ATYPICAL ANTIBODY RESPONSES IN DENGUE VACCINE RECIPIENTS

Eight of 69 (12%) healthy adult volunteers vaccinated with monovalent live-attenuated dengue virus (DENV) vaccine candidates had atypical antibody responses, with depressed IgM:IgG antibody ratios and induction of high-titer hemagglutination-inhibiting and neutralizing (NT) antibodies to all four DENV serotypes. These features suggested flavivirus exposure prior to DENV vaccination, yet no volunteer had a history of previous flavivirus infection, flavivirus vaccination, or antibody to flaviviruses evident before DENV vaccination. Moreover, production of antibody to DENV by atypical responders (AR) was not accelerated compared with antibody responses in the 61 flavivirus-naive responders (NR). Further evaluation revealed no differences in sex, age, race, DENV vaccine candidate received, or clinical signs and symptoms following vaccination between AR and NR. However, viremia was delayed at the onset in AR compared with NR. A comparative panel of all AR and five randomly selected NR found flavivirus cross-reactive antibody after vaccination only in AR. Unexpectedly, six of eight AR had NT antibodies to yellow fever virus (YFV) > 1:10 before vaccination while NR had none (P = 0.04). The AR also universally demonstrated YFV NT antibody titers > or = 1:160 after DENV vaccination, whereas four of five NR failed to seroconvert (P = 0.02). Yellow fever virus priming broadens the antibody response to monovalent DENV vaccination. The effect of flavivirus priming on the clinical and immunologic response to tetravalent DENV vaccine remains to be determined.

Short report: absence of protective neutralizng antibodies to West Nile virus in subjects following vaccination with Japanese encephalitis or dengue vaccines

Protection of individuals against West Nile (WN) encephalitis is an emerging concern in the United States and Europe. We investigated whether immunization with licensed inactivated Japanese encephalitis (JE) vaccine or experimental live attenuated dengue vaccines resulted in induction of cross-neutralizing antibodies against WN virus. Protective neutralizing antibody titers to WN virus were not detected in any volunteer despite successful immunization to related flaviviruses. Vaccination against JE or dengue is unlikely to prevent WN virus infection but may still protect against disease.

Combined effects of Venezuelan equine encephalitis IIIA virus and gamma irradiation in mice

The combined effects of injury from exposure to ionizing radiation and the potential biological warfare agent Venezuelan equine encephalitis (VEE) virus remain largely unknown. To study these effects, 4- to 5-week-old B6D2F1/J female mice were given a sublethal whole-body 7 Gy dose of 60Co gamma-photon radiation followed 48 hours later by aerosol or intraperitoneal challenge with enzootic VEE IIIA virus. Survival was observed for 30 days. A single sublethal 7 Gy dose of gamma radiation reduced the LD50/30 of VEE IIIA virus, in intraperitoneal challenged mice by a factor of 10(4) from 1.1 x 10(6) plaque-forming units (pfu) to 1 x 10(2) pfu, and in aerosol challenged mice, by a factor of 5 from 70 pfu to 14 pfu. These findings further confirm there is a combined effect of exposure to ionizing radiation and biological warfare agents, which could be devastating to unprotected populations and thus should be investigated further.

Onset and duration of protective immunity to IA/IB and IE strains of Venezuelan equine encephalitis virus in vaccinated mice

Three vaccines developed for protection against IA/IB subtypes of Venezuelan equine encephalitis (VEE) virus were evaluated in mice for the ability to protect against systemic and mucosal challenges with a virulent virus of the IE subtype. The vaccines were the formaldehyde-inactivated C-84 and live attenuated TC-83 vaccines currently administered to people under investigational new drug (IND) status, and a new live attenuated vaccine candidate, V3526. V3526 was superior for inducing protection to VEE IA/IB within a week of vaccination, and protection persisted for at least a year. All three vaccines induced long-term clinical protection against peripheral or mucosal challenge with IE virus, with the mucosal immunity induced by attenuated vaccines lasting longer than that induced by the inactivated vaccine. These data show that the molecularly cloned V3526 vaccine induces equivalent or improved immunity to homologous and heterologous VEE viruses than the existing vaccines.

