Cross reactivity of neutralizing antibodies to the encephalitic California Serogroup orthobunyaviruses varies by virus and genetic relatedness

The California Serogroup (CSG) of Orthobunyaviruses comprises several viruses capable of causing neuroinvasive disease in humans, including La Crosse (LACV), Snowshoe Hare (SSHV), Tahyna (TAHV), Jamestown Canyon (JCV), and Inkoo (INKV) viruses. Diagnosis of specific CSG viruses is complicated by the high degree of antibody cross-reactivity between them, with laboratory standards requiring a fourfold higher titer of neutralizating antibody (NAb) activity to positively identify the etiologic virus. To help elucidate NAb relationships between neuroinvasive CSG viruses, we directly compared the cross-reactivity of NAb between LACV, SSHV, TAHV, JCV, and INKV. Mice were inoculated with individual viruses and the NAb activity of plasma samples was compared by plaque reduction neutralization tests against all five viruses. Overall, the results from these studies show that the CSG viruses induced high levels of NAb against the inoculum virus, and differing amounts of cross-reactive NAb against heterologous viruses. LACV, SSHV, and INKV elicited the highest amount of cross-reactive NAb. Interestingly, a fourfold difference in NAb titer between the inoculum virus and the other CSG viruses was not always observed. Thus, NAb titers, which are the gold-standard for diagnosing the etiologic agent for viral encephalitis, may not clearly differentiate between different CSG viruses.

California Serogroup Virus Infection Associated with Encephalitis and Cognitive Decline, Canada, 2015

California serogroup (CSG) viruses, such as Jamestown Canyon and snowshoe hare viruses, are mosquitoborne pathogens that cause febrile illness and neurologic disease. Human exposures have been described across Canada, but infections are likely underdiagnosed. We describe a case of neuroinvasive illness in a New Brunswick, Canada, patient infected with a CSG virus.

Roles of host species, geographic separation, and isolation in the seroprevalence of Jamestown Canyon and snowshoe hare viruses in Newfoundland

California serogroup viruses, including Jamestown Canyon virus (JCV) and snowshoe hare virus (SSHV), are mosquito-borne members of the Bunyaviridae family and are endemic across North America. These arboviruses are potential pathogens which occasionally cause neuroinvasive disease in humans and livestock. A neutralization assay was used to document JCV and SSHV seroprevalence using blood collected from a variety of domestic and wildlife host species. These species were sampled in an island setting, Newfoundland, which contains diverse ecoregions, ecological landscapes, and habitats. Seroprevalence rates for each virus differed significantly among host species and within certain species across different geographic areas. JCV was significantly associated with large mammals, and SSHV was significantly associated with snowshoe hares. Seroprevalence rates in the 5 species of animals tested for prior exposure to JCV ranged from 0% in snowshoe hares to 64% in horses. Seroprevalence rates for SSHV ranged from less than 1% in bovines to 55% in all snowshoe hares. The seroprevalence of SSHV differed significantly (P < 0.05) among hares occupying the discrete habitats of watersheds separated by 14 to 35 km. Cattle on farms in boreal forest landscapes displayed significantly higher JCV seroprevalence (P < 0.001) than those on farms located in seacoast landscapes. Lifelong geographic isolation of cattle to insular Newfoundland was associated with significantly lower JCV seroprevalence (P < 0.01) than that for cattle which had lived off-island.

[Investigation of Tahyna virus infection among unknown fever cases in Xinjiang, China]

To investigate the infection status and the spatial distribution of Tahyna virus infection among unknown fever cases in Xinjiang, China. Sera samples of unknown fever cases from Kashi in southern Xin-jiang and Yili in northern Xinjiang were tested against Tahyna virus by IFA. Partial positive cases were tested against Tahyna virus/Snowshoe hare virus/Inkoo virus parrelled. Finally, 742 sera samples of unknown fever cases were collected from Kashi, Southern Xinjiang in 2007-2008, the positive rate of IgM antibody against Tahyna virus was 5.3%, the positive rate of IgG antibody against Tahyna virus was 18.3%. 222 sera samples of unknown fever cases were collected from Yili, Northern Xinjiang in 2008, no positive case of IgM antibody against Tahyna was found. 10 cases showed antibody neutralization against Tahyna virus by plaque reduction neutralization test. Our results demonstrate that there is current infection and past infection of Tahyna virus among Southern Xinjiang residents.

[Adverse immunologic effects of immunomodulators revealed in experiment and ways to their surmounting]

Immunomodulators licopid (synthetic analogue of muramylpeptide) and purified staphylococcal toxoid (PST) in some variants of experiments on mice caused adverse immunologic effects: enhancement of virus-induced immunosupression, shift from latent immunosupression (revealed only by low, but not standard, doses of test-antigen) to manifested one. Described adverse effects are not a contraindication for use of the studied drugs in practice. Their adverse effects were revealed only after single inoculation, whereas in clinical conditions PST and licopid are used by courses with duration of 5-7 and 10 days respectively. Our experiments show that inoculation of suppressive doses of the preparations repeated by 2-4 times can prevent the shift from latent to manifested immunosupression. Enhancement of immunosupression was not observed in case of combined administration of suppressive doses of PST and adjuvant dose of licopid.

