La Crosse Virus Infection Research Articles

Cemeteries are effective sites for monitoring la crosse virus (LACv) and these environments may play a role in LACv infection.

La Crosse encephalitis (LAC) is the leading arboviral disease among children, and was previously limited to the upper Midwest. In 2012 nine pediatric cases of LAC occurred in eastern Tennessee, including one fatal case. In an attempt to identify sites near an active LACv infection and describe the abundance and distribution of potential LACv vectors near a fatal LAC case in the Appalachian region, we initiated an end of season study using a combination of questing and oviposition mosquito traps placed at forty-nine sites consisting of cemeteries and houses within 16 radial kilometers of two pediatric infections. LACv was isolated from three Aedes triseriatus pools collected from cemeteries and spatial clustering analysis identified clusters of Ae. triseriatus and Ae. albopictus populations that overlapped in the same area as the 2012 LACv cases. Results indicate cemeteries are effective sites for monitoring LACv. The role of cemeteries and specific environmental features will be the focus of future investigations.

Innate immune response to La Crosse virus infection

Viral encephalitis represents a significant, and costly, public health threat particularly for high-risk pediatric populations. An emerging mosquito-borne pathogen endemic to the United States, La Crosse virus (LACV) is one of the most common causes of viral encephalitis in children in the United States. However, no licensed therapeutics or vaccines currently exist for treatment. Hampering development efforts, the host response to LACV and its role in disease pathogenesis has only recently been examined. In this review, we discuss the current understanding of innate immune response in the context of viral pathogenesis and host susceptibility to LACV. In addition, we address the need for a clearer understanding of the early host-virus interactions in LACV infections as it relates to viral pathogenesis in the central nervous system.

Effect of oral infection ofLa Crossevirus on survival and fecundity of nativeOchlerotatus triseriatusand invasiveStegomyia albopicta

Arboviruses can have benign, deleterious, or beneficial effects on the vector. We tested the hypothesis that oral infection with La Crosse virus (LACV) will have little to no effect on mosquito longevity and fecundity, a prediction of low virulence selected in a system with frequent vertical transmission. We tested the effects of infection in native Ochlerotatus triseriatus Say and invasive Stegomyia albopicta Skuse (Diptera: Culicidae). We artificially fed adult female mosquitoes of each species with either LACV-infected or uninfected bovine blood and determined adult longevity and fecundity. For females fed LACV-infected blood, bodies and legs, respectively, were separately homogenized and assayed by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) to determine the LACV infection and dissemination rates. Ochlerotatus triseriatus had a higher infection and dissemination rate than St. albopicta. For both species, female size had no effect on infection status. Infection status also had no effect on longevity or fecundity for both species. We suggest that the high frequency of vertical transmission may have selected for strains of the virus with low virulence in two vectors, in spite of their different evolutionary histories with the virus.

Activation of the Innate Signaling Molecule MAVS by Bunyavirus Infection Upregulates the Adaptor Protein SARM1, Leading to Neuronal Death

La Crosse virus (LACV), a zoonotic Bunyavirus, is a major cause of pediatric viral encephalitis in the United States. A hallmark of neurological diseases caused by LACV and other encephalitic viruses is the induction of neuronal cell death. Innate immune responses have been implicated in neuronal damage, but no mechanism has been elucidated. By using invitro studies in primary neurons and invivo studies in mice, we have shown that LACV infection induced the RNA helicase, RIG-I, and mitochondrial antiviral signaling protein (MAVS) signaling pathway, resulting in upregulation of the sterile alpha and TIR-containing motif 1 (SARM1), an adaptor molecule that we found to be directly involved in neuronal damage. SARM1-mediated cell death was associated with induced oxidative stress response and mitochondrial damage. These studies provide an innate-immune signaling mechanism for virus-induced neuronal death and reveal potential targets for development of therapeutics to treat encephalitic viral infections.

La Crosse virus infection alters blood feeding behavior in Aedes triseriatus and Aedes albopictus (Diptera: Culicidae).

The effects of La Crosse virus (LACV) infection on blood feeding behavior in Aedes triseriatus (Say) and Aedes albopictus (Skuse) were investigated in the laboratory by measuring the size of the bloodmeal imbibed and the extent of refeeding by virus-infected and uninfected mosquitoes. LACV-infected Ae. triseriatus and Ae. albopictus took significantly less blood compared with uninfected mosquitoes. Twice as many virus-infected Ae. triseriatus mosquitoes refed compared with uninfected individuals (18 vs. 9%; P < 0.05); however, virus infection had no significant effect on the refeeding rate of Ae. albopictus. Reduction in bloodmeal size followed by an increased avidity for refeeding may lead to enhanced horizontal transmission of the LACV by its principal vector, Ae. triseriatus.

