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Echovirus
View on WikipediaEchovirus is a polyphyletic group of viruses associated with enteric disease in humans. The name is derived from "enteric cytopathic human orphan virus". These viruses were originally not associated with disease, but many have since been identified as disease-causing agents. The term "echovirus" was used in the scientific names of numerous species, but all echoviruses are now recognized as strains of various species, most of which are in the family Picornaviridae.[1]
List of echoviruses
[edit]Thirty-four echoviruses are known:[1]
- Human echoviruses 1–7, 9, 11–21, 24–27, and 29–33 are strains of the species Enterovirus B of the genus Enterovirus.[2]
- Human echovirus 8 was shown to be identical to Human echovirus 1 and was abolished as a species.
- Human echovirus 10 was reclassified as a strain of the species Reovirus type 1, currently named Mammalian orthoreovirus of the genus Orthoreovirus, which belongs to the family Reoviridae. As such, Human echovirus 10 is the only echovirus that does not belong to the family Picornaviridae.
- Human echoviruses 22 and 23 are strains of the species Parechovirus A of the genus Parechovirus.[3]
- Human echovirus 28 was reclassified as the species Human rhinovirus 1A, which was later merged with other rhinovirus strains into the currently named species Rhinovirus A of the genus Enterovirus.
- Human echovirus 34 was abolished as a species and reclassified as a strain of Human coxsackievirus A24, which is now classified as a strain of the species Enterovirus C of the genus Enterovirus.
Symptoms
[edit]When one is infected with echovirus, symptoms are rare but can occur. When symptoms occur, they often include a cough, rash, and influenza-like symptoms. Rare symptoms include viral meningitis, which affects the brain and spinal cord.[4]
Treatment
[edit]Echovirus infection mostly clears up on its own. Doctors may give an immune-system treatment called IVIG, which can help those with weak immune systems. No medicines are known to help against the virus.[4]
References
[edit]- ^ a b Mahy, B. W. J. (26 February 2009). The Dictionary of Virology. Academic Press, 2009. pp. 218–220. ISBN 9780080920368.
- ^ "ICTV Taxonomy history: Enterovirus B". talk.ictvonline.org. International Committee on Taxonomy of Viruses. Retrieved 27 June 2020.
- ^ "ICTV Taxonomy history: Parechovirus A". talk.ictvonline.org. International Committee on Taxonomy of Viruses. Retrieved 27 June 2020.
- ^ a b Jatin M. Vyas (December 2018). "ECHO virus". Medline Plus. Retrieved 10 April 2021.
Echovirus
View on GrokipediaOverview
Definition and characteristics
Echoviruses represent a group of non-polio enteroviruses classified within the species Human enterovirus B of the genus Enterovirus in the family Picornaviridae.[6] They comprise 28 serotypes that were initially isolated from human fecal specimens and identified as distinct from polioviruses and coxsackieviruses.[6] The term "echovirus" originates from "enteric cytopathic human orphan," coined in 1955 to describe these viruses that caused cytopathic effects in cell cultures derived from the enteric tract but were initially not linked to any known disease, hence "orphan."[6] Although subsequent research reclassified many enteroviruses and removed the "orphan" status, the "echo" prefix persists in nomenclature for these serotypes.[6] These viruses exhibit key structural and genomic properties typical of the Picornaviridae family. Echoviruses are non-enveloped particles with icosahedral symmetry, featuring a protein capsid that protects the genome.[7] The virion measures approximately 28-30 nm in diameter, rendering it resistant to environmental stresses such as low pH.[6] Their genome consists of a single-stranded positive-sense RNA molecule, roughly 7,400 nucleotides in length, which enables direct translation upon infection without requiring a reverse transcription step.[7] Echoviruses play an etiological role in a range of human infections, primarily affecting the gastrointestinal and respiratory systems before potentially disseminating to other sites.[8] Unlike polioviruses, which are specialized for causing paralytic poliomyelitis, or coxsackieviruses, often linked to myocarditis and herpangina, echoviruses are more commonly associated with aseptic meningitis and nonspecific febrile illnesses, particularly in children.[6] This distinction underscores their position as non-polio enteroviruses within the broader enterovirus spectrum.[8]Medical importance