Micromodification of virus-neutralisation assay with vital staining in 96-well plate and its use in diagnostics of Tahyna virus infections

Virus neutralization test (VNT) is considered to be the gold standard for arbovirus serology because of its high specificity and sensitivity. Its micromodification in 96-well plate with vital staining of cell cultures was developed in the National Reference Laboratory (NRL) for Arboviruses of the Czech Republic and is used for the detection of specific antibodies against various viruses, mainly arboviruses. The test procedure is described for the Tahyna virus micromodified neutralization assay in 96-well plate. Results of an anti-Tahyna antibody survey conducted among the population of northern Moravia using the VNT assay are presented. The overall anti-Tahyna seroprevalence among 1001 tested persons was 3.80%. The highest positivity rate was found in persons aged over 59 years (17.53%) comparing to children with the seroprevalence rates of 0.00% and 0.56% in the age groups 0-5 years and 6-14 years, respectively.

[Isolation of influenza virus A (Orthomyxoviridae, Influenza A virus), Dhori virus (Orthomyxoviridae, Thogotovirus), and Newcastle's disease virus (Paromyxoviridae, Avulavirus) on the Malyi Zhemchuzhnyi Island in the north-western area of the Caspian Sea]

The paper presents the results of the 2003 and 2006 environmental virological monitoring surveys on the Malyi Zhemchuzhnyi Island where a large breeding colony of sea gull (Laridae) is located. In the past several years, expansion of cormorants (Phalacrocorax carbo) has enhanced the intensity of populational interactions. The investigators isolated 13 strains of influenza A virus (Orthomyxoviridae, Influenza A virus) subtype H13N1 (from sea gulls (n = 4), cormorants (n = 9) 1 strain of Dhori virus (Orthomyxoviridae, Thogotovirus) from a cormorantwith clinical symptoms of the disease, 3 strains of Newcastle disease virus (Paramyxoviridae, Avulavirus) from cormorants. RT-PCR revealed influenza A virus subtype H5 in 3.1% of the cloacal lavages from cormorants. Neutralization test indicated that sera from cormorants contained specific antibodies against West Nile (Flaviviridae, Flavivirus) (15.0%), Sindbis (Togaviridae, Alphavirus) (5.0%), Dhori (10.0%), and Tahini (Bunyaviridae, Orthobunyavirus) (5.0%); sera from herring gulls had antibodies against Dhori virus (16.7%); there were no specific antibodies to Inco (Bunyaviridae, Orthobunyavirus) and mountain hare (Lepus timidus) (Bunyaviridae, Orthobunyavirus) virus.

Seroprevalence of tick-borne and mosquito-borne arboviruses in European brown hares in Northern and Western Germany

Tríbec virus (Kemerovo serogroup, genus Orbivirus), Eyach virus (genus Coltivirus), and Tahyna virus (California encephalitis serogroup, genus Bunyavirus) are arthropod-borne viruses known to occur in Germany. These viruses are also suspected to cause human disease. So far, no information is available on their geographical distribution in Germany and their natural transmission cycles. A total of 166 sera from European brown hares (Lepus europaeus) collected in seven districts of the Federal State of Schleswig-Holstein and in four districts of the Federal State of North Rhine-Westphalia was tested by plaque reduction neutralization test (PRNT) for antibodies against Tríbec virus, Eyach virus, Tahyna virus, and Central European encephalitis virus. One out of 22 sera (4.5%) collected in the district Nord-Friesland in Schleswig-Holstein was found positive (PRNT(90) 1:10) against Tríbec virus. Neither did sera from other regions of Schleswig-Holstein nor from hares from North Rhine-Westphalia react against any of the arboviruses tested. For the first time, antibodies against Tríbec virus could be found in a European brown hare in Germany. The negative serological results for Central European encephalitis virus are in line with the current knowledge of its natural distribution within Germany. The negative serological results for Tahyna virus or Eyach virus argue against an autochthonous circulation of these viruses in the regions tested.

[The ecology and prevalence of arboviruses on the territory of the Saratov Region]

The territorial spread of Tahyna, Batai, Sindbis, West Nile fever and Crimean-Congo hemorrhagic fever viruses throughout the Saratov region in 1998 - 2000 was analyzed. The characteristics of the epizootic activity of the natural foci of these arboviruses in different landscape zones (temperate forest-steppes, steppes and semi-deserts) were calculated. The species composition of small mammals, the natural reservoirs of the causative agents of arbovirus infections, was determined.

Mosquitoborne viruses, Czech Republic, 2002

Specimens from residents (n = 497) of an area affected by the 2002 flood were examined serologically for mosquitoborne viruses. Antibodies were detected against Tahyna (16%), Sindbis (1%), and Batai (0.2%) viruses, but not West Nile virus. An examination of paired serum samples showed 1 Tahyna bunyavirus (California group) infection.

[Antibodies against mosquito-born viruses in human population of an area of Central Bohemia affected by the flood of 2002]

