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Venezuelan equine encephalitis virus (VEEV) is an important, naturally emerging zoonotic virus. VEEV was a significant human and equine pathogen for much of the past century, and recent outbreaks in Venezuela and Colombia (1995), with about 100,000 human cases, indicate that this virus still poses a serious public health threat. The live attenuated TC-83 vaccine strain of VEEV was developed in the 1960s using a traditional approach of serial passaging in tissue culture of the virulent Trinidad donkey (TrD) strain. This vaccine presents several problems, including adverse, sometimes severe reactions in many human vaccinees. The TC-83 strain also retains residual murine virulence and is lethal for suckling mice after intracerebral (i.c.) or subcutaneous (s.c.) inoculation. To overcome these negative effects, we developed a recombinant, chimeric Sindbis/VEE virus (SIN-83) that is more highly attenuated. The genome of this virus encoded the replicative enzymes and the cis-acting RNA elements derived from Sindbis virus (SINV), one of the least humanpathogenic alphaviruses. The structural proteins were derived from VEEV TC-83. The SIN-83 virus, which contained an additional adaptive mutation in the nsP2 gene, replicated efficiently in common cell lines and did not cause detectable disease in adult or suckling mice after either i.c. or s.c. inoculation. However, SIN-83-vaccinated mice were efficiently protected against challenge with pathogenic strains of VEEV. Our findings suggest that the use of the SINV genome as a vector for expression of structural proteins derived from more pathogenic, encephalitic alphaviruses is a promising strategy for alphavirus vaccine development.Venezuelan equine encephalitis virus (VEEV) is a member of the Alphavirus genus in the Togaviridae family. VEEV is an enveloped virus with a nonsegmented, positive-sense RNA genome of approximately 11.5 kb. The 5Ј two-thirds of the genome encodes four nonstructural proteins (nsP1 to nsP4) that form an enzyme complex required for viral replication (45). After viral RNA entry into the cytoplasm, a nonstructural polyprotein is translated directly from the viral genome and utilized in the production of a full-length, negative-sense replicative RNA intermediate. This RNA is then used as a template for synthesis of positive-sense genomic RNA and for transcription of a subgenomic 26S RNA. The ca. 4-kb subgenomic RNA corresponds to the 3Ј one-third of the viral genome and is translated into a structural polyprotein that is proteolytically cleaved into the capsid and envelope glycoproteins E2 and E1 (39). Two hundred forty copies of the capsid protein combine with the genomic viral RNA to form an icosahedral nucleocapsid. Finally, the nucleocapsid buds from the plasma membrane to acquire a lipid envelope with embedded protein spikes containing E1-E2 heterodimers (42,45).VEEV was a significant human and equine pathogen for much of the past century, and recent epidemics (40, 50) indicate that VEEV still represents a serious public health threat. Furthermore, ...

RNA viruses are notorious for their genetic plasticity and propensity to exploit new host-range opportunities, which can lead to the emergence of human disease epidemics such as severe acute respiratory syndrome, AIDS, dengue, and influenza. However, the mechanisms of host-range change involved in most of these viral emergences, particularly the genetic mechanisms of adaptation to new hosts, remain poorly understood. We studied the emergence of Venezuelan equine encephalitis virus (VEEV), an alphavirus pathogen of people and equines that has had severe health and economic effects in the Americas since the early 20th century. Between epidemics, VEE disappears for periods up to decades, and the viral source of outbreaks has remained enigmatic. Combined with phylogenetic analyses to predict mutations associated with a 1992-1993 epidemic, we used reverse genetic studies to identify an envelope glycoprotein gene mutation that mediated emergence. This mutation allowed an enzootic, equine-avirulent VEEV strain, which circulates among rodents in nearby forests to adapt for equine amplification. RNA viruses including alphaviruses exhibit high mutation frequencies. Therefore, ecological and epidemiological factors probably constrain the frequency of VEE epidemics more than the generation, via mutation, of amplification-competent (high equine viremia) virus strains. These results underscore the ability of RNA viruses to alter their host range, virulence, and epidemic potential via minor genetic changes. VEE also demonstrates the unpredictable risks to human health of anthropogenic changes such as the introduction of equines and humans into habitats that harbor zoonotic RNA viruses.alphavirus ͉ arbovirus ͉ equine ͉ evolution

