Common Diseases in Human Beings - Viral Diseases

Viral diseases:

• Viruses are the smallest intracellular obligate parasites, which multiply within living cells.
• Outside the living cells, they cannot carry out the characteristics of a living organism.
• Viruses invade living cells, forcing the cells to create new viruses. The new viruses break out of the cell, killing it and invade other cells in the body, causing diseases in human beings.
• Viral diseases are generally grouped into four types on the basis of the symptoms produced in the body organs.
  (i) Pneumotropic diseases (respiratory tract infected by influenza)
  (ii) Dermotropic diseases (skin and subcutaneous tissues affected by chicken pox and measles)
  (iii) Viscerotropic diseases (blood and visceral organs affected by yellow fever and dengue fever)
  (iv) Neurotropic diseases (central nervous system affected by rabies and polio)

1) Common cold:

• It is an infection that affects the nose and respiratory passage.  
• Causative organism: Rhinoviruses (group of viruses)  
• Mode of transmission: Through inhalation of droplets resulting from the infected person directly or transmitted through contaminated objects like pens, books, cups, computer parts, towels, etc.  
   

• Symptoms: Nasal congestion and discharge, sore throat, coughing, sneezing, headache, tiredness, hoarseness, etc., are the symptoms that last for 3 to 7 days. 
• The common cold is caused by some 100 types of Rhino viruses. 
• Rhino viruses are a group of viruses that cause the common cold. They infect the nose and respiratory passage but not the lungs. 

2) Nipah virus:

• Nipah virus is a zoonotic virus (transmitted from animals to humans) and also transmitted through contaminated food.
• In infected people, it causes a range of illnesses from asymptomatic infection to acute respiratory illness and fatal encephalitis.

Some of the diseases caused by viruses in humans are as follows: