Peter McMinn

Enterovirus 71 (EV71) causes epidemics of hand, foot, and mouth disease associated with neurological complications in young children. We report an ou

An infectious cDNA clone of Murray Valley encephalitis virus prototype strain 1-51 (MVE-1-51) was constructed by stably inserting genome-length cDNA into the low-copy-number plasmid vector pMC18. Designated pMVE-1-51, the clone consisted of genome-length cDNA of MVE-1-51 under the control of a T7 RNA polymerase promoter. The clone was constructed by using existing components of a cDNA library, in addition to cDNA of the 3′ terminus derived by RT–PCR of poly(A)-tailed viral RNA. Upon comparison with other flavivirus sequences, the previously undetermined sequence of the 3′ UTR was found to contain elements conserved throughout the genus Flavivirus. RNA transcribed from pMVE-1-51 and subsequently transfected into BHK-21 cells generated infectious virus. The plaque morphology, replication kinetics and antigenic profile of clone-derived virus (CDV-1-51) was similar to the parental virus in vitro. Furthermore, the virulence properties of CDV-1-51 and MVE-1-51 (LD₅₀ values and mortality profiles) were found to be identical in vivo in the mouse model. Through site-directed mutagenesis, the infectious clone should serve as a valuable tool for investigating the molecular determinants of virulence in MVE virus.

A study of immunopathology in the central nervous system (CNS) during infection with a virulent strain of Murray Valley encephalitis virus (MVE) in weanling Swiss mice following peripheral inoculation is presented. It has previously been shown that virus enters the murine CNS 4 days after peripheral inoculation, spreads to the anterior olfactory nucleus, the pyriform cortex, and the hippocampal formation at 5 days postinfection (p.i.), and then spreads throughout the cerebral cortex, caudate putamen, thalamus, and brain stem between 6 and 9 days p.i. (P. C. McMinn, L. Dalgarno, and R. C. Weir, Virology 220:414–423, 1996). Here we show that the encephalitis which develops in MVE-infected mice from 5 days p.i. is associated with the development of a neutrophil inflammatory response in perivascular regions and in the CNS parenchyma. Infiltration of neutrophils into the CNS was preceded by increased expression of tumor necrosis factor alpha and the neutrophil-attracting chemokine N51/KC within the CNS. Depletion of neutrophils with a cytotoxic monoclonal antibody (RB6-8C5) resulted in prolonged survival and decreased mortality in MVE-infected mice. In addition, neutrophil infiltration and disease onset correlated with expression of the enzyme-inducible nitric oxide synthase (iNOS) within the CNS. Inhibition of iNOS by aminoguanidine resulted in prolonged survival and decreased mortality in MVE-infected mice. This study provides strong support for the hypothesis that Murray Valley encephalitis is primarily an immunopathological disease.

Peter McMinn, Angela Carrello, Catherine Cole, David Baker, Alan Hampson; Antigenic Drift of Influenza A (H3N2) Virus in a Persistently Infected Immunocompromi