title: Rift valley Fever virus encephalitis is associated with an ineffective systemic immune response and activated T cell infiltration into the CNS in an immunocompetent mouse model.
abstract: BACKGROUND
  Rift Valley fever virus (RVFV) causes outbreaks of severe disease in livestock and humans throughout Africa and the Arabian Peninsula. In people, RVFV generally causes a self-limiting febrile illness but in a subset of individuals, it progresses to more serious disease. One manifestation is a delayed-onset encephalitis that can be fatal or leave the afflicted with long-term neurologic sequelae. In order to design targeted interventions, the basic pathogenesis of RVFV encephalitis must be better understood.
  
  
  RESULTS
  To characterize the host immune responses and viral kinetics associated with fatal and nonfatal infections, mice were infected with an attenuated RVFV lacking NSs (ΔNSs) that causes lethal disease only when administered intranasally (IN). Following IN infection, C57BL/6 mice developed severe neurologic disease and succumbed 7-9 days post-infection. In contrast, inoculation of ΔNSs virus subcutaneously in the footpad (FP) resulted in a subclinical infection characterized by a robust immune response with rapid antibody production and strong T cell responses. IN-inoculated mice had delayed antibody responses and failed to clear virus from the periphery. Severe neurological signs and obtundation characterized end stage-disease in IN-inoculated mice, and within the CNS, the development of peak virus RNA loads coincided with strong proinflammatory responses and infiltration of activated T cells. Interestingly, depletion of T cells did not significantly alter survival, suggesting that neurologic disease is not a by-product of an aberrant immune response.
  
  
  CONCLUSIONS
  Comparison of fatal (IN-inoculated) and nonfatal (FP-inoculated) ΔNSs RVFV infections in the mouse model highlighted the role of the host immune response in controlling viral replication and therefore determining clinical outcome. There was no evidence to suggest that neurologic disease is immune-mediated in RVFV infection. These results provide important insights for the future design of vaccines and therapeutic options.
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; University of California, Davis, School of Veterinary Medicine, Davis, California, United States of America.
authors.forename: Kimberly A
authors.initials: KA
authors.lastname: Dodd
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; Emory University School of Medicine, Department of Pediatrics, Atlanta, Georgia, United States of America.
authors.forename: Anita K
authors.initials: AK
authors.lastname: McElroy
authors.affiliation: Infectious Disease Pathology Branch, Division of High Consequence Pathogens and Pathology, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America.
authors.forename: Tara L
authors.initials: TL
authors.lastname: Jones
authors.affiliation: Infectious Disease Pathology Branch, Division of High Consequence Pathogens and Pathology, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America.
authors.forename: Sherif R
authors.initials: SR
authors.lastname: Zaki
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: Christina F
authors.initials: CF
authors.lastname: Spiropoulou
mesh_terms: D000349:Africa; D000818:Animals; D001921:Brain / Q000473:pathology*; D004195:Disease Models, Animal; D018792:Encephalitis, Viral / Q000276:immunology / Q000473:pathology*; D005260:Female; D006801:Humans; D008213:Lymphocyte Activation; D008810:Mice, Inbred C57BL; D012295:Rift Valley Fever / Q000276:immunology / Q000473:pathology*; D012296:Rift Valley fever virus / Q000276:immunology* / Q000502:physiology; D013534:Survival; D013601:T-Lymphocytes / Q000276:immunology*; D014779:Virus Replication