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Reisen WK, Fang Y, Martinez VM. Vector competence of Culiseta incidens and Culex thriambus for West Nile virus. JOURNAL OF THE AMERICAN MOSQUITO CONTROL ASSOCIATION 2006; 22:662-5. [PMID: 17304934 DOI: 10.2987/8756-971x(2006)22[662:vcocia]2.0.co;2] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
The vector competence of Culiseta incidens (Thomson) and Culex thriambus Dyar for West Nile virus (WNV) were compared to Cx. quinquefasciatus Say or Cx. tarsalis Coquillett and Cx. stigmatasoma Dyar collected concurrently in California. Culiseta incidens were less susceptible to oral infection than Cx. quinquefasciatus, but transmitted virus at a significantly higher rate, thereby yielding comparable population transmission rates. Culex thriambus was equally susceptible to oral infection and transmitted virus at rates comparable to Cx. tarsalis or Cx. stigmatosoma. A mammalian host selection pattern most likely precluded detection of natural infection in Cs. incidens, a fairly abundant peridomestic species. In contrast, an avian host selection pattern and efficient vector competence resulted in repeated detection of WNV in Cx. thriambus; however, limited abundance and restrictive riparian larval habitat requirements would seem to limit the involvement of Cx. thriambus in WNV epidemiology.
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Morales-Betoulle ME, Morales H, Blitvich BJ, Powers AM, Davis EA, Klein R, Cordón-Rosales C. West Nile virus in horses, Guatemala. Emerg Infect Dis 2006; 12:1038-9. [PMID: 16752479 PMCID: PMC3373039 DOI: 10.3201/eid1206.051615] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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Payne AF, Binduga-Gajewska I, Kauffman EB, Kramer LD. Quantitation of flaviviruses by fluorescent focus assay. J Virol Methods 2006; 134:183-9. [PMID: 16510196 DOI: 10.1016/j.jviromet.2006.01.003] [Citation(s) in RCA: 151] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2005] [Revised: 01/03/2006] [Accepted: 01/10/2006] [Indexed: 11/21/2022]
Abstract
An indirect immunofluorescence assay for quantitation of flaviviruses was developed as an alternative to the standard plaque assay. The assay was validated with West Nile virus (WNV), St. Louis encephalitis virus (SLEV), and Dengue virus (DENV) types 1-4. Vero cells were plated in 8-well chamber slides, and infected with 10-fold serial dilutions of virus. About 1-3 days after infection, cells were fixed, incubated with specific monoclonal antibody, and stained with a secondary antibody labeled with a fluorescent tag. Fluorescent foci of infection were observed and counted using a fluorescence microscope, and viral titers were calculated as fluorescent focus units (FFU) per ml. The optimal time for performing the fluorescent focus assay (FFA) on Vero cells was 24 h for WNV, and 48 h for SLEV and the four DENV serotypes. In contrast, the time required to complete a standard Vero cell plaque assay for these viruses range from 3 days for WNV to 11 days for DENV-1. Thus, the FFA method of virus titration is useful for viruses whose plaques develop slowly. In addition, these viruses can be quantitated by FFA on a mosquito cell line (C6/36), which does not support plaque formation. The FFA for flaviviruses was validated for accuracy, precision, specificity, and robustness of the assay.
