Virus and Common Viral Diseases


Virus is a small substance made of nucleic acids and proteins. Viruses cannot live freely in nature. They can exist only inside other cells. They can take over the metabolism of the host cell, produce more viruses and ultimately kill the host cell.


Differences between Virus and Bacteria

Very smallLarge
Visible only under an electron microscopeVisible under a light microscope
Have no metabolismHave metabolism
Do not take in any foodTake in food by absorption
Do not grow and divideGrow and divide to produce more bacteria
Can be crystallizedCannot be crystallized
Command the host cell to produce virusSelf-reproducing
All produce diseases in man, animals or
Some harmless, some useful and some

Also Read Bacteria ~ Useful & Harmful Bacteria

Common Viral Diseases

Poliomyelitis (Polio virus):

Incubation Period7–14 days
Mode of TransmissionExcreta or secretion of the nose; incubates in the intestine, passes to the brain through the blood vessels
SymptomsMuscle paralysis of legs
Common cold, sore throat, fever, fatigue, headache,
vomiting and reddening of the throat
Preventive MeasuresVaccination, polio vaccine

Mumps (Myxovirus parotitis):

Incubation Period12–26 days
Mode of TransmissionContact, contaminated
food or milk and air
Symptoms1. Characteristic painful swelling of salivary glands
2. Pain while opening the
mouth, earache, headache and fever
Preventive Measures1. Avoid sexual contact
2. Vaccination of gamma globulin
3. Complete isolation

Rabies (Rhabdovirus):

Incubation Period30 days or
Mode of TransmissionMad dog bite
(canine disease)
Symptoms1. Hydrophobia
2. Attacks the
central nervous
Preventive MeasuresImmunization of
the dog

AIDS (HIV) ~ Read here

Chicken pox ~ Read here

Hepatitis (Hepatitis A ) ~ Read here

Hepatitis (Hepatitis B ) ~ Read here

Hepatitis (Hepatitis C ) ~ Read here

Hepatitis (Hepatitis D ) ~ Read here

Hepatitis (Hepatitis E ) ~ Read here

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