Western Equine Encephalitis Research Articles

Hemolytic activity of the envelope glycoproteins of western equine encephalitis virus in reconstitution experiments

Hemolytic activity of the purified glycoproteins (E 1 and E2) of western equine encephalitis virus was examined. To identify which of two glycoproteins of the virus is responsible for the activity, a reconstitution experiment using purified E 1 and E2 glycoproteins was performed. Results showed that hemolytic activity was associated with the E1 glycoprotein which acts as hemagglutinin.

Dissemination barriers for western equine encephalomyelitis virus in Culex tarsalis infected after ingestion of low viral doses.

There are two dose-dependent barriers to the transmission of western equine encephalomyelitis virus in infected female Culex tarsalis. In the first, virus multiplies in the mesenteron, but does not invade other tissues regardless of the length of extrinsic incubation. We call this the "mesenteronal escape" barrier. In some mosquitoes virus escapes from the infected mesenteron but a second barrier prevents infection of the salivary glands and perhaps neural tissues. We designate this the "salivary gland infection" barrier. The effectiveness of the second barrier decreases with time but still is evident after 21 days of extrinsic incubation. The distribution of virus in the tissues of nontransmitting females with either of these barriers is described.

Nucleoside triphosphate phosphohydrolase produced in BHK cells infected with western equine encephalitis virus is probably associated with the 82K dalton nonstructural polypeptide

The origin of the nucleoside triphosphate phosphohydrolase (NTPase) found in western equine encephalitis (WEE) virus-infected BHK cells was examined. (i) When the infected cells were treated with actinomycin D, the enzyme activity was not affected. (ii) The enzyme was also found in chick embryo and mosquito cells infected with WEE virus. (iii) When viral proteins were fractionated by gradient centrifugation and analyzed by gel electrophoresis, the enzyme activity was found to be associated with the 82K dalton viral nonstructural protein. These results suggest that the NTPase originates from a gene of WEE virus.

22] Induction and production of guinea pig interferon

Publisher Summary The experiments involving the guinea pig interferon system have been extremely limited in number and range, which may be because of the paucity of continuous guinea pig cell culture lines available. Nevertheless, the procedure for the induction and assay of guinea pig interferon has been developed. Various reports have indicated that guinea pig type I interferon can be induced in vivo . Intravenous injection of guinea pigs with 10 9 plaque-forming units (PFU) of herpes simplex virus results in induction of circulating serum interferon. The assay of guinea pig interferon activity is complicated by the lack of guinea pig cell lines, although a recent report suggests that a newly established long-term guinea pig tongue cell culture may prove to be useful for assay of interferon. A bulk of assays of guinea pig interferon involves primary cell culture systems. These include: plaque reduction of vesicular stomatitis virus (VSV) on guinea pig kidney cells, plaque reduction of encephalomyocarditis virus on guinea pig heart cells, cytopathic effect of western equine encephalitis virus on guinea pig kidney cells, and cytopathic effect of Sindbis virus on guinea pig lung cells.

Characterization of Fort Morgan virus, an alphavirus of the western equine encephalitis virus complex in an unusual ecosystem.

An alphavirus isolated from nestling Cliff Swallows (Petrochelidon pyrrhonota) and House Sparrows (Passer domesticus) and from cimicid bugs (Oeciacus vicarius) in eastern Colorado, for which we propose the name Fort Morgan (FM) virus, is sensitive to the action of sodium deoxycholate, unstable at pH 2.0-4.0, and demonstrates no characteristics of temperature-sensitive mutants. Unpassaged field strains are nonpathogenic, or of low pathogenicity, for suckling mice; however, plaque-purified FM virus is pathogenic for a variety of laboratory hosts. By hemagglutination-inhibition (HI), complement-fixation, and neutralization tests, cross-reactions were observed between FM virus and members of the western equine encephalitis (WEE) virus antigenic complex. Short-incubation HI tests indicated that the new isolate shared closer antigenic relationships with WEE complex virus strains from the eastern United States (Highlands J virus) than with other WEE complex viruses. On the basis of these serological findings, as well as characterization of the structural polypeptides and oligonucleotides, we suggest that FM is a distinct virus belonging to the WEE antigenic complex. A reconsideration of the taxonomy of the WEE complex and discussion of the epizoologic significance of FM virus are presented.

