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

Snowshoe hare virus: discovery, distribution, vector and host associations, and medical significance

Snowshoe hare virus (SSHV), within the California serogroup of the genus Orthobunyavirus, family Peribunyaviridae, was first isolated from a snowshoe hare (Lepus americanus) in Montana, United States, in 1959. The virus, closely related to LaCrosse virus (LACV) and Chatanga virus (CHATV), occurs across Canada and the northern latitudes of the United States, primarily in the northern tier of states bordering Canada. Reports of SSHV in northern Europe and Asia are probably the closely related to CHATV, or the less closely related Tahyna virus. Vertebrate associations include snowshoe hares and ground squirrels, demonstrated by field isolation of virus from wild-caught animals, seroconversion of snowshoe hares, seroconversion of sentinel rabbits, isolation of virus from sentinel rabbits, and experimental infections demonstrating viremia. Isolations of virus from field populations of mosquitoes include primarily univoltine and boreal mosquitoes of the genus Aedes, Culiseta impatiens and Culiseta inornata; and, rarely, certain multivoltine floodwater Aedes species. Experimental transmission studies in mosquitoes show infection in and transmission by boreal Aedes and Culiseta inornata. Isolation of SSHV from larval Aedes on three occasions, and experimentation in Culiseta inornata, reveal transovarial transmission of the virus in mosquitoes. Serosurveys reveal exposure to SSHV in human and domestic animals, with rates of seropositivity commonly high in some settings in Alaska and Canada, but disease in humans or horses has rarely been reported, only in Canada.

Genomic characterization of orthobunyavirus of veterinary importance in America

During 2013, in Argentina, three new isolates of serogroup Bunyamwera virus (genus Orthobunyavirus, family Peribunyaviridae) were recovered from two horses with encephalitis, and from an aborted equine fetus. In the present study, we report the complete genome sequence, genetic characterization, and phylogenetic analysis of three new strains isolated in Argentina to clarifying their relationship within the Bunyamwera serogroup virus and to investigate the evolutionary history of viruses with segmented genomes.

Development of reverse genetics systems and investigation of host response antagonism and reassortment potential for Cache Valley and Kairi viruses, two emerging orthobunyaviruses of the Americas

Orthobunyaviruses such as Cache Valley virus (CVV) and Kairi virus (KRIV) are important animal pathogens. Periodic outbreaks of CVV have resulted in the significant loss of lambs on North American farms, whilst KRIV has mainly been detected in South and Central America with little overlap in geographical range. Vaccines or treatments for these viruses are unavailable. One approach to develop novel vaccine candidates is based on the use of reverse genetics to produce attenuated viruses that elicit immune responses but cannot revert to full virulence. The full genomes of both viruses were sequenced to obtain up to date genome sequence information. Following sequencing, minigenome systems and reverse genetics systems for both CVV and KRIV were developed. Both CVV and KRIV showed a wide in vitro cell host range, with BHK-21 cells a suitable host cell line for virus propagation and titration. To develop attenuated viruses, the open reading frames of the NSs proteins were disrupted. The recombinant viruses with no NSs protein expression induced the production of type I interferon (IFN), indicating that for both viruses NSs functions as an IFN antagonist and that such attenuated viruses could form the basis for attenuated viral vaccines. To assess the potential for reassortment between CVV and KRIV, which could be relevant during vaccination campaigns in areas of overlap, we attempted to produce M segment reassortants by reverse genetics. We were unable to obtain such viruses, suggesting that it is an unlikely event.

