April 20, 2024
Medical Science



A disorder that affects the functioning of the live body of an animal or plant, or one of its sections, and is often characterized by specific signs and symptoms is called disease.

The disease is any harmful variation from the normal structural or functional condition of an organism that is typically accompanied by a set of symptoms and is distinct from a physical injury in origin. A sick organism usually shows signs or symptoms that reflect its abnormal state. Thus, it is necessary to understand an organism’s normal state in order to identify the symptoms of the illness. However, there is not always a clear distinction between sickness and wellness.

The term pathology describes the study of disease. The etiology of the illness must be identified, together with the mechanisms underlying its pathogenesis, structural alterations brought on by the infection process (morphological alterations), and the functional effects of those alterations. The right cause of an illness must be correctly identified in order to determine the best course of treatment.

All living things, including humans, animals, and plants, are susceptible to many infections. The normal operation of one type of organism may be impacted, but the other types may not be affected.

1. Classifications of Diseases:

Anatomic ClassificationAnatomic Classification refers to the affected organ or tissue.Heart problems
Topographical ClassificationFurther divided into categories like abdominal, gastrointestinal, chest, and vascular diseases.An ENT specialist (Ear-Nose-Throat)
A Gastroenterology specialist etc.
Physiological ClassificationThis category comprises ailments that interfere with a process or function (such as metabolism, digestion, or respiration).Diabetes
Pathological ClassificationThis kind takes into consideration the disease’s characteristics. For example, there are various varieties of cancer, which are characterized by unchecked cell development.Neoplastic diseases
Epidemiological ClassificationThis classification deals with the frequency, spread, and management of the disease within a population.Like Epidemic infections such as the plague and Influenza pandemic of 1918–1919.

2. Categories of Disease:

There are two main categories of disease.

  1. Infectious diseases (Communicable)
  2. Non-infectious diseases (Non-communicable)

2.1. Infectious disease (Communicable):

Communicable diseases are those that can transfer from one person to another. They are typically brought on by pathogens, which are microbes (fungi, rickettsia, bacteria, viruses, protozoans, and worms). Pathogens may leave the host when an infected person releases body fluids and infect a new person (sneezing, coughing, etc). Examples include malaria, chicken pox, and cholera.

We are surrounded by various sizes, forms, and locations of infectious agents. They can be grouped according to some shared traits. Some, like fungi, bacteria, and viruses, are single-celled organisms. It is also recognized that other multi-cellular organisms, such as worms, can transmit sickness.

Infection, presence, and development of pathogenic (able to cause disease) biologic agents in a specific human or other animal host are the causes of communicable infections, commonly referred to as infectious diseases or transmissible infections. From asymptomatic (without symptoms) to severe and lethal, infections can vary in intensity. Because some infections do not result in illness in the host, the word infection does not have the same significance as infectious disease.

Viral, bacterial, fungal, protozoal, multicellular parasitic and abnormal proteins such as prions are examples of biological agents that cause illness. These biological agents can be spread in a number of ways, such as through direct physical contact with an infectious person, eating or drinking contaminated food or beverages, contact with affected objects, and when an affected insect bit or tick that is carrying the infection. Some affection agents can spread from animals to people, and some of these agents have multiple modes of transmission.

2.1.1. List of Communicable diseases (Infectious):

  • Chickenpox / Shingles
  • Ending the HIV Epidemic (EHE)
  • Hepatitis B
  • Hepatitis C
  • HIV / AIDS
  • HIV / STDs / Hepatitis
  • Influenza
  • Corona Virus
  • Mumps
  • Pink Eye
  • Pertussis
  • Rabies
  • Tick-Borne
  • Tuberculosis
  • Viral Hepatitis
  • West Nile Virus

2.2. Non-infectious diseases (Non-Communicable):

Although microorganisms are the primary cause of many illnesses, lifestyle choices, nutritional deficiencies, age, and gender of the patient also have an impact. These are non-communicable diseases.  Examples include cancer, diabetes, and hypertension. They contain the individual who has contracted them and does not spread to others. Other non-infectious disorders include Alzheimer’s sickness, asthma, cataracts, and heart conditions.

Chronic diseases are another name for non-communicable diseases, which are often long-lasting and advance slowly. They can result from exposure to the environment or from genetic defects, which may be visible at birth or only later in life. Four main categories of non-communicable diseases have been identified by the World Health Organization (WHO): cancer, cardiovascular illness (including heart attack and stroke), chronic respiratory illness (including asthma), and diabetes mellitus. According to estimates from the WHO, these four types of illness account for 82 percent of all non-communicable disease-related fatalities.

Non-communicable diseases caused by inherited genetic defects can leave a person unprepared to survive without medical care. Cystic fibrosis, Down syndrome, and inborn metabolic abnormalities are a few examples of genetic diseases that manifest at birth. Huntington’s illness and several cancers are examples of hereditary conditions that show in adulthood (e.g., familial breast cancer involving inherited mutations in either of the genes BRCA1 or BRCA2).

