C-C motif chemokine receptor 2 and 7 synergistically control inflammatory monocyte recruitment but the infecting virus dictates monocyte function in the brain

Inflammatory monocytes (iMO) are recruited from the bone marrow to the brain during viral encephalitis. C-C motif chemokine receptor (CCR) 2 deficiency substantially reduces iMO recruitment for most, but not all encephalitic viruses. Here we show CCR7 acts synergistically with CCR2 to control this process. Following Herpes simplex virus type-1 (HSV-1), or La Crosse virus (LACV) infection, we find iMO proportions are reduced by approximately half in either Ccr2 or Ccr7 knockout mice compared to control mice. However, Ccr2/Ccr7 double knockouts eliminate iMO recruitment following infection with either virus, indicating these receptors together control iMO recruitment. We also find that LACV induces a more robust iMO recruitment than HSV-1. However, unlike iMOs in HSV-1 infection, LACV-recruited iMOs do not influence neurological disease development. LACV-induced iMOs have higher expression of proinflammatory and proapoptotic but reduced mitotic, phagocytic and phagolysosomal transcripts compared to HSV-1-induced iMOs. Thus, virus-specific activation of iMOs affects their recruitment, activation, and function.

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.

The CARD9-Associated C-Type Lectin, Mincle, Recognizes La Crosse Virus (LACV) but Plays a Limited Role in Early Antiviral Responses against LACV

La Crosse virus (LACV) is a mosquito-transmitted arbovirus and the main cause of virus-mediated neurological diseases in children. To date, little is known about the role of C-type lectin receptors (CLRs)—an important class of pattern recognition receptors—in LACV recognition. DC-SIGN remains the only well-described CLR that recognizes LACV. In this study, we investigated the role of additional CLR/LACV interactions. To this end, we applied a flow-through chromatography method for the purification of LACV to perform an unbiased high-throughput screening of LACV with a CLR-hFc fusion protein library. Interestingly, the CARD9-associated CLRs Mincle, Dectin-1, and Dectin-2 were identified to strongly interact with LACV. Since CARD9 is a common adaptor protein for signaling via Mincle, Dectin-1, and Dectin-2, we performed LACV infection of Mincle^−/− and CARD9^−/− DCs. Mincle^−/− and CARD9^−/− DCs produced less amounts of proinflammatory cytokines, namely IL-6 and TNF-α, albeit no reduction of the LACV titer was observed. Together, novel CLR/LACV interactions were identified; however, the Mincle/CARD9 axis plays a limited role in early antiviral responses against LACV.

Human MxA protein protects mice lacking a functional alpha/beta interferon system against La crosse virus and other lethal viral infections

The human MxA protein is part of the antiviral state induced by alpha/beta interferon (IFN-alpha/beta). MxA inhibits the multiplication of several RNA viruses in cell culture. However, its antiviral potential in vivo has not yet been fully explored. We have generated MxA-transgenic mice that lack a functional IFN system by crossing MxA-transgenic mice constitutively expressing MxA with genetically targeted (knockout) mice lacking the beta subunit of the IFN-alpha/beta receptor (IFNAR-1(-/-) mice). These mice are an ideal animal model to investigate the unique antiviral activity of human MxA in vivo, because they are unable to express other IFN-induced proteins. Here, we show that MxA confers resistance to Thogoto virus, La Crosse virus, and Semliki Forest virus. No Thogoto virus progeny was detectable in MxA-transgenic mice, indicating an efficient block of virus replication at the primary site of infection. In the case of La Crosse virus, MxA restricted invasion of the central nervous system. In contrast, Semliki Forest virus multiplication in the brain was detectable in both MxA-expressing and nonexpressing IFNAR-1(-/-) mice. However, viral titers were clearly reduced in MxA-transgenic mice. Our results demonstrate that MxA does not need the help of other IFN-induced proteins for activity but is a powerful antiviral agent on its own. Moreover, the results suggest that MxA may protect humans from potential fatal infections by La Crosse virus and other viral pathogens.

DNA-based vaccine against La Crosse virus: protective immune response mediated by neutralizing antibodies and CD4+ T cells

