Causes Of Diseases

What Is A Disease?

A disease is any dangerous divergence from a functional or normal state of an entity. When a person is inflicted with a disease, he exhibits a few symptoms and signs that range from normal to severe depending upon the medical condition. Hence, in order to identify different diseases, the normalcy of an entity needs to be studied and understood as a clear demarcation between disease and disease-free is not always apparent.  

We say we have fallen sick or have a disease when we feel unwell, or are unable to carry out our activities. These diseases are usually caused by many factors rather than a single cause. When we have a disease, we eventually show some signs, such as headaches, cough, cold, weakness. These signs are referred to as “symptoms.” In almost all diseases, symptoms are shown immediately after having been struck by the disease. However, it varies depending upon the seriousness of the disease.

Diseases can be caused due to external or internal factors. Immediate causes of diseases can be of two types:

  • Infectious causes of diseases
  • Non-infectious causes of diseases

Infectious And Non-infectious Causes Of Diseases

Infectious diseases are diseases where microorganisms are immediate causes of disease. They cause diseases as they can spread in the community passing the infected pathogens. Non-infectious causes, on the other hand, are diseases that are not usually caused by any microbial activity, they exhibit internal and not external factors. For instance, a few cancers are caused due to genetic abnormalities, high blood pressure can be caused due to a sedentary lifestyle.

Each disease is caused due to different reasons hence treatment for a particular disease too is carried out accordingly. Some can be treated with over-the-counter drugs while other diseases require us to consult a physician.

Infectious Diseases – Infectious Agents

We have seen the classification of different entities based on various characteristics, for simplification, we classify organisms to group them together and study about them as a class. Similarly, diseases are caused by different microorganisms and can be classified as diseases caused by bacteria, fungi, viruses etc. Some diseases are also caused by multicellular organisms such as worms.

Listed below are few diseases and the disease-causing agents

Name of Pathogen Disease Caused
Leishmania (Protozoa) kala-azar
Staphylococci (Bacteria) Acne
Trypanosoma (Protozoa) Sleeping sickness
Worms Elephantiasis
Viruses Common cold, influenza, AIDS, dengue fever
Bacteria Typhoid, Cholera, Fever
  • Categorizing diseases helps us understand the kind of treatment that would be required to treat them as they have many biological characteristics in common.
  • Viruses live inside the host and multiply rapidly like bacteria and fungi. Worms, however, are slow at multiplying.
  • Bacteria build a cell-wall around to protect themselves. Antibiotic penicillin blocks the building of cell-wall by bacteria and hence causes their death, not only of one but multiple bacteria. Human cells do not build cell walls hence penicillin cannot cause any harm to our cells. Viruses do not have such pathways hence they cannot be treated using an antibiotic.

Names Of Diseases

Following table depicts a few names of diseases:


  • Food allergy
  • Hives
  • Chronic Rhinitis
  • Sinusitis
  • Flu/cold/Allergies
  • Anaphylaxis
  • Liver cancer
  • Lung cancer
  • Brain tumour
  • Bladder cancer
  • Breast cancer
  • Cervical cancer
  • Skin cancer
  • Prostate cancer
  • Testicular cancer
  • Insulin
  • Diabetes Mellitus
  • Diabetes Insipidus
  • Acid flux
  • Appendicitis
  • Diarrhoea
  • Constipation
  • Inflammatory Bowel Disease
  • Motion sickness
  • Lactose Intolerance
  • Haemorrhoids
  • Eye allergy
  • Cataract
  • Conjunctivitis
  • Glaucoma
  • Retinal Detachment
  • Coronary heart disease
  • Heart attack
  • Angina
  • Atherosclerosis
  • Coronary angiogram
  • Coronary artery bypass
  • Stroke
  • High cholesterol
High blood pressure
Urinary Tract Infections
Bone density
Cirrhosis of the liver
Sexually transmitted diseases

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