Rhinovirus (from the Greek
rhin- which means "nose") was a genus of the
Picornaviridae family of
virusA virus is an infectious agent too small to be seen directly with a light microscope. They are not made of cells and can only replicate inside the cells of another organism . Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
es.
It has been now merged into Enteroviruses, a group of Picornaviridae that includes
PoliovirusPoliovirus, the causative agent of poliomyelitis, is a human enterovirus and member of the family of Picornaviridae. Poliovirus is composed of a RNA genome and a protein capsid. The genome is single-stranded positive-sense RNA genome that is about 7500 nucleotides long. The viral particle is about...
,
Coxsackie A virusCoxsackie A virus is a cytolytic coxsackie virus of the Picornaviridae family, an enterovirus .-Diseases:...
, and
Hepatitis AHepatitis A is an acute infectious disease of the liver caused by the hepatitis A virus , which is most commonly transmitted by the fecal-oral route via contaminated food or drinking water. Every year, approximately 10 million people worldwide are infected with the virus...
.
Rhinoviri are the most common viral infective agents in humans, and a causative agent of the
common coldAcute viral rhinopharyngitis, or acute coryza, known as an upper respiratory virus, or commonly called a cold, is a contagious, viral infectious disease of the upper respiratory system, primarily caused by rhinoviruses, or coronaviruses...
(about 50% of the cases of the common cold are caused by this virus). It is lytic in nature. There are over a 100 recognized types of rhinoviri that differ based on their varying surface proteins.
Rhinoviri are among the smallest viri, with diameters of about only 30 nanometers (other viri such as
smallpoxSmallpox is an infectious disease unique to humans, caused by either of two virus variants, Variola major and Variola minor. The disease is also known by the Latin names Variola or Variola vera, which is a derivative of the Latin varius, meaning spotted, or varus, meaning "pimple"...
and
vacciniaVaccinia virus is a large, complex, enveloped virus belonging to the poxvirus family. It has a linear, double-stranded DNA genome approximately 190 kbp in length, and which encodes for approximately 250 genes. The dimensions of the virion are roughly 360 × 270 × 250 nm, with a weight of...
viri are 10 times larger at about 300 nanometers).
Rhinoviri have single-stranded positive sense
RNARibonucleic acid is a biologically important type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nitrogenous base, a ribose sugar, and a phosphate...
genomes of between 7.2 and 8.5
kbIn molecular biology, two nucleotides on opposite complementary DNA or RNA strands that are connected via hydrogen bonds are called a base pair . In the canonical Watson-Crick base pairing, adenine forms a base pair with thymine , as does guanine with cytosine in DNA. In RNA, thymine is replaced...
in length. At the 5' end of the
genomeIn modern molecular biology the genome refers to all of its hereditary information encoded in DNA .The genome includes both the genes and the non-coding sequences of the DNA. The term was adapted in 1920 by Hans Winkler, Professor of Botany at the University of Hamburg, Germany...
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 3' end. This is the same for all picornaviri. The viral particles themselves are not
envelopedMany viruses have viral envelopes covering their protein capsids. The envelopes typically are derived from portions of the host cell membranes , but include some viral glycoproteins. Functionally, viral envelopes are used to help viruses enter host cells...
and are icosahedral in structure.
The rhinovirus also grows best in the temperatures between 33–35 °C, and this may be why reproduction occurs in the nose. It is sensitive to acidic environments.
The viral proteins are transcribed as a single, long polypeptide, which is cleaved into the structural and nonstructural viral proteins.
Structure
Rhinoviri are composed of a
capsidA capsid is the protein shell of a virus. It consists of several oligomeric structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may not correspond to individual proteins, are called capsomeres. The capsid encloses the genetic...
