Establishment, steady state and cure of a chronic infection of LLC cells with West Nile virus

Pathogenesis of flavivirus encephalitis

Within the flavivirus family, viruses that cause natural infections of the central nervous system (CNS) principally include members of the Japanese encephalitis virus (JEV) serogroup and the tick-borne encephalitis virus (TBEV) serocomplex. The pathogenesis of diseases involves complex interactions of viruses, which differ in neurovirulence potential, and a number of host factors, which govern susceptibility to infection and the capacity to mount effective antiviral immune responses both in the periphery and within the CNS. This chapter summarizes progress in the field of flavivirus neuropathogenesis. Mosquito-borne and tickborne viruses are considered together. Flavivirus neuropathogenesis involves both neuroinvasiveness (capacity to enter the CNS) and neurovirulence (replication within the CNS), both of which can be manipulated experimentally. Neuronal injury as a result of bystander effects may be a factor during flavivirus neuropathogenesis given that microglial activation and elaboration of inflammatory mediators, including IL-1β and TNF-α, occur in the CNS during these infections and may accompany the production of nitric oxide and peroxynitrite, which can cause neurotoxicity.

Characterization of west nile virus persistent infections in genetically resistant and susceptible mouse cells. II. Generation of temperature-sensitive mutants

Long-term persistent infections were established with the flavivirus, West Nile virus (WNV), strain E101, in embryofibroblast cultures derived from susceptible C3H/HE and congenic-resistant C3H/RV mice. Cultures were initially maintained by weekly subculture at 37 degrees, but at passage 6 sister cultures were shifted to 32 degrees. Virus progeny titers were observed to increase after the shift to 32 degrees indicating the possible presence of temperature-sensitive mutants. Temperature-sensitive mutants were found to arise in cultures of both susceptible and resistant cells. However, only in the resistant cultures did temperature-sensitive virus become the majority population. Temperature-sensitive mutants did not appear to be essential for either initiation or maintenance of WNV-persistant infections. The resistant cells appear to provide an environment which is advantageous for the amplification of temperature-sensitive mutants.

Study on West Nile virus persistence in monkeys

Experiments in M. rhesus showed persistence to be a typical property of West Nile virus. This property was exhibited by strains belonging to different antigenic types, and varying in virulence and in the isolation area (U.S.S.R., Uganda, India). The duration of persistence was at least 5 1/2 months in asymptomatic infection and in convalescence after encephalitis or a febrile disease. The virus isolated within the first 2 weeks after inoculation of monkeys has the standard properties. The virus persisting for 2 months retains its cytopathic and antigenic activity, however, is non-pathogenic for white mice. After 5 1/2 months of persistence the virus has no neurovirulence or cytopathic properties but is capable of infecting the susceptible cells and induces in them the synthesis of virus-specific antigen detectable by immunofluorescence. The persisting virus has been isolated by cocultivation of trypsinized monkey organ cells and cells of the indicator culture. This virus was located mostly in the cerebellum, cerebral subcortical ganglia, lymph nodes, and kidneys. The monkeys experiencing encephalitis, febrile, or asymptomatic infection showed in morphological examinations a subacute inflammatory-degenerative process in the central nervous system. The results suggest that West Nile virus, one of the most widely spread arboviruses in Africa, Asia, and Europe, may be implicated in the etiology of subacute diseases of the CNS.