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Rocco IM, Santos CLS, Bisordi I, Petrella SMCN, Pereira LE, Souza RP, Coimbra TLM, Bessa TAF, Oshiro FM, Lima LBQ, Cerroni MP, Marti AT, Barbosa VM, Katz G, Suzuki A. St. Louis encephalitis virus: first isolation from a human in São Paulo State, Brazil. Rev Inst Med Trop Sao Paulo 2005; 47:281-5. [PMID: 16302112 DOI: 10.1590/s0036-46652005000500008] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This paper reports the isolation of St. Louis encephalitis virus (SLEV) from a febrile human case suspected to be dengue, in São Pedro, São Paulo State. A MAC-ELISA done on the patient's acute and convalescent sera was inconclusive and hemagglutination inhibition test detected IgG antibody for flaviviruses. An indirect immunofluorescent assay done on the C6/36 cell culture inoculated with the acute serum was positive for flaviviruses but negative when tested with dengue monoclonal antibodies. RNA extracted from the infected cell culture supernatant was amplified by RT-PCR in the presence of NS5 universal flavivirus primers and directly sequenced. Results of BLAST search indicated that this sequence shares 93% nucleotide similarity with the sequence of SLEV (strain-MSI.7), confirmed by RT-PCR performed with SLEV specific primers. Since SLEV was identified as the cause of human disease, it is necessary to improve surveillance in order to achieve early detection of this agent in the state of São Paulo and in Brazil. This finding is also an alert to health professionals about the need for more complete clinical and epidemiological investigations of febrile illnesses as in the reported case. SLEV infections can be unrecognized or confused with other ones caused by an arbovirus, such as dengue.
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Johnson AJ, Noga AJ, Kosoy O, Lanciotti RS, Johnson AA, Biggerstaff BJ. Duplex microsphere-based immunoassay for detection of anti-West Nile virus and anti-St. Louis encephalitis virus immunoglobulin m antibodies. CLINICAL AND DIAGNOSTIC LABORATORY IMMUNOLOGY 2005; 12:566-74. [PMID: 15879016 PMCID: PMC1112082 DOI: 10.1128/cdli.12.5.566-574.2005] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
West Nile (WN) virus was introduced into the United States in 1999, when the first human cases of WN fever and encephalitis appeared in New York City. From there, the virus has spread throughout North America, in some areas cocirculating with the related flavivirus St. Louis encephalitis (SLE) virus. Public health laboratories currently use an immunoglobulin M (IgM) antibody capture enzyme-linked immunosorbent assay (MAC-ELISA) as a primary test for human serodiagnosis, followed by a confirmatory plaque-reduction neutralization test (PRNT). The MAC-ELISAs take 2 days to perform; therefore there is a need for a more rapid test. This report describes a duplex microsphere-based immunoassay (MIA) that shortens the test processing time to about 4.5 h. The assay employs two sets of microspheres coupled to a single flavivirus group-reactive antibody, which are used to capture the WN and SLE viral antigens independently. Immunoglobulin G-depleted serum is concurrently assayed for IgM antibodies to each of the viral antigens. The results are standardized and classified by using quadratic discriminant analysis so that a single result, anti-WN IgM-positive, anti-SLE IgM-positive, negative, or nonspecific, can be determined. The duplex MIA results compared favorably to those of the plaque-reduction neutralization test and MAC-ELISA. The assay proved to be reproducible, produced accurate classifications as to the infecting virus, and was specific.
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Vinayagamoorthy T, Mulatz K, Drebot M, Hodkinson R. Molecular typing of West Nile Virus, Dengue, and St. Louis encephalitis using multiplex sequencing. J Mol Diagn 2005; 7:152-9. [PMID: 15858138 PMCID: PMC1867533 DOI: 10.1016/s1525-1578(10)60541-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/18/2004] [Indexed: 11/16/2022] Open
Abstract
We report the development of an assay to simultaneously identify three of the clinically important flaviviruses (West Nile Virus, Dengue, and St. Louis encephalitis). This assay is based on the nucleotide sequence variations within a 266-bp region of the non-structural protein 5. Further, based on the nucleotide variations in the same region of the non-structural protein 5, four of the present Dengue serotypes were identified. To identify some of the subtypes of WNV we have developed a second assay using multiplex sequencing technology. The format of the result of this assay is an electropherogram of two genomic segments of the WNV genome: a 48-nucleotide sequence from the anchored core protein C and a 45-nucleotide sequence coding for the non-structural proteins (proteinase and putative helicase genes).