Innate immune response contributes to virus-mediated neuronal death through activation of SARM (170.2)

Abstract Neuronal cell death is a hallmark of various neurological diseases including virus infection. The innate immune response in the CNS contributes to neuronal damage through cytokine and neurotoxin production as well as the recruitment of inflammatory cells. However, the role of the innate immune response in the induction of neuronal death is poorly understood. La Crosse virus (LACV), which is a major cause of pediatric encephalitis in the United States, predominantly infects neurons and is associated with neurodegenerative changes. Infection results in neuronal apoptosis. In the current studies we identified sterile alpha and HEAT/Armadillo motif containing 1 (SARM1) protein, a negative regulator of TLR signaling, as a moderator of LACV induced neuronal apoptosis. SARM 1 was induced in neurons following LACV infection and SARM1 knock down studies in neurons demonstrated increased viability during LACV infection as compared to wild-type controls. Direct TLR stimulation of neurons induced SARM 1 which correlated with neuronal apoptosis. Thus, SARM induced as a response to innate immune activation appears to contribute to neuronal death. We are currently investigating the mechanisms underlying SARM induced neuronal death following LACV infection.

Modulation of La Crosse Virus Infection in Aedes albopictus Mosquitoes Following Larval Exposure to Coffee Extracts

The mosquito-borne La Crosse virus (LACV; Family Bunyaviridae) may cause encephalitis, primarily in children, and is distributed throughout much of the eastern United States. No antivirals or vaccines are available for LACV, or most other mosquito-borne viruses, and prevention generally relies on mosquito control. We sought to determine whether coffee extracts could interfere with LACV replication and vector mosquito development. Both regular and decaffeinated coffee demonstrated significant reductions in LACV replication in direct antiviral assays. This activity was not due to the presence of caffeine, which did not inhibit the virus life cycle. Aedes albopictus (Skuse; Diptera: Culicidae) mosquito larvae suffered near total mortality when reared in high concentrations of regular and decaffeinated coffee and in caffeine. Following larval exposure to sublethal coffee concentrations, adult A. albopictus mosquitoes had significantly reduced whole-body LACV titers 5 days post-infection, compared to larvae reared in distilled water. These results suggest that it may be possible to both control mosquito populations and alter the vector competence of mosquitoes for arthropod-borne viruses by introducing antiviral compounds into the larval habitat.

The Demographic and Socioeconomic Factors Predictive for Populations at High-Risk for La Crosse Virus Infection in West Virginia

Although a large body of literature exists for the environmental risk factors for La Crosse virus (LACV) transmission, the demographic and socioeconomic risk factors for developing LACV infection have not been investigated. Therefore, this study investigated the demographic and socioeconomic risk factors for LACV infection in West Virginia from 2003 to 2007, using two forward stepwise discriminant analyses. The discriminant analyses were used to evaluate a number of demographic and socioeconomic factors for their ability to predict: 1) those census tracts with at least one reported case of LACV infection versus those census tracts with no reported cases of LACV infection and 2) to evaluate significantly high-risk clusters for LACV infection versus significantly low-risk clusters for LACV infection. In the first model, a high school education diploma or a general education diploma or less and a lower housing densitywere found to be predictive of those census tracts with at least one case of LACV infection. A high school or a general education diploma or less, lower housing density, and housing built in 1969 and earlier were all found to be predictive of those census tracts displaying high-risk clusters versus census tracts displaying low-risk clusters in the second model. The cluster discriminant analysis was found to be more predictive than the census tract discriminant analysis as indicated by the Eigenvalues, canonical correlation, and grouping accuracy. The results of this study indicate that socioeconomically disadvantaged populations are at the highest risk for LACV infection and should be a focus of LACV infection prevention efforts.

