Pathophysiology, rhinovirus

Pathophysiology

Several viruses can cause viral pharyngitis.

Rhinovirus

More than 100 different serotypes of rhinovirus cause approximately 20% of cases of pharyngitis and 30-50% of common colds. These viruses enter the body through the ciliated epithelium that lines the nose, causing edema and hyperemia of the nasal mucous membranes. This condition leads to increased secretory activity of the mucous glands; swelling of the mucous membranes of the nasal cavity, eustachian tubes, and pharynx; and narrowing of nasal passages, causing obstructive symptoms. Bradykinin and lysyl-bradykinin are generated in the nasal passages of patients with rhinovirus colds, and these mediators stimulate pain nerve endings. The virus does not invade the pharyngeal mucosa. Transmission occurs by large particle aerosols or fomites.

Adenovirus

In children, adenovirus causes uncomplicated pharyngitis (most commonly caused by adenovirus types 1-3 and 5) or pharyngoconjunctival fever. The latter is characterized by fever, sore throat, and conjunctivitis. Unlike rhinovirus infections, adenovirus directly invades the pharyngeal mucosa, as shown by the viral cytopathic effect.

Epstein-Barr virus

Epstein-Barr virus (EBV) is the causal agent of infectious mononucleosis. EBV usually spreads from adults to infants. Among young adults, EBV spreads through saliva and, rarely, through blood transfusion. In addition to edema and hyperemia of the tonsils and pharyngeal mucosa, an inflammatory exudate and nasopharyngeal lymphoid hyperplasia also develop. Pharyngitis or tonsillitis is present in about 82% of patients with infectious mononucleosis.

Herpes simplex virus

Herpes simplex virus (HSV) types 1 and 2 cause gingivitis, stomatitis, and pharyngitis. Acute herpetic pharyngitis is the most common manifestation of the first episode of HSV-1 infection. After HSV enters the mucosal surface, it initiates replication and infects either sensory or autonomic nerve endings. The neurocapsid of the virus is intra-axonally transported to the nerve cell bodies in the ganglia and contiguous nerve tissue. The virus then spreads to other mucosal surfaces through centrifugal migration of infectious virions via peripheral autonomic or sensory nerves. This mode of spread explains the high frequency of new lesions distant from the initial crop of vesicles characteristic of oral-labial HSV infection.

Influenza virus

Pharyngitis and sore throat develop in about 50% of the patients with influenza A and in a lesser proportion of patients with influenza B. Severe pharyngitis is particularly common in patients with type A. The influenza virus invades the respiratory epithelium, causing necrosis, which predisposes the patient to secondary bacterial infection. Transmission of influenza occurs by aerosolized droplets.

Parainfluenza virus

Pharyngitis caused by parainfluenza virus types 1-4 usually manifests as the common cold syndrome. Parainfluenza virus type 1 infection occurs in epidemics, mainly in late fall or winter, while parainfluenza virus type 2 infection occurs sporadically. Parainfluenza virus type 3 infection occurs either epidemically or sporadically.

Coronavirus

Pharyngitis caused by coronavirus usually manifests as the common cold. As in rhinovirus colds, viral mucosal invasion of the respiratory tract does not occur.

Enterovirus

The major groups of enteroviruses that can cause pharyngitis are coxsackievirus and echovirus. Although enteroviruses are primarily transmitted by the fecal-oral route, airborne transmission is important for certain serotypes. Enteroviral lesions in the oropharyngeal mucosa are usually a result of secondary infection of endothelial cells of small mucosal vessels, which occurs during viremia following enteroviral infection in the GI tract.

Respiratory syncytial virus

Transmission of respiratory syncytial virus (RSV) occurs by fomites or large-particle aerosols produced by coughing or sneezing. The pathogenesis of RSV infection remains unclear, although a number of theories exist. Immunologic mechanisms may contribute to the pathogenesis of the severe disease in infants and elderly patients.

Cytomegalovirus

Acute acquired cytomegalovirus (CMV) infection is transmitted by sexual contact, in breast milk, via respiratory droplets among nursery or day care attendants, and by blood transfusion. Infection in the immunocompetent host rarely results in clinically apparent disease. Infrequently, immunocompetent hosts exhibit a mononucleosislike syndrome with mild pharyngitis.

Human immunodeficiency virus

Pharyngitis develops in patients infected with human immunodeficiency virus (HIV) as part of the acute retroviral syndrome, a mononucleosislike syndrome that is the initial manifestation of HIV infection in one half to two thirds of recently infected individuals.

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