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Farajollahi A, Gates R, Crans W, Komar N. Serologic Evidence of West Nile Virus and St. Louis Encephalitis Virus Infections in White-Tailed Deer (Odocoileus virginianus) from New Jersey, 2001. Vector Borne Zoonotic Dis 2004; 4:379-83. [PMID: 15671740 DOI: 10.1089/vbz.2004.4.379] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Serum samples from 689 hunter-killed white-tailed deer (Odocoileus virginianus) collected during the 2001 fall hunting season in New Jersey were tested for neutralizing antibodies to West Nile virus (WNV) and St. Louis encephalitis virus (SLEV) by plaque-reduction neutralization tests. WNV-neutralizing antibodies were detected in six (0.9%) of the samples, and SLEV-neutralizing antibodies were found in 11 (1.6%) of the samples. We provide the first report of WNV infection in white-tailed deer.
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Pugachev KV, Guirakhoo F, Mitchell F, Ocran SW, Parsons M, Johnson BW, Kosoy OL, Lanciotti RS, Roehrig JT, Trent DW, Monath TP. Construction of yellow fever/St. Louis encephalitis chimeric virus and the use of chimeras as a diagnostic tool. Am J Trop Med Hyg 2004; 71:639-45. [PMID: 15569798] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/01/2023] Open
Abstract
St. Louis encephalitis (SLE) and West Nile (WN) flaviviruses are genetically closely related and cocirculate in the United States. Virus neutralization tests provide the most specific means for serodiagnosis of infections with these viruses. However, use of wild-type SLE and WN viral strains for laboratory testing is constrained by the biocontainment requirements. We constructed two highly attenuated yellow fever (YF) virus chimeras that contain the premembrane-envelope (prM-E) protein genes from the virulent MSI-7 (isolated in the United States) or the naturally attenuated CorAn9124 (Argentina) SLE strains. The YF/SLE (CorAn version) virus and the previously constructed YF/WN chimera were shown to specifically distinguish between confirmed human SLE and WN cases in a virus neutralization test using patient sera. These chimeras have the potential for use as diagnostic reagents and vaccines against SLE and WN.
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de Thoisy B, Dussart P, Kazanji M. Wild terrestrial rainforest mammals as potential reservoirs for flaviviruses (yellow fever, dengue 2 and St Louis encephalitis viruses) in French Guiana. Trans R Soc Trop Med Hyg 2004; 98:409-12. [PMID: 15138077 DOI: 10.1016/j.trstmh.2003.12.003] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2003] [Revised: 11/20/2003] [Accepted: 12/02/2003] [Indexed: 11/29/2022] Open
Abstract
A serological survey for yellow fever virus (YFV), dengue 2 virus (DENV-2), and St Louis encephalitis virus (SLEV) was undertaken using a seroneutralization technique in 27 wild forest mammal species (574 individuals) in French Guiana. Evidence of yellow fever infection was observed in 10 species, with high prevalence recorded in howler monkey (18%) and agouti (20%). Antibodies against DENV-2 and SLEV were found sporadically in various species. This potential host diversity and the range of potential vectors might explain the behaviour of the viruses in epidemic outbreaks and the emergence of periurban loci.
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Reisen WK, Chiles R, Martinez V, Fang Y, Green E, Clark S. Effect of dose on house finch infection with western equine encephalomyelitis and St. Louis encephalitis viruses. JOURNAL OF MEDICAL ENTOMOLOGY 2004; 41:978-981. [PMID: 15535631 DOI: 10.1603/0022-2585-41.5.978] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
House finches, Carpodacus mexicanus, were experimentally infected with high and standard doses of western equine encephalomyelitis virus (WEEV) or St. Louis encephalitis virus (SLEV) to determine whether high doses would produce an elevated viremia response and a high frequency of chronic infections. Finches inoculated with approximately100,000 plaque forming units (PFU) of WEEV or SLEV produced viremia and antibody responses similar to those in finches inoculated with approximately 100 PFU of WEEV or 1000 PFU of SLEV, the approximate quantities of virus expectorated by blood-feeding Culex tarsalis Coquillett. Infected finches were held through winter and then necropsied. Only one finch inoculated with the high dose of SLEV developed a chronic infection. Our data indicated that elevated infectious doses of virus may not increase the viremia level or the frequency of chronic infection in house finches.