Comparison of dissociation-enhanced lanthanide fluorescent immunoassays to enzyme-linked immunosorbent assays for detection of staphylococcal enterotoxin B, Yersinia pestis-specific F1 antigen, and Venezuelan equine encephalitis virus

The dissociation-enhanced lanthanide fluorescent immunoassays (DELFIA) were developed for the detection of staphylococcal enterotoxin B, Yersinia pestis-specific F1 antigen, and Venezuelan equine encephalitis virus. These assays were compared to previously developed enzyme-linked immunosorbent assays (ELISAs) by determining the sensitivity or limit of detection (LOD), the dynamic range, and the reproducibility of each assay in a number of different sample matrices. The sensitivity and specificity of each assay were then determined by using a small panel of blinded spiked and nonspiked samples. All three DELFIAs demonstrated at least 1 log greater sensitivity than corresponding ELISAs utilizing the same reagents and showed an increase in dynamic range of at least 2 log(10) concentrations. This increased LOD resulted in higher sensitivity rates for the DELFIA. The specificity of all of the assays evaluated was 100%, and no sample matrix effects were observed in either format. However, the reproducibility of the DELFIA was poor due to randomly distributed wells exhibiting excessive background signal (hot wells), which occurred throughout the evaluation. As this technology matures, the reproducibility of these assays should improve, as will the ability to identify hot wells. Despite its sensitivity, the logistical burden associated with the DELFIA and the technical expertise required to complete assays and interpret the data limit the application of this technology to reference or large clinical laboratories.

Current laboratory methods for biological threat agent identification

The authors present an integrated approach for the identification of biological threat agents. The methods used have been used extensively in field exercises and during response to incidents of biological terrorism. A diagnostic system, which integrates the clinical diagnosis or medical intelligence with immunodiagnostic tests, rapid gene amplification assays, and standard culture, provides results of the highest quality and confidence. In the future, selected reagents and technologies will be distributed through a network of civilian and military laboratories.

Pharmacokinetics study of a novel chimeric single-chain variable fragment antibody against western equine encephalitis virus

A novel recombinant single-chain fragment variable (scFv) antibody against western equine encephalitis (WEE) virus has been previously constructed and partially characterized. The RS10B5huFc antibody was made by fusing an anti-WEE scFv to a human heavy-chain IgG1 constant region. The RS10B5huFc antibody was functional in binding to WEE virus in enzyme-linked immunosorbent assays (ELISAs), and the Fc domain of the antibody was capable of effector functions, such as binding to protein G and human complement. In this study, the RS10B5huFc antibody was further characterized by BIAcore analyses and was found to possess a binding affinity to a WEE virus epitope (K[D] = 9.14 x 10(-6) M), 4.5-fold lower than its parental mouse monoclonal antibody (MAb) 10B5 E7E2 (K[D] = 2 x 10(-6) M). No cross-reactivity was found between the RS10B5huFc antibody and three other alphaviruses (Sindbis virus [SIN], Venezuelan equine encephalitis [VEE] virus, and eastern equine encephalitis [EEE] virus). Pharmacokinetics studies showed that the RS10B5huFc antibody (free and encapsulated) was found to be retained in the lungs of mice for greater than 48 h when administered intranasally. In contrast, when administered intramuscularly to mice, the RS10B5huFc antibody was not detected in the lungs and only found in the liver and kidneys.