Venezuelan equine encephalitis virus (VEEV) is an important, naturally emerging zoonotic pathogen. Recent outbreaks in Venezuela and Colombia in 1995, involving an estimated 100,000 human cases, indicate that VEEV still poses a serious public health threat. To develop a safe, efficient vaccine that protects against disease resulting from VEEV infection, we generated chimeric Sindbis (SIN) viruses expressing structural proteins of different strains of VEEV and analyzed their replication in vitro and in vivo, as well as the characteristics of the induced immune responses. None of the chimeric SIN/VEE viruses caused any detectable disease in adult mice after either intracerebral (i.c.) or subcutaneous (s.c.) inoculation, and all chimeras were more attenuated than the vaccine strain, VEEV TC83, in 6-day-old mice after i.c. infection. All vaccinated mice were protected against lethal encephalitis following i.c., s.c., or intranasal (i.n.) challenge with the virulent VEEV ZPC738 strain (ZPC738). In spite of the absence of clinical encephalitis in vaccinated mice challenged with ZPC738 via i.n. or i.c. route, we regularly detected high levels of infectious challenge virus in the central nervous system (CNS). However, infectious virus was undetectable in the brains of all immunized animals at 28 days after challenge. Hamsters vaccinated with chimeric SIN/VEE viruses were also protected against s.c. challenge with ZPC738. Taken together, our findings suggest that these chimeric SIN/VEE viruses are safe and efficacious in adult mice and hamsters and are potentially useful as VEEV vaccines. In addition, immunized animals provide a useful model for studying the mechanisms of the anti-VEEV neuroinflammatory response, leading to the reduction of viral titers in the CNS and survival of animals.Venezuelan equine encephalitis virus (VEEV) is an enveloped virus with a nonsegmented, positive-sense RNA genome of approximately 11.4 kb and belongs to the Alphavirus genus in the Togaviridae family. The 5Ј two-thirds of the genome contains four nonstructural proteins (nsP1 to nsP4) that form an enzyme complex required for viral replication (46-48). After release of the viral genome into the cytoplasm, a nonstructural polyprotein is translated directly from this RNA and utilized in the production of a full-length, negative-sense replicative RNA intermediate (45). The full-length RNA then serves as a template for the synthesis of positive-sense genomic RNA and for transcription of a subgenomic 26S RNA (46). The approximately 4-kb-long, subgenomic RNA corresponds to the 3Ј onethird of the viral genome and is translated into a structural polyprotein that is proteolytically cleaved into the capsid and the envelope glycoproteins E2 and E1 (34). Two hundred forty copies of the capsid protein enclose the genomic viral RNA to form an icosahedral nucleocapsid that buds from the plasma membrane, acquiring a lipid envelope with embedded protein spikes formed by E1/E2 heterodimers (41, 48).Venezuelan equine encephalitis virus is a zoonotic pathogen...

Since Venezuelan equine encephalitis virus (VEEV) was isolated in Peru in 1942, >70 isolates have been obtained from mosquitoes, humans, and sylvatic mammals primarily in the Amazon region. To investigate genetic relationships among the Peru VEEV isolates and between the Peru isolates and other VEEV strains, a fragment of the PE2 gene was amplified and analyzed by single-stranded conformation polymorphism. Representatives of seven genotypes underwent sequencing and phylogenetic analysis. The results identified four VEE complex lineages that cocirculate in the Amazon region: subtypes ID (Panama and Colombia/Venezuela genotypes), IIIC, and a new, proposed subtype IIID, which was isolated from a febrile human, mosquitoes, and spiny rats. Both ID lineages and the IIID subtype are associated with febrile human illness. Most of the subtype ID isolates belonged to the Panama genotype, but the Colombia/Venezuela genotype, which is phylogenetically related to epizootic strains, also continues to circulate in the Amazon basin.