of defensive barriers.
  3. Multiplication and invasion, requiring nutrients taken from the affected body.
  4. Production of alterations in tissues and organs.

Fungal Diseases

Some fungi can produce infections known as mycoses. Different types of fungal infections include:

  • Superficial Mycoses: Affect the skin. Common examples include ringworm, affecting the skin and scalp.
  • Subcutaneous Mycoses: Originate through wounds, encouraging fungal growth under the skin.
  • Systemic Mycoses: Affect internal organs. Candidiasis, a common systemic mycosis, can affect the skin, respiratory organs, and genitals. Aspergillosis, caused by Aspergillus fungi, can cause allergic reactions.

Diseases Caused by Viruses and Prions

Viruses are responsible for serious diseases like AIDS, rabies, and smallpox. Prions are particles that cause diseases in animals and can potentially affect humans, such as spongiform encephalopathy.

AIDS is caused by the human immunodeficiency virus (HIV), which attacks the immune system. HIV is transmitted sexually or from mother to child through the placenta or breast milk. AIDS is a serious pandemic with over 300 million people affected.

Diseases Caused by Animal Parasites

Some animals are parasites of humans, using the human body as a habitat and source of nutrients. There are two main types of parasites:

  • Ectoparasites: Live on the body’s surface. Arthropods like lice, fleas, and ticks are common ectoparasites and can transmit infectious diseases.
  • Endoparasites: Live in internal body cavities and may use intermediate hosts. Most endoparasites are worms, such as tapeworms. Some cause diseases leading to cyst formation in tissues and organs, as seen in trikinosis (caused by consuming infected meat) and hydatid disease (caused by a dog tapeworm).

Cardiovascular Disease

Cardiovascular diseases affect the heart and blood vessels. Some high-risk conditions include:

  • Atherosclerosis: Thickening of artery walls due to the deposition of fibrous tissue and cholesterol, leading to hardening and loss of elasticity (arteriosclerosis). Arteriosclerosis can favor thrombus formation.
  • Thrombosis: A blood clot (thrombus) in an artery obstructs blood flow. Arterial thrombosis is often caused by arteriosclerosis. Venous thrombosis can lead to an embolism if the clot travels to another location.
  • Aneurysm: A weakening of the arterial wall causes dilation, which can rupture and lead to hemorrhage.
  • Stroke: Interruption of blood supply to the brain, also known as a cerebrovascular accident.
  • Coronary Heart Disease (CHD): Narrowing of the arteries supplying blood to the myocardium reduces blood flow (ischemia) to the heart muscle. Severe ischemia can cause a heart attack due to cell death from lack of oxygen.

Oncological Diseases (Cancer)

Cancer results from a loss of control over cell division. Several factors contribute to cancer development:

  • Proto-oncogenes: Genes that stimulate cell division.
  • Carcinogens: Agents that induce tumor formation.
  • Tumor Suppressor Genes: Genes like the oncosupressor gene can activate apoptosis (programmed cell death).

A malignant tumor consists of cancer cells capable of infiltrating and invading surrounding tissues. These cells can also spread to other parts of the body, forming new tumors (metastasis).