Comparative neurovirulence of attenuated and non-attenuated strains of Venezuelan equine encephalitis virus in mice

A candidate live-attenuated virus vaccine for protection against Venezuelan equine encephalitis (VEE) (designated V3526) was tested in mice to measure the magnitude, duration, and kinetics of virus replication in the blood and the central nervous system and its phenotypic stability after multiple passages in mice and cell culture. All results were compared to parallel experiments with parental virus and the existing VEE virus vaccine, TC-83. Maximum virus titers in the brains of V3526-inoculated mice were between 10- and 100-fold less than those observed in brains of mice inoculated intracranially (i.c.) with either the parental virus or TC-83. Neither V3526 nor TC-83 was lethal in BALB/c mice inoculated i.c.. However, mice inoculated with TC-83 developed acute symptoms lasting at least 14 days. In contrast, i.c. inoculation of TC-83 was uniformly lethal for C3H/HeN mice. V3526 was avirulent in both BALB/c and C3H/HeN mice after i.c. inoculation. The virulence characteristics of V3526 remained unchanged after five serial i.c. passages in mouse brains or after five cell culture passages. Finally, pathologic changes induced after i.c. inoculation of V3526 were consistently less severe and of shorter duration than those observed in TC-83-inoculated mice. Based on these results, V3526 is stable and appears to be significantly less neurovirulent in mice than TC-83.

Recombinant RNA replicons derived from attenuated Venezuelan equine encephalitis virus protect guinea pigs and mice from Ebola hemorrhagic fever virus

RNA replicons derived from an attenuated strain of Venezuelan equine encephalitis virus (VEE), an alphavirus, were configured as candidate vaccines for Ebola hemorrhagic fever. The Ebola nucleoprotein (NP) or glycoprotein (GP) genes were introduced into the VEE RNA downstream from the VEE 26S promoter in place of the VEE structural protein genes. The resulting recombinant replicons, expressing the NP or GP genes, were packaged into VEE replicon particles (NP-VRP and GP-VRP, respectively) using a bipartite helper system that provided the VEE structural proteins in trans and prevented the regeneration of replication-competent VEE during packaging. The immunogenicity of NP-VRP and GP-VRP and their ability to protect against lethal Ebola infection were evaluated in BALB/c mice and in two strains of guinea pigs. The GP-VRP alone, or in combination with NP-VRP, protected both strains of guinea pigs and BALB/c mice, while immunization with NP-VRP alone protected BALB/c mice, but neither strain of guinea pig. Passive transfer of sera from VRP-immunized animals did not confer protection against lethal challenge. However, the complete protection achieved with active immunization with VRP, as well as the unique characteristics of the VEE replicon vector, warrant further testing of the safety and efficacy of NP-VRP and GP-VRP in primates as candidate vaccines against Ebola hemorrhagic fever.

Construction and characterization of monoclonal antibodies against western equine encephalitis virus

A repertoire of mouse monoclonal antibodies (MAbs) against western equine encephalitis virus (WEE) was constructed and characterized. Anti-WEE antibodies were expressed from hybridomas and purified by protein G chromatography. Each of the antibodies was functionally assessed by indirect enzyme-linked immunosorbent assays (ELISAs), Western blotting, and immunoprecipitations. All antibodies bound to WEE antigen in ELISAs, whereas only a subgroup of antibodies was found to be active in Western blotting and immunoprecipitations. A subset of antibodies was found to cross-react with other alphaviruses, such as Sindbis virus (SIN), Venezuelan equine encephalitis (VEE), and eastern equine encephalitis (EEE). Because many of the antibodies were highly reactive to WEE antigen in one or more of the assays, these antibodies are excellent candidates for immunodetection and immunotherapy studies.

Comparison of noninvasive sampling sites for early detection of Bacillus anthracis spores from rhesus monkeys after aerosol exposure

Bacillus anthracis, a spore-forming bacterium, is the etiologic agent of anthrax. B. anthracis spores can be aerosolized, are relatively easy to produce, and are capable of producing high mortality when inhaled. The prompt use of postexposure antibiotics combined with vaccination greatly increases the survival rate. Rapid detection of exposure is critical to effective case management. Using common collection swabs, culture medium, and culturing equipment, we compared six different noninvasive sampling sites to determine which might best be used to rapidly detect the presence of B. anthracis spores on rhesus monkeys after aerosolization. The results indicate that the greatest number of spores were deposited in the nares, on the face, and on the haired portions of the head, suggesting that these locations are the most effective sampling sites when attempting to detect B. anthracis aerosol exposure.