Echoviruses, a group of non-polio enteroviruses, are associated with a broad spectrum of clinical illnesses ranging from asymptomatic infections to severe manifestations, including aseptic meningitis as the most common severe form, acute flaccid paralysis, myocarditis, and neonatal sepsis-like illness.[9] These viruses can also cause encephalitis, respiratory infections, hand-foot-and-mouth disease, hepatitis, exanthems, and gastrointestinal symptoms such as vomiting and diarrhea.[9] While most infections resolve without intervention, severe cases can lead to significant neurological damage, cardiac complications, or multi-organ failure.[10] Neonates, infants, young children, and immunocompromised individuals face the highest risk of severe outcomes, with echovirus infections exhibiting higher morbidity and mortality in these groups compared to healthy adults.[9] Overall mortality remains low in the general population, but outbreaks—typically occurring in summer and fall seasons—can strain healthcare resources due to increased cases of hospitalization-requiring illnesses.[10] Transmission primarily occurs via the fecal-oral route or respiratory droplets, facilitating seasonal surges in temperate regions.[11] Globally, non-polio enteroviruses like echoviruses contribute to millions of infections annually, serving as a leading cause of acute febrile illnesses and aseptic meningitis, particularly in children, though underreporting is common due to the prevalence of mild or subclinical cases.[12] In the United States alone, these viruses account for 10 to 15 million infections and tens of thousands of hospitalizations each year.[10] Among echovirus serotypes, echovirus 11 stands out for its association with neonatal outbreaks, often resulting in severe sepsis, hepatitis, and high case fatality rates in preterm infants.[11] This serotype's clinical relevance differentiates it from other enteroviruses by its propensity for vertical transmission and rapid progression in vulnerable newborns.[11]Virology
Viral structure
Echoviruses belong to the Picornaviridae family and feature a non-enveloped, icosahedral capsid approximately 30 nm in diameter, assembled from 60 copies each of four structural proteins: VP1, VP2, VP3, and VP4. These proteins form a pseudo T=3 symmetry shell, with VP1, VP2, and VP3 constituting the external layer while VP4 resides internally, lining the inner surface and interfacing with the packaged RNA genome.[13][14][15] The capsid surface displays distinct morphological features that underpin its function, including a prominent canyon—a deep, narrow depression encircling the fivefold symmetry axes—which serves as the primary site for receptor binding in many enteroviruses. VP1 acts as the major external protein, with its exposed loops and a hydrophobic pocket within the canyon accommodating cellular receptors such as decay-accelerating factor (DAF, also known as CD55) or the neonatal Fc receptor (FcRn), with usage varying by serotype, thereby facilitating host cell attachment.[14][16][15] This canyon architecture also shields receptor-binding residues from neutralizing antibodies, contributing to immune evasion.[14] The lack of an envelope renders echoviruses highly stable in diverse environmental conditions, including acidic environments like the gastrointestinal tract, which supports their resilience during fecal-oral transmission. High-resolution structural analyses, including cryo-electron microscopy (cryo-EM) reconstructions at resolutions up to 2.9 Å for echovirus 30 and X-ray crystallography at 3.1 Å for echovirus 7, have elucidated antigenic sites primarily on the surface loops of VP1, VP2, and VP3, as well as precise receptor-capsid interactions that influence infectivity and serotype specificity.[16][14][15]Genome and replication