La Crosse virus (LACV)-mediated encephalitis is the most frequently reported arboviral disease in the United States, but to date no vaccine against this virus is available. We have established a new animal model, genetically targeted mice lacking a functional interferon type I receptor (IFNAR-1). These mice show an age-independent susceptibility to LACV and develop an acute encephalitis within 6 days of infection, thereby allowing the evaluation of vaccines against LACV. Taking advantage of this knockout mouse model, we have assessed the feasibility of DNA vaccination against this viral disease. Plasmid DNAs, encoding either the virus surface glycoproteins G1 and G2 or the internal nucleocapsid protein N, were used to immunize IFNAR-1-deficient mice. Mice vaccinated with DNA encoding the glycoproteins G1 and G2 produced neutralizing antibodies and exhibited a high degree of protection against challenge with high doses of LACV. Depletion of CD4+ T cells in mice vaccinated with DNA encoding G1/G2 reduced their capacity to control the infection. Virus titration and immunohistological analysis revealed that the protected mice showed no evidence of LACV particles in the brain. This indicates that the vaccine-induced immune response efficiently blocked viral spreading from the primary replication site to the brain. In contrast, immunization with DNA encoding protein N yielded only a partial protective effect that can be attributed to the cellular immune response. Taken together, this study shows that DNA vaccines can be designed to efficiently induce a protective immune response based on neutralizing antibodies and CD4+ T cells.

La Crosse viremias in white-tailed deer and chipmunks exposed by injection or mosquito bite

To further understand the role of wild mammals in the maintenance of La Crosse virus (LACV) in nature, we investigated the effects of inoculation method and virus source on the duration and amplitude of LACV viremia in vertebrate hosts. Earlier work suggested that deer are not sufficiently susceptible to LACV to play an important role in its maintenance. We re-evaluated the susceptibility of deer since subsequent studies showed that they constitute 65% of Aedes triseriatus blood meals, and thus would be exposed frequently to the virus. In our study, deer developed higher and longer viremia following exposure to LACV by infected Ae. triseriatus than those previously reported by inoculation with needle and syringe. However, susceptible Ae. triseriatus that fed on these viremic animals did not become infected. Because a large number of uninfected mosquitoes can feed upon a viremic deer in nature, we believe that deer should not be disregarded completely as a possible amplifier in the LACV transmission cycle. We also infected chipmunks to determine if there were significant differences in viremia response from mosquito delivery of virus to the chipmunk host, compared with artificial exposure by injection. Chipmunks exposed to infected mosquitoes had higher and longer viremias than the ones produced by intramuscular injection of an LACV suspension. These findings show the importance of using LACV infected mosquitoes for transmission experiments in mammals.

Seroepidemiology of La Crosse virus infection in humans in western North Carolina

On the Cherokee Indian Reservation and surrounding area of western North Carolina, an area-wide serosurvey was conducted to determine the prevalence of neutralizing antibody to La Crosse (LAC) virus. A questionnaire was used to identify risk factors important in exposure to virus-infected mosquitoes in populations near the reservation. Of 1,008 serum samples tested, 9.6% were positive for LAC virus antibody. For samples solely collected from on (n = 311) or off (n = 697) the reservation, the prevalence of seropositive samples was 20.6% on the reservation and only 4.7% off the reservation. Seropositivity increased directly with age, indicating that transmission of LAC virus was highly endemic. Age and location residence (on versus off the reservation) were significant risk factors for exposure to LAC virus. Persons on the reservation were 5.5 times more likely to have been exposed to LAC virus than were people who reside off the reservation. An additive increase in risk of 1.5 times over each age group was found, so that the oldest age group ( > or = 75 years) was 7.5 times more likely to have been exposed to LAC virus than was the youngest age group ( < 1-14 years).

Protection from La Crosse virus encephalitis with recombinant glycoproteins: role of neutralizing anti-G1 antibodies

La Crosse virus, a member of the California serogroup of bunyaviruses, is an important cause of pediatric encephalitis in the midwestern United States. Like all bunyaviruses, La Crosse virus contains two glycoproteins, G1 and G2, the larger of which, G1, is the target of neutralizing antibodies. To develop an understanding of the role of each of the glycoproteins in the generation of a protective immune response, we immunized 1-week-old mice with three different preparations: a vaccinia virus recombinant (VV.ORF) that expresses both G1 and G2, a vaccinia virus recombinant (VV.G1) that expresses G1 only, and a truncated soluble G1 (sG1) protein prepared in a baculovirus system. Whereas VV.ORF generated a protective response that was mostly directed against G1, VV.G1 was only partially effective at inducing a neutralizing response and at protecting mice from a potentially lethal challenge with La Crosse virus. Nevertheless, a single immunization with the sG1 preparation resulted in a robust immune response and protection against La Crosse virus. These results indicate that (i) the G1 protein by itself can induce an immune response sufficient for protection from a lethal challenge with La Crosse virus, (ii) a neutralizing humoral response correlates with protection, and (iii) the context in which G1 is presented affects its immunogenicity. The key step in the defense against central nervous system infection appeared to be interruption of a transient viremia that occurred just after La Crosse virus inoculation.