In the Central-Bohemian area affected by the flood of 2002, 497 residents were screened for antibodies against the mosquito-borne viruses Tahyna (TAHV), West Nile (WNV), Sindbis (SINV) and Batai (BATV; syn. Calovo) using the haemagglutination-inhibition (HIT) and plaque-reduction neutralization (PRNT) tests. Blood samples were collected in September 2002 when the mosquito populations showed the maximum density following the flood. Antibodies against TAHV (16.5% persons in PRNT, 14.9% in HIT), SINV (1.4% in HIT) and BATV (1.4% in HIT, 0.2% in PRNT) were detected. Although 6.8% and 1.2% of the subjects tested reactive with WNV in HIT and PRNT, respectively, the results were interpreted as cross-reactivity with tick-borne encephalitis virus. The seroprevalence of TAHV (both in PRNT and HIT) showed no association with gender (15.8% of males, 16.9% of females), increased with age (1.4% of persons younger than 20 years, 11.2% of persons aged between 20 and 50 years, and 26.2% of persons older than 50 years were positive), and correlated with the mosquito peri-residential challenge (5.0% residents seropositive in a mosquito-free control zone D--mostly Prague, 14.7% in a mild-risk zone C, 20.5% in a moderate-risk zone B, and 28.0% in the most heavily mosquito-infested risk zone A). The highest TAHV seropositivity rate (> 25%) was found amongst the inhabitants of the villages Obríství, Kozly, Tuhan, Chrást, Chlumín and Hostín. Paired blood samples were obtained from 150 of the persons at a 6-month interval: an infection episode with TAHV during or after the flood was clearly evidenced in one person living in Obríství, and less convincing findings of recent TAHV infections were found in other three residents of Chlumín and Obríství (seroconversion and/or significant antibody titres increase detected in HIT only). This serosurvey indicated the existence of an active natural focus of Valtice fever (TAHV infection) stretched along the river Labe nearby Neratovice (Obríství, Chlumín, Tuhan; Kozly, Tisice, Chrást), and a low TAHV activity area along the lower reaches of the river Vltava between Zloncice and Bukol/Zálezlice. An increased population density of mosquitoes after the flood may have boosted the incidence of mosquito-borne virus diseases, particularly Valtice fever, in Central Bohemia. An optimum prophylactic strategy to control these diseases would be epidemiological surveillance (including monitoring of both the density of mosquitoes and their rate of infection with viruses in natural foci) on the basis of which antiepidemic measures such as integrated mosquito control can be taken.

Prevalence of antibodies against Saint Louis encephalitis and Jamestown Canyon viruses in California horses

Jamestown Canyon (JC) and Saint Louis encephalitis (SLE) viruses are mosquito-transmitted viruses that have long been present in California. The objective of this study was to determine the seroprevalence of these two viruses in horses prior to the introduction of West Nile (WN) virus. Approximately 15% of serum samples collected in 1998 from 425 horses on 44 equine operations horses throughout California had serum antibodies to JC virus, whereas antibodies were not detected to SLE virus. The results indicate that horses in California were commonly infected prior to 1998 with mosquito-transmitted Bunyaviruses that are identical or closely related to JC virus, but not with SLE virus. The different seroprevalence of SLE and JC viruses in horses likely reflects the unique ecology of each virus, and it is predicted that WN virus will have a wider distribution in California than closely related SLE virus.

Identification and localization of conserved antigenic epitopes on the G2 proteins of California serogroup Bunyaviruses

California (CAL) serogroup Bunyaviruses are significant agents of arboviral encephalitis in humans. They are maintained and transmitted in nature by mosquitoes to preferred vertebrate amplifying hosts. The G2 envelope glycoprotein of La Crosse virus (LAC) was proposed by Ludwig et al. to be a determinant for virus attachment to mosquito midgut cells. Monoclonal antibodies to G2 neutralize the infectivity of pronase-treated virus for mosquito cells. We determined the location of antigenic sites on the LAC G2. We showed that antigenic areas present on the LAC G2 protein are conserved among viruses in the California encephalitis and Melao subgroups of the CAL serogroup, but not in trivatattus virus, nor within the BUN serogroup. A comparison of the G2 exodomain amino acid sequences of eight CAL and three BUN viruses with monoclonal antibodies (MAb) binding data predicted the possible location of the antigenic sites. We used in vitro mutagenesis of the LAC G2 gene to construct a set of G2 genes with replacement sequences in the coding regions for the suspected MAb binding sites. The native and mutated proteins were expressed in Hela cells and the ability of MAbs to bind to the expressed proteins was tested. Four discontinuous amino acid sequences, conserved among eight CAL serogroup viruses, were identified as contributing to two conformational binding domains for neutralizing LAC G2 MAbs.

The first reported case of California encephalitis in more than 50 years

A recent case of California encephalitis, a rare mosquito-borne viral disease, represents only the fourth ever reported and the first since the initial three cases in 1945. This case was diagnosed retrospectively on the basis of a rise in antibody titer between acute- and convalescent-phase serum samples.

Seroepidemiology of California and Bunyamwera serogroup (Bunyaviridae) virus infections in native populations of Alaska

This study investigated the geographic distribution and prevalence of antibodies to California and Bunyamwera serogroup viruses in Native populations of Alaska, and demographic and ecologic risk factors associated with exposure. Sera (n = 1,635) from 18 communities were screened using an ELISA. All age groups were tested for antibodies to Jamestown Canyon (JC), Inkoo (INK), snowshoe hare (SSH), and Northway (NOR) viruses; persons > or = 45 years old (n = 90) from six communities were additionally tested for antibodies to Tahyna (TAH), Batai (BAT), Cache Valley (CV), and Sindbis (SIN) viruses. Thirty free-ranging mammals were tested by a plaque reduction neutralization test (PRNT) for antibodies to all eight viruses and to Getah (GET) virus. In Natives, overall antibody prevalence was 24.9% (JC = 17.6%, monotypic JC = 6.5%, INK = 11.1%, monotypic INK = 0.6%, SSH = 6.8%, monotypic SSH = 3.5%, and NOR = 6.2%). Five TAH, CV, and BAT virus exposures may be serologic cross-reactions, and no SIN virus antibodies were detected. Sindbis-like virus antibodies were found in 30% of the mammals. Most mammals had antibodies to NOR (83.3%) and California serogroup (70.0%) viruses; no GET virus exposures were found. Significant risk factors for human bunyavirus exposures were age group, ethnic-linguistic group, biotic province, climate zone, terrestrial vegetation, and presence of some ungulates and small mammals in communities. Sex was not a significant risk factor.