The genome of echovirus is a linear, positive-sense single-stranded RNA molecule approximately 7.4 kilobases (kb) in length, featuring a 5' untranslated region (UTR) of about 740 nucleotides, a 3' UTR of around 100 nucleotides, and a single open reading frame (ORF) that encodes a polyprotein of roughly 2,194 amino acids.[17] This polyprotein is post-translationally cleaved into 11 functional proteins: four structural capsid proteins (VP1–VP4) derived from the P1 region, and seven non-structural proteins from the P2 (2A–2C) and P3 (3A–3D) regions.[18] The 5' end is covalently linked to a viral protein (VPg, or 3B), and the 3' end terminates in a poly(A) tail, structures that facilitate genome stability, translation initiation via an internal ribosome entry site (IRES) in the 5' UTR, and replication.[18] The replication cycle of echovirus begins with viral attachment to host cell receptors, such as decay-accelerating factor (DAF) or integrins, mediated by the canyon-like depression on the capsid surface.[18] Following receptor binding, the virus undergoes receptor-mediated endocytosis and uncoating, releasing the genomic RNA into the cytoplasm.[18] Host ribosomes then translate the positive-sense RNA directly into the polyprotein using the IRES, bypassing the need for a 5' cap.[18] This polyprotein is rapidly processed by viral proteases: the 2A protease (2Apro) performs initial cleavages, including at the P1–P2 junction, while the 3C protease (3Cpro) executes most subsequent cleavages to generate mature proteins.[18] Notably, 2Apro also cleaves eukaryotic initiation factor 4G (eIF4G), disrupting host cap-dependent translation and favoring viral protein synthesis.[19] Viral RNA replication occurs in cytoplasmic membrane-bound compartments, such as double-membrane vesicles induced by non-structural proteins 2BC and 3A.[18] The RNA-dependent RNA polymerase 3Dpol initiates replication by uridylylating VPg using a cis-acting replication element (cre) in the genome, forming a VPg-pUpU primer for synthesizing a complementary negative-sense RNA strand.[18] This negative strand serves as a template for producing multiple positive-sense progeny RNAs, which are either translated into new polyproteins, replicated further, or packaged into virions by structural proteins.[18] Assembly of new capsids occurs in the cytoplasm, with mature virions released primarily through host cell lysis.[18] Echovirus replication is characterized by a high mutation rate, approximately 10−4 to 10−5 substitutions per nucleotide per replication cycle, driven by the error-prone nature of 3Dpol lacking proofreading activity.[18] This leads to the formation of heterogeneous viral quasispecies populations within infected hosts, enabling rapid adaptation, antigenic drift, and evasion of immune responses.[18]Classification
Serotypes and nomenclature
Echoviruses are classified into distinct serotypes primarily based on antigenic differences, as determined by serum neutralization assays that measure the ability of specific antibodies to inhibit viral infectivity.[20] Originally identified in the 1950s and 1960s, 34 serotypes (designated E1 through E34) were established under the term "enteric cytopathic human orphan" viruses, reflecting their isolation from the gastrointestinal tract without known disease associations at the time.[20] Over time, this nomenclature evolved with advancements in virology; several serotypes were reclassified due to genetic and antigenic reevaluations, such as E22 and E23, which are now recognized as parechoviruses rather than enteroviruses.[20] Today, 28 serotypes remain classified within the Enterovirus B species, with the standard abbreviation "E" followed by the number (e.g., E6, E11).[21] While serotyping relies on antigenic properties, modern classification also incorporates genetic criteria, such as greater than 25% nucleotide sequence divergence in the VP1 gene between types.[20] This dual approach—antigenic and genotypic—facilitates precise identification amid the group's diversity, though neutralization remains the cornerstone for traditional typing. The integration of echoviruses into the Enterovirus B species underscores their shared genomic and structural features with other non-polio enteroviruses.[20] Certain serotypes are notably associated with specific clinical manifestations, guiding diagnostic and surveillance efforts. For instance, E11 and E30 are among the most frequently linked to aseptic meningitis, while E6 and E9 often correlate with exanthematous rashes alongside neurological symptoms.[22] [23]| Serotype | Primary Disease Associations |
|---|---|
| E6 | Aseptic meningitis, rashes |
| E9 | Aseptic meningitis, rashes |
| E11 | Aseptic meningitis |
| E30 | Aseptic meningitis |