Weather, host and vector--their interplay in the spread of insect-borne animal virus diseases.

The spread of insect-borne animal virus diseases is influenced by a number of factors. Hosts migrate, move or are conveyed over long distances: vectors are carried on the wind for varying distances in search of hosts and breeding sites; weather and climate affect hosts and vectors through temperature, moisture and wind. As parasites of host and vector, viruses are carried by animals, birds and insects, and their spread can be correlated with the migration of hosts and the carriage of vectors on winds associated with the movements of the Intertropical Convergence Zone (ITCZ) and warm winds to the north and south of the limits of the ITCZ. The virus is often transmitted from a local cycle to a migratory cycle and back again.Examples of insect-borne virus diseases and their spread are analysed. Japanese, Murray Valley, Western equine, Eastern equine and St Louis encephalitis represent viruses transmitted by mosquito-bird or pig cycles.THE AREAS EXPERIENCING INFECTION WITH THESE VIRUSES CAN BE DIVIDED INTO A NUMBER OF ZONES: A, B, C, D, E and F. In zone A there is a continuous cycle of virus in host and vector throughout the year; in zone B, there is an upsurge in the cycle during the wet season, but the cycle continues during the dry season; there is movement of infected vectors between and within zones A and B on the ITCZ and the virus is introduced to zone C by infected vectors on warm winds; persistence may occur in zone C if conditions are right. In zone D, virus is introduced each year by infected vectors on warm winds and the arrival of the virus coincides with the presence of susceptible nestling birds and susceptible piglets. The disappearance of virus occurs at the time when migrating mosquitoes and birds are returning to warmer climates. The virus is introduced to zone E only on occasions every 5-10 years when conditions are suitable. Infected hosts introduced to zone F do not lead to circulation of virus, since the climate is unsuitable for vectors. Zones A, B and C correspond to endemic and zones D and E to epidemic conditions.Similar zones can be recognized for African horse sickness, bluetongue, Ibaraki disease and bovine ephemeral fever - examples of diseases transmitted in a midge-mammal cycle. In zones A and B viruses are transported by infected midges carried on the wind in association with the movement of ITCZ and undergo cycles in young animals. In these zones and in zone C there is a continual movement of midges on the warm wind between one area and another, colonizing new sites or reinforcing populations of midges already present. Virus is introduced at times into fringe areas (zones D and E) and, as there is little resistance in the host, gives rise to clinical signs of disease. In some areas there is persistence during adverse conditions; in others, the virus is carried back to the endemic zones by infected midges or vectors.Examples of viruses maintained in a mosquito/biting fly-mammal cycle are Venezuelan equine encephalitis and vesicular stomatitis. These viruses enter a migratory cycle from a local cycle and the vectors in the migratory cycle are carried over long distances on the wind. Further examples of virus spread by movement of vectors include West Nile, Rift Valley fever, yellow fever, epizootic haemorrhagic disease of deer and Akabane viruses.In devising means of control it is essential to decide the relationship of host, vector and virus and the nature of the zone in which the area to be controlled lies. Because of the continual risk of reintroduction of infected vectors, it is preferable to protect the host by dipping, spraying or by vaccination rather than attempting to eliminate the local population of insects.

Purification of the envelope glycoproteins of western equine encephalitis virus by glass wool column chromatography

Glass wool column chromatography was used for separation of the two glycoproteins of western equine encephalitis virus. Cross-contamination of each protein separated was confirmed to be negligible by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

Western Equine Encephalitis Mimicking Herpes Simplex Encephalitis

A patient with severe encephalitis had focal findings suggesting herpes simplex encephalitis. After brain biopsy and administration of vidarabine, the patient's condition improved but was ultimately diagnosed as a case of western equine encephalitis. Further complicating laboratory diagnosis, an endogenous murine coronavirus was isolated from newborn mice inoculated with the patient's brain biopsy tissue. This case illustrates the need for caution in attributing therapeutic responses to antiviral agents or in attributing human illness to viruses that are actually endogenous to animals and tissue culture used in diagnostic virology.