Interactions Between La Crosse Virus and Bacteria Isolated From the Digestive Tract of Aedes albopictus (Diptera: Culicidae)

Aedes albopictus (Skuse) is a potential vector for many arboviruses, including La Crosse virus (LACV), the leading cause of pediatric encephalitis in North America. Bacteria isolated from the midgut and diverticula of field-caught female Ae. albopictus were cultured and identified using 16S ribosomal RNA gene amplification and sequencing. Members of seven and six bacterial families were identified from the midguts and diverticula, respectively, with nearly half of the isolates identified to the family Enterobacteriaceae. Many are related to bacteria identified in other invertebrates, and several may represent previously unknown species or genera. Of the 24 isolated bacteria, 12 (50%) showed a significant reduction in infectivity of LACV for Vero cells. Inhibition of infectivity ranged from 0 to 44% and was not dependent on bacterial classification. The antiviral activity of these bacteria warrants further investigation as an alternate means to interrupt the LACV transmission cycle.

The spatial epidemiology and clinical features of reported cases of La Crosse Virus infection in West Virginia from 2003 to 2007

BackgroundLa Crosse virus (LACV) is a major cause of pediatric encephalitis in the United States. Since the mid-1980s, the number of reported cases of LACV infection in West Virginia has continued to rise and the state currently reports the most cases in the United States. The purpose of this study was to investigate and describe the spatial epidemiology and clinical presentation of LACV infection cases reported in West Virginia, as well as to provide a description of the environmental conditions present at the residences of the LACV infection cases.MethodsDescriptive and spatial analyses were performed on LACV infection cases reported to the West Virginia Department of Health from 2003 to 2007. Clinical and environmental variables were available for 96 cases and residence data were available for 68 of these cases. Spatial analyses using the global Moran's I and Kulldorff's spatial scan statistic were performed using the population 15 years and younger at both the county and census tract levels to identify those geographic areas at the highest risk of infection.ResultsTwo statistically significant (p < 0.05) high-risk clusters, involving six counties, were detected at the county level. At the census tract level, one statistically significant high-risk cluster involving 41 census tracts spanning over six counties was identified. The county level cumulative incidence for those counties in the primary high-risk cluster ranged from 100.0 to 189.0 cases per 100,000 persons (median 189.0) and the census tract level cumulative incidence for those counties in the high-risk cluster ranged from 61.7 to 505.9 cases per 100,000 persons (median 99.0). The counties and census tracts within high-risk clusters had a relative risk four to nine times higher when compared to those areas not contained within high-risk clusters. The majority of LACV infection cases were reported during the summer months in children 15 years and younger. Fever, vomiting, photophobia, and nausea were the most commonly reported signs and symptoms. A case fatality rate (CFR) of 3.1% was observed. Wooded areas and containers were present at the majority of case residences.ConclusionsThe cumulative incidences of LACV infection from 2003 to 2007 were considerably higher than previously reported for West Virginia, and statistically significant high-risk clusters for LACV infection were detected at both the county and census tract levels. The finding of a high CFR and the identification of those areas at highest risk for infection will be useful for guiding future research and intervention efforts.

Assessing Risk in Focal Arboviral Infections: Are We Missing the Big or Little Picture?

BackgroundFocal arboviral infections affecting a subset of the overall population present an often overlooked set of challenges in the assessment and reporting of risk and the detection of spatial patterns. Our objective was to assess the variation in risk when using different at-risk populations and geographic scales for the calculation of incidence risk and the detection of geographic hot-spots of infection. We explored these variations using a pediatric arbovirus, La Crosse virus (LACV), as our model.Methods and FindingsDescriptive and cluster analyses were performed on probable and confirmed cases of LACV infections reported to the Tennessee Department of Health from 1997 to 2006, using three at-risk populations (the total population, the population 18 years and younger, and the population 15 years and younger) and at two geographic levels (county and census tract) to assess the variation in incidence risk and to investigate evidence of clustering using both global and local spatial statistics. We determined that the most appropriate at-risk population to calculate incidence risk and to assess the evidence of clustering was the population 15 years and younger. Based on our findings, the most appropriate geographical level to conduct spatial analyses and report incidence risk is the census tract level. The incidence risk in the population 15 years and younger at the county level ranged from 0 to 226.5 per 100,000 persons (median 41.5) in those counties reporting cases (n = 14) and at the census tract level it ranged from 50.9 to 673.9 per 100,000 persons (median 126.7) in those census tracts reporting cases (n = 51). To our knowledge, this is the highest reported incidence risk for this population at the county level for Tennessee and at the census tract level nationally.ConclusionThe results of this study indicate the possibility of missing disease clusters resulting from performing incidence risk investigations of focal diseases using inappropriate at-risk populations and/or at large geographic scales. Improved disease surveillance and health planning will result through the use of well defined at-risk populations and the use of appropriate geographic scales for the analysis and reporting of diseases. The finding of a high incidence risk of LACV infections in eastern Tennessee demonstrates that the vast majority of these infections continue to be under-diagnosed and/or underreported in this region. Persistent prevention and surveillance efforts will be required to reduce exposure to infectious vectors and to detect new cases of infection in this region. Application of this study's observations in future investigations will enhance the quantification of incidence risk and the identification of high-risk groups within the population.