Limited potential for mosquito transmission of genetically engineered, live-attenuated Venezuelan equine encephalitis virus vaccine candidates

In an attempt to improve the current live-attenuated vaccine (TC-83) for Venezuelan equine encephalitis (VEE), specific mutations associated with attenuation of VEE virus in rodent models were identified. These mutations were inserted into full-length cDNA clones of the Trinidad donkey strain of VEE virus by site-directed mutagenesis, and isogenic virus strains with these mutations were recovered after transfection of baby hamster kidney cells with infectious RNA. We evaluated 10 of these strains for their ability to replicate in and be transmitted by Aedes taeniorhynchus, a natural vector of epizootic VEE virus. Two vaccine candidates, one containing a deletion of the PE2 furin cleavage site, the other a combination of three separate point mutations in the E2 glycoprotein, replicated in mosquitoes and were transmitted to hamsters significantly less efficiently than was either parental (wild type) VEE virus or TC-83 virus. Although the attenuated strains were transmitted to hamsters by mosquitoes, after intrathoracic inoculation, there was no evidence of reversion to a virulent phenotype. The mutations that resulted in less efficient replication in, or transmission by, mosquitoes should enhance vaccine safety and reduce the possibility of environmental spread to unintentional hosts.

Expression, processing, and immunogenicity of the structural proteins of Venezuelan equine encephalitis virus from recombinant baculovirus vectors

Recombinant baculoviruses expressing the structural proteins of Venezuelan equine encephalitis virus (VEE) have been constructed and the intracellular processing, antigenicity, and immunogenicity of the expression products have been assessed. Baculoviruses expressing the entire structural protein region (C-E3-E2-6K-E1), or the complete glycoprotein region (E3-E2-6K-E1), generated products in Sf9 cells that were accurately and completely processed, and resulted in mature proteins that were antigenically and electrophoretically indistinguishable from authentic viral proteins. These products were highly immunogenic in BALB/c mice, induced efficient VEE neutralizing responses, and protected these animals against challenge with virulent VEE. Expression of individual glycoprotein regions (E3-E2 and 6K-E1) generated products that were accurately but incompletely processed, and induced non-neutralizing antibodies that reacted more efficiently with denatured than native VEE proteins. Nonetheless, immunization with the 6K-E1 expression product provided complete protection against VEE challenge.

Association of Venezuelan equine encephalitis virus subtype IE with two equine epizootics in Mexico

Two outbreaks of encephalitis consistent with an etiology of Venezuelan equine encephalitis (VEE) virus occurred in equines on the Pacific coast of southern Mexico in 1993 (Chiapas State) and in 1996 (Oaxaca State). In Chiapas, there were 125 cases, of which 63 were fatal and in Oaxaca, there were 32 cases and 12 fatalities. Virus was isolated from two horses from each outbreak, including three brain isolates and one from blood. Virus isolates (93-42124, ISET-Chi93, Oax131, and Oax142) were shown by indirect immunofluorescence, hemagglutination inhibition, monoclonal antibody ELISA, and nucleotide sequencing to be VEE virus, subtype IE, a type previously thought to be equine-avirulent. Genetic characterization and phylogenetic analysis indicated that the outbreak viruses were identical or nearly identical to one another and that they were closely related to equine-avirulent IE strains from Guatemala and the Gulf coast of Mexico. In a plaque-reduction neutralization test, sera collected from healthy horses in Chiapas and Oaxaca reacted significantly better with isolate 93-42124 than with Guatemala IE isolate 68U201, suggesting that subtle genetic changes may have resulted in alteration of neutralization domains. It is not clear whether these differences may also influence equine virulence. However, renewed VEE virus subtype IE activity in Mexico, and its apparent conversion to equine virulence, underscores the need for increased surveillance, additional laboratory and epidemiologic studies in VEE-endemic regions, and possibly new vaccines.