A serologic survey for selected infectious diseases of black bears in Idaho.

Two hundred sixty-five black bears (Ursus americanus) from northcentral Idaho were examined serologically over a five-year period for antibodies against selected infectious disease agents. The number of positive serum samples number of sera tested and percent positive for each infectious agent is: tularemia, 65/340 (19); brucellosis, 18/332 (5); toxoplasmosis, 23/303 (8); leptospirosis, 2/196 (1); trichinosis, 16/122 (13); Q-fever, 13/210 (6); St. Louis encephalitis, 3/340 (1); western equine encephalitis, 4/334 (1); Rocky Mountain Spotted Fever, 6/282 (2). Black bears may serve as an indicator for infection in other wildlife, domestic animals and humans in the area..

The significance of western equine encephalomyelitis viral infections in Aedes trivittatus (Diptera: Culicidae) in Iowa. I. Variation in susceptibility of Aedes trivittatus to experimental infection with three strains of western equine encephalomyelitis virus.

F1 pregnancy obtained from field-collected Aedes trivittatus were evaluated for susceptibility to infection with western equine encephalomyelitis (WEE) virus by intrathoracic inoculation and by oral imbibition of virus-blood suspensions through a membrane. Mosquitoes were uniformly susceptible to infection by intrathoracic inoculation of three strains of WEE virus, but minimum infective doses varied as much as 2,000 to 12,000-fold between strains by membrane feeding. Dose-response data obtained by membrane feeding also indicated that field strains of A. trivittatus were quite heterogeneous in their susceptibility to WEE virus since some individual mosquitoes could be infected by ingestion of low virus concentrations while others could not be infected by a 20,000-fold increase in virus concentration. Moreover, A. trivittatus showed a greater affinity for a WEE viral strain isolated from this species than for a WEE viral strain isolated from Culex tarsalis, even though the site, date of collection, and passage history of these isolates were identical. Field strains of A. trivittatus were relatively refractory to oral infection with WEE virus.

Antibody development in garter snakes (Thamnophis spp.) experimentally infected with western equine encephalitis virus.

Garter snakes (Thamnophis spp.) have been considered to possibly play an important role in the ecology of western equine encephalitis (WEE) virus. Serological tests (hemagglutination-inhibition, complement-fixation, neutralization test in mice, and plaque neutralization) to detect antibody in these reptiles following laboratory exposure t this virus have, in our experience, been unsatisfactory. A new test, the snake globulin precipitation (SGP) test, has been developed and we consider it to be reliable in detecting antibody in WEE virus-infected garter snakes. Antibody has been detected in these snakes over 4.5 years following inoculation with WEE virus. The SGP test should be a valuable tool in obtaining further information regarding the possible role of these cold-blooded vertebrates in the ecology of this important arbovirus.

Inhibition of DNA synthesis in BHK cells infected with western equine encephalitis virus 2. Properties of the inhibitory factor of DNA polymerase induced in infected cells