, that contains four viral proteins VP1, VP2, VP3 and VP4. VP1, VP2, and VP3 form the major part of the protein capsid. The much smaller VP4 protein has a more extended structure, and lies at interface between the capsid and the RNA genome. There are 60 copies of each of these proteins assembled as an
icosahedronIn geometry, an icosahedron is a regular polyhedron with 20 identical equilateral triangular faces, 30 edges and 12 vertices. It is one of five Platonic solids....
. Antibodies are a major defense against infection with the epitopes lying on the exterior regions of VP1-VP3.
Transmission and epidemiology
There are two modes of transmission: via aerosols of respiratory droplets and from contaminated surfaces, including direct person-to-person contact. A high majority of colds are transmitted by autoinoculation by contact with contaminated surfaces.
Rhinoviri occur worldwide and are the primary cause of
common coldAcute viral rhinopharyngitis, or acute coryza, known as an upper respiratory virus, or commonly called a cold, is a contagious, viral infectious disease of the upper respiratory system, primarily caused by rhinoviruses, or coronaviruses...
s.
SymptomA symptom is a departure from normal function or feeling which is noticed by a patient, indicating the presence of disease or abnormality...
s include
sore throatPharyngitis is an inflammation of the throat or pharynx. In most cases it is painful and the initial infection can extent for a lengthy time period, and is often referred to as a sore throat....
,
runny noseRhinitis , commonly known as a runny nose, is the medical term describing irritation and inflammation of some internal areas of the nose. The primary symptom of rhinitis is nasal dripping. It is caused by chronic or acute inflammation of the mucous membrane of the nose due to viruses, bacteria or...
,
nasal congestionNasal congestion is the blockage of the nasal passages usually due to membranes lining the nose becoming swollen from inflamed blood vessels. It is also known as nasal blockage, nasal obstruction, blocked nose, runny nose, stuffy nose, or stuffed up nose.Nasal congestion has many causes and can...
,
sneezingA sneeze is a semi-autonomous, convulsive expulsion of air from the lungs through the nose and mouth, caused by foreign particles irritating the nasal mucosa. Sneezing can be triggered through sudden exposure to bright light, a particularly full stomach, or viral infection...
and
coughA cough , in medicine, is a sudden and often repetitively occurring defense reflex which helps to clear the large breathing passages from excess secretions, irritants, foreign particles and microbes...
; sometimes accompanied by
muscle achesMyalgia means "muscle pain" and is a symptom of many diseases and disorders. The most common causes are the overuse or over-stretching of a muscle or group of muscles. Myalgia without a traumatic history is often due to viral infections...
, fatigue,
malaiseMalaise is a feeling of general discomfort or uneasiness, an "out of sorts" feeling, often the first indication of an infection or other disease...
,
headacheIn medicine a headache or cephalalgia is a symptom of a number of different conditions of the head. Some of the causes are benign while others are medical emergencies.There are a number of different classification systems for headaches...
,
muscle weaknessMuscle weakness, also known as muscle fatigue, is a direct term for the inability to exert force with one's muscles to the degree that would be expected given the individual's general physical fitness. A test of strength is often used during a diagnosis of a muscular disorder before the etiology...
, or
loss of appetiteAnorexia is the decreased sensation of appetite...
.
FeverFever is a frequent medical sign that describes an increase in internal body temperature to levels above normal...
and extreme exhaustion are more usual in
influenzaInfluenza, commonly referred to as the flu, is an infectious disease caused by RNA viruses of the family Orthomyxoviridae , that affects birds and mammals. The name influenza is Italian and means "influence"...
. Children may have six to twelve colds a year. In the United States, the incidence of colds is higher in the fall and winter, with most infections occurring between September to April. The seasonality may be due to the start of the school year, or due to people spending more time indoors (thus in closer proximity with each other), increasing the chance of transmission of the virus.
Pathogenesis
The primary route of entry for rhinoviri is the upper
respiratory tractIn humans the respiratory tract is the part of the anatomy that has to do with the process of respiration.The respiratory tract is divided into 3 segments:*Upper respiratory tract: nose and nasal passages, paranasal sinuses, and throat or pharynx...