Histocompatibility antigens and La Crosse encephalitis

Major histocompatibility complex antigens (HLA-ABC and -DR loci) on lymphocytes from 79 patients with La Crosse encephalitis were compared with those of 69 control subjects. Nine patients (11%) and none of the control population had HLA-B49 (P < .01, uncorrected for multiple comparisons). Of La Crosse encephalitis patients with acute-phase seizures, only 2 (7%) were positive for HLA-DR5, whereas 16 (37%) of nonseizure patients were positive for that antigen (P < .025). These findings suggest that susceptibility and complications associated with this disease may have an immunogenetic component.

[The capacity of purified staphylococcal anatoxin to correct antigen-specific and antigen-nonspecific immunological defects]

Purified staphylococcal toxoid is capable of partially preventing the development of antigen-specific (induced by the supraoptimal dose of sheep red blood cells) and antigen-nonspecific (induced by Tahyna virus) defects of humoral immune response, as well as abolishing these defects. The presence and manifestation of the correction of virus-induced immunodeficiency is determined by the dose of the toxoid and the interval between the injections of purified staphylococcal toxoid and the infective agent.

[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.

Infection of white-tailed deer (Odocoileus virginianus) in Michigan with Jamestown Canyon virus (California serogroup) and the importance of maternal antibody in viral maintenance

Sera collected from a captive population of white-tailed deer (Odocoileus virginianus) penned in the lower peninsula of Michigan were assayed over a 29-mo period for neutralizing antibody to California serogroup viruses. In all, 130 individual white-tailed deer were bled one to 22 times between June 1983 and November 1985. Of the 130 sampled after active transmission had ceased, or passage of maternal antibody in colostrum had occurred, only one (0.8%), a newborn fawn, had no serum neutralizing antibody to California group viruses. All 18 1-yr-old does sampled acquired specific neutralizing antibody to Jamestown Canyon (JC) virus within a 6-wk period in 1984 and within a 10-wk period in 1985 indicating the prevalence of infection in this nonimmune age group was 100% for 2 successive yr. All 32 2- to 7-yr-old adult does and eight bucks sampled between June 1983 and June 1985 had specific neutralizing antibody to JC virus. No white-tailed deer had specific neutralizing antibody to trivittatus or La Crosse/snowshoe hare viruses at this study site. In 1984 and 1985, 78% and 63% of the adult does respectively exhibited significant anamnestic responses; all 19 adult does sampled over two seasons (between October 1983 and June 1985) showed a significant anamnestic response during at least 1 of the 2 yr. One-third of adult does with significant springtime antibody titer increases apparently experienced reexposure prior to the emergence of aedine mosquitoes, suggesting an alternate vector may overwinter at this site and transmit viruses in early spring. Specific neutralizing antibody was detected in 98% (66/67) of nursing fawns bled within 5 wk of birth in May-June 1984 and 1985, including three of three nursing fawns bled within 24-96 hr of birth. Of the 66 newborn fawns with specific neutralizing antibody to JC virus in June 1984 and 1985, 95% (54/57) of the surviving fawns lost maternal antibody and had no measurable titer when sampled 20-24 wk after birth, however. Serum antibody titers in 25 newborn (1984-cohort) fawns and their mothers and titers in 38 newborn (1985-cohort) fawns and their mothers were significantly correlated at the 5% and 1% levels respectively, suggesting that maternal antibody rather than a naturally acquired infection was the source of immunity in these suckling fawns.(ABSTRACT TRUNCATED AT 400 WORDS)

Serodiagnosis of La Crosse virus infections in humans by detection of immunoglobulin M class antibodies

Sera from 92 humans with illnesses clinically compatible with those caused by California serogroup virus infections were tested for antibody to La Crosse (LAC) virus by using the immunoglobulin M (IgM) antibody-capture enzyme-linked immunosorbent assay (MAC ELISA), the IgG ELISA, and the hemagglutination inhibition (HI), complement fixation and serum dilution-plaque reduction neutralization tests. On the reported day of onset of illness in 18 individuals, 94% had IgM antibody, 50% had neutralization antibody, 33% had HI antibody, and 11% had IgG antibody. Neutralization, HI, and IgG antibody prevalence rates increased thereafter, whereas IgM antibody prevalence remained high (92% 2 or more weeks after the onset of illness). It was concluded that the MAC ELISA is a sensitive test for the presence of antibody to LAC virus. The sensitivity of the MAC ELISA and the rapidity with which it can be performed appear to provide a powerful tool for the clinically relevant serodiagnosis of LAC virus infections in humans.

[Isolation of the Tahyña bunyavirus in the Arctic]

Tahyna virus (Bunyaviridae, Bunyavirus, the California encephalitis complex) was isolated from Aedes communis complex mosquitoes collected at the border of the north-taiga landscape zone (in latitude 68 degrees North and longitude 33 degrees East) at the Kolsky peninsula (the Murmansk region). The LEIV-9843 Mur strain was isolated from 2.4 thousand mosquitoes collected there (altogether 3.8 thousand mosquitoes had been collected in the Murmansk region). This is the first isolation in the USSR of a California complex virus in the Arctic and the northernmost site of Tahyna virus isolation in the world. 18% of the human population residing near the site of the virus isolation had virus-neutralizing antibody to Tahyna virus.