Replicon-helper systems from attenuated Venezuelan equine encephalitis virus: expression of heterologous genes in vitro and immunization against heterologous pathogens in vivo

A replicon vaccine vector system was developed from an attenuated strain of Venezuelan equine encephalitis virus (VEE). The replicon RNA consists of the cis-acting 5' and 3' ends of the VEE genome, the complete nonstructural protein gene region, and the subgenomic 26S promoter. The genes encoding the VEE structural proteins were replaced with the influenza virus hemagglutinin (HA) or the Lassa virus nucleocapsid (N) gene, and upon transfection into eukaryotic cells by electroporation, these replicon RNAs directed the efficient, high-level synthesis of the HA or N proteins. For packaging of replicon RNAs into VEE replicon particles (VRP), the VEE capsid and glycoproteins were supplied in trans by expression from helper RNA(s) coelectroporated with the replicon. A number of different helper constructs, expressing the VEE structural proteins from a single or two separate helper RNAs, were derived from attenuated VEE strains Regeneration of infectious virus was not detected when replicons were packaged using a bipartite helper system encoding the VEE capsid protein and glycoproteins on two separate RNAs. Subcutaneous immunization of BALB/c mice with VRP expressing the influenza HA or Lassa virus N gene (HA-VRP or N-VRP, respectively) induced antibody responses to the expressed protein. After two inoculations of HA-VRP, complete protection against intranasal challenge with influenza was observed. Furthermore, sequential immunization of mice with two inoculations of N-VRP prior to two inoculations of HA-VRP induced an immune response to both HA and N equivalent to immunization with either VRP construct alone. Protection against influenza challenge was unaffected by previous N-VRP immunization. Therefore, the VEE replicon system was characterized by high-level expression of heterologous genes in cultured cells, little or no regeneration of plaque-forming virus particles, the capability for sequential immunization to multiple pathogens in the same host, and induction of protective immunity against a mucosal pathogen.

Re-emergence of epidemic Venezuelan equine encephalomyelitis in South America. VEE Study Group

BACKGROUND

Venezuelan equine encephalomyelitis (VEE) virus has caused periodic epidemics among human beings and equines in Latin America from the 1920s to the early 1970s. The first major outbreak since 1973 occurred in Venezuela and Colombia during 1995, and involved an estimated 75,000 to 100,000 people. We report an epidemiological and virological investigation of this epidemic.

METHODS

Virus isolates were made in cell culture from human serum, human throat swabs, and brain tissue from aborted and stillborn human fetuses, as well as from horse brain tissue and pooled mosquito collections. Human sera were also tested for VEE-specific antibodies. The serotypes of VEE isolates were identified by antigen assays, and viruses were characterised genetically by sequencing PCR products generated from the E3 and E2 genes. Phylogenetic analyses were done to determine evolutionary relations with respect to previous epidemic/epizootic and enzootic VEE virus isolates. Mosquito collections were made to identify possible vectors, and clinical findings were determined by direct observation of patients visiting hospitals and clinics in affected regions, and by inspecting patient records. Equine vaccination and vector control were used in an attempt to halt the spread of the outbreak.

FINDINGS

Most affected people had an acute, self-limited febrile illness of 3 to 4 days duration. However, convulsions were often seen in children, and abortions and fetal deaths occurred in pregnant women infected with VEE virus. Antigenic characterisation of 12 virus isolates spanning the temporal and spatial range of the outbreak indicated that all are VEE serotype IC. Phylogenetic analysis revealed that all of the 1995 viruses were closely related to serotype IC viruses isolated during a large VEE outbreak that occurred in the same regions of Colombia and Venezuela from 1962-1964. A 1983 mosquito isolate from north central Venezuela was also closely related to the 1995 isolates.

INTERPRETATION

This outbreak was remarkably similar to one that occurred in same regions of Venezuela and Colombia during 1962-1964. Symptoms of infected patients, estimated mortality rates, meteorological conditions preceding the epidemic, and seasonal patterns of transmission were all very similar to those reported in the previous outbreak. In addition, viruses isolated during 1995 were antigenically and genetically nearly identifical to those obtained during 1962-1964. These findings suggest that the epidemic resulted from the re-emergence of an epizootic serotype IC VEE virus. Identification of a similar virus isolate in mosquitoes in Venezuela in 1983, 10 years after epidemic/epizootic VEE activity ceased, raises the possibility of a serotype IC enzootic transmission cycle in northern Venezuela.