. Afterward, the virus binds to
ICAM-1ICAM-1 also known as CD54 is a human gene.- Function :The protein encoded by this gene is a type of intercellular adhesion molecule continuously present in low concentrations in the membranes of leukocytes and endothelial cells. Upon cytokine stimulation, the concentrations greatly increase...
(Inter-Cellular Adhesion Molecule 1) also known as CD54 (Cluster of Differentiation 54)
receptorIn biochemistry, a receptor is a protein molecule, embedded in either the plasma membrane or cytoplasm of a cell, to which a mobile signaling molecule may attach...
s on respiratory epithelial cells. As the virus replicates and spreads, infected cells release distress signals known as
chemokineChemokines are a family of small cytokines, or proteins secreted by cells. Their name is derived from their ability to induce directed chemotaxis in nearby responsive cells; they are chemotactic cytokines...
s and cytokines (which in turn activate inflammatory mediators).
Infection occurs rapidly, with the virus adhering to surface receptors within 15 minutes of entering the respiratory tract. The
incubation periodIncubation period is the time elapsed between exposure to a pathogenic organism, a chemical or radiation, and when symptoms and signs are first apparent...
is generally 8-10 hours before symptoms begin to occur.
Rhinoviri preferentially grow at 32°C as opposed to 37°C, hence infect the
upper respiratory tractThe upper respiratory tract refers to the following parts of the respiratory system:* nose and paranasal sinuses* oral cavity * throat**pharynx*** genioglossus *** hyoid muscles**larynx**trachea...
.
Novel antiviral drugs
InterferonInterferons are natural cell-signaling proteins produced by the cells of the immune system of most vertebrates in response to challenges such as viruses, parasites and tumor cells. They belong to the large class of glycoproteins known as cytokines and are produced by a wide variety of cells in...
-alpha used intranasally was shown to be effective against rhinovirus infections. However, volunteers treated with this drug experienced some side effects, such as nasal bleeding, and began developing resistance to the drug. Subsequently, research into the treatment was abandoned.
PleconarilPleconaril is an antiviral drug being developed by Schering-Plough for prevention of asthma exacerbations and common cold symptoms in asthmatic subjects exposed to picornavirus respiratory infections...
is an orally bioavailable
antiviralAntiviral may refer to:*Antiviral drug*Antiviral protein*Antivirus software*Antiviral Therapy, an academic journal...
drug being developed for the treatment of infections caused by picornaviruses. This drug acts by binding to a hydrophobic pocket in VP1, and stabilizes the protein capsid to such an extent that the virus cannot release its RNA genome into the target cell. When tested in volunteers, during the clinical trials, this drug caused a significant decrease in
mucusIn vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. It is a viscous colloid containing antiseptic enzymes and immunoglobulins that serves to protect epithelial cells in the respiratory,...
secretions and illness-associated symptoms. Pleconaril is not currently available for treatment of rhinoviral infections, as its efficacy in treating these infections is under further evaluation.
There are potentially other substances such as Iota-Carrageenan that may lead to the creation of drugs to combat the rhinovirus.
Vaccine
There are no vaccines against these viri as there is little-to-no cross-protection between
serotypeFor the term's use in bacteriology, see serovar.A serotype is a group of related microorganisms that all contain a common set of antigens.The immune system is capable of discerning 'self' from 'non-self' cells by their cell-surface proteins. For this reason, transplants between genetically...
s. At least 99 serotypes of rhinoviruses affecting humans have been
sequencedThe term DNA sequencing refers to sequencing methods for determining the order of the nucleotide bases—adenine, guanine, cytosine, and thymine—in a molecule of DNA....
.
However, recent study of the VP4 protein has shown it to be highly conserved amongst many serotypes of Rhinovirus, opening up the potential for a future pan-serotype Rhinovirus vaccine.
External links