Common Cold

The common cold is a mild viral infection that affects the upper respiratory tract and is one of the most common viral infections in humans. The main culprits behind the common cold are the rhinoviruses. After the rhinoviruses, the paramyxoviruses and the coronaviruses are contributors. The cold virus can be transmitted in many ways including airborne particles, direct contact, and fomites. Its cycle typically lasts two weeks. There is no cure for the common cold, but there are treatments that boost the immune system, prevent complications, and reduce symptoms.

The common cold is one of the most common human diseases; there are an estimated 1 billion annual cases in the United States.

The molecular structure for the common cold is based on the viruses that cause the infections. Rhinoviruses have small single-stranded ribonucleic acid (RNA) genomes with a 5′ protein and a 3′ poly-A tail like human DNA. They are encased in a capsid that contains four proteins. There are 60 copies each of these proteins within an icosohedral capsid. These proteins are the major components to which human antibodies react. Coronaviruses are large viruses with a single-stranded RNA genome. The name corona, Latin for crown, is derived from the findings of small viral spike peplomers that resemble a crown. These peplomers coat the exterior of the virus and are integral to antibody binding.

[Page 434]Paramyxoviruses, indirect causative agents of the common cold or respiratory tract infections, are also worth mentioning. Paramyxoviruses include RSV (respiratory syncytial virus), bronchiolitis, and pneumonia. They, too, are contained inside a capsid but their structure is quite pleomorphic and they contain many attachment proteins used for fusion with host membranes. They also have an RNA genome inside the capsid. The genome contains the code for the N, M, P, and F proteins. The N protein is a nucleocapsid that encapsulates the genome. The M protein is the matrix protein and is used for assembly of the virion. The P protein is used as a helper protein in other processes. The F protein is the fusion protein and is used in concordance with the attachment proteins for cell binding with host membranes.