The mosquitoes of eastern Tennessee: studies on abundance, habitat preferences, and host-seeking behaviors

A significant increase in the number of reported cases of La Crosse virus (LACV) infections in eastern Tennessee has occurred in the last ten years. The objective of this study was to determine the abundance and habitat preferences of the potential vectors of LACV in this region. Adult host-seeking mosquitoes were collected using CO(2)-baited CDC light traps and a series of human-landing catches in eastern Tennessee from 2004 to 2006. A total of 4,200 female mosquitoes of 23 species was collected by CO(2)-baited CDC trapping at ten sites during the study period. Aedes albopictus (Skuse) was the most abundant mosquito collected at all sites and vegetation types, with the ratios of total Ae. albopictus to Ae. triseriatus (Say) females collected being 2.1:1 in 2004, 3.8:1 in 2005, and 4.9:1 in 2006. Ten species were collected during a series of human-landing catches made at four different sites; one probable and three confirmed case sites of LACV infections, totaling 528 female mosquitoes. Aedes albopictus was the most abundant species collected, with a 4:1 ratio of Ae. albopictus to Ae. triseriatus females. Aedes albopictus exhibited two clear peaks of "landing" activity, one in the early morning and one in the late afternoon or early evening. Simple and multiple regression analyses of the predictors of the number of mosquitoes collected showed that populations of Ae. albopictus were three times more likely to be collected overall than Ae. triseriatus. Species (Ae. albopictus), vegetation (residential), and the previous cumulative precipitation for the four weeks prior to collection were significantly (P < 0.05) associated with the number of mosquitoes collected by CO(2)-baited CDC trapping. Aedes albopictus was also more likely to be collected than Ae. triseriatus at confirmed cases of LACV infections.

The Incidence Risk, Clustering, and Clinical Presentation of La Crosse Virus Infections in the Eastern United States, 2003–2007

BackgroundAlthough La Crosse virus (LACV) is one of the most common causes of pediatric arboviral infections in the United States, little has been done to assess its geographic distribution, identify areas of higher risk of disease, and to provide a national picture of its clinical presentation. Therefore, the objective of this study was to investigate the geographic distribution of LACV infections reported in the United States, to identify hot-spots of infection, and to present its clinical picture.Methods and FindingsDescriptive and cluster analyses were performed on probable and confirmed cases of LACV infections reported to the Centers for Disease Control and Prevention from 2003–2007. A total of 282 patients had reported confirmed LACV infections during the study period. Of these cases the majority (81 percent) presented during the summer, occurred in children 15 years and younger (83.3 percent), and were found in male children (64.9 percent). Clinically, the infections presented as meningioencephalitis (56.3 percent), encephalitis (20.7 percent), meningitis (17.2 percent), or uncomplicated fever (5 percent). Deaths occurred in 1.9 percent of confirmed cases, and in 8.6 percent of patients suffering from encephalitis. The majority of these deaths were in patients 15 years and younger. The county-level incidence risk among counties (n = 136) reporting both probable and confirmed cases for children 15 years and younger (n = 355) ranged from 0.2 to 228.7 per 100,000 persons. The southern United States experienced a significantly higher (p<0.05) incidence risk during the months of June, July, August, and October then the northern United States. There was significant (p<0.05) clustering of high risk in several geographic regions with three deaths attributed to complications from LAC encephalitis occurring in two of these hot-spots of infections.ConclusionsBoth the incidence risk and case fatality rates were found to be higher than previously reported. We detected clustering in four geographic regions, a shift from the prior geographic distributions, and developed maps identifying high-risk areas. These findings are useful for raising awareness among health care providers regarding areas at a high risk of infections and for guiding targeted multifaceted interventions by public health officials.