California serogroup viruses in New York State: the role of subtypes in human infections

The roles of various subtypes of the California serogroup viruses as infectious agents and as neuropathogens were evaluated by using the plaque reduction neutralization test. Sera from 394 patients with central nervous system (CNS) infections during 1971-1982 and from 501 persons without CNS manifestations were studied. Jamestown Canyon (JC) and La Crosse (LAC) viruses were found to have been common infectious agents in New York State for at least 16 years. JC virus was the prevalent indicated agent in patients with antibody to California serogroup viruses in screening tests (62 of 93 cases), followed by LAC virus (11 cases), snowshoe hare (2 cases), and trivittatus (1 case). In the remaining 17 patients the subtype was undetermined. LAC virus appears to be more pathogenic for children and to produce more serious illness, as judged by the frequent clinical diagnosis of encephalitis. JC virus affects mainly adults, and meningitis was the most common diagnosis. JC virus appears to cause a stronger neutralizing antibody response than does LAC virus, with a longer persistence of high levels of antibody. Some cases of JC virus infection may have been missed in the past due to the choice of a LAC-like isolate from New York State as the sole antigen in hemagglutination-inhibition (HI) screening tests. Comparison of the HI test and a single-dilution neutralization assay for screening for the two major subtypes, JC and LAC, indicated that the latter procedure is more broadly reactive and is less likely to miss cases if only one test antigen is used.

[Effectors of in vivo delayed hypersensitivity in experimental flavivirus infections and vaccination against tick-borne encephalitis in mice]

The development of experimental infections caused by tick-borne encephalitis (TBE) virus, Langat virus and dengue virus type 2 in mice or the immunization of these animals with live yellow fever vaccine (prepared from strain 17D) and inactivated TBE vaccine were accompanied by the formation of delayed hypersensitivity (DH) to viral antigens, determined in vivo. In experimental TBE infection the effectors of DH were identified as T-lymphocytes whose action was specific and followed the rule of H-2 restriction. The T-effectors of DH, induced by inactivated TBE vaccine, had no cytotoxic effect on an infected syngeneic tissue culture and, after their adoptive transfer by intravenous injection in vivo, did not protect syngeneic recipients against TBE virus.

Serological evidence of infection with California serogroup viruses (family Bunyaviridae) in residents of Long Hua, suburb of Shanghai, People's Republic of China

Sera from 126 residents of Long Hua, a suburb of Shanghai, in the People's Republic of China, were studied. Sera were tested for haemagglutination inhibiting antibodies to alphavirus (eastern equine encephalitis, western equine encephalitis), flavivirus (St. Louis encephalitis, Powassan, dengue) and California serogroup (snowshoe hare) antigens. Flavivirus antibodies were found in 14 (11.1%) and California serogroup antibodies in 5 (3.9%) individuals. Neutralizing antibodies with highest titres to snowshoe hare virus were demonstrated in 3 of the 5 California serogroup reactors. We believe this to be the first report of California serogroup virus antibodies in Chinese residents and the first evidence to suggest that California serogroup viruses may be circulating in the Orient.

Lower rates of oral transmission of La Crosse virus by Aedes triseriatus venereally exposed after engorgement on immune chipmunks

Transmission rates of La Crosse (LAC) virus observed in Aedes triseriatus females that had engorged on chipmunks with antibody to LAC and had been mated by infected males 5-11 days later (24%, 69/288) were 40% lower than in those fed on chipmunks without antibody (38%, 112/293). Similar results were obtained in three separate trials using males infected 1) by inoculation with prototype LAC virus, 2) transovarially with a field strain, or 3) transovarially with the field strain following passage through a viremic chipmunk. Similar rates were also observed in trials with F2 and F3 progeny of several strains of Ae. triseriatus collected from LAC-endemic and non-endemic areas. Reduction of oral transmission by venereally infected females mated by transovarially infected males following engorgement of antibody in chipmunks or other vertebrates could be important in the natural control of LAC virus, since most adult chipmunks sampled in endemic areas have antibodies neutralizing LAC. Ten-fold higher rates of venereal infection found in females mated by infected males 5 or more days after engorgement on LAC antibody-negative chipmunks than in those mated without prior engorgement extend previous findings of higher rates of transmission after engorgement on laboratory mice to include the natural vertebrate host.

