Rhinovirus

Human rhinovirus A (HRV-A)
Human rhinovirus B (HRV-B)

Rhinovirus (from the Greek rhin-, which means "nose") is a genus of the Picornaviridae family of viruses. Rhinoviruses are the most common viral infective agents in humans, and the causative agent of the common cold. There are over 105 serologic virus types that cause cold symptoms, and rhinoviruses are responsible for approximately 50% of all cases.

Rhinoviruses have single-stranded positive sense RNA genomes of between 7.2 and 8.5kb in length. At the 5′ end of the genome is a virus-encoded protein, and like mammalian mRNA, there is a 3′ poly-A tail. Structural proteins are encoded in the 5′ region of the genome and non structural at the end. This is the same for all picornaviruses. The viral particles themselves are not enveloped and are icosahedral in structure.

Rhinovirus Structure

Rhinoviruses are composed of a capsid, which contains four viral proteins VP1, VP2, VP3 and VP4. Proteins VP1, VP2 and VP3 are organised into 60 repeating protameric icosahedral units. These are thought to be the cause of antigen diversity associated with these viruses.

Transmission and epidemiology

Rhinoviruses have two main modes of transmission: In the past it was obvious that these viruses were transmitted directly from person-to-person via aerosols of respiratory droplets. However, now they can be transmitted indirectly via respiratory droplets that were deposited on the hands and then transported by fingers to the nose or eyes.

Rhinoviruses occur worldwide causing disease especially at schools for example which enhance transmission during fall and winter. They show symptoms such as fever, cough, and nasal congestion. The frequency of colds is high in childhood and decreases during adulthood most probably because of the possession of immunity.

Pathogenesis

Most people are infected with a rhinovirus. The common cold occurs only when the immune system is weakened. The most common reason for this is stress. The primary route of entry for rhinoviruses is the upper respiratory tract. Afterwards, the virus binds to ICAM-1 (intracellular adhesion molecule -1) receptors on respiratory epithelial cells. As the virus replicates and spreads, infected cells release distress signals known as chemokines and cytokines (which in turn activate inflammatory mediators).

Rhinoviruses rarely cause lower respiratory tract disease probably because they grow poorly at 37°C.

Novel antiviral drugs

Interferon-alpha used intranasally was shown to be protective to rhinovirus infections. However, volunteers treated with this drug experienced some side effects, such as nasal bleeding, and resistance was also developing toward the drug. Hence, all research put into this drug was ceased.

Pleconaril, which is a 3c protease inhibitor is a bioavailable antiviral drug which is taken orally for treating infections caused by picornaviruses. This antiviral agent was shown to be safe and effective in experimental models. When tested in volunteers, during the clinical trials, this drug caused a significant decrease in mucus secretions and illness-associated symptoms. It was observed in vitro that pleconaril blocks viral attachment to the host-cell receptors by integrating into the viral capsid cavities, which inhibits viral capsid uncoating. This finally results in the inhibition of viral replication required for effective rhinoviral pathogenesis. Hopefully, this antiviral agent might soon be available for treatment of rhinoviral infections, however, its efficacy in treating these infections is under further evaluation.

Vaccine

There are no vaccines against this virus as there is little-to-no cross-protection between serotypes.

References

Anzueto A., Niederman M. S.; Diagnosis and Treatment of Rhinovirus Respiratory Infections; Chest; 2003; 1664-1672
Rhinovirus: an unstoppable cause of the common cold?
Rhinovirus

Infectious diseases | Picornaviruses