Diseases caused by viruses

1. Common cold

It is caused by Rhinoviruses. It is one of the most infectious human ailments. Rhinovirus infects the nose and respiratory passage but not the lungs.


The common cold is characterized by nasal congestion and discharge, sore throat, cough, headache, tiredness, hoarseness etc. for 3 to 7 days.

2. Influenza

It is commonly known as “Flu” and is highly infectious. The disease is caused by various types of influenza viruses (e.g., Myxovirus influenzae).


It causes fever and pain all over the body and affects the nose, throat, and air passages as in the common cold.

I t starts with fever, headache, sore throat, cold with sneezing and pain all over the body with restlessness.In neglected cases, complications like pneumonia, bronchitis and ear infections may develop.

There is no vaccine at present that can give protection against all types of influenza viruses as each epidemic is of a different type.

3. Small Pox (Variola)

This disease is caused by a ds DNA smallpox virus named Variola virus. It is a highly infectious disease starting with high fever, chill, backache and headache, followed by the appearance of a rash on the third day of illness.


The rash appears first on the face, then on the rest of the body. It is more on the face and limbs and less on the trunk.

The rash starts as small reddish spots which change into papules. These in turn change into small vesicles containing clear fluid. Vesicles change into pustules.

Finally, a scab is formed and it falls off by the third week. These scabs leave deep pits or scars known as pockmarks. Many children become blind and develop discharge from the ear.


The virus is present in the oral and nasal discharges of the patients and is ejected during the acts of coughing, sneezing, fomites etc., and infects healthy people.

Vaccination against smallpox is one of the best preventive remedies available today.

This was discovered by Edward Jenner in 1798. Smallpox has been eradicated from India.

4. Chicken Pox (Varicella)

The disease is caused by a virus of chicken-pox named Varicella zoster which is passed out in the discharges of the respiratory tract of an infected person directly as droplets or through contaminated articles used by the patient.


It is a mild but highly infectious disease causing slight slight fever and a rash which undergoes changes into vesicles, pustules and finally a dark brown scab that falls off leaving no scar, unlike smallpox.

The rash comes out in crops and with each fresh crop, there may be a slight fever again. The rash first appears on the trunk and there are more lesions on the trunk than on the face and limbs.

Vaccination against chickenpox is now available. The most common late complication of chickenpox is shingles caused by the reactivation of varicella-zoster.

5. Measles (Rubeola Disease)

It is caused by the Rubeola virus (RNA virus) which is passed out in the secretions of the nose and throat of the infected persons as droplets or in articles soiled by these secretions.


Measles is a highly infectious disease causing fever, inflammation of the air passages and a rash all over the body.

It attacks especially children below the age of 5 years and those who have escaped may be attacked even in later life. The disease starts with catarrh’ of the nose and throat and fever.

The eyes are red and watery, and the face is flushed. The rash which is slightly pinkish in color appears first on the back of the ear and face and spreads downwards on the body.

6. Mumps (Infectious Parotitis)

It is caused by Paramyxovirus (RNA virus), which comes out in the saliva of the infected person.


It is an infectious disease causing fever, difficulty in opening the mouth, and painful swelling of the parotid glands which lie just below the lobe of the ears.

The patient should take complete bed rest till the swelling subsides in order to avoid complications.

Usually, there are no complications, but in some cases, there may be pain and swelling of the testes (orchitis) or pain in the abdomen.

7. Poliomyelitis

This disease was called infantile paralysis. It is caused by the Polio virus (ss RNA). This virus usually enters the body via the alimentary canal where it multiplies and reaches the nervous system (spinal cord) through the bloodstream.

It is now known that the disease may occur at any age. This disease spreads mainly through intestinal discharges.

It may also spread through contaminated food or drink and by flies or other insects that may contaminate food or drink.


Its incubation period is 7-14 days.

It produces inflammation of the nervous system.

The earliest sign of this disease is the involvement of the central nervous system causing the inability to bend the head forward.