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Mahmood F, Chiles RE, Fang Y, Barker CM, Reisen WK. Role of nestling mourning doves and house finches as amplifying hosts of St. Louis encephalitis virus. JOURNAL OF MEDICAL ENTOMOLOGY 2004; 41:965-972. [PMID: 15535629 DOI: 10.1603/0022-2585-41.5.965] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Nestling mourning doves and house finches produced elevated viremias after inoculation with 2-3 log10 plaque-forming units (PFU) of St Louis encephalitis (SLE) virus and infected 67 and 70% of Culex tarsalis Coquillett that engorged upon them, respectively. Mosquito infection rates as well as the quantity of virus produced after extrinsic incubation increased as a function of the quantity of virus ingested and peaked during days 3-5 postinoculation in mourning doves and days 2-4 in house finches. Only female Cx. tarsalis with body titers > or = 4.6 log10 PFU were capable of transmitting virus. Overall, 38% of females infected by feeding on mourning doves and 22% feeding on house finches were capable of transmission. The quantity of virus expectorated was variable, ranging from 0.8 to 3.4 log10 PFU and was greatest during periods when avian viremias were elevated. Our data indicated that nestling mourning doves and house finches were competent hosts for SLE virus and that the quantity of virus ingested from a viremic avian host varies during the course of the infection and determines transmission rates by the mosquito vector.
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Shaman J, Day JF, Stieglitz M, Zebiak S, Cane M. Seasonal forecast of St. Louis encephalitis virus transmission, Florida. Emerg Infect Dis 2004; 10:802-9. [PMID: 15200812 PMCID: PMC3323226 DOI: 10.3201/eid1005.030246] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Disease transmission forecasts can help minimize human and domestic animal health risks by indicating where disease control and prevention efforts should be focused. For disease systems in which weather-related variables affect pathogen proliferation, dispersal, or transmission, the potential for disease forecasting exists. We present a seasonal forecast of St. Louis encephalitis virus transmission in Indian River County, Florida. We derive an empirical relationship between modeled land surface wetness and levels of SLEV transmission in humans. We then use these data to forecast SLEV transmission with a seasonal lead. Forecast skill is demonstrated, and a real-time seasonal forecast of epidemic SLEV transmission is presented. This study demonstrates how weather and climate forecast skill verification analyses may be applied to test the predictability of an empirical disease forecast model.
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Chiles RE, Green EN, Fang Y, Goddard L, Roth A, Reisen WK, Scott TW. Blinded laboratory comparison of the in situ enzyme immunoassay, the VecTest wicking assay, and a reverse transcription-polymerase chain reaction assay to detect mosquitoes infected with West Nile and St. Louis encephalitis viruses. JOURNAL OF MEDICAL ENTOMOLOGY 2004; 41:539-544. [PMID: 15311443 DOI: 10.1603/0022-2585-41.4.539] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
A blinded laboratory evaluation compared the accuracy, sensitivity, and specificity of an in situ enzyme immunoassay (EIA), VecTest wicking assay, and reverse transcription-polymerase chain reaction (RT-PCR) to detect and distinguish West Nile (WN) and St. Louis encephalitis (SLE) viruses in pools of 50 mosquitoes. Adult female Culex tarsalis Coquillett were inoculated with either WN or SLE viruses, held for 0-11 d at 28 degrees C, killed by freezing, and then were added to 49 or 48 uninfected mosquitoes to make up 14 pools positive for WN virus, 14 positive for SLE virus, 14 positive for both WN and SLE viruses, and 14 negative for virus. Pools were number coded and tested blindly. Virus was not detected in known negative pools. VecTest and RT-PCR assays were comparably sensitive and accurate, detecting virus in pools containing females held for 3 d postinoculation; only RT-PCR detected SLE virus in pools on days 0-1. The VecTest and RT-PCR produced a single false-positive result for WN and SLE, respectively. RT-PCR detected RNA in samples positive by the VecTest, indicating that the detergent in the wicking buffer did not prevent RT-PCR from confirming VecTest results. Detector antibodies used in the in situ EIA cross-reacted between SLE and WN viruses, reducing accuracy. Both the VecTest and RT-PCR provided rapid and specific results, but they detected only those viruses known to be present. Plaque assay on Vero cells was comparably sensitive and had the added benefit of detecting newly emerging viruses, but this method required virus culture followed by identification, thereby delaying reporting.