La Crosse virus infectivity, pathogenesis, and immunogenicity in mice and monkeys

BackgroundLa Crosse virus (LACV), family Bunyaviridae, was first identified as a human pathogen in 1960 after its isolation from a 4 year-old girl with fatal encephalitis in La Crosse, Wisconsin. LACV is a major cause of pediatric encephalitis in North America and infects up to 300,000 persons each year of which 70–130 result in severe disease of the central nervous system (CNS). As an initial step in the establishment of useful animal models to support vaccine development, we examined LACV infectivity, pathogenesis, and immunogenicity in both weanling mice and rhesus monkeys.ResultsFollowing intraperitoneal inoculation of mice, LACV replicated in various organs before reaching the CNS where it replicates to high titer causing death from neurological disease. The peripheral site where LACV replicates to highest titer is the nasal turbinates, and, presumably, LACV can enter the CNS via the olfactory neurons from nasal olfactory epithelium. The mouse infectious dose50 and lethal dose50 was similar for LACV administered either intranasally or intraperitoneally. LACV was highly infectious for rhesus monkeys and infected 100% of the animals at 10 PFU. However, the infection was asymptomatic, and the monkeys developed a strong neutralizing antibody response.ConclusionIn mice, LACV likely gains access to the CNS via the blood stream or via olfactory neurons. The ability to efficiently infect mice intranasally raises the possibility that LACV might use this route to infect its natural hosts. Rhesus monkeys are susceptible to LACV infection and develop strong neutralizing antibody responses after inoculation with as little as 10 PFU. Mice and rhesus monkeys are useful animal models for LACV vaccine immunologic testing although the rhesus monkey model is not optimal.

Invasive mosquitoes, larval competition, and indirect effects on the vector competence of native mosquito species (Diptera: Culicidae)

Invasive arthropods that vector pathogens have the potential to influence pathogen transmission both directly, by becoming a novel pathogen vector, or indirectly, by interacting with native vectors. Adult mosquito size is influenced by food availability in the larval stage, and smaller, nutrient-deprived mosquitoes are, in some studies, more efficient viral vectors in the laboratory. This is the first study to examine the indirect impacts that larval competition between Aedes albopictus, an introduced mosquito species, and Ochlerotatus triseriatus, a native mosquito species and the primary vector for La Crosse virus (LACV) in the US, has on native mosquito larval survival, adult size, and vector competence. A. albopictus presence decreased Oc. triseriatus larval survival, but surviving Oc. triseriatus females were larger, potentially owing to a release from intraspecific competition. These larger, native females were more likely to develop both midgut and disseminated LACV infections than females emerging from monospecific treatments. Collectively, these results suggest a need to better understand the ecology of both native and invasive vector species, their interactions, and the potential for those interactions to alter vector-borne disease transmission.

Genome sequence analysis of La Crosse virus and in vitro and in vivo phenotypes

BackgroundLa Crosse virus (LACV), family Bunyaviridae, is a mosquito-borne virus recognized as a major cause of pediatric encephalitis in North America with 70–130 symptomatic cases each year. The virus was first identified as a human pathogen in 1960 after its isolation from a 4 year-old girl who suffered encephalitis and died in La Crosse, Wisconsin. The majority of LACV infections are mild and never reported, however, serologic studies estimate infection rates of 10–30/100,000 in endemic areas.ResultsIn the present study, sequence analysis of the complete LACV genomes of low-passage LACV/human/1960, LACV/mosquito/1978, and LACV/human/1978 strains and of biologically cloned derivatives of each strain, indicates that circulating LACVs are genetically stable over time and geographic distance with 99.6–100%, 98.9–100%, 97.8–99.6%, and 99.2–99.7% amino acid identity for N, NsS, M polyprotein, and L proteins respectively. We identified 5 amino acid differences in the RNA polymerase and 4 nucleotide differences in the non-coding region of the L segment specific to the human virus isolates, which may result in altered disease outcomes.ConclusionAll three wild type viruses had similar in vitro growth kinetics and phenotypes in mosquito C6/36 and Vero cells, and similar levels of neurovirulence and neuroinvasiveness in Swiss Webster mice. The biologically cloned derivative of LACV/human/1960 was significantly less neuroinvasive than its uncloned parent and differed in sequence at one amino acid position in the GN glycoprotein, identifying this residue as an attenuating mutation.

