Echovirus

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

An echovirus is a type of RNA virus that belongs to the genus Enterovirus of the Picornaviridae family.[1] Echoviruses are found in the gastrointestinal tract (hence it being part of the enterovirus genus) and exposure to the virus causes other opportunistic infections and diseases.

Historical Perspective

The first isolation of echoviruses occurred from the feces of asymptomatic children early in the 1950s, just after cell culturing had been developed. The echo– part of the name was originally an acronym for "enteric cytopathic human orphan" virus: Orphan virus means a virus that is not associated with any known disease. Even though Echoviruses have since been identified with various diseases, the original name is still used.[2]

Microbiology

Viral Structure

An echovirus measures 24-30 nanometres (nm), and is similar to other viruses, since it has a naked protein capsid, which makes up 75% of the virus particle that encloses a dense central core of single-stranded RNA. This RNA has a length of approximately 7.5 kilobase (kb), contains an RNA replicase, viral-coded proteins, and a single polyprotein that is responsible for the formation of structural proteins and other proteins necessary for cellular replication. The structural proteins determine host range and play a very important role in delivering the RNA genome into the cytoplasm of new host cells.

Replication

Some viral replication of an echovirus occurs in the nasopharynx after infection and then spreads to regional lymph nodes. However, most viral particles are swallowed and they reach the lower gut tract, where the virus is presumed to bind to specific receptors. The virus then spreads to the lower intestinal tract, replicating but not causing any major cellular effects along the way. Next, the virus spreads to many secondary sites in the body such as the central nervous system, liver, spleen, bone marrow, heart and finally the lungs. Additional replication of the virus will occur, causing symptoms 4 to 6 days after infection. The most deadly part however is delayed when symptoms of a central nervous system disease start to appear. Enteroviruses are capable of infecting any cell in the body. These viruses are highly infectious. They can spread through the air to other hosts 1-3 weeks after infection and can spread through feces to other hosts eight weeks after infection.

Manifestation

Echovirus is a highly infectious, and its primary target is children. The echovirus is among the leading causes of acute febrile illness in infants and young children, and is the most common cause of aseptic meningitis. Infection of an infant with this virus following birth may cause severe systemic diseases, and is associated with high infant mortality rates. The echovirus can mimic symptoms caused by other common bacterial and viral infections, so echovirus infections are often treated with therapies aimed for other infections. This can lead to the evolution of antibiotic-resistant bacteria.

Causes of Infection

Causes of echovirus infections can be placed in several categories. Main causes of infection are from overcrowded conditions such as the poor districts of a city and poor hygiene. Echoviruses are transmitted person-to-person; the fecal-oral route is the predominant mode, although transmission sometimes occurs via respiration of oral secretions such as saliva. Indirect transmission occurs through numerous routes, including via contaminated water, food, and fomites (inanimate objects). Contaminated swimming and wading pools can also transmit the virus. Also, there are well-documented reports of transmission via the contaminated hands of hospital personnel.

Diagnosis

Symptoms

Echovirus disease occurs disproportionately in males. Infection within the first two weeks of birth can cause devastating and potentially fatal disease. In this population, death usually results from overwhelming liver failure or myocarditis, rather than infection of the central nervous system. Older children and adults have a better prognosis. Myocarditis is the most frequent complication in adults.

Echovirus infections can occur in people of all age groups. However, with increasing age, there is increased production of specific antibodies to the echovirus. Several studies performed during epidemics show that infants become infected at notably higher rates than older children and adults.

Treatment

No specific treatment for echovirus infection is currently available. Care is directed at relief of symptoms. The anti-viral drug pleconaril interferes with the binding of the echovirus particle to the cell membrane and the drug also hinders the uncoating of virions by attaching itself to the viral protein capsid. The pharmaceutical company, ViroPharma Incorporated, ended development of pleconaril in 2004.

References

  1. Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed. ed.). McGraw Hill. pp. 537–9. ISBN 0838585299.
  2. Yin-Murphy M, Almond JW (1996). Picornavirues. in: Baron's Medical Microbiology (Baron S et al, eds.) (4th ed. ed.). Univ of Texas Medical Branch. ISBN 0-9631172-1-1.

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