Surveillance for California encephalitis group virus illness in Wisconsin and Minnesota, 1978

During the summer and fall of 1978, active surveillance for encephalitis in southwestern Wisconsin and southeastern Minnesota resulted in the detection of the largest number of cases of California encephalitis group (CEG) virus infections ever documented in that region, where CEG virus is known to be endemic. A total of 75 laboratory-confirmed and eight presumptive cases of CEG virus infections were identified as a result of serologic testing completed in the Wisconsin and Minnesota State Laboratories. Cases included 46 residents of Wisconsin, 25 of Minnesota, 10 residents of Iowa and two from Illinois. The outbreak peaked during the last half of August and the first half of September. Eighty percent of patients were less than 10 years of age; only one case was documented in an adult (greater than or equal to 18 years). The clinical picture in patients ranged from mild aseptic meningitis to encephalitis with coma; convulsions occurred in 31% (22/72) of patients. One patient, a 3-year-old girl, died. The high incidence of infection detected in this investigation may be representative of the endemic incidence of CEG illness in the region and suggests that CEG infections in children residing in endemic areas in Wisconsin and Minnesota may be a greater public health problem than previously recognized.

[Suppression of the macrophage function in mice in experimental Tahyña virus infection]

The effect of Tahyña virus on the phagocytic activity of macrophages of BALB/c mice and their capacity to transmit the antigenic stimulus was studied. The phagocytic activity of mononuclear cells of different localization in Tahyña virus-infected mice was shown to vary. The capacity for elimination of Indian ink particles from the blood stream associated mainly with the function of liver macrophages in asymptomatic infection increases 24 hours postinoculation, then gets back to normal, and decreases on day 7. At the same time, no disorders in the phagocytosis of heterologous red cells by peritoneal macrophages were observed. In the period of maximum inhibition of humoral response to sheep red cells (days 4-7 of the test) the infected mice exhibited the most marked disorders in the capacity of peritoneal macrophages to transmit the antigenic stimulus in intact syngeneic recipients. It is this defect which appears to underlie the suppression of immune response to heterologous antigens caused by Tahyña virus.

A nonspecific inhibitor of hemagglutination by Tahyna virus in acetone-extracted mouse sera and its removal

A nonspecific inhibitor of hemagglutination of Tahyna virus was present in acetone-extracted sera of 3-week old ICR mice but in a much lower level in the 3-day old mice of the same strain. This inhibitor did not neutralize Tahyna virus in vitro and did not protect mice against the lethal challenge by this virus. The inhibitor could not be removed by treatment with: acetone; kaolin, trypsin; heating at 56 degrees C for 30 min or 60 degrees C for 20 min, filtration through Seitz EK pads, a successive treatment with either acetone + trypsin, acetone + filtration, acetone + pH 2.0, or trypsin + heating. However, the inhibitory activity was eliminated by a combined treatment with acetone and heat (56 degrees C/30 min) - or vice versa, or by the isolation of gammaglobulin with the use of rivanol. Fractionated precipitation of serum proteins suggested that the nonspecific inhibitor is a lipoprotein, this being supported by a comparison of the lipoprotein content between samples with the inhibitor present and removed. The course of specific globulin (IgG and IgM) production in mice infected with Tahyna virus was studied in hemagglutination-inhibition test (HIT) using the sera treated with acetone plus heat. This combined treatment of sera might also be suggested for use in routine serological surveys (HIT) of small rodents with Tahyna virus antigen.

Serologic evidence of Jamestown Canyon and Keystone virus infection in vertebrates of the DelMarVa Peninsula

Serological data accumulated during the past decade indicated that a variety of feral and domestic animals of the Delaware-Maryland-Virginia (DelMarVa) Peninsula were infected with Jamestown Canyon (JC) and/or Keystone (KEY) viruses (Bunyaviridae, California serogroup). Neutralizing (N) antibody to JC virus was most prevalent in white-tailed deer, sika deer, cottontail rabbits and horses. KEY virus N antibody was detected most frequently in gray squirrels and domestic goats. N antibody indicative of past infection by one or both viruses also was found in raccoons, horses and humans. JC and/or KEY virus N antibodies were not demonstrable in sera of several other species of small mammals and reptiles. Investigations were extended to evaluate the role of domestic goats as an amplifying host of JC and KEY viruses and to assess their potential as sentinels of virus transmission. Goats maintained in the Pocomoke Cypress Swamp during the summer season of 1978, acquired N antibodies to JC and KEY viruses. Following experimental inoculation with either JC or KEY virus, all goats developed N antibody despite the absence of a demonstrable viremia in most animals. Goats proved to be effective as sentinels for monitoring the transmission of JC and KEY viruses; however, the exceptionally low titers or absence of viremia following inoculation with these viruses would seem to preclude a potential virus-amplifying role for this species. Although findings implicated primarily gray squirrels and white-tailed deer as possible amplifying hosts of KEY and JC virus, respectively, further investigations will be required to clarify their role, particularly since both viruses may be maintained entirely by transovarial transmission.

