Eastern equine encephalitis virus (EEEV) causes sporadic epidemics of human and equine disease in NorthAmerica, but South American strains have seldom been associated with human neurologic disease or mortality, despite serological evidence of infection. In mice, most North American and South American strains of EEEV produce neurologic disease that resembles that associated with human and equine infections. We identified a South American strain that is unable to replicate efficiently in the brain or cause fatal disease in mice yet produces 10-fold higher viremia than virulent EEEV strains. The avirulent South American strain was also sensitive to human interferon (

Venezuelan equine encephalitis virus (VEEV) is a reemerging pathogen and a continuing threat to humans and equines in the Americas. Identification of the genetic determinants that enable epizootic VEEV strains to arise and exploit equines as amplification hosts to cause widespread human disease is pivotal to understanding VEE emergence. The sensitivity to murine alpha/beta interferon-mediated antiviral activity was previously correlated to the epizootic phenotype of several VEEV strains. Infectious cDNA clones were generated from an epizootic subtype IC VEEV strain (SH3) isolated during the 1992 Venezuelan outbreak and a closely related enzootic, sympatric subtype ID strain (ZPC738). These VEEV strains had low-cell-culture-passage histories and differed by only 12 amino acids in the nonstructural and structural proteins. Rescued viruses showed similar growth kinetics to their parent viruses in several cell lines, and murine infections resulted in comparable viremia and disease. Unlike what was found in other studies of epizootic and enzootic VEEV strains, the sensitivities to murine alpha/beta interferon did not differ appreciably between these epizootic versus enzootic strains, calling into question the reliability of interferon sensitivity as a marker of epizootic potential.

Serological diagnosis of West Nile virus (WNV) infection is complicated by extensive antigenic crossreactivity with other closely related flaviviruses, such as St. Louis encephalitis virus.Here we describe a recombinant, bacterially expressed antigen equivalent to structural domain III of the WNV envelope protein that has allowed clear discrimination of antibody responses to WNV from those against other related flaviviruses in indirect enzyme-linked immunosorbent assays using standardized control antisera and field-collected samples.Since 1999, the United States has experienced annual epidemics of disease in humans and animals caused by West Nile virus (WNV) over an expanding geographical range. To date during 2003, WNV has been isolated in 46 states and the District of Columbia, and more than 8,500 cases of human disease, resulting in 199 deaths, have been reported (1). Outbreaks of WNV disease with neurological manifestations have also been reported in Eastern Europe, North Africa, and Israel since the mid-1990s (reviewed in reference 17). WNV is clearly an emerging and significant public health problem. Research priorities to limit the impact of WNV include the development of more-specific rapid diagnostic assays (5, 18).WNV is a member of the Japanese encephalitis (JE) virus group of the genus Flavivirus, family Flaviviridae; other members include Japanese encephalitis virus (JEV), found throughout Asia, St. Louis encephalitis virus (SLEV), found in the Americas, and Murray Valley encephalitis virus (MVEV), found in Australia and New Guinea. These viruses have a similar ecology and are antigenically related to WNV, and their cocirculation in several regions of the world has complicated the specific diagnosis of infections by these viruses in humans and other vertebrate hosts (10, 15). Cross-reactions in patients ultimately diagnosed with probable dengue virus infections have also been reported in evaluations of WNV testing assays (19).Previously we have reported the identification of WNVspecific neutralizing epitopes within structural domain III of the WNV envelope (E) protein (2). Earlier investigations with other flaviviruses have also reported the presence of virusspecific epitopes within this region of the E protein (e.g., see references 6, 22, and 25), and other authors have suggested the utility of domain III from dengue virus types 1 to 4 or JEV as antigens for specific serological diagnosis of infections with those flaviviruses (10, 24). These observations led us to investigate the utility of a recombinant, bacterially expressed domain III (r-EIII) antigen derived from the envelope protein of a North American WNV strain (385-99) for discrimination of WNV from other JE virus group infections. MATERIALS AND METHODSExpression and purification of recombinant WNV E protein domain III. Regions corresponding to structural domain III of the WNV strain 385-99 E protein were reverse transcription-PCR amplified for cloning and expression either as a glutathione S-transferase (GST) fusion using the pGEX-2T syste...

We characterized Everglades virus infection of cotton rats from South Florida to validate their role as reservoir hosts in the enzootic transmission cycle.

Enzootic strains of Venezuelan equine encephalitis virus (VEEV) circulate in forested habitats of Mexico, Central, and South America, and spiny rats (Proechimys spp.) are believed to be the principal reservoir hosts in several foci. To better understand the host-pathogen interactions and resistance to disease characteristic of many reservoir hosts, we performed experimental infections of F1 progeny from Proechimys chrysaeolus collected at a Colombian enzootic VEEV focus using sympatric and allopatric virus strains. All animals became viremic with a mean peak titer of 3.3 log10 PFU/mL, and all seroconverted with antibody titers from 1:20 to 1:640, which persisted up to 15 months. No signs of disease were observed, including after intracerebral injections. The lack of detectable disease and limited histopathologic lesions in these animals contrast dramatically with the severe disease and histopathologic findings observed in other laboratory rodents and humans, and support their role as reservoir hosts with a long-term coevolutionary relationship to VEEV.