A putative receptor for Venezuelan equine encephalitis virus from mosquito cells

We have identified a cellular protein from a continuous mosquito cell line (C6/36) that appears to play a significant role in the attachment of Venezuelan equine encephalitis (VEE) virus to these cells. VEE virus bound to a 32-kDa polypeptide present in the C6/36 plasma membrane fraction, and binding to this polypeptide was dose dependent and saturable and competed with homologous and heterologous alphaviruses. These observations suggest that this polypeptide binds virus via a receptor-ligand interaction. The 32-kDa polypeptide was expressed on the surfaces of C6/36 cells, and monoclonal antibodies directed against either this cell polypeptide or the VEE virus E2 glycoprotein, which is thought to be the viral attachment protein, interfered with virus attachment. Collectively, these data provide evidence suggesting that the 32-kDa polypeptide serves as a receptor for VEE virus infection of cells. We have characterized this cell polypeptide as a laminin-binding protein on the basis of its ability to interact directly with laminin as well as its immunologic cross-reactivity with the high-affinity human laminin receptor.

Short report: prevalence of hantavirus infection in rodents associated with two fatal human infections in California

Rodents living near two fatal human cases of hantavirus pulmonary syndrome in California were surveyed for evidence of hantavirus infection. Seventeen (15%) (14 Peromyscus maniculatus and one each of P. truei, Eutamias minimus, and Microtus californicus) of 114 rodents tested had evidence (enzyme-linked immunosorbent assay or polymerase chain reaction) of hantavirus infection. This suggests that Peromyscus mice, and P. maniculatus in particular, may be the reservoir for the virus causing this newly recognized disease in California, as previously reported for New Mexico and Arizona.

Insect-transmitted vertebrate viruses: flaviviridae

The Flaviviridae include almost 70 viruses, nearly half of which have been associated with human disease. These viruses are among the most important arthropod-borne viruses worldwide and include dengue, yellow fever, and Japanese encephalitis viruses. Morbidity and mortality caused by these viruses vary, but collectively they account for millions of encephalitis, hemorrhagic fever, arthralgia, rash, and fever cases per year. Most of the members of this family are transmitted between vertebrate hosts by arthropod vectors, most commonly mosquitoes or ticks. Transmission cycles can be simple or complex depending on the hosts, vectors, the virus, and the environmental factors affecting both hosts and viruses. Replication of virus in invertebrate hosts does not seem to result in any significant pathology, which suggests a close evolutionary relationship between virus and vector. Another example of this relationship is the ability of these viruses to grow in invertebrate cell culture, where replication usually results in a steady state, persistent infection, often without cytopathic effect. Yields of virus from insect cell culture vary but are generally similar to yields in vertebrate cells. Replication kinetics are comparable between insect and vertebrate cell lines, despite differences in incubation temperature. Both vertebrate and insect cell culture systems continue to play a significant role in flavivirus isolation and the diagnosis of disease caused by these agents. Additionally, these culture systems permit the study of flavivirus attachment, penetration, replication, and release from cells and have been instrumental in the production and characterization of live-attenuated vaccines. Both vertebrate and insect cell culture systems will continue to play a significant role in basic and applied flavivirus research in the future.