[Indication and identification of California serogroup viruses in experimentally infected Ae. aegypti mosquitos by a lanthanum immunofluorescent analysis method]

The sensitivity and specificity of lanthanide fluoroimmunoassay (LFIA) and enzyme immunoassay (EIA) for indication and identification of California antigens in suspensions of infected Aedes aegypti mosquitoes are compared. The sensitivity of LFIA was 2.3 Ig TCD50/ml, EIA was less sensitive and detected virus antigens in mosquito suspensions at infective titer of 4.1 Ig TCD50/ml. If a pool contained mosquitoes infected with different California viruses, they could be identified only at the level of serological complex.

[Diseases associated with viruses of the California encephalitis serogroup, in Russia]

Studies of 1986-1995 revealed diseases etiologically connected with California serogroup viruses (Bunyaviridae, Bunyavirus) all over the country. Highly endemic zones are the tundra, taiga, and leafy forest. The disease occurs mainly in summer, the patients are mostly young: under 30 years of age. Analysis of 183 cases confirmed by laboratory findings enabled us to distinguish the following forms: influenza-like (70.9%) with the predominant involvement of the bronchopulmonary system (bronchitis and pneumonia) and neuroinfection (20.2%) (serous meningitis and meningoencephalitis).

Serologic evidence of Jamestown Canyon virus infection in white-tailed deer populations from Connecticut

We determined the prevalence and distribution of Jamestown Canyon (JC) virus antibody in white-tailed deer (Odocoileus virginianus) populations in Connecticut, USA. Sera were collected from hunter-killed deer during 1993. Antibody to JC virus was detected by enzyme-linked immunosorbent assay (ELISA) in 92 (21%) of 446 deer sera, and was uniformly distributed among geographic sites. Twenty-one ELISA-positive sera were tested and confirmed positive by plaque reduction neutralization testing. This represents the first serologic evidence of JC virus in a reservoir host population from the northeastern United States. No cross-reactivity was seen with California encephalitis, Keystone, or snowshoe hare viruses, but a varying degree of cross-reactivity was obtained with Guaroa, Jerry Slough, La-Crosse, San Angelo, and trivittatus viruses. We conclude from this investigation and previous isolations of JC virus from mosquitoes in the state that JC virus occurs enzootically in Connecticut.

Summing up, weak immunomodulating signals of Tahyna virus and immunomodulating drugs induce immunosuppression in mice

The successive injection of non-immunomodulating doses of Tahyna virus (100 LD50) and non-immunomodulating doses of immunomodulating drugs, such as purified staphylococcal toxoid or glucosaminylmuramyldipeptide (Likopid), to mice were accompanied by a decrease in the IgM plaque-forming cell response to sheep red blood cells.

[A circulation study of California serogroup and Batai viruses (fam. Bunyaviridae, genus Bunyavirus) on the territory of Saratov Province]

Examining 337 sera from Saratov healthy residents in the neutralization test with Tyaginya and Inco viruses has revealed 56 positive results (16.6%), of which 19 (5.6%) reacted only with Tyaginya virus, 13 (3.9%) did only with Inco virus, and 24 (7.1%) simultaneously with these two viruses. Batai virus antibodies were not detected in the population. Among 80 bovine serum samples collected in the Saratov district of the region, type-specific antibodies to Tyaginya virus were found in 10 (12.5%) and a serum (1.2%) reacted with Tyaginya and Inco viruses; 49 sera (61.2%) contained Batai virus antibodies.

Ecology of Jamestown Canyon virus (Bunyaviridae: California serogroup) in coastal California

This paper reports the first isolation of Jamestown Canyon (JC) virus from coastal California and the results of tests for antibody to JC virus in mammals living in coastal California. The virus isolation was made from a pool of 50 Aedes dorsalis females collected as adults from Morro Bay, San Luis Obispo County, California. The virus isolate was identified by two-way plaque reduction-serum dilution neutralization tests done in Vero cell cultures. Sera from the mammals were tested for antibody to JC virus by a plaque-reduction serum dilution neutralization method. A high prevalence of JC virus-specific antibody was found in horses and cattle sampled from Morro Bay. This finding is additional evidence for the presence of a virus antigenically identical or closely related to JC virus in Morro Bay and indicates that the vectors of the virus in Morro Bay feed on large mammals. A high prevalence of virus-specific antibody was also found in horses sampled from Marin and San Diego counties. This finding suggests that viruses antigenically identical or closely related to JC virus are geographically widespread in coastal California.

[The circulation of the California encephalitis complex and Batai viruses in the Lake Baikal region (serological research data)]

The serological materials of the indigenous population and cattle suggest that there are viral foci of a complex of California encephalitis with the circulation of viruses of Inkoo, Tahyna [correction of Tyagin], and the white hare. The results of examining the residents of Irkutsk also suggest that there are urban viral foci of a complex of California encephalitis. The epidemiological potential of the natural foci of Batai virus is insignificant in the Baikal region.

[Outcomes and prognosis of diseases caused by Inkoo and Tahyna viruses]

The outcomes of diseases caused by Inkoo and Tahyna viruses are favorable. No lethal cases were observed. Altogether 16.7% of convalescents after the febrile form of the disease and 30.7% convalescents after the neuroinfections form develop 1 to 2.5 years after the disease (follow-up period) asthenoneurologic disturbances and microfocal neurologic symptoms. Blood sera of 118 patients with chronic neurologic diseases were tested in the neutralization test with Inkoo and Tahyna viruses. Summary antibodies to Inkoo and Tahyna viruses were detected in 26 (70.3%) of 37 examined patients with disseminated encephalomyelitis. The findings point to necessity of further study of the possible role of California encephalitis group viruses in the etiology of chronic neuroviral infections.