A case of encephalitis in a human associated with a serologic rise to Jamestown Canyon virus

An 8-year-old girl living in rural southwestern Michigan experienced sudden onset of symptoms beginning with headache, dizziness and fever which rapidly progressed to central nervous system involvement with seizures and coma. Following 27 days of hospitalization her recovery was uneventful, with no apparent sequelae 15 months after discharge. Serologic studies of paired sera showed a rise in antibody to Jamestown Canyon virus, a member of the California serogroup (family Bunyaviridae). Specific IgM anti-Jamestown Canyon virus antibody was detected in sera drawn 9 days after onset. A concomitant rise in complement fixation antibody to herpesvirus was also noted. We believe this is the first reported case of encephalitis associated with Jamestown Canyon virus infection. Reasons are presented for the current inability to routinely detect infection and clinical illness caused by this virus.

Capture immunoglobulin M system for rapid diagnosis of La Crosse (California encephalitis) virus infections

A capture immunoglobulin M (IgM) enzyme immunoassay was developed to diagnose La Crosse virus infections by the detection of specific IgM in acutephase serum specimens. IgM was detected by the capture IgM system in the serum of 24 of 29 (83%) of the patients studied. In comparison, IgM was detected in 19 of 29 (66%) of the patients by an indirect immunofluorescence technique. Specific IgM was detected in 83% (20 of 24) of patient serum specimens by day 3 after the onset of clinical symptoms.

[Characteristics of bunyavirus- and togavirus-induced nonspecific suppressors inhibiting delayed hypersensitivity]

Some properties and mechanisms of action of nonspecific suppressor cells, inhibiting delayed hypersensitivity to sheep red blood cells and activated in vivo in experimental tick-borne encephalitis and Tahyna virus infections in mice, have been studied. These nonspecific suppressor cells have been identified as T-lymphocytes in experiments with the use of antisera to T- and B-lymphocytes. The function of the suppressor cells can be realized without their proliferation and is mediated by a soluble factor whose formation requires the synthesis of protein. In respect to hydrocortisone, the above-mentioned suppressor cells are subdivided into 2 subpopulations: hydrocortisone-resistant in the thymus and hydrocortisone-sensitive in the spleen.

Detection of La Crosse (California encephalitis) virus antigen in mouse skin samples

La Crosse (LAC) viral antigen was detected in the skin of inoculated mice. Antigen was detected principally in the dermis of 102 of 120 (85%) mice with clinical signs of illness. To demonstrate the specificity of the fluorescence, LAC virus was isolated from selected samples and was identified by the complement-fixation test. Antigen was most often detected in skin rich in vascular and nerve tissue and was probably disseminated by hematogenous spread. Antigen was found in muscle, vascular, nervous, and other tissues of the dermis, depending on the age of the mice. Antigen was first detected in the skin of 80% of the mice (5 to 6 days of age) on postinoculation day (PID) 3. On PID 4, 100% of these mice were positive, but on PID 5, only 40% were positive, indicating that clearance or neutralization of antigen had occurred in peripheral areas. The skin biopsy technique may be applicable to diagnosis of arboviral infections in other vertebrates.

Indirect fluorescent-antibody technique for serological diagnosis of La Crosse (California) virus infections

A clinically relevant indirect fluorescent-antibody technique (IFA) was developed for the serological diagnosis of La Crosse virus infections. The IFA (67%) was as sensitive as the hemagglutination inhibition (58%) and neutralization (58%) tests in the detection of antibodies in acute-phase specimens. Immunoglobulin M antibodies were detected by the IFA test in 48% (11 of 23) of these specimens. Diagnostically significant increases in IFA titer were detected in 86% (19 of 22) of the paired samples. Antibodies were detectable in some patients 7 years after infection; however, the IFA test was not as sensitive as the other two tests in the detection of previous infections.

Effect of cyclophosphamide on the infection of mice with Tahyna virus

Juvenile SPF randombred ICR mice were given intraperitoneally (i.p.) a single dose of cyclophosphamide (CPA - 80 mg/kg), and 10(3.7) SMicLD 50 of Tahyna virus (California group, Bunyaviridae) one day later. The mice survived, but low concentrations of the virus were recovered from their brains 21 days after infection. No virus was detected in the brains of the animals infected but CPA-untreated. A lower body weight gain and a twofold decrease of virus neutralizing (VN) antibody titre were also observed in the CPA-treated mice. When mice were infected i.p. with 10(4.5) SMicLD50 of the virus, and CPA given 2 days (130 mg/kg) and 5 days (160 mg/Kg) later, the animals died of an acute encephalitis (with a mean virus titre at death of 10(7.3) SMicLD50/g brain), while all the infected but saline-treated animals survived, with no virus recovered from their brains. VN antibody was absent in the CPA-treated infected mice compared to high titres of antibodies detected in the CPA-untreated, infected animals.