2.2.1. List of Non-communicable diseases (Infectious):

  • Cardiovascular
  • Alzheimer’s disease
  • Amyotrophic lateral sclerosis
  • Arthritis
  • Attention deficit hyperactivity disorder (ADHD)
  • Autism spectrum disorder (ASD)
  • Bell’s palsy
  • Bipolar disorder
  • Birth defects
  • Cerebral palsy
  • Chronic kidney
  • Chronic pain
  • Chronic pancreatitis
  • Chronic traumatic encephalopathy (CTE)
  • Clotting/bleeding disorders
  • Congenital hearing loss
  • Cooley’s anemia (also called beta thalassemia)
  • Crohn’s disease
  • Depression
  • Down syndrome
  • Eczema
  • Epilepsy
  • Fetal alcohol syndrome
  • Fibromyalgia
  • Fragile X syndrome (FXS)
  • Hemochromatosis
  • Hemophilia
  • Inflammatory bowel disease (IBD)
  • Insomnia
  • Jaundice in newborns
  • Kidney failure
  • Lead poisoning
  • Liver disease
  • Muscular dystrophy (MD)
  • Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS)
  • Myelomeningocele (a type of spina bifida)
  • Obesity
  • Primary thrombocythemia
  • Psoriasis
  • Seizure disorder
  • Sickle cell anemia
  • Sleep disorders
  • Stress
  • Systematic lupus erythematosus (also called lupus)
  • Systemic sclerosis (also called scleroderma)
  • Temporomandibular joint (TMJ) disorder
  • Tourette syndrome (TS)
  • Traumatic brain injury (TBI)
  • Ulcerative colitis
  • vision impairment
  • Von Willebrand disease (VWD)

3. Different Types of Diseases:

Here are some different types:

3.1. Degenerative Diseases:

They are primarily brought on by the body’s essential organs malfunctioning as a result of the aging process of cells. Increased bone brittleness is a sign of degenerative illness in conditions like osteoporosis. Bone fractures are now more likely as a result.

A neurodegenerative disorder is a condition that results in the deterioration of central nervous system cells like neurons. A notable example of this disorder is Alzheimer’s. Aging and bodily wear are the two main causes of degenerative disorders. Some are genetic, while others are caused by lifestyle decisions.

3.2. Allergies:

When the body develops a heightened sensitivity to specific external chemicals known as allergens, an allergic reaction occurs. This typically occurs when an apparently harmless drug triggers an aberrant immunological response. Dust, pollen, animal dander, mites, feathers, latex, and certain food items like almonds and gluten are examples of common allergies. Extreme allergic responses, such as those brought on by peanuts and other nuts, have the potential to result in potentially fatal illnesses such as anaphylactic shock, difficulty breathing, tissue swelling and obstructing the airways, and others.

Coughing, sneezing, running nose, itchy and red eyes, and skin rashes are additional, less serious symptoms. Asthma is one of the best illustrations of this allergic reaction. Occasionally, ant bites and bee stings can also cause allergies. Allergies can be brought on by shellfish consumption and some drugs.

Asthma is a chronic condition that primarily affects the lungs’ bronchi and bronchioles. Airborne allergens like pollen or dust are one of the causes of this. Breathing issues, coughing, and wheezing are symptoms.

3.3. Deficiency Diseases:

They develop as a result of hormone, mineral, nutritional, and vitamin deficits. For instance, goiter is primarily brought on by an iodine shortage, diabetes is brought on by an inability to generate or utilize insulin, and kwashiorkor is brought on by a diet lacking in proteins. Beriberi is brought on by a vitamin B1 deficiency.

3.4. Goitres:

The esophagus or other chest and neck organs are obstructed as a result of the thyroid glands’ abnormally big size. Eating and breathing become difficult as a result.

3.5. Blood Diseases:

Red blood cells, platelets, white blood cells, and plasma are all components of blood. Blood diseases may result from problems with any of these parts. For instance, when a person has sickle cell disease, their red blood cells are damaged. The red blood cells lose their capacity to carry oxygen and are deformed into the shape of a sickle (thus the name). As a result, this illness is marked by signs and symptoms like chronic anemia, fatigue, and shortness of breath.

This category also includes conditions like eosinophilic disorders, leukemia, myeloma (bone marrow plasma cell malignancy), Sickle Cell Anemia, Aplastic Anemia, hemochromatosis, and Von Miller Disease (blood-clotting illness).

Pale complexion, swollen lymph nodes, fever, bleeding, bruises, skin rashes, etc. are common symptoms.

4. Disease-Causing Agents:

Experts have observed the categorization of diverse entities based on a variety of criteria; therefore, in order to simplify things, we categorize creatures in order to study them as a class. The same is true for disease, which can be categorized as being brought on by bacteria, fungus, viruses, etc. Multi-cellular creatures like worms can also be responsible for some illnesses or infections.

4.1. List of a few diseases and their causing agents:

List of diseases:

Disease:Causative Agent:
PlaguePasteurella pestis
CholeraVibrio comma (Vibrio cholera)
TetanusClostridium tetani
AnthraxBacillus anthracis
Whooping coughBordetella pertussis
Human papillomavirus infectionHuman papillomavirus
Acquired Immune Deficiency Syndrome (AIDS).Human Immunodeficiency Virus (HIV).
HepatitisThe Hepatitis A, Hepatitis B, Hepatitis C, Hepatitis D, and Hepatitis E viruses
ChickenpoxVaricella-zoster virus (VZV)
MeningoencephalitisNaegleria fowleri (amoeba)