Mutagenesis of the La Crosse Virus glycoprotein supports a role for Gc (1066–1087) as the fusion peptide

The La Crosse Virus (LACV) M segment encodes two glycoproteins (Gn and Gc), and plays a critical role in the neuropathogenesis of LACV infection as the primary determinant of neuroinvasion. A recent study from our group demonstrated that the region comprising the membrane proximal two-thirds of Gc, amino acids 860–1442, is critical in mediating LACV fusion and entry. Furthermore, computational analysis identified structural similarities between a portion of this region, amino acids 970–1350, and the E1 fusion protein of two alphaviruses: Sindbis virus and Semliki Forrest virus (SFV). Within the region 970–1350, a 22-amino-acid hydrophobic segment (1066–1087) is predicted to correlate structurally with the fusion peptides of class II fusion proteins. We performed site-directed mutagenesis of key amino acids in this 22-amino acid segment and determined the functional consequences of these mutations on fusion and entry. Several mutations within this hydrophobic domain affected glycoprotein expression to some extent, but all mutations either shifted the pH threshold of fusion below that of the wild-type protein, reduced fusion efficiency, or abrogated cell-to-cell fusion and pseudotype entry altogether. These results, coupled with the aforementioned computational modeling, suggest that the LACV Gc functions as a class II fusion protein and support a role for the region Gc 1066–1087 as a fusion peptide.

QUANTITATIVE ANALYSIS OF LA CROSSE VIRUS TRANSCRIPTION AND REPLICATION IN CELL CULTURES AND MOSQUITOES

La Crosse (LAC) virus (family Bunyaviridae, genus Orthobunyavirus) small (S) segment negative-sense RNA genome (vRNA), positive-sense full-length RNA complement (vcRNA), and subgenomic mRNA were assayed in infected cell cultures and female Aedes (Ochlerotatus) triseriatus mosquito tissues using quantitative PCR (Q-PCR). During persistent infection of C6/36 (Aedes albopictus) and MAT (Aedes triseriatus) cultured cells and cytolytic infection of BHK-21 cultured cells, LAC vRNA was the most abundant RNA species, followed by mRNA and vcRNA. RNA copy numbers per cell were quantified and vRNA correlated to virus titer in cell culture medium. The Q-PCR assay proved more sensitive than reverse transcription (RT)-PCR and immunofluorescence assays (IFA) for detecting LAC virus infection of mosquitoes. After infection of female mosquitoes orally, quantities of LAC RNA increased in ovaries for 6 days, and as ovarian biosynthetic activity quiesced, LAC RNA quantities decreased then remained detectable at a low level. After a second, noninfectious blood meal, quantities of LAC RNA in ovaries increased significantly, quantitatively confirming correlation of LAC virus RNA synthesis with vector metabolic activity. Coregulation of viral replication and mosquito ovary metabolic activity may condition efficient transovarial transmission.

La Crosse encephalitis in Eastern Tennessee: clinical, environmental, and entomological characteristics from a blinded cohort study.

A blinded cohort study was conducted in 2000 to better understand the emergence of La Crosse virus infection in eastern Tennessee, with special emphasis on the potential mosquito vector(s). Children with suspected central nervous system infection were enrolled at the time of clinical presentation at a large pediatric referral hospital. Clinical, environmental, and entomological data were collected prior to case confirmation. Sixteen of the 40 children included in the final analysis were confirmed to have La Crosse infection by a fourfold increase in antibody titers between collection of acute- and convalescent-phase sera. Factors significantly associated with La Crosse infection included average number of hours per day spent outdoors (5.9 for La Crosse virus cases vs. 4.0 for noncases, p = 0.049); living in a residence with one or more tree holes within 100 m (relative risk = 3.96 vs. no tree holes within 100 m, p = 0.028); and total burden of Aedes albopictus (number of female and male larvae and adults collected at a site), which was more than three times greater around the residences of La Crosse virus cases versus noncases (p = 0.013). Evidence is accumulating that the newly introduced mosquito species Ae. albopictus may be involved in the emergence of La Crosse virus infection in eastern Tennessee.

Serological survey and active surveillance for La Crosse virus infections among children in Tennessee.

In 1998 and 1999, we performed a serosurvey and active surveillance for La Crosse encephalitis at a children's hospital in eastern Tennessee. Fifteen cases of La Crosse encephalitis were confirmed. Only 5 (0.5%) of 1000 serum samples being tested at the state laboratory for other diseases had evidence of antibodies to La Crosse virus. These findings suggest that La Crosse virus is newly endemic to eastern Tennessee.