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Lillibridge KM, Parsons R, Randle Y, Travassos da Rosa APA, Guzman H, Siirin M, Wuithiranyagool T, Hailey C, Higgs S, Bala AA, Pascua R, Meyer T, Vanlandingham DL, Tesh RB. The 2002 introduction of West Nile virus into Harris County, Texas, an area historically endemic for St. Louis encephalitis. Am J Trop Med Hyg 2004; 70:676-81. [PMID: 15211013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/29/2023] Open
Abstract
Harris County, Texas, is an endemic area of St. Louis encephalitis (SLE); and an active surveillance program that monitors SLE virus activity in mosquitoes, birds, and humans has been in place there for the past 28 years. In June of 2002, West Nile (WN) virus appeared in Houston and quickly spread throughout the region. This report describes the results of 12 years of SLE surveillance in Harris County and the contrasting pattern of WN virus activity, when it arrived in 2002. Our data indicate that both SLE and WN viruses can coexist, despite their ecologic, antigenic, and genetic similarities, and that both viruses will probably persist in this geographic region.
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Nelson DM, Gardner IA, Chiles RF, Balasuriya UB, Eldridge BF, Scott TW, Reisen WK, Maclachlan NJ. Prevalence of antibodies against Saint Louis encephalitis and Jamestown Canyon viruses in California horses. Comp Immunol Microbiol Infect Dis 2004; 27:209-15. [PMID: 15001316 DOI: 10.1016/j.cimid.2003.11.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/05/2003] [Indexed: 11/28/2022]
Abstract
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.
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Reisen WK, Chiles RE, Martinez VM, Fang Y, Green EN. Encephalitis virus persistence in California birds: experimental infections in mourning doves (Zenaidura macroura). JOURNAL OF MEDICAL ENTOMOLOGY 2004; 41:462-466. [PMID: 15185951 DOI: 10.1603/0022-2585-41.3.462] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
After-hatching and hatching year, mourning doves were infected by inoculation with either western equine encephalomyelitis (WEE) or St. Louis encephalitis (SLE) viruses; some birds in each group also were treated with the immunosuppressant cyclophosphamide before and during infection. Cyclophosphamide treatment significantly increased the WEE viremia but did not alterthe antibody response. In contrast, cyclophosphamide-treated and -untreated doves did not develop a detectable SLE viremia but became antibody positive. Antibody peaked at 10 wk after inoculation for both viruses and remained detectable in most birds throughout the 26-wk study. When treated with cyclophosphamide the following spring, birds did not relapse and develop a detectable viremia. Previously infected birds were protected when challenged with conspecific virus (i.e., none produced a detectable viremia), but there was no anamnestic antibody response to reinfection. In agreement with our failure to detect relapses, all birds were negative for viral RNA when sera, spleen, lung, and kidney tissues were tested by reverse transcriptase-polymerase chain reaction after necropsy. Our results indicated that adult mourning doves were an incompetent host for SLE virus and probably do not serve as a suitable overwintering or dispersal host for either WEE and SLE viruses.
