BACKGROUND: La Crosse encephalitis is a mosquito-borne disease that can be mistaken for herpes simplex encephalitis. It has been reported in 28 states but may be underrecognized. METHODS: We investigated the manifestations and clinical course of La Crosse encephalitis in 127 patients hospitalized from 1987 through 1996. The diagnosis was established by serologic testing for IgM and IgG antibodies to La Crosse virus. Data were collected by chart review. RESULTS: Most of the patients were school-aged children (mean [+/-SD] age, 7.8+/-3.5 years; range, 0.5 to 15.0). Symptoms included headache, fever, and vomiting (each in 70 percent or more of the patients), seizures (in 46 percent), and disorientation (in 42 percent). Thirteen percent had aseptic meningitis. Hyponatremia developed in 21 percent, and there were signs of increased intracranial pressure in 13 percent. Six patients, including three with cerebral herniation, underwent intracranial-pressure monitoring. The 13 patients (11 percent) whose condition deteriorated in the hospital had decreases in serum sodium levels (P=0.007), and increases in body temperature (P=0.003) at the time of deterioration. At admission, these patients more often had a history of vomiting (P=0.047) and a score of 12 or lower on the Glasgow Coma Scale (P=0.02) than the others; a trend toward a greater prevalence of seizures at admission was also evident in this group (P=0.07). All the patients survived, but 15 of them (12 percent) had neurologic deficits at discharge. Follow-up assessments, performed in 28 children, suggested an increase in cognitive and behavioral deficits 10 to 18 months after the episode of encephalitis. CONCLUSIONS: La Crosse virus infection should be considered in children who present with aseptic meningitis or encephalitis. Hyponatremia and increasing body temperature may be related to clinical deterioration. (+info)
The effect of mosquito passage on the La Crosse virus genotype.
(10/75)
The genetic consequences of passing three different strains of La Crosse (LAC) virus orally and transovarially in Aedes triseriatus mosquitoes were examined. Two of the LAC strains (WT LAC and LAC ORI) had been passaged numerous times in cell culture; the third strain (SM1-78) had been passaged only once in suckling mice. Genetic changes were monitored in three regions of the LAC genome after oral infection and dissemination in the mosquito, and transovarial transmission (TOT) of the virus to progeny. Sequence analyses were used to characterize the genetic changes occurring in regions of G1, G2 and N open reading frames (ORFs) during passage. Only one mutation was detected in the G1 ORF of SM1-78 virus after mosquito passage; however, numerous nucleotide and amino acid substitutions were detected in the G1 ORF of WT LAC and LAC ORI (cell culture-adapted viruses). In contrast to G1, the N and G2 ORF sequences examined were stable. Mutations introduced into viral genomes during replication in parental mosquitoes were expressed in progeny mosquitoes following TOT. Genetic diversity of virus populations from a single mosquito was examined by single-strand conformation polymorphisms analysis of the variable region of glycoprotein G1. LAC virus RNA genotype diversity was greatest in virus that infected and replicated in the midgut, and declined as virus disseminated from the midgut and infected ovaries and salivary glands. (+info)
First isolation of La Crosse virus from naturally infected Aedes albopictus.
(11/75)
La Crosse (LAC) virus, a California serogroup bunyavirus, is the leading cause of pediatric arboviral encephalitis in the United States and an emerging disease in Tennessee, West Virginia, and North Carolina. Human cases of LAC encephalitis in Tennessee and North Carolina have increased above endemic levels during 1997 to 1999 and may represent an expansion of a new southeastern endemic focus. This report describes the isolation of LAC virus from the exotic mosquito Aedes albopictus. The discovery of LAC virus in wild populations of Ae. albopictus coupled with its expanding distribution in the southeastern United States, suggests that this mosquito may become an important accessory vector, potentially increasing the number of human cases in endemic foci or expanding the range of the disease. (+info)
Antivirally active MxA protein sequesters La Crosse virus nucleocapsid protein into perinuclear complexes.
(12/75)
Bunyaviruses replicate in the cytoplasm of infected cells. New viral particles are formed by budding of nucleocapsids into the Golgi apparatus. We have previously shown that the IFN-induced human MxA protein inhibits bunyavirus replication by an unknown mechanism. Here we demonstrate that MxA binds to the nucleocapsid protein of La Crosse virus (LACV) and colocalizes with the viral protein in cytoplasmic complexes. Electron microscopy revealed that these complexes accumulated in the perinuclear area and consisted of highly ordered fibrillary structures. A similar MxA-mediated redistribution of viral nucleocapsid proteins was detected with other bunyaviruses, such as Bunyamwera virus and Rift Valley fever virus. MxA(E645R), a carboxy-terminal mutant of MxA without antiviral activity against LACV, did not lead to complex formation. Wild-type MxA, but not MxA(E645R), was able to bind to LACV nucleocapsid protein in coimmunoprecipitation assays, demonstrating the importance of the carboxy-terminal effector domain of MxA. These results illustrate an efficient mechanism of IFN action whereby an essential virus component is trapped in cytoplasmic inclusions and becomes unavailable for the generation of new virus particles. (+info)
La Crosse encephalitis in Eastern Tennessee: clinical, environmental, and entomological characteristics from a blinded cohort study.