[Effect of the Tahyña virus on Langat virus persistence in the central nervous system of the mouse]

The features of development of a mixed infection in which one of the infectious agents (Tahyña virus) had a marked immunodepressive activity and the other (Langat virus) caused predominantly asymptomatic course of the disease were studied. Successive infection with these agents increased the severity of the disease (lethality in monoinfection 7-18%, in mixed infection 57%). At the same time the duration of persistence in the brain of mice of Langat virus but not of Tahyña virus increased up to 110 days. It was demonstrated by the method of linear labyrinth that long-term asymptomatic carrier state of Langat virus was accompanied by disorders in the orienting-analysing function of the central nervous system. It is suggested that an increase in the duration of asymptomatic virus carrier state is due to the inhibiting effect of Tahyña virus on the T-dependent mechanisms of virus elimination from the body.

Serodiagnosis of La Crosse virus infections in humans

Serological diagnoses of human infections with California serogroup viruses are usually made by means of complement fixation or hemagglutination inhibition tests or both. An analysis of antibody titers in sera from 128 humans with California (La Crosse) virus infections indicated that exclusive use of the complement fixation tests would have detected only 50% of the actual seroconversions, whereas hemagglutination inhibition and neutralization tests alone would have been sufficient to make the diagnosis in 79.3% and 84.8% of the cases, respectively. These and other results presented demonstrate that the complement fixation test is not sufficiently useful as a primary tool for diagnosis of La Crosse virus infections. We suggest the use of the hemagglutination inhibition test for preliminary screening of sera from individuals with suspect infections caused by California serogroup viruses. The neutralization test should then be used or confirmation and subtype identification. If hemagglutination inhibition and neutralization titers are high and stable, the complement fixation test should then be used as a last, but specific, resort.

Effects of sex and dose of inoculum on the antibody response of mice to Tahyna virus (Bunyaviridae)

Six weeks old random bred ICR mice were inoculated intraperitoneally with two different doses of Tahyna virus (125 and 12 500 smicLD50). The higher dose caused marked involvement of the central nervous system in a few animals and induced high virus neutralization (VN) antibody titres in more animals than the lower dose. The dose of inoculum had no effect on the height of VN antibody titre in mice with antibody titres > 64. The proportion of mice with VN antibody titres > 64 was 72.7% in males and 56.8% in females. Male mice thus appeared to be somewhat more susceptible to Tahyna virus infection than female mice.

Experimental infection of vertebrates of the Pocomoke Cypress Swamp, Maryland with Keystone and Jamestown Canyon viruses

Experimental studies were conducted to assess the susceptibility of white-tailed deer (Odocoileus virginianus), gray squirrels (Sciurus carolinensis), and cottontail rabbits (Sylvilagus floridanus) to Jamestown Canyon (JC) and/or Keystone (KEY) virus infection. Viremia occurred in 5 of 6 deer inoculated with JC virus; however, all deer developed KEY virus neutralizing antibody. Based on the observation that antibody elicited by primary infection of deer with either KEY or JC virus exhibited partial heterologous neutralization in vitro, cross-challenge experiments were performed in these animals. Keystone virus failed to infect deer 30 days post primary JC virus infection; however, deer became infected when challenged with KEY virus 80 days after the initial JC virus infection as indicated by a substantial increase in antibody titer. Similarly, JC virus failed to produce viremia in immune animals infected with KEY virus 80 days previously, although 2 of the 3 animals challenged had serological evidence of infection. Three field-collected cottontail rabbits with no evidence of KEY antibody were readily susceptible to KEY virus infection and developed viremias of 1-4 days' duration; rabbits with KEY virus antibody did not develop viremia upon KEY virus challenge. Eight antibody-negative field-collected gray squirrels became viremic following injection with KEY virus; however, a comparable group of squirrels did not become viremic when injected with JC virus.

