Info: Rhinovirus Infections
Rhinoviruses are members of the Picornaviridae family, small (15- to
30-nm) nonenveloped viruses that contain a single-stranded RNA genome
and have been divided into three genetic species: HRV-A, HRV-B, and
HRV-C. In contrast to other members of the picornavirus family, such as
enteroviruses, rhinoviruses are acid-labile and are almost completely
inactivated at pH 3. Rhinoviruses grow
preferentially at 33°–34°C (the temperature of the human nasal passages)
rather than at 37°C (the temperature of the lower respiratory tract).
Of the 102 recognized serotypes of rhinovirus, 91 use intercellular
adhesion molecule 1 (ICAM-1) as a cellular receptor and constitute the
"major" receptor group, 10 use the low-density lipoprotein receptor
(LDLR) and constitute the "minor" receptor group, and 1 uses
Rhinoviruses are a
prominent cause of the common cold and have been detected in up to 50%
of common cold–like illnesses by tissue culture and polymerase chain
reaction (PCR) techniques. Overall rates of rhinovirus infection are
higher among infants and young children and decrease with increasing
Rhinoviruses appear to spread through direct contact with
infected secretions, usually respiratory droplets. In some studies of
volunteers, transmission was most efficient by hand-to-hand contact,
with subsequent self-inoculation of the conjunctival or nasal mucosa.The
incubation period for rhinovirus illness is short, generally 1–2 days.
Rhinoviruses infect cells through
attachment to specific cellular receptors; as mentioned above, most
serotypes attach to ICAM-1, while a few use LDLR. Relatively limited
information is available on the histopathology and pathogenesis of acute
rhinovirus infections in humans. Examination of biopsy specimens
obtained during experimentally induced and naturally occurring illness
indicates that the nasal mucosa is edematous, is often hyperemic,
and—during acute illness—is covered by a mucoid discharge.
The most common clinical manifestations of rhinovirus infections are
those of the common cold. Illness usually begins with rhinorrhea and
sneezing accompanied by nasal congestion. The throat is frequently sore,
and in some cases sore throat is the initial complaint. Systemic signs
and symptoms, such as malaise and headache, are mild or absent, and
fever is unusual.
In children, bronchitis, bronchiolitis, and
bronchopneumonia have been reported; nevertheless, it appears that
rhinoviruses are not major causes of lower respiratory tract disease in
children. Rhinoviruses may cause exacerbations of asthma and chronic
pulmonary disease in adults.
rhinoviruses are the most frequently recognized cause of the common
cold, similar illnesses are caused by a variety of other viruses, and a
specific viral etiologic diagnosis cannot be made on clinical grounds
alone. Rather, rhinovirus infection is diagnosed by isolation of the
virus from nasal washes or nasal secretions in tissue culture.
•Treatment: Rhinovirus Infections
Because rhinovirus infections are generally mild and self-limited,
treatment is not usually necessary. Therapy in the form of
first-generation antihistamines and nonsteroidal anti-inflammatory drugs
may be beneficial in patients with particularly pronounced symptoms,
and an oral decongestant may be added if nasal obstruction is
application of interferon sprays has been effective in the prophylaxis
of rhinovirus infections but is also associated with local irritation of
the nasal mucosa.
Courtesy: Harrison's, Netter's Altas of Anatomy