Common cold. Numerous viruses are capable of causing the syndrome known as the common cold. Among these are rhinoviruses, coronaviruses, and hundreds of strains of adenoviruses. Most cases are associated with sneezing, nasal discharge, congestion, coughing, and in some cases, middle ear infection. Therapies are directed at lessening the symptoms, and antiviral therapies are generally not available.
Influenza. The influenza virus consists of eight RNA strands, helically wound and enclosed in a capsid. The virus has an envelope with spikes containing hemagglutinin (H) and neuraminidase (N). Variations in the chemical character of the spikes account for the different forms and strains of influenza virus. The viruses are grouped as types A, B, and C and have names such as A(H2N4).
Influenza is accompanied by characteristic respiratory symptoms and muscle aches. Although the disease is rarely fatal, secondary bacterial infections may be a cause of death, and antibiotics may be given as precautionary measures. The drug amantadine has been found to lessen the symptoms of influenza, especially when used early in the infection.
RS virus disease. A serious form of viral pneumonia can be caused by the respiratory syncytial virus. This RNA virus causes cell cultures to fuse and form clusters called syncytia (singular, syncytium). In the human body, the virus causes severe coughing and wheezing, especially in children. Ribavirin may be administered to lessen the severity of disease.