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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. (+info)
Functional L polymerase of La Crosse virus allows in vivo reconstitution of recombinant nucleocapsids.
(14/75)
La Crosse virus (LACV), a member of the family Bunyaviridae, is the primary cause of paediatric encephalitis in the United States. In this study, a functional RNA polymerase (L) gene of LACV was cloned and a reverse genetics system established. A reporter minireplicon mimicking the viral genome was constructed by flanking the Renilla luciferase gene with the 3' and 5' noncoding regions of the genomic M segment. These noncoding regions serve as promoters for the viral polymerase. Both L and nucleocapsid (N) genes were expressed by means of T7 RNA polymerase, which was provided by the recombinant T7-expressing modified vaccinia virus Ankara. Renilla reporter activity in transfected cells reflected reconstitution of recombinant nucleocapsids by functional L and N gene products. Time-course experiments revealed a rapid increase in minireplicon activity from 10 to 18 h after the onset of L and N expression. Minireplicon activity was found to be dependent on the correct ratio of L to N plasmids, with too much of either construct resulting in downregulation. Furthermore, a specific inhibitory effect of LACV NSs protein on minireplicon activity was found. In passaging experiments using parental helper virions, it was demonstrated that the recombinant nucleocapsids are a useful model for transcription, replication and packaging of LACV. (+info)
Economic and social impacts of La Crosse encephalitis in western North Carolina.
(15/75)
La Crosse encephalitis (LACE), a human illness caused by a mosquito-transmitted virus, is endemic in western North Carolina. To assess the economic and social impacts of the illness, 25 serologically confirmed LACE case patients and/or families were interviewed to obtain information on the economic costs and social burden of the disease. The total direct and indirect medical costs associated with LACE over 89.6 life years accumulated from the onset of illness to the date of interview for 24 patients with frank encephalitis totaled dollar 791,374 (range = dollar 7,521-175,586), with a mean +/- SD per patient cost of dollar 32,974 +/- dollar 34,793. The projected cost of a case with lifelong neurologic sequelae ranged from dollar 48,775 to dollar 3,090,798 (n = 5). For the 25 LACE patients, 55.15 (54.83%) of the 100.59 cumulative life years (CLYs) were impaired to some degree. Disability adjusted life years (DALYs) were calculated to measure the productive life years lost to LACE. Approximately 13.00 DALYs were accumulated over 100.59 CLYs of study. Projected DALYs for case patients (n = 5) with lifelong neurologic sequelae ranged from 12.90 to 72.37 DALYs. An Impact of La Crosse Encephalitis Survey (ILCES) was used to measure the social impact of LACE over time for case patients and their families. The ILCES scores demonstrated that the majority of the social burden of the illness is borne by the five patients with lifelong neurologic sequelae. The socioeconomic burden resulting from LACE is substantial, which highlights the importance of the illness in western North Carolina, as well as the need for active surveillance, reporting, and prevention programs for the infection. (+info)
La Crosse virus nonstructural protein NSs counteracts the effects of short interfering RNA.
(16/75)
Through a process known as RNA interference (RNAi), double-stranded short interfering RNAs (siRNAs) silence gene expression in a sequence-specific manner. Recently, several viral proteins, including the nonstructural protein NSs of tomato spotted wilt virus (a plant-infecting bunyavirus), the interferon antagonist protein NS1 of influenza virus, and the E3L protein of vaccinia virus, have been shown to function as suppressors of RNAi, presumably as a counterdefense against cellular mechanisms that decrease viral production. La Crosse virus (LACV), a member of the California serogroup of orthobunyaviruses, has a trisegmented negative-stranded genome comprised of large (L), medium (M), and small (S) segments. To develop a strategy for segment-specific inhibition of transcription, we designed 13 synthetic siRNAs targeting specific RNA segments of the LACV genome that decreased LACV replication and antigen expression in mammalian (293T) and insect (C6/36) cells. Furthermore, NSs, a LACV nonstructural protein, markedly inhibited RNAi directed both against an LACV M segment construct and against a host gene (glyeraldehyde-3-phosphate dehydrogenase), suggesting a possible role for this viral protein in the suppression of RNA silencing. Segment-specific siRNAs will be useful as a tool to analyze LACV transcription and replication and to obtain recombinant viruses. Additionally, NSs will help us to identify molecular pathways involved in RNAi and further define its role in the innate immune system. (+info)