A serologic survey for some bacterial and viral zoonoses in game animals in the Czech Republic

Between 1986 and 1991, sera were collected from 33 roe deer (Capreolus capreolus), 24 red deer (Cervus elaphus), four fallow deer (Dama dama), two mouflon (Ovis musimon), 34 wild boars (Sus scrofa), and 48 hares (Lepus europaeus) shot in two areas of the Czech Republic. Collectively, the sera contained antibodies to Coxiella burnetii (prevalence of 12%), Francisella tularensis (4%), Brucella spp. (2%), Central European tick-borne encephalitis virus (8%), Tahyna (California serogroup) virus (36%), and Calovo (= Batai) virus (23%). We propose that these mammals may play a role in maintaining natural foci of Q-fever, Tahyna fever and Calovo virus infection.

Vector and host relationships of California serogroup viruses in western Siberia

During 1990 and 1991, adult mosquitoes were collected along the Ob River and its tributaries in western Siberia from approximately 51 degrees 18'N to 66 degrees 4'N. Fifteen virus strains were isolated from 74,196 mosquitoes tested in 1,874 pools. These included Tahyna virus from Aedes cataphylla-punctor subgroup (one) and Ae. excrucians (one), and Inkoo (INK) virus from Ae. communis (one), Ae. communis subgroup (one), Ae. hexodontus (two), Ae. punctor subgroup (two), Ae. punctor complex (one), and unidentified Aedes species (three). In addition, a single Ae. euedes yielded a strain of snowshoe hare (SSH) virus and a strain of Getah, an alphavirus. A Bunyamwera serogroup virus was isolated from Ae. excrucians. With the exception of the two isolates from a single mosquito, minimum infection rates among mosquito taxa ranged from 0.4 to 16.7 per 1,000. The INK virus isolates were widely distributed geographically; however, seven of the 10 isolates were from two sites north of the Arctic Circle. During 1991, sera from two mouse species, five vole species, and four shrew species were collected along the upper Ob River for serologic tests. The prevalence of neutralizing antibody to SSH virus in these sera was 80%. Prevalence rates in the four most abundant species were Apodemus agrarius, 73%; Clethrionomys rutilus, 71%; Microtus arvalis, 80%; and Sorex araneus, 91%. This is the first attempt to clarify the vector and vertebrate host relationships of California serogroup viruses in western Siberia.

Isolation of Jamestown Canyon and snowshoe hare viruses (California serogroup) from Aedes mosquitoes in western Massachusetts

Three isolates of Jamestown Canyon virus and one isolate of snowshoe hare virus (California serogroup) were obtained from adult Aedes females collected in western Massachusetts in 1982. Jamestown Canyon virus was isolated from Aedes abserratus/punctor once, and from Aedes intrudens twice. Snowshoe hare virus was isolated from Aedes stimulans group mosquitoes. La Crosse encephalitis (LAC) virus was not isolated from 1,552 adult Aedes triseriatus, nor from 22,557 Aedes triseriatus larvae. However, sera from 1/178 eastern chipmunks, 5/31 gray squirrels, and 8/144 white-tailed deer had neutralizing antibody to LAC virus. No sentinel rabbits placed at sites yielding virus isolates seroconverted to CAL viruses in either year.

Genomic and biologic analyses of snowshoe hare virus field and laboratory strains

Low-passage field strains of snowshoe hare (SSH) virus (Bunyaviridae), the prototype SSH virus (originally isolated in Montana), and La Crosse (LAC) virus were compared serologically by plaque-reduction neutralization (PRNT) and molecularly by oligonucleotide fingerprinting (ONF). The PRNT and ONF results confirmed the identity of the field strains, although some differences in the fingerprints were observed. We have examined the RNA genome variability in the two field and three laboratory strains of SSH virus, using direct sequence analysis of selected RNase T1 oligonucleotides. Few changes were observed among three Montana prototype-derived laboratory isolates, although they have different passage histories. In contrast, the field isolates differed greatly from the laboratory strains. In addition, we have located several of the larger T1 oligonucleotides within the known sequence of the small and large RNA genome segments. We then compared the viruses for their ability to replicate in and be transmitted by Aedes triseriatus mosquitoes. The oral infection rates for LAC, the field isolates, and the SSH prototype, as determined by immunofluorescent examination of midgut tissues, were 100%, 82%, and 47%, respectively. All viruses were also transmissible from mosquitoes to mice.

Monoclonal antibody characterization of Jamestown Canyon (California serogroup) virus topotypes isolated in Canada

Jamestown Canyon (JC) virus of the California (CAL) serogroup has been isolated in 12 American states and 6 Canadian provinces. A study was undertaken to produce monoclonal antibodies (MAbs) to JC virus and to use these MAbs to assay for possible heterogeneity among naturally occurring JC topotypes in Canada. MAbs were produced to the prototype strain of JC virus using BALB/c mice. Twenty-seven secreting MAbs were obtained and three of these MAbs were propagated and studied. All three MAbs, M1 (IgG1), M2 (IgG2b), and M3 (IgG2a), were reactive by immunofluorescent antibody assay against JC-infected vero cells and by ELISA against JC antigen. MAb M2 reacted with all members of the Melao complex, MAb M1 reacted only with Keystone virus, while MAb M3 exhibited no reactivity with other CAL serogroup viruses. Only MAb M3 possessed neutralization and hemagglutination inhibition activities against JC virus. The MAbs were also tested by ELISA and for neutralizing activity against 13 JC topotypes isolated in 5 provinces from Newfoundland to Saskatchewan. ELISA confirmed closer identity of the Canadian topotypes to JC as opposed to the closely related South River virus. The MAbs verified all Canadian topotypes to be JC virus but revealed different patterns of reactivity between these topotypes and prototype JC virus.

