Common Cold

The common cold is probably the most common infectious disease in humans. It is self limiting and usually subsides in about a week. They are actually a group of symptoms in the upper respiratory tract caused by huge numbers of viruses. Bacteria- free filtrates of nasal secretions from patients has been shown to transmit colds to human volunteers.

The virus fastens to the inner layer of the nose or throat. This is how cold sets off. The WBC’s are released to fight the virus, but are in vain they are not able to encounter the exact strain. This creates copious mucus and inflammation. Since these activities require lots of energy, the person seems to be exhausted, tired and feels fed up.

 Rhinoviruses seems to be more acid labile, but more heat stable. They are inactivated below pH 6 and completely destroyed at pH 3. They seem to be stable at 20-37^oC and remain viable on fomites for days. Some of them can even survive for one hour at 50^oC.

Apart from humans, rhinoviruses can produce experimental infection only in chimpanzees. They can be grown in tissue cultures of human. Depending on the growth in tissue culture, rhinovirus is classified into three groups; H, M, and O.

H strains grow only on human cells. M strains grow on humans as well as monkey cells. O starins could be grown only in nasal or tracheal ciliated epithelium.

This classification is no longer in use, as the growth characteristics are not stable and changes with adaptation.

The virus attaches to receptors on nasal epithelial cells, enters and replicates within them, spreading to other cells. The cilia and cells are damaged and the epithelium is subjected to secondary bacterial infections.

Local inflammation and the cytokines released may be responsible for the symptoms of common cold. Interferons are produced early and specific antibody appears in nasal secretions.

All these help in the recovery. The antibody response, both nasal and systemic, varies in intensity and duration with different strains.

Laboratory diagnosis is the isolation of the virus may be obtained from nasal or throat swabs collected early in the infection, in human cell cultures. Due to the large number of serotypes, serology is difficult as a method of diagnosis.

The common cold is an infectious disease transmitted by droplets. Hand – to – hand contact, followed by self – inoculation of conjunctival or nasal mucosa appears to be an important mode of transmission.

Itching and running nose with sore throat, sneezing, nasal blockage, watery eyes, and lots of draining mucus are the commonest symptoms.

The incubation period is about 2 days, and may be up to 7 days. Prolonged shedding of virus is usually uncommon. On contrary to the popular belief, there is no direct relation for climate with the common cold.

The multiplicity of the serotypes makes vaccination impossible. Moreover, the common cold is a syndrome produced not only by rhinoviruses, but also by a variety of other groups like corona, coxsackie, echo, adeno, influenza and parainfluenza viruses.

The only hope lies in the development of specific control with the help of antiviral chemotherapy.

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