Serological Survey for Antibodies to Mosquito-Borne Bunyaviruses Among US National Park Service and US Forest Service Employees

Serum samples from 295 employees of Great Smoky Mountains National Park (GRSM), Rocky Mountain National Park (ROMO), and Grand Teton National Park with adjacent Bridger-Teton National Forest (GRTE-BTNF) were subjected to serological analysis for mosquito-borne bunyaviruses. The sera were analyzed for neutralizing antibodies against six orthobunyaviruses: La Crosse virus (LACV), Jamestown Canyon virus (JCV), snowshoe hare virus (SSHV), California encephalitis virus, and Trivittatus virus (TVTV) belonging to the California serogroup and Cache Valley virus (CVV) belonging to the Bunyamwera serogroup. Sera were also tested for immunoglobulin (Ig) G antibodies against LACV and JCV by enzyme-linked immunosorbent assay (ELISA). The proportion of employees with neutralizing antibodies to any California serogroup bunyavirus was similar in all three sites, with the prevalence ranging from 28% to 36%. The study demonstrated a seroprevalence of 3% to CVV across the three parks. However, proportions of persons with antibodies to specific viruses differed between parks. Participants residing in the eastern regions had a higher seroprevalence to LACV, with 24% (18/75) GRSM employees being seropositive. In contrast, SSHV seroprevalence was limited to employees from the western sites, with 1.7% (1/60) ROMO and 3.8% (6/160) GRTE-BTNF employees being positive. Seroprevalence to JCV was noted in employees from all sites at rates of 6.7% in GRSM, 21.7% in ROMO, and 15.6% in GRTE-BTNF. One employee each from ROMO (1.7%) and GRTE-BTNF (1.9%) were positive for TVTV. This study also has illustrated the greater sensitivity and specificity of plaque reduction neutralization test compared to IgG ELISA in conducting serosurveys for LACV and JCV.

Jamestown Canyon Virus Disease in the United States-2000-2013

Jamestown Canyon virus (JCV) is a mosquito-borne orthobunyavirus in the California serogroup that can cause an acute febrile illness, meningitis, or meningoencephalitis. We describe epidemiologic and clinical features for JCV disease cases occurring in the United States during 2000-2013. A case of JCV disease was defined as an acute illness in a person with laboratory evidence of a recent JCV infection. During 2000-2013, we identified 31 cases of JCV disease in residents of 13 states. The median age was 48 years (range, 10-69) and 21 (68%) were male. Eleven (35%) case patients had meningoencephalitis, 6 (19%) meningitis, 7 (23%) fever without neurologic involvement, and 7 (23%) had an unknown clinical syndrome. Fifteen (48%) were hospitalized and there were no deaths. Health-care providers and public health officials should consider JCV disease in the differential diagnoses of viral meningitis and encephalitis, obtain appropriate specimens for testing, and report cases to public health authorities.

Orthobunyaviruses, a common cause of infection of livestock in the Yucatan peninsula of Mexico

To determine the seroprevalence of selected orthobunyaviruses in livestock in the Yucatan Peninsula of Mexico, a serologic investigation was performed using serum samples from 256 domestic animals (182 horses, 31 sheep, 1 dog, 37 chickens, and 5 turkeys). All serum samples were examined by plaque reduction neutralization test using Cache Valley virus (CVV), Cholul virus (CHLV), South River virus (SOURV), Kairi virus, Maguari virus, and Wyeomyia virus. Of the 182 horses, 60 (33.0%) were seropositive for CHLV, 48 (26.4%) were seropositive for CVV, 1 (0.5%) was seropositive for SOURV, 60 (33.0%) had antibodies to an undetermined orthobunyavirus, and 13 (7.1%) were negative for orthobunyavirus-specific antibody. Of the 31 sheep, 6 (19.3%) were seropositive for CHLV, 3 (9.7%) were seropositive for CVV, 4 (12.9%) were seropositive for SOURV, 16 (51.6%) had antibodies to an undetermined orthobunyavirus, and 2 (6.5%) were negative for orthobunyavirus-specific antibody. The single dog was seropositive for SOURV. Four (11%) chickens had antibodies to an undetermined orthobunyavirus, and 1 (20%) turkey was seropositive for CHLV. These data indicate that orthobunyaviruses commonly infect livestock in the Yucatan Peninsula.

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.

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.