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.

California serogroup virus infections in the Ryazan region of the USSR

Serum samples from 60 people diagnosed in the summer of 1989 as having acute respiratory infections, meningitis or meningoencephalitis, acute pneumonia, Lyme disease, or other illnesses were tested by neutralization and hemagglutination-inhibition with Tahyna, Inkoo, and snowshoe hare viruses of the California serogroup (family Bunyaviridae, genus Bunyavirus). Demonstration of a diagnostic increase in antibody titers between paired serum samples from seven people showed that their illnesses were probably caused by Inkoo or Tahyna viruses. The clinical pictures were less specific. One patient had signs of meningoencephalitis, three had signs of meningitis, and three had influenza-like illnesses. These observations and other results suggest that California serogroup viruses are widespread in Russia and may account for an unexpectedly large number of presently undiagnosed febrile illnesses, some with central nervous system involvement.

A serologic study of California serogroup bunyaviruses in Sri Lanka

A seroepidemiologic study of California (CAL) serogroup viruses (genus bunyavirus, family Bunyaviridae) was carried out on 952 human and 1,834 animal sera collected from different ecological zones of Sri Lanka (latitudes 5-10 degrees N, longitudes 79-82 degrees E). The sera were screened for neutralizing antibody to Lumbo (LUM), snowshoe hare (SSH), and trivittatus (TVT) viruses by plaque neutralization tests on Vero cells. Of 2,786 sera screened, 262 (9.5%) had antibody to one or more viruses Twenty-two sera, selected to represent different species of origin and reaction profiles, were titrated against nine CAL viruses: LUM, SSH, TVT, Tahyna (TAH), California encephalitis (CE), La Crosse (LAC), Inkoo (INK), Melao (MEL), and Guaroa (GRO). Results suggested that there were multiple CAL viruses active in Sri Lanka, one or more of them closely related to LUMBO and SSH viruses, and another related to MELAO virus. These viruses were active in both the wet and dry zones of the country, and infected humans as well as a range of domestic livestock.

California serogroup viruses from mosquitoes collected in the USSR

Four California serogroup viruses isolated from mosquitoes in the USSR were tested for antigenic analogy with prototype viruses of the California serogroup. The topotype isolates are biologically similar to, but antigenically different from each other. One is a subtype of snowshoe hare virus, two are different subtypes of Tahyna, Lumbo, and snowshoe hare viruses, and one is identical to Inkoo virus, previously isolated only in Finland. The results indicate that molecular studies of these viruses are necessary to comprehend their evolution.

Serological evidence of California group and Cache Valley virus infection in Minnesota white-tailed deer

Blood samples were obtained from 138 white-tailed deer (Odocoileus virginianus) harvested at three sites surrounding the greater Minneapolis-St. Paul, Minnesota, metropolitan area (USA) and tested for neutralizing antibody to Cache Valley virus and three California serogroup (Jamestown Canyon, La Crosse, trivittatus) viruses (Bunyaviridae). Deer at each site had neutralizing antibody to one or more California serogroup viruses and/or Cache Valley virus. The majority of adult deer (85%) had antibody to both a California serogroup virus and Cache Valley virus. Antibody prevalence varied significantly with age of the deer. Fawns had a significantly lower prevalence of antibody to either a California serogroup (17%) or Cache Valley virus (39%) than did older (greater than 1-yr-old) deer (89% for a California serogroup virus and 91% for Cache Valley virus). The geometric mean titers of antibody in fawns to California serogroup (1:6) and Cache Valley viruses (1:17) were also less than that seen in older animals (1:11 and 1:28 for California serogroup and Cache Valley viruses, respectively). Of 76 older deer with antibody to the California serogroup, 91% had antibody specific for Jamestown Canyon virus. Jamestown Canyon is the primary California serogroup virus circulating in the suburban/rural Minneapolis-St. Paul area. Transmission occurs in an enzootic pattern similar to that documented in Indiana and Michigan. Cache Valley virus also appears to be enzootically transmitted in this area. However, the impact on domestic or wild animal populations is unknown.

Effects of specific monoclonal antibodies on La Crosse virus neutralization: aggregation, inactivation by Fab fragments, and inhibition of attachment to baby hamster kidney cells

At high concentrations, several monoclonal antibodies to the G1 glycoprotein of La Crosse (LAC) virus aggregated the virus. To determine whether this accounted for the neutralization, the monoclonal antibodies were digested to make Fab fragments. With one exception, each monovalent antibody neutralized LAC virus to the same extent that bivalent antibody did, although higher concentrations were needed. Fab fragments of synergistic pairs of antibodies also exhibited enhanced binding in a competition binding assay but did not increase neutralization. To determine specific mechanisms for neutralization, the effects of polyclonal or monoclonal antibodies on virus attachment were examined. Polyclonal antibody to LAC virus reduced virus attachment by only 68% although it neutralized 99.99% of the virus. When virus was preincubated with a neutralizing monoclonal antibody to each of seven antigenic regions on G1, only antibody to one region reduced attachment of virus by as much as 92%. Antibodies to two regions that neutralize virus by 90-98% only inhibited attachment by 9 and 13%, respectively. The other antibodies showed intermediate degrees of neutralization and inhibition of attachment. Pairs of antibodies previously shown to be synergistic in neutralizing activity did not inhibit attachment any more than the single antibodies did.

