Clinical Importance of Rhinovirus to Human Health
Rhinoviruses are isolated commonly from the nose and throat but very rarely from feces. These virus as well as Corona viruses and some reo-, adeno-, entero-, para-influenza, and influenza viruses, cause upper respiratory tract infections, including the “common cold”.
Animal susceptibility and Growth of VirusThese viruses are infectious only for humans and Chimpanzees. They have been grown in cultures of human embryonic ling fibroblasts (W1-W38) and in organ cultures of ferret and human tracheal epithelium. They are grown best at 33 degrees Celsius in rolled cultures.
Antigenic propertiesOver 100 serotypes are known, some cross-react (e.g types 9 and 32).
Pathogenesis and PathologyThe virus enters via the upper respiratory tract. High titers of virus in nasal secretions-which can be found as early as 2-4 days after exposure-are associated with maximal illness. Thereafter, viral titers fall, although illness persists. Histopathologic changes are limited to the submucosa and surface epithelium. These include engorgement of blood vessels, edema, mild cellular infiltration, and desquamation of surface epithelium, which is complete by the third day, Nasal secretion increase susceptibility to the virus. Chilliness is an early symptom of the common cold.
Clinical findingsThe incubation period is brief, from 2 to 4 days, and the acute illness usually lasts for 7 days although a non-productive cough may persist for 2-3 weeks. The average adult has 1-2 attacks each year. Usual symptoms in adults include irritation in the upper respiratory tract, nasal discharge, headache, mild cough, malaise, and a chilly sensation. There is little of no fever. The nasal and nasopharyngeal mucosa becomes red and swollen, and the sense of smell becomes less keen. Mild hoarseness may be present. Prominent cervical adenopathy does not occur. Secondary bacterial infection may produce acute otitis media, sinusitis, bronchitis, or pneumonitis, especially in children. Type- specific antibodies appear or rise with each infection.
EpidemiologyThe disease occurs throughout the world. In the temperate zones, the attack rates are highest in early fall and winter, declining in the late spring. Members of isolated communities form highly susceptible groups. The virus is believed to be transmitted through close contact by large droplets. Under some circumstances, transmission of the virus by self-inoculation through hand contamination may be a more important mode of spread than that by airborne particles. Colds in children spread more easily to others than do colds in adults. Adults in households with a child in school have twice as many colds as adults in households without school children. In a single community, many rhinovirus serotypes cause outbreaks of diseases in a single season, and different serotypes predominate during different respiratory disease seasons.
Treatment and controlNo specific treatment is available. The development of a potent rhinovirus vaccine is unlikely because of the difficulty in growing rhinovirus to high titer in culture, the fleeting immunity and the many serotypes causing colds. In addition, many rhinovirus serotypes are present during single respiratory disease outbreaks and may recur only rarely in the same area. Injection of purified vaccines has shown that the high levels of serum antibody are frequently not associated with similar elevation of local secretory antibody, which may be the most significant factor in disease prevention.