title: Deletion of the NSm virulence gene of Rift Valley fever virus inhibits virus replication in and dissemination from the midgut of Aedes aegypti mosquitoes.
abstract: BACKGROUND
  Previously, we investigated the role of the Rift Valley fever virus (RVFV) virulence genes NSs and NSm in mosquitoes and demonstrated that deletion of NSm significantly reduced the infection, dissemination, and transmission rates of RVFV in Aedes aegypti mosquitoes. The specific aim of this study was to further characterize midgut infection and escape barriers of RVFV in Ae. aegypti infected with reverse genetics-generated wild type RVFV (rRVF-wt) or RVFV lacking the NSm virulence gene (rRVF-ΔNSm) by examining sagittal sections of infected mosquitoes for viral antigen at various time points post-infection.
  
  
  RESULTS
  Ae. aegypti mosquitoes were fed an infectious blood meal containing either rRVF-wt or rRVF-ΔNSm. On days 0, 1, 2, 3, 4, 6, 8, 10, 12, and 14 post-infection, mosquitoes from each experimental group were fixed in 4% paraformaldehyde, paraffin-embedded, sectioned, and examined for RVFV antigen by immunofluorescence assay. Remaining mosquitoes at day 14 were assayed for infection, dissemination, and transmission. Disseminated infections were observed in mosquitoes as early as three days post infection for both virus strains. However, infection rates for rRVF-ΔNSm were statistically significantly less than for rRVF-wt. Posterior midgut infections in mosquitoes infected with rRVF-wt were extensive, whereas midgut infections of mosquitoes infected with rRVF-ΔNSm were confined to one or a few small foci.
  
  
  CONCLUSIONS
  Deletion of NSm resulted in the reduced ability of RVFV to enter, replicate, and disseminate from the midgut epithelial cells. NSm appears to have a functional role in the vector competence of mosquitoes for RVFV at the level of the midgut barrier.
authors.affiliation: Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado, United States of America.
authors.forename: Rebekah C
authors.initials: RC
authors.lastname: Kading
authors.affiliation: Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado, United States of America.
authors.forename: Mary B
authors.initials: MB
authors.lastname: Crabtree
authors.affiliation: Viral Special Pathogens Branch, Division of High-Consequence Pathogens and Pathology, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America.
authors.forename: Brian H
authors.initials: BH
authors.lastname: Bird
authors.affiliation: Viral Special Pathogens Branch, Division of High-Consequence Pathogens and Pathology, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America.
authors.forename: Stuart T
authors.initials: ST
authors.lastname: Nichol
authors.affiliation: Viral Special Pathogens Branch, Division of High-Consequence Pathogens and Pathology, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America.
authors.forename: Bobbie Rae
authors.initials: BR
authors.lastname: Erickson
authors.affiliation: Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado, United States of America.
authors.forename: Kalanthe
authors.initials: K
authors.lastname: Horiuchi
authors.affiliation: Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado, United States of America.
authors.forename: Brad J
authors.initials: BJ
authors.lastname: Biggerstaff
authors.affiliation: Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado, United States of America.
authors.forename: Barry R
authors.initials: BR
authors.lastname: Miller
mesh_terms: D000330:Aedes / Q000821:virology*; D000818:Animals; D005260:Female; D041981:Gastrointestinal Tract / Q000821:virology*; D017353:Gene Deletion; D054884:Host-Pathogen Interactions / Q000235:genetics; D012296:Rift Valley fever virus / Q000235:genetics* / Q000472:pathogenicity*; D014779:Virus Replication / Q000235:genetics*