Distribution of neutralizing antibodies to California and Bunyamwera serogroup viruses in horses and rodents in California

Neutralization tests were done on sera from 141 horses from high elevation regions of California. Antibody prevalences to Jamestown Canyon, snowshoe hare, and California encephalitis viruses in the California serogroup and Northway virus in the Bunyamwera serogroup were 55%, 43%, 18%, and 46%, respectively. In 51 horses from rural low elevation regions, seroprevalences were 31%, 35%, 35%, and 37%, respectively. Twenty-four horses from a suburban lowland area were seronegative, except for a single horse with a low titer to snowshoe hare virus. Seroprevalence to Jamestown Canyon and snowshoe hare viruses was associated with increasing age. Only 2 of 177 rodents from the Sierra Nevada had antibodies to Northway virus; none had antibodies to Jamestown Canyon or snowshoe hare viruses.

Monoclonal antibodies specific for the G1 glycoprotein of La Crosse virus that react with other California serogroup viruses

Various degrees of cross-reactivity have been observed among members of the California serogroup of bunyaviruses. Since the G1 glycoprotein of La Crosse (LAC) virus, a member of this serogroup, has been shown to contain the antigenic determinants involved in neutralization, monoclonal antibodies to this glycoprotein were used in enzyme immunosorbent and kinetics of neutralization assays with the other California viruses to detect cross-reactive sites that may be involved in neutralization. The results first indicated that five of the antigenic regions previously mapped on the LAC G1 glycoprotein contained overlapping epitopes within them. In all, a total of 16 epitopes within eight antigenic regions were identified on the G1 glycoprotein of LAC virus. One epitope was found on all of the California viruses and is therefore a group-specific antigenic determinant. A LAC-specific epitope was also identified. Different patterns of reactivity were observed among the California viruses for the rest of the antibodies. When the monoclonal antibodies (MAbs) were assayed with the uncloned reference strain of LAC and with two New York isolates, differences were found for epitopes within two antigenic regions. With one exception (snowshoe hare virus, a variety of LAC), pairs of antibodies shown to enhance neutralization of LAC virus did not increase neutralization of the other California viruses having the corresponding pairs of epitopes.

[The clinico-laboratory characteristics of cases of diseases connected with viruses of the California encephalitis complex in the inhabitants of Moscow]

To study the role of viruses of the California encephalitis virus complex (the family Bunyaviridae) in infectious pathology, 187 fever patients admitted to the Clinical Infectious Hospital in May-September 1986 were examined. In 10 of these patients the neutralization test revealed the presence of diagnostically significant changes in neutralizing antibodies (neutralization indices), which was indicative of the role played by Tahyna virus or other related viruses belonging to the California encephalitis virus complex in the etiology of the diseases. The analysis of the clinical picture showed that in all patients the disease took an acute course in its initial stage, starting with shivering and characterized by high fever, headache, pronounced toxicosis, the possibility of the formation of intracerebral hypertension and pneumonia.

[Significance of viruses of antigen complex of California encephalitis in pathology]

A study was undertaken to examine 320 patients with seasonal fevers occurred in June to September. These included fever of unknown etiology, acute respiratory virus diseases, pneumonias, bronchitis, enterovirus diseases, and serous meningitis. Serological tests revealed that in 20 (6.3%) of them the viruses of the complex in California encephalitis (Tyagin's virus or antigenically related virus) contributed to the etiology of the disease. Major clinical symptoms of the disease were defined in this group of patients. The disease appeared as neuroinfections (serous meningitis), influenza-like conditions (fever, symptoms of intoxication), occasionally, infiltrative changes in the lung. Thus, the viruses of the antigen complex of California encephalitis makes an etiological contribution to infectious abnormalities.

[Antiviral activity of ribamidyl in experimental infections with California encephalitis group viruses]

A preparation of ribamydil, an analogue of natural nucleosides, synthesized at the Latvian SSR Institute of Organic Chemistry showed a sufficiently high activity against bunyaviruses of California encephalitis complex both in vitro and in vivo. Various modifications of the enzyme immunoassay may be used for control of the effectiveness of treatment with this drug. Some advantages of the subcutaneous route over the intramuscular one were found. Ribamydil may be useful for treatment of infections of California encephalitis complex.

[Isolation of viruses of antigenic complexes of California encephalitis and Bunyamwera (Bunyaviridae, Bunuavirus) from mosquitoes in northeast Asia]

Studies in suckling mice and by direct solid-phase enzyme immunoassay were carried out with 111,1 thousand Aedes mosquitoes collected in July, 1986, in tundra, forest-tundra, and northern taiga of Kamchatka region and Chukotka autonomous district of Magadan region (North-Pacific natural area within 69 degrees-53 degrees North and 156 degrees-177 degrees East). Eleven strains were isolated of which 7 were classified as members of the California encephalitis complex (Tahyna-like strains) and 4 as members of the Bunyamwera complex (Batai-like strains). According to electron-microscopic studies of 2 strains (one from each antigenic complex), both were classified as belonging to the family of Bunyaviridae. Strains of both complexes were isolated in all landscape zones examined--tundra, forest-tundra, northern taiga. Virus-neutralizing antibodies to them were found in human and reindeer sera also in all the landscape zones, to Tahyna virus in 11%-61%, to Batain virus in 2%-6% blood specimens. No antibody to Uukuniemi virus was found.