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Reisen WK, Chiles RE, Martinez VM, Fang Y, Green EN. Experimental infection of California birds with western equine encephalomyelitis and St. Louis encephalitis viruses. JOURNAL OF MEDICAL ENTOMOLOGY 2003; 40:968-982. [PMID: 14765678 DOI: 10.1603/0022-2585-40.6.968] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
A total of 27 bird species from the San Joaquin and Coachella valleys of California were inoculated subcutaneously with sympatric strains of western equine encephalomyelitis (WEE) and St. Louis encephalitis (SLE) viruses. Overall, 133 of 164 birds inoculated with WEE virus developed a viremia detected by plaque assay; significantly greater than 72 of 163 birds inoculated with SLE virus. Host competence was calculated as the average number of days that each avian species had a viremia > or = 2 log10 plaque-forming units per 0.1 ml, the threshold for infecting susceptible Culex tarsalis Coquillett, the primary vector of these viruses in California. Eleven of 20 species inoculated with WEE virus had a value > or = 1 and were considered to be competent hosts, whereas only six of 22 species inoculated with SLE virus had a value > or = 1. Overall, 133 of 164 birds inoculated with WEE virus and 105 of 163 inoculated with SLE virus produced antibody detectable by enzyme immunoassay and/or plaque reduction neutralization test. Six birds infected with WEE virus (one house finch, three mourning doves, one Brewer's sparrow, and one white-crowned sparrow) and nine birds infected with SLE virus (two house finches, three white-crowned sparrows, one song sparrow, two Western scrub-jays, and one orange crowned warbler) contained viral RNA detected by reverse transcription-polymerase chain reaction at necropsy > 6 wk postinoculation; infectious WEE and SLE viruses were only recovered from three mourning doves and an orange-crowned warbler, respectively, after blind passage in mosquito cells. Our study indicated that birds with elevated field antibody prevalence rates may not be the most competent hosts for encephalitis viruses and that relatively few birds developed chronic infections that could be important in virus persistence and dispersal.
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Shaman J, Day JF, Stieglitz M. St. Louis encephalitis virus in wild birds during the 1990 south Florida epidemic: the importance of drought, wetting conditions, and the emergence of Culex nigripalpus (Diptera: Culicidae) to arboviral amplification and transmission. JOURNAL OF MEDICAL ENTOMOLOGY 2003; 40:547-554. [PMID: 14680125 DOI: 10.1603/0022-2585-40.4.547] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
We analyzed the prevalence of hemagglutination inhibition (HI) antibodies to St. Louis encephalitis (SLE) virus in wild birds during the 1990 SLE epidemic in Indian River County. The initial presence of SLE HI antibody was associated significantly with modeled drought 15 wk prior, wetting conditions 1 wk prior, and the emergence of the Florida SLE virus vector, Culex nigripalpus, 5 wk prior. Our findings indicated that three factors conspired to create the 1990 epidemic: (1) a large population of susceptible wild birds; (2) severe springtime drought, which facilitated amplification of the SLE virus among the Cx. nigripalpus and a portion of the wild bird population; and (3) continued rainfall and wetting of the land surface in the summer and early fall, which sustained a large, host-seeking Cx. nigripalpus population. The continued biting and reproductive activity of Cx. nigripalpus maintained epizootic transmission throughout the summer and early fall in Indian River County. The high level of SLE virus amplification resulted in spillover transmission to humans. We hypothesize that without the continued reproductive activity of the vector mosquito, brought about by excessive summer and fall wetness, the unprecedented SLE virus amplification and consequent transmission to humans would not have been realized in 1990.
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Hirsch MS, Werner B. Case records of the Massachusetts General Hospital. Weekly clinicopathological exercises. Case 17-2003. A 38-year-old woman with fever, headache, and confusion. N Engl J Med 2003; 348:2239-47. [PMID: 12773652 DOI: 10.1056/nejmcpc030015] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Reisen WK, Chiles RE, Green EN, Fang Y, Mahmood F. Previous infection protects house finches from re-infection with St. Louis encephalitis virus. JOURNAL OF MEDICAL ENTOMOLOGY 2003; 40:300-305. [PMID: 12943108 DOI: 10.1603/0022-2585-40.3.300] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Antibody titers against St. Louis encephalitis virus (SLE) measured by a plaque reduction neutralization test (PRNT) decreased rapidly in house finches (Capodacus mexicanus) after initial infection, whereas antibodies measured by enzyme immunoassay (EIA) remained detectable in all birds for the length of the experiment, indicating long-term persistence and greater assay sensitivity of the EIA. After 52 wk, birds were challenged by subcutaneous inoculation with the same strain of SLE virus. Virus was not detected for 1-4 d postchallenge in blood samples tested by plaque assay and RT-PCR or by xenodiagnosis in Culex tarsalis fed concurrently and then held for 11 d at 26 degrees C. Virus was detected by all three methods in control birds infected concurrently for the first time. Challenge with SLE produced a rapid and marked ananmestic rise in both neutralizing and EIA antibody titers that exceeded the primary response in the same birds or in concurrently inoculated control birds. At necropsy 4 wk postchallenge, 3 of 7 challenged and 1 of 2 positive control birds were chronically infected, with viral RNA detected by RT-PCR in brain, spleen, lung, and/or kidney tissues. Our results indicated that persistence of protective antibody prevents reinfection during the following season and may prevent the recrudescence of infectious virus in chronically infected birds.