California encephalitis group viruses isolated from mosquitoes collected in Southern and Arctic Norway

Three virus strains serologically related to the California encephalitis group (Bunyaviridae) of arboviruses were isolated from 7331 mosquitoes collected in Norway in June-August 1975. Two of the isolates (S 548 and S 618) seemed to be closely related and the third, S 568, more distantly related by serological techniques to Tahyna virus. Viruses were found in the mosquito species Aedes sticticus, A. diantaeus and A. hexodontus colllected (in order) from Oyern (59 degrees N, 11 degrees 12' E), Trandum (60 degrees 08' N, 11 degrees 10' E) and Masi (69 degrees 26' N, 23 degrees 39' E). The Masi isolate seems to be the northernmost arbovirus isolate in the world so far. Strain S 568 was from 16 male A. diantaeus, indicating transovarial transmission of the virus. An accidental infection demonstrated the potential human pathogenicity of one of the newly-isolated strains (S 568), and the ability of CE viruses to persistently infect suckling mouse brains was indicated by in vivo findings. The biological characteristics of the new strains so far investigated are consistent with those of the California encephalitis group. During this work the Aerosil absorption method for production of haemagglutinating antigens proved useful for Tahyna virus and the newly-isolated strains. Trypsinization of erythrocytes improved the haemagglutinating capacities of these viruses.

Natural transmission of Keystone virus to sentinel rabbits on the Delmarva Peninsula

Domestic rabbits were exposed in the Pocomoke Cypress Swamp from early May through October 1973, to act as sentinel indicators of Keystone (KEY) virus transmission on the Delaware-Maryland-Virginia (DelMarVa) Peninsula. Rabbits were bled weekly and their sera were tested for the presence of neutralizing antibody to both KEY and James-town Canyon (JC) viruses. Adult mosquito activity was monitored concurrently by CDC miniature light traps with Dry Ice. Of 100 rabbits exposed, 20 rabbits acquired neutralizing antibody to KEY virus as a result of their exposure; none acquired antibody to JC virus. Eighty-three percent of susceptible rabbits exposed converted immediately after the emergence of Aedes atlanticus adult mosquitoes in early September. Rabbit seroconversions were not limited to any particular habitat within the swamp. The conversion of a large proportion of sentinel rabbits immediately following emergence of A. atlanticus, and the previous demonstration of transovarial transmission of KEY virus by A. atlanticus, suggest that vertically infected individuals are capable of viral transmission at their initial engorgement. Such transmission provides the initial step in a vertebrate amplification cycle.

California arbovirus (La Crosse) infections. III. Epidemiology of California encephalitis in Minnesota

Mosquitoes (eggs, larvae, and adults), small woodland animals, and residents of an area where California encephalitis is endemic were studied to elucidate the host-vector cycle of La Crosse virus. Elementary schoolchildren from surrounding communities and gray squirrels from another area were tested to compare the prevelence of serum antibodies to La Crosse virus in areas where the disease is endemic with the prevalence of these antibodies in areas where the disease is not endemic. From 1971 to 1974, eight isolations of La Crosse virus were made. Three of the isolates were from adult mosquitoes, one from Aedes triseriatus eggs, and four from A. triseriatus larvae. The isolation of virus from field-collected eggs and larvae confirms previous studies from Wisconsin that suggest that La Crosse virus overwinters in eggs of the mosquite A. triseriatus. In an area where California encephalitis is endemic, 10 of 19 small woodland animals (53%), which are the natural hosts of A. triseriatus, had hemagglutination-inhibiting and neutralizing antibodies to La Crosse virus. In contrast, none of 10 squirrels from an area where the disease is not endemic had such antibodies. Fourteen of 79 residents of this area (17.7%) had both types of antibody. Eleven of the 14 seropositive residents lived in one small sector of the community studied, an indication that foci of La Crosse virus activity may be very localized. Elementary schoolchildren from surrounding communitites had a significantly lower prevalence of hemagglutination-inhibiting antibody to La Crosse virus than did the residents of the area where California encephalitis was endemic.

Isolation of La Crosse virus (California encephalitis group) from the chipmunk (Tamias striatus), an amplifier host

La Crosse (LAC) virus was isolated from the blood of seven chipmunks (Tamias striatus) captured during the summer of 1970 in southwestern Wisconsin. With the exception of the original isolate obtained from human brain after fatal encephalitis, these represent the first known isolations of LAC virus from a naturally infected free-living vertebrate. The chipmunks were trapped and periodically recaptured in two study areas where 59 chipmunks became infected and developed neutralizing antibody during the summer cycle of virus transmission. All isolates were obtained from blood samples collected within a 7 week period between 11 July and 23 August, and all were from seronegative chipmunks; 6 of these were recaptured and found to be seropositive 2 to 3 weeks later. The isolates proved identical to each other in comparative micro-neutralization tests using BHK21 cell cultures and immune chipmunk serum or hyperimmune mouse ascitic fluids. Neutralization tests showed the isolates to be different from snowshoe hare, trivittatus, and Jamestown Canyon prototype virus strains but indistinguishable from the LAC prototype. Findings demonstrate multiplication and transmissibility of LAC virus in a naturally infected host and are consistent with the thesis that chipmunks are important amplifying hosts for LAC virus and that Aedes triseriatus mosquitoes serve as vectors in transmitting their infections. Ecological significance of the findings are discussed in regard to current perspectives.