Detection of La Crosse and snowshoe hare viral nucleic acids by in situ hybridization

A molecular hybridization technique was developed to detect bunyavirus RNA in cells. Complementary DNAs (cDNAs) to the small (S) RNA segment of La Crosse (LAC) virus and to a portion of the middle (M) RNA segment of snowshoe hare (SSH) virus were used as probes to detect LAC or SSH viral RNA by in situ hybridization. Protocols were developed and standardized using radiolabeled DNA probes, and adapted for use with biotin labeled probes. The in situ hybridization procedure detected an estimated 3,600 copies of viral S RNA/cell at 24 hr postinfection. In growth curve studies, LAC nucleocapsid antigen was detectable slightly before S RNA. LAC S RNA synthesis was first seen about the nucleus. By 12 hr postinfection, hybridization signal was detected throughout the cytoplasm of the cell. The LAC S RNA probe was group-specific and cross-hybridized to 5 other California group viruses. The SSH M RNA probe was type-specific.

Prevalence of neutralizing antibodies against California and Bunyamwera serogroup viruses in deer from mountainous areas of California

Plaque reduction-serum dilution neutralization was used to evaluate the status of bunyavirus activity in deer in mountainous areas of California. Antibodies against 9 bunyaviruses were measured in 337 mule deer (Odocoileus hemionus hemionus, O. hemionus californicus, and O. hemionus inyoensis) and black-tailed deer (O. hemionus columbianus). More deer from high mountainous areas had neutralizing antibodies against Jamestown Canyon virus than did deer from low mountainous areas (23% vs. 9%; P less than 0.01). This finding is consistent with transmission by snow pool Aedes mosquitoes. Results for Jerry Slough virus were nearly identical to those for Jamestown Canyon virus, which is further evidence that these are strains of the same virus. Neutralizing antibodies against Northway virus were present in 26% of deer from high mountainous areas and 23% of deer from low mountainous areas, suggesting the involvement of a widespread vector, such as Culiseta inornata. Northway virus is not known to occur outside of Alaska and northwestern Canada. Low prevalences of antibodies were detected in deer to California encephalitis, La Crosse, and snowshoe hare viruses of the California serogroup; and Cache Valley, Lokern, and Main Drain viruses of the Bunyamwera serogroup.

Serologic evidence of arboviral infections in white-tailed deer from central Wisconsin

A survey conducted during 1979-1980 on white-tailed deer (Odocoileus virginianus) in central Wisconsin revealed serological evidence of infection by selected arboviruses. Among sera from 41 deer, antibody was detected for Jamestown Canyon virus (56%) and Bunyamwera group virus (80%), demonstrating their continuing endemic activity. Antibody for La Crosse virus, not found previously in sera from deer in central Wisconsin, also was detected (5%) in this study.

[An arbovirus study of pregnant women in Southern Moravia]

The authors revealed by means of the haemagglutination-inhibition test (HIT) and the plaque reduction neutralization test (PRNT) that in 1983 to 1985 pregnant women in the Breclav district became infected with the Tahyna virus. HI antibodies against the virus were detected in 96 (28.4%) women from a total of 338 examined. A new infection was proved in 15 (4.4%) women. The majority of infections was contracted in August to October. Positive results were supported by the PRNT. Antibodies against arboviruses Sindbis, Calovo, West Nile, tick-borne encephalitis, Bhandza were not detected in any of the women.

California serogroup virus infections in Wisconsin domestic animals

A serologic survey and experimental virus transmission studies were done to assess the role of domestic animals as amplifier hosts of La Crosse (LACV) and Jamestown Canyon (JCV) viruses. Serum from 319 cows, 88 dogs, 122 equines, 47 swine, 10 goats, and 4 cats were tested for neutralizing antibody to LACV, JCV, trivittatus (TVTV), and snowshoe hare (SSHV) viruses. Antibody prevalences of LACV, TVTV, and SSHV were less than 10% in all species. Antibody to JCV was detected in all species except cats. Prevalence ranged from 10% in goats and swine to 29% in dogs. No age-associated trends in JCV prevalence were noted. Two of 6 adult dogs, and 2 of 4 pigs inoculated with 6.3-6.5 log10 suckling mouse intracerebral 50% lethal doses (SMICLD50) of LACV developed viremias ranging of less than 1.0-2.9 log10 SMICLD50/ml 1-3 days after inoculation. Of 4 puppies inoculated with LACV, 3 developed fatal infections. Viremias were not detected in 4 cows, 4 ponies, 7 cats, or 6 sheep. Two cats fed LACV infected suckling mice shed virus from the oropharynx for 1 day each. All animals except 1 cow, 1 cat, and 1 sheep had greater than or equal to 4-fold rise in antibody titers. Five additional dogs fed upon by LACV-infected Aedes triseriatus mosquitoes did not develop viremias or antibody and uninfected Ae. triseriatus engorging on the dogs 1-5 days after feeding by infected mosquitoes failed to become infected. Five ponies, 6 calves, 2 ewes, 6 dogs, and 5 piglets were inoculated with 3.6-7.3 log10 SMICLD50 of JCV. None developed detectable viremias, although greater than or equal to 4-fold rises in antibody titers developed in 60% of the ponies, 17% of the calves, 50% of the dogs, and 1 of 2 ewes. None of the pigs developed corresponding rises in antibody titers. We conclude that juvenile and adult animals of the species tested are not efficient amplifier hosts of LACV or JCV, but may be useful sentinels of local virus transmission.

Interference to oral superinfection of Aedes triseriatus infected with La Crosse virus

Aedes triseriatus orally infected with a temperature-sensitive mutant of La Crosse virus were, at predetermined times post-infection, orally challenged with wild type La Crosse or Tahyna virus. Most mosquitoes challenged with wild type La Crosse virus within 24 hr of ingestion of the temperature-sensitive virus became superinfected. In contrast, the majority of mosquitoes challenged at 72 hr were resistant to superinfection. Mosquitoes challenged at 7 days or thereafter were refractory to superinfection with La Crosse or Tahyna virus. The onset of interference was correlated with virus titer and antigen expression in midgut cells.