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Neuroattenuated bunyavirus variant: derivation, characterization, and revertant clones
M J Endres1, A Valsamakis, F Gonzalez-Scarano
1Department of Microbiology, University of Pennsylvania Medical Center, Philadelphia 19104-6076.
Journal of Virology
|May 1, 1990
Summary
A new neuroattenuated bunyavirus variant, RFC/25B.5 (B.5), shows significantly reduced virulence in mice. This attenuated virus is a valuable tool for studying bunyavirus neurovirulence genetics.
Area of Science:
- Virology
- Neuroscience
- Genetics
Background:
- Bunyaviruses, particularly California serogroup viruses, can cause neuroinvasive disease.
- Understanding the genetic basis of bunyavirus neurovirulence is crucial for developing effective countermeasures.
Purpose of the Study:
- To develop and characterize a neuroattenuated Bunyavirus variant for genetic studies.
- To investigate the relationship between temperature sensitivity, neurovirulence, and neuroinvasiveness.
Main Methods:
- Serial passage of a California serogroup virus reassortant clone (RFC virus) in BHK-21 cells to generate a neuroattenuated variant (RFC/25B.5 or B.5).
- Virulence and neuroinvasiveness assessment in adult and neonatal mice via intracerebral and subcutaneous inoculation, respectively.
- In vitro replication studies using BHK-21 cells and a murine neuroblastoma cell line (NA cells).
- Temperature sensitivity (ts) analysis and selection of ts revertants at 38.9 degrees C.
Main Results:
- Clone B.5 demonstrated over 40,000-fold reduced virulence compared to the parent RFC virus after intracerebral inoculation in adult mice.
- Clone B.5 exhibited reduced neuroinvasiveness in neonatal mice but retained replication and lethal potential in suckling mice after intracerebral injection.
- Clone B.5 showed significantly lower replication titers in NA cells compared to neurovirulent California serogroup viruses, suggesting NA cells as an in vitro surrogate for adult mouse brain.
- Clone B.5 was temperature-sensitive (ts), with restricted replication at 38.9 degrees C. Ten ts revertants regained neurovirulence and the ability to kill adult mice.
Conclusions:
- RFC/25B.5 (B.5) is the first described California serogroup virus variant truly attenuated after intracerebral inoculation.
- The characterized attenuated bunyavirus variant (B.5) provides a valuable model for genetic analysis of bunyavirus neurovirulence.
- Temperature sensitivity is linked to the loss of neurovirulence and neuroinvasiveness in this bunyavirus model.