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Spinsanti L, Basquiera AL, Bulacio S, Somale V, Kim SCH, Ré V, Rabbat D, Zárate A, Zlocowski JC, Mayor CQ, Contigiani M, Palacio S. St. Louis encephalitis in Argentina: the first case reported in the last seventeen years. Emerg Infect Dis 2003; 9:271-3. [PMID: 12604006 PMCID: PMC2901953 DOI: 10.3201/eid0902.020301] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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Ryan J, Davé K, Emmerich E, Fernández B, Turell M, Johnson J, Gottfried K, Burkhalter K, Kerst A, Hunt A, Wirtz R, Nasci R. Wicking assays for the rapid detection of West Nile and St. Louis encephalitis viral antigens in mosquitoes (Diptera: Culicidae). JOURNAL OF MEDICAL ENTOMOLOGY 2003; 40:95-99. [PMID: 12597660 DOI: 10.1603/0022-2585-40.1.95] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The recent outbreaks of West Nile (WN) encephalitis and St. Louis encephalitis (SLE) in the United States have highlighted the need for rapid and specific methods of detecting arboviral antigens in mosquitoes. We evaluated rapid, field-usable assays for detecting and differentiating WN and SLE viruses in mosquito pools, based on a patent-pending, immunochromatographic technology (VecTest) formatted on a dipstick. The device provides results in less than 20 min and can be used in laboratories with adequate containment facilities. In laboratory assessments, both the SLE and WN virus tests demonstrated sensitivity comparable with that of an antigen capture ELISA, but less than can be achieved with Vero cell plaque or reverse-transcriptase polymerase chain reaction assays. There was no evidence of cross-reaction when tested with high concentrations of heterologous flavivirus antigens or with Eastern equine encephalitis or Western equine encephalitis viruses. Both the WN and SLE dipstick tests delivered a clear positive result with a single positive specimen in a pool of 50 mosquitoes. This virus assay technology reduces the time required to obtain test results and will allow rapid medical threat assessment and effective targeting of vector control measures.
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Abstract
We used a dynamic hydrology model to simulate water table depth (WTD) and quantify the relationship between Saint Louis encephalitis virus (SLEV) transmission and hydrologic conditions in Indian River County, Florida, from 1986 through 1991, a period with an SLEV epidemic. Virus transmission followed periods of modeled drought (specifically low WTDs 12 to 17 weeks before virus transmission, followed by a rising of the water table 1 to 2 weeks before virus transmission). Further evidence from collections of Culex nigripalpus (the major mosquito vector of SLEV in Florida) suggests that during extended spring droughts vector mosquitoes and nestling, juvenile, and adult wild birds congregate in selected refuges, facilitating epizootic amplification of SLEV. When the drought ends and habitat availability increases, the SLEV-infected Cx. nigripalpus and wild birds disperse, initiating an SLEV transmission cycle. These findings demonstrate a mechanism by which drought facilitates the amplification of SLEV and its subsequent transmission to humans.