Infection of baby hamster kidney cells with western equine encephalitis virus results in rapid inhibition of cellular DNA synthesis. We previously reported that an inhibitory factor of cellular DNA polymerase activity was found in infected cell extracts. The mechanism of this inhibitory action was studied by varying the amount of each component involved in the DNA polymerase reaction mixture. Increase in DNA polymerase or template DNA showed no effect on the inhibitory activity, whereas that in substrate deoxynucleotides markedly suppressed the inhibition. Accordingly, the target of the inhibitory factor may be deoxynucleotides, and the factor was expected to be a phosphohydrolytic enzyme. In fact, deoxynucleotides were markedly hydrolyzed in the reaction mixture incubated with the inhibitory factor. This phosphohydrolytic enzyme activity was identified as a nucleoside triphosphate phosphohydrolase, which had little specificity to the base or the sugar of nucleotides, but high specificity to the triphosphate moiety. This enzyme showed the maximal activity at pH 7.5, and required a low concentration of Mg 2+, which could not be replaced by Mn 2+ or Ca 2+. Monovalent cations were not required. Furthermore, the enzyme activity was strikingly enhanced by addition of nucleic acids. The significance of this unique enzyme induced in infected cells is discussed in relation to inhibition of cellular DNA synthesis and viral replication.

Growth of California encephalitis and other viruses in Aedes dorsalis (Diptera: Culicidae) cell cultures.

Aedes dorsalis cells were evaluated for their susceptibility to California encephalitis (CE) virus, a bunyavirus, and 13 other viruses (6 bunyaviruses, 5 togaviruses, 2 rhabdoviruses). Those viruses naturally vectored by mosquitoes (CE, Jamestown Canyon, Trivittatus, Turlock, Hart Park, Western equine encephalomyelitis and St. Louis encephalitis) and by Culicoides (Lokern, Main Drain and Buttonwillow) grew well in Ae. dorsalis cells. A tick-borne virus (Powassan) and 2 nonarthropod-borne viruses (Modoc and Rio Bravo) failed to replicate. The 2 rhabdoviruses Kern Canyon and Harl Park, grew in the Ae. dorsalis cultures, but multiplication occurred only after a 3-day latent period. Kern Canyon virus (insect vector, if any, unknown) has not been previously reported to replicate in mosquito cells. None of the viruses that grew in the mosquito cells produced overt cytopathic effects. Two subpopulations of Ae. dorsalis cells were more susceptible than parental cells to CE Virus by infectivity and immunofluorescent-antibody assays.

Isolation of the structural proteins of western equine encephalitis virus by isoelectric focusing.

Western equine encephalitis virus was disrupted with Triton X-100 and subjected to isoelectric focusing in a sucrose or urea gradient. The two envelope proteins, E1 and E2 were not well separated in a sucrose gradient, while the E1 and E2 proteins were distinguished as two major peaks which focused in a urea gradient at about pH 7.5 and 10, respectively. Isolated E1 protein refocused at pH 6.5 in a sucrose gradient isoelectric focusing column. When Western equine encephalitis virus was treated with Triton X-100 in 0.01 M phosphate buffer (pH6), hemagglutinating E1 protein was solubilized, which isoelectrofocused at pH 6.5. Purified nucleocapsids focused at pH 4 in a sucrose gradient on an isoelectric focusing column. After ribonuclease treatment of the purified nucleocapsid more than 95 per cent of the viral RNA was acid-soluble, and hte nucleocapsid protein isoelectrofocused at about pH 4.

Antiviral activity of virus-like particles fromLentinus edodes (Shiitake)

Interferon (IF) induction and antiviral activity by purified spherical (S) or filamentous (F) virus-like particles and S-derived RNA was studied. A single administration of S particles prior to virus challenge reduced significantly the mortality of mice infected with western equine encephalitis (WEE) virus.

Effects of influenza, mumps, and western equine encephalitis viruses on fetal rhesus monkeys (Macaca mulatta).

Pregnant Rhesus monkeys were infected via instillation of influenza, mumps and western equine encephalomyelitis viruses respectively into the amniotic sacs at approximately 90 days gestation to determine if fetal infections would occur. Virus was recovered from fetal tissues after seven days in 100% of the exposed animals. Thus, the viruses are capable of causing fetal infection. Rhesus monkey fetuses were inoculated with influenza, mumps and WEE viruses by the direct intracerebral route at approximately 90 days gestation to determine possible teratogenicity of the viruses. influenza virus caused no malformations or measurable fetal effects. Mumps virus resulted in significant fetal mortality. WEE virus resulted in a 100% incidence of encephalitis and hydrocephalus. Thus, mumps and WEE viruses are teratogens in primates and are potential teratogens of man.