Monoclonal antibodies directed against the envelope glycoproteins of La Crosse virus

Neutralizing monoclonal antibodies directed against the envelope glycoproteins of La Crosse virus (LACV) were prepared. Two antibodies immunoprecipitated the 120 kDa virus attachment protein for vertebrate cells, G1, while five immunoprecipitated the 35 kDa G2 protein, whose function is currently unknown. Two monoclonal antibodies were obtained that specifically precipitated both G1 and G2 from [35S]cysteine labeled LACV infected cell lysates. The G2 specific monoclonal antibodies had high neutralizing titers when assayed in mosquito cells but limited ability to neutralize virus in mammalian cells. The G1/G2 specific antibodies neutralized virus infectivity in both vertebrate and invertebrate cells at high titers. These results suggest that G2 is involved in the interaction of virus with mosquito cells and that G1 and G2 may share a common structural epitope relevant to their role as attachment proteins in vertebrate and mosquito cells. Monoclonal antibodies directed against G2 or G1/G2 have not previously been reported and should be useful tools for characterizing the biological functions of these molecules in the divergent micro-environments of vertebrate and invertebrate hosts.

Role of La Crosse virus glycoproteins in attachment of virus to host cells

Data presented in this report demonstrate that the initial event of La Crosse virus (LACV) infection of cells is probably the interaction of viral glycoproteins with specific cellular receptor sites. We have shown that LACV glycoprotein G1 binds, in a dose-dependent manner, to continuous vertebrate and mosquito cell lines, but not to mosquito midguts isolated ex vivo. This binding can be inhibited by the pretreatment of cells with excess homologous glycoprotein but not with excess heterologous LACV glycoprotein. In contrast, we have shown that LACV glycoprotein G2 binds to the continuous mosquito cell line and vector midgut cells, but not to vertebrate cells. LACV infection of vertebrate cells can be inhibited by treatment of cells with purified G1, while infection in mosquito cells can be reduced by treatment of cells with a combination of G1 and G2. The results suggest that G1 is the viral attachment protein (VAP) for vertebrate cells, and that G2 serves the same purpose for mosquito midgut cells. We speculate that the protease-resistant G2 molecule may have evolved to serve as the VAP in the midgut under conditions in which G1 might be altered or removed from the virus envelope, and thus is essential to the evolution and maintenance of vertebrate-invertebrate transmission cycles.

Enzyme processing of La Crosse virus glycoprotein G1: a bunyavirus-vector infection model

Efficient transmission, amplification, and dissemination of arboviruses require viral replication in vertebrate and invertebrate hosts. As a result, virions are exposed to two significantly different environments. Exposure of LaCrosse virus (LACV) to proteolytic enzymes, such as those that may be found in the mosquito midgut, increases virus affinity for mosquito cells. These enzymes remove the major envelope glycoprotein (G1) while leaving the second glycoprotein (G2) intact. Processing of LACV glycoproteins in the mosquito midgut may be necessary to expose attachment proteins on the virion surface before attachment to, and infection of, midgut cells can occur. This model may suggest answers to questions regarding the molecular basis for midgut infection barriers and species susceptibility to arbovirus infection in nature.

Temporal control of bovine herpesvirus 1 glycoprotein synthesis

The gI, gIII, and gIV glycoproteins are major bovine herpesvirus 1 antigens involved in virus neutralization. Results indicate that the gI and gIV glycoproteins were expressed as beta proteins, whereas the gIII glycoprotein was expressed strictly as a gamma protein. These findings suggest that gI and gIV may be superior to gIII as vaccine candidates.

Viremic enhancement due to transovarially acquired antibodies to St. Louis encephalitis virus in birds

Adult house sparrows (Passer domesticus) were captured and experimentally inoculated with St. Louis encephalitis (SLE) virus to produce high concentrations of circulating antiviral antibody. Nestlings, 5-7 and 14-16 days of age, from SLE immune adult females and challenged with SLE virus, exhibited viremic enhancement by producing viremias of greater duration and magnitude than did controls. Nestlings possessing maternal antibody and challenged with SLE virus between 8 and 13 days of age did not produce viremias differing significantly from controls in magnitude, duration, or temporal appearance. Experimental nestling sparrows possessed detectable amounts of maternally derived passive antibody to SLE virus prior to challenge with this virus. Passive geometric mean antibody titers ranged from a high of 1:34.5 in nestlings tested 5-7 days posthatching, to a low of 1:11.2 in 14-16-day-old birds. Results presented imply that enhancement of SLE virus infections could lead to increased viral amplification and dissemination rates during natural disease cycles.