There is a group of viruses, named Rhinoviruses (rhino referring to ‘nose’ the primarily affected). These viruses are responsible to common cold in human. The common cold is the most infectious disease of human.
Viruses of these group differ form enterovirus is being more acid labile, but more heat stable. They are inactivated below pH 6. They are relatively stable at 20-37 C and may remain viable for days.
On the bases of their type specific antigen, over 100 serotypes has been classified.
These viruses attaches to receptors on nasal ciliated epithelial cells, enters and replicates within them spreading to other cells.
Morphologically and biochemically, rhinoviruses are similar to other members of the family piconaviridae. Rhinoviruses are small RNA viruses.
They can be differentiated from the enteroviruses on the basis of their acid lability (thus their inability to infect the intestinal tract) and their optimal temperature for replication. They are inactivated below pH 5. They are relatively stable in temperature, range from 20 – 37 C and can survive on environmental surfaces such as door knobs for several days. Some rhinoviruses may survive heating at 50 C for 1 hour. They are resistant to 20 % ether and 5 % chloroform but are sensitive to aldehydes and hypochlorites. Rhinoviruses can be preserved at – 70 C.
Half of all common cold are caused by Rhinoviruses. We can say that it is the main cause of common cold in humans. Other viruses which may also caused common cold are coronaviruses etc.
During the acute phase of the illness high concentrations of virus are present in nasal secretions which may contaminate hands, fingers, handkerchiefs or paper tissues, door knobs etc and the normal individuals who touch these, contaminate their fingers which may touch the eye or nasal mucosa leading to cold.
In case of Rhinoviruses, hand contact seems to be the prime mode of transmission. Rhinovirus infections are observed throughout the year, but the incidence of cold in temperate climates increases in the autumn and spring and in the tropics the peak incidence occurs in the rainy season.
Reference: The Text Book Of Microbiology