Abstract
Herpes simplex virus (HSV) usually produces cytopathic effect (CPE) within 24-72 h post-infection (P.I.). Clinical isolates from recurrent HSV infections in patients on Acyclovir therapy were collected between 2016 and 2019 and tested in cell cultures for cytopathic effects and further in-depth characterization. Fourteen such isolates did not show any CPE in A549 or Vero cell lines even at 120 h P.I. However, these cultures remained positive for HSV-DNA after several passages. Sequence analysis revealed that the non-CPE isolates were all HSV-1. Analysis of the thymidine kinase gene from the isolates revealed several previously reported and two novel ACV-resistant mutations. Immunofluorescence and Western blot data revealed a low-level expression of the immediate early protein, ICP4. Late proteins like ICP5 or capsid protein, VP16 were almost undetectable in these isolates. AFM imaging revealed that the non-CPE viruses had structural deformities compared to wild-type HSV-1. Our findings suggest that these strains are manifesting an unusual phenomenon of being non-CPE herpesviruses with low level of virus protein expressions over several passages. Probably these HSV-1 isolates are evolving towards a more “cryptic” form to establish chronic infection in the host thereby unraveling yet another strategy of herpesviruses to evade the host immune system.
Highlights
Herpes simplex virus (HSV) usually produces cytopathic effect (CPE) within 24-72 h post-infection (P.I.)
The filtered materials were inoculated in A549 cell culture
Four of the eighteen isolates namely HM3PP, PB3PP, AKS-A1 and BKN-A1 showed visible cytopathic effect (CPE) which was evident from the classical plaque formation within 48–72 h (Fig. 1a)
Summary
Herpes simplex virus (HSV) usually produces cytopathic effect (CPE) within 24-72 h post-infection (P.I.). Clinical isolates from recurrent HSV infections in patients on Acyclovir therapy were collected between 2016 and 2019 and tested in cell cultures for cytopathic effects and further in-depth characterization. Our findings suggest that these strains are manifesting an unusual phenomenon of being non-CPE herpesviruses with low level of virus protein expressions over several passages. These HSV-1 isolates are evolving towards a more “cryptic” form to establish chronic infection in the host thereby unraveling yet another strategy of herpesviruses to evade the host immune system. Patient Age/Sex 42 M 40 M 32 M 32 F 18 F 30 F 23 M 18 F 24 F 24 M 48 M 33 M 38 M 38 M 42 M 20 F
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