Fetal mortality and malformations associated with experimental infections of Western equine encephalomyelitis vaccine virus in Rhesus monkeys (Macaca mulatta)

Pregnant Rhesus monkeys were infected via installation of Western Equine Encephalomyelitis (WEE) vaccine virus into the amniotic sacs at 50 and 80 days gestation to determine if the resulting infections would produce fetal mortality or fetal malformations, particularly within the central nervous system. Of those receiving virus at 50 days gestation, 13 of 18 fetuses were aborted or dead in utero at time of Caesarean section; 2 of 18 were malformed (hydrocephalus and polyarthrosis); and 3 of 18 were anatomically normal. Of those receiving virus at 80 days gestation four of eight fetuses were aborted or dead in utero at time of Caesarean section, one of eight was malformed (hydrocephalus) and three of eight were anatomically normal. Three of three controls receiving neutralized virus at each gestational age were anatomically normal. Fetal WEE vaccine virus infection significantly increased fetal mortality and resulted in a significant incidence of fetal malformations.

Interaction of alphaviruses with human peripheral leukocytes: in vitro replication of Venezuelan equine encephalomyelitis virus in monocyte cultures.

Human peripheral blood leukocytes (PBL) were examined for their ability to support growth of several group A arboviruses in vitro. Cells were refractory to infection with eastern (EEE) and western (WEE) equine encephalitis viruses, whereas Venezuelan equine encephalomyelitis (VEE) virus was shown to infect and replicate to a substantially high titer. When PBL were fractionated into purified subpopulations, only the monocytes were susceptible to predictive VEE virus infection. Lymphocytes treated 24 h before virus inoculation with phytohemagglutinin (10 microgram/ml) were capable of propagating significant amounts of VEE virus. A monocytic cell line, J-111, was also susceptible to infection with VEE, EEE, and WEE viruses, whereas a lymphocytic cell line, Raji, was refractory. Additional information on the participation of PBL during human infection with these viruses may add considerably to our understanding of their differing pathogenicities and clinical pictures.

Inhibition of DNA synthesis in BHK cells infected with western equine encephalitis virus 1. Induction of an inhibitory factor of cellular DNA polymerase activity

Abstract Infection of baby hamster kidney cells with western equine encephalitis virus results in rapid inhibition of cellular DNA synthesis. As reported previously (Simizu et al., 1976), this inhibition is not due to degradation of DNA nor suppression of precursor uptake. As the next approach, it was examined whether cellular DNA polymerase activity is inhibited or not. DNA polymerase activity in infected cell extracts was found to be decreased parallel to the decline of DNA synthesis with time after infection. This inhibition was ascribed to an inhibitory factor(s), much of which was found in 105,000 g pellet of the extract. This factor was thermolabile and was solubilized with high concentration of salt, but not with Triton X-100 or urea. Molecular weight of the solubilized factor was determined to be 83,000 by sedimentation analysis. No apparent specificity of inhibition was observed with several DNA polymerase species tested. Furthermore, activity of the inhibitory factor was suppressed by inorganic phosphate. These results may predict that the factor does not affect the DNA polymerase molecule itself, but is a hydrolytic enzyme of precursor deoxynucleotides. The possibility that this inhibitory factor is a virus-coded protein is discussed.

Prevalence of selected zoonotic diseases in vertebrates from Haiti, 1972.

Vertebrate animals collected in Haiti in 1972 were tested for selected zoonotic diseases. No rabies virus or neutralizing (N) antibody was detected in bats (Artibeus jamaicensis). However, N antibody against St. Louis encephalitis, Western equine encephalitis (WEE), and Eastern equine encephalitis were detected in resident species of birds and WEE antibody in bats. No N antibody against Venezuelan equine encephalitis was found. The possible introduction by migratory birds and local transmission of these arboviruses is discussed.