The stiffness of the neck is an important sign. Paralysis starts following the weakness of particular skeletal muscles.

The attack of paralysis begins with high fever, headache, chills, and pain all over the body. If muscles of the larynx and pharynx are involved it proves fatal.

Within two to three days the paralysis reaches its maximum.


There is no sure cure for polio. The patient should be kept isolated. He should be given complete rest.

An adequate arrangement for the proper disposal of urine and faeces of the patient must be provided because they contain poliovirus.

Overcrowding of children in schools, playgrounds and cinemas should be avoided.

Polio is preventable. The Polio vaccine is safe and effective.

Nowadays multiple vaccines are used against polio, diphtheria, whooping cough and tetanus simultaneously

8. Trachoma

It is caused by Chlamydia trachomatis. Trachoma is a chronic inflammatory disease of the eye affecting the conjunctiva and cornea.


It is characterized by the development of granules. Its common symptoms are inflammation, pain and watering of the eye.

It can lead to blindness. The infection spreads by direct contact, by use of handkerchiefs, towels, and pillows of the patient.

9. Rabies (Hydrophobia)

It is caused by a virus named Rhabdo virus. It is introduced in the body by the bite of rabid (mad) dogs usually.

It can be injected by the bite of jackals, wolves, cats etc., the Incubation period is from 10 days to one year.


Fear of water is the most important characteristic symptom of this disease known as hydrophobia.

Other symptoms are saliva from the mouth, severe headache, high fever, alternating periods of excitement and depression, and inability to swallow even fluids due to a choked throat.

The virus destroys the brain and spinal cord. Rabies is 100% fatal.

There should be compulsory immunization of dogs and cat population.

10. Dengue fever

Dengue fever is caused by an RNA-containing Arbovirus (Arthropod-borne virus) of flavivirus group which also causes yellow fever (not found in India).

Thus, the virus which causes dengue fever is a mosquito-borne flavi-ribo virus.

The virus of dengue fever is transmitted by the bite of a female Aedes aegypti (mosquito).

The incubation period is 3-8 days.

Types of Dengue fever

The are two types of it

  1. Classical dengue fever
  2. Dengue hemorrhagic fever

Symptoms of Classical Dengue Fever

  1. Abrupt onset of high fever.
  2. Severe frontal headache.
  3. Pain behind the eyes which worsens with eye movement.
  4. Muscles and joint pain.
  5. Loss of sense of taste and appetite.
  6. Measles like rash over chest and upper limbs.
  7. Nausea and vomiting.

Symptoms of Dengue Haemorrhagic Fever

symptoms are similar to classical dengue fever except the following

  1. Bleeding from the nose, mouth, gums and skin bruising.
  2. Severe and continuous stomach pains.
  3. Frequent vomiting with or without blood.
  4. Pale cold or clammy skin.
  5. Excessive thirst (dry mouth).
  6. Rapid weak pulse.
  7. Difficulty in breathing.
  8. Restlessness and constant crying.
  9. If there is fever consult the doctor at once, take paracetamol tablets on the advice of doctor.
  10. Don’t take Aspirin and Dispirin.
  11. Do cold sponging if fever is high. Give plenty of liquids to the patient.


Rush the patient to the hospital if there is bleeding from any part of the body or if the patient becomes unconscious.

No vaccine for Dengue fever is available.

Eliminate mosquito breeding places by covering small water containers, and water tanks, changing the water of the cooler every week, and where Aedes mosquito breed. Wear clothes which cover arms and legs.

Do not allow children to play in shorts and half-sleeved clothes. Use mosquito repellents, and repellent cream and sleep in a mosquito net.

11. Chikungunya

It is caused by the Chikungunya virus.

This virus was first isolated from human patients and Aedes aegypti mosquitoes from Tanzania in 1952.

The name ‘Chikungunya’ is derived from the native word for the disease in which a patient walks “doubled up” due to severe joint pain.


Its symptoms include sudden onset of fever, crippling joint pain, lymphadenopathy and conjunctivitis.

Some show hemorrhagic manifestations.

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