Open Access Open Badges Research

Substitution of the premembrane and envelope protein genes of Modoc virus with the homologous sequences of West Nile virus generates a chimeric virus that replicates in vertebrate but not mosquito cells

Rungrat Saiyasombat1, Jimena Carrillo-Tripp2, Wyatt Allen Miller2, Peter J Bredenbeek3 and Bradley J Blitvich1*

Author Affiliations

1 Department of Veterinary Microbiology and Preventive Medicine, College of Veterinary Medicine, Iowa State University, Ames, Iowa, USA

2 Department of Plant Pathology and Microbiology, College of Agriculture and Life Sciences, Iowa State University, Ames, Iowa, USA

3 Department of Medical Microbiology, Leiden University Medical Center, Leiden, RC, NL-2300, The Netherlands

For all author emails, please log on.

Virology Journal 2014, 11:150  doi:10.1186/1743-422X-11-150

Published: 24 August 2014



Most known flaviviruses, including West Nile virus (WNV), are maintained in natural transmission cycles between hematophagous arthropods and vertebrate hosts. Other flaviviruses such as Modoc virus (MODV) and Culex flavivirus (CxFV) have host ranges restricted to vertebrates and insects, respectively. The genetic elements that modulate the differential host ranges and transmission cycles of these viruses have not been identified.


Fusion polymerase chain reaction (PCR) was used to replace the capsid (C), premembrane (prM) and envelope (E) genes and the prM-E genes of a full-length MODV infectious cDNA clone with the corresponding regions of WNV and CxFV. Fusion products were directly transfected into baby hamster kidney-derived cells that stably express T7 RNA polymerase. At 4 days post-transfection, aliquots of each supernatant were inoculated onto vertebrate (BHK-21 and Vero) and mosquito (C6/36) cells which were then assayed for evidence of viral infection by reverse transcription-PCR, Western blot and plaque assay.


Chimeric virus was recovered in cells transfected with the fusion product containing the prM-E genes of WNV. The virus could infect vertebrate but not mosquito cells. The in vitro replication kinetics and yields of the chimeric virus were similar to MODV but the chimeric virus produced larger plaques. Chimeric virus was not recovered in cells transfected with any of the other fusion products.


Our data indicate that genetic elements outside of the prM-E gene region of MODV condition its vertebrate-specific phenotype.

Modoc virus; West Nile virus; Culex flavivirus; Chimeric flavivirus; Fusion PCR