Enterovirus 68
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Chetan Lokhande, M.B.B.S [2] Vidit Bhargava, M.B.B.S [3]
Overview
Origin and serotypes
Enteroviruses were divided into four subgroups based on the diseases they cause in humans. The Four subgroups were polioviruses, coxsackie A viruses, coxsackie B viruses, and echovirus. However, on further studies it was found and understood that, some coxsackie and echoviruses had overlapping antigenic properties with respect to the diseases they caused in mice. As a result, they were all later described as enteroviruses and numbered sequentially, beginning with enterovirus 68 (EV68). Current classifications systems are based on molecular, antigenic as well as biological properties of these viruses. The enterovirus family is presently subgrouped into 5 categories: Poliovirus, Human enterovirus A (HEV-A), HEV-B, HEV-C and HEV-D.
EV68 first came into picture when it caused pneumonia and bronchiolitis in foru children in california in 1962. Ten times EV68 has been isolated the most recent being 2014. The other isolations were in the years 1970, 1987, 1994, 1997, 2000 and 2003. Antigen typing reagents are not available in all facilities and hence EV68 involvement might be underestimated.
Human rhinovirus 87 was isolated at the same time as EV68. Corn is a prototype of HRV87 and is very unique in its receptor quality. Cross neutralization and partial capsid sequence studie shave revealed that HRV-87 Corn belongs to the same group as EV68.
A study on 1962 isolates of EV68 have shown genome sequences of the 5′-non-translated (NTR) and 3D polymerase coding regions and complete VP1 capsid protein coding region sequence.
Identification of Isolates
Oberste etal used rabbit antisera for typing of isolates. To the isolates, serotype specific rabbit antisera was added. Other method used for sequencing was partial sequencing of VP1 capsid gene, using primer 292 (5'-MIGCIGYIGARACNGG-3') and 222 (5'-CICCIGGIGGIAYRWACAT-3'). The serotype was determined by comparing partial sequence of isolates with a database containing partial sequences of all known enterovirus serotypes as described previously by the same group.
Life cycle
Enterovirus 68 is acid labile and prefers a lower temperature, whereas rhinoviruses are more acid stable and can survive at higher temperatures. In a study to predict the effect of acidity and temperature on viral growth, 5 clinical isolates were tested for acid stability versus EV-68 FERMON strain. It was shown that all strains showed 100-1000 fold reduction in infectivity titres, after incubation for 1 hour in pH 3 buffer. The results were in agreement with a similar study done by Blomqvist et al. Also, in the study each of EV 68 strains also grew to a lower titre at 37 °C than at 33 °C.