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Spinsanti LI, Ré VE, Díaz MP, Contigiani MS. Age-related seroprevalence study for St. Louis encephalitis in a population from Cordoba, Argentina. Rev Inst Med Trop Sao Paulo 2002; 44:59-62. [PMID: 12048540 DOI: 10.1590/s0036-46652002000200001] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A serological screening was performed in 615 individuals aged 0-87 years, living in the city of Cordoba, Argentina to study the relationship between antibody prevalence for the SLE virus and age. A 13.98% prevalence of neutralizing antibodies was obtained and its relation to age was significantly high (p = 0.045). The highest seroprevalence was noted on individuals over 60 years old (>20%), whereas no subject under 10 was seropositive for this virus. Our results confirm that the agent is endemic in this area and neurological pathology studies should be performed on those individuals aged 60 since they represent the most susceptible group to SLE virus.
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Kramer LD, Wolfe TM, Green EN, Chiles RE, Fallah H, Fang Y, Reisen WK. Detection of encephalitis viruses in mosquitoes (Diptera: Culicidae) and avian tissues. JOURNAL OF MEDICAL ENTOMOLOGY 2002; 39:312-323. [PMID: 11931031 DOI: 10.1603/0022-2585-39.2.312] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
ABSTRACT Diagnostic assays for the detection of St. Louis encephalitis (SLE) and western equine encephalomyelitis (WEE) viruses in mosquito pools and avian tissues were compared for sensitivity, accuracy and specificity. The in situ enzyme immunoassay (EIA), plaque assay on Vero cells, passage in Aedes albopictus Skuse C6/36 and C7/10 cells, antigen capture enzyme immunoassay (AC-EIA), and single and multiplex reverse transcription-polymerase chain reactions (RT-PCR) were evaluated using pools of 50 mosquitoes containing 1-2 experimentally infected individuals. RT-PCR was the most sensitive assay, with a detection limit of <0.1 plaque forming unit. AC-EIA was the fastest and most economical procedure, but was the least sensitive, detecting only 38% of positive pools. The in situ EIA included initial virus amplification on Vero cells, thereby improving assay sensitivity to detect 68% of positive pools. Passage in C6/36 and/or C7/10 cell culture revealed the presence of infectious virus in samples positive by RT-PCR, but initially negative by plaque assay on Vero cell culture, indicating that detection was related to assay sensitivity and not to the absence of intact infectious virus. Combining WEE and SLE RT-PCR assays into a multiplex assay reduced sensitivity, but stilldetected viral RNA at titers below plaque assay sensitivity. Plaque assay on Vero cells, mosquito cell passage, and several RT-PCR procedures were evaluated for their ability to detect WEE and SLE in white-crowned sparrow tissues during acute and chronic stages of infection. All assays detected virus during acute infection at times of high viremia; however, only RT-PCR assays were positive by day 7 when virus was not detected in sera. RT-PCR detected SLE RNA in spleen tissue from one bird 51 d after infection. Assay sensitivity also was compared using extracts of homogenized bird organs spiked with known titers of WEE and SLE. Trizol RNA extraction followed by Qiagen one-step RT-PCR was the most sensitive method, but occasionally resulted in the presence of secondary bands confounding interpretation and requiring confirmatory assays. A balanced surveillance program should combine systems that allow the detection of new agents and the sensitive monitoring of endemic agents to provide an early warning of pending health risks.
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MESH Headings
- Aedes/virology
- Animals
- Bird Diseases/pathology
- Bird Diseases/virology
- Chlorocebus aethiops
- Culex/virology
- DNA, Viral/analysis
- Encephalitis Virus, St. Louis/genetics
- Encephalitis Virus, St. Louis/immunology
- Encephalitis Virus, St. Louis/isolation & purification
- Encephalitis Virus, Western Equine/genetics
- Encephalitis Virus, Western Equine/immunology
- Encephalitis Virus, Western Equine/isolation & purification
- Encephalitis, St. Louis/pathology
- Encephalitis, St. Louis/veterinary
- Encephalitis, St. Louis/virology
- Encephalomyelitis, Western Equine/pathology
- Encephalomyelitis, Western Equine/veterinary
- Encephalomyelitis, Western Equine/virology
- Female
- Sensitivity and Specificity
- Songbirds/virology
- Vero Cells
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