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West Nile virus cluster analysis and vertical transmission in
Culex pipiens
complex mosquitoes in Sacramento and Yolo Counties, California, 2011
| Fechter-Leggett, Ethan | 2012 |
KeywordsCalifornia, California: epidemiology, Culex, West Nile virus: pathogenicity, West Nile virus, West Nile Fever: transmission, West Nile Fever, Infectious Disease Transmission, Vertical, Female, Culex: virology, Animals AbstractWest Nile virus (WNV) is now endemic in California, with annual transmission documented by the statewide surveillance system. Although much is known about the horizontal avian-mosquito transmission cycle, less is known about vertical transmission under field conditions, which may supplement virus amplification during summer and provide a mechanism to infect overwintering female mosquitoes during fall. The current study identified clusters of WNV-infected mosquitoes in Sacramento and Yolo Counties, CA, during late summer 2011 and tested field-captured ovipositing female mosquitoes and their progeny for WNV RNA to estimate the frequency of vertical transmission. Space-time clustering of WNV-positive Culex pipiens complex pools was detected in the northern Elk Grove area of Sacramento County between July 18 and September 18, 2011 (5.22 km radius; p<0.001 and RR=7.80). Vertical transmission by WNV-infected females to egg rafts was 50% and to larvae was 40%. The estimated minimal filial infection rate from WNV-positive, ovipositing females was 2.0 infected females/1,000. The potential contribution of vertical transmission to WNV maintenance and amplification are discussed. AuthorsFechter-Leggett, Ethan, Nelms, Brittany M., Barker, Christopher M. and Reisen, William K. Year Published2012 PublicationJournal of Vector Ecology LocationsDOI10.1111/j.1948-7134.2012.00248.x Additional Information:http://www.ncbi.nlm.nih.gov/pubmed/23181869 |
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West Nile Virus in Overwintering
Culex
Mosquitoes, New York City, 2000
| Nasci, Roger S. | 2001 |
KeywordsWNV AbstractAfter the 1999 West Nile (WN) encephalitis outbreak in New York, 2,300 overwintering adult mosquitoes were tested for WN virus by cell culture and reverse transcriptase-polymerase chain reaction. WN viral RNA and live virus were found in pools of Culex mosquitoes. Persistence in overwintering Cx. pipiens may be important in the maintenance of WN virus in the northeastern United States. AuthorsMiller, James R., WHITE, DENNIS J., Nasci, Roger S., Savage, Harry M., Cropp, Bruce C., Godsey, Marvin S., Kerst, Amy J., Bennett, Paul, Gottfried, Kristy and Lanciotti, Robert S. Year Published2001 PublicationEmerging Infectious Diseases LocationsDOI10.3201/eid0704.010426 Additional Information:http://www.ncbi.nlm.nih.gov/pubmed/11585542 |
| Culex restuans (Diptera: Culicidae) Oviposition Behavior Determined by Larval Habitat Quality and Quantity in Southeastern Michigan | Reiskind, Michael H. | 2004 |
Keywords mosquito oviposition, larval habitat, landscape ecology, density dependence, West Nile virus, WNV AbstractOviposition is a critical stage in the mosquito lifecycle, and may determine population levels, distribution, biting behavior, and pathogen transmission. Knowledge of the oviposition behavior of Culex restuans Theobald has become particularly important with the emergence of West Nile virus (WNV) in North America. Laboratory and field studies have examined some factors that contribute to oviposition choice in Culex spp., but few studies have investigated responses to cues of future competition and breeding habitat availability in the field. We hypothesized that female Cx. restuans mosquitoes avoid laying eggs in habitats containing cues of larval competition, and that increased availability of larval habitat decreases egg density. To test these hypotheses, a series of field experiments were conducted in southeastern Michigan during summer 2002. We found that female mosquitoes prefer nutrient-enriched containers and decrease ovipositing in containers with conspecific larvae. In addition, greater habitat abundance decreased egg clutch density per container, although there was considerable aggregation of egg clutches. These results support our hypotheses and have potentially important implications for pathogen transmission by mosquitoes. AuthorsReiskind, Michael H. and Wilson, Mark L. Year Published2004 PublicationJournal of Medical Entomology LocationsDOI10.1603/0022-2585-41.2.179 Additional Information:http://www.ncbi.nlm.nih.gov/pubmed/15061276 |
| Culex restuans (Diptera: Culicidae) Relative Abundance and Vector Competence for West Nile Virus | Ebel, Gregory D. | 2005 |
KeywordsCulex pipiens, Culex restuans, West Nile virus, Flavivirus, transmission, WNV AbstractThe abundance and vector competence of Culex restuans Theobald and Culex pipiens L. were compared to determine the relative importance of these species as West Nile virus (WNV) vectors in the northeastern United States. Abundance was estimated from egg raft collections at 12 sites in Albany, Suffolk, and Richmond counties, New York, during July, August, and September 2002 and 2003. Cx. restuans was more abundant than Cx. pipiens in both urban and rural areas, comprising 86% of 1,623 egg rafts collected. Vector competence for WNV was estimated after feeding on an artificial bloodmeal and in vitro transmission assays. The vector competence of the two species for WNV was similar, but the dynamics of infection seems to be mosquito species dependent. These findings suggest an important role for Cx. restuans in WNV transmission cycles in New York. AuthorsEbel, Gregory D., Rochlin, Ilia, Longacker, Jennifer and Kramer, Laura D. Year Published2005 PublicationJournal of Medical Entomology LocationsDOI10.1603/0022-2585(2005)042[0838:CRDCRA]2.0.CO;2 Additional Information:http://www.ncbi.nlm.nih.gov/pubmed/16363169 |
| A COMPARISON OF TWO WEST NILE VIRUS DETECTION ASSAYS (TAQMAN REVERSE TRANSCRIPTASE POLYMERASE CHAIN REACTION AND VECTEST ANTIGEN ASSAY) DURING THREE CONSECUTIVE OUTBREAKS IN NORTHERN ILLINOIS | LAMPMAN, RICHARD L. | 2006 |
KeywordsCulex, VecTest™, TaqMan™ reverse transcriptase polymerase chain reaction, West Nile virus, infection rate, Cook County, Illinois, Diptera, Culicidae, WNV AbstractMosquitoes identified as female Culex (Culex) species, primarily mixtures or uniform batches of Culex pipiens and Culex restuans, were collected daily from gravid traps by 2 mosquito abatement districts (MADs) in Cook County, Illinois. From 2002 through 2004, batches (pools) of mosquitoes were tested by the MADs for West Nile virus (WNV) by using VecTest™ WNV antigen assays and the same samples were retested, usually within 1–2 wk, for WNV RNA by the TaqMan™ reverse transcriptase polymerase chain reaction (RT-PCR). There were 952 TaqMan-positive pools out of 3,953 pools over the 3 years, and about one half of that number were VecTest-positive. The difference between the 2 detection assays varied between and within years. The VecTest assays detected about 57% and 69% of the TaqMan RT-PCR–positive pools from Des Plaines Valley MAD and Northwest MAD in 2002, but only about 40% and 46% in 2003, and 36% and 55% in 2004, respectively. Based on a subset of the 2004 data, a linear relationship was found between VecTest detection of WNV and TaqMan cycle threshold between 18 and 28 cycles. A temporal decrease in the difference between the 2 assays was observed in 2003 and 2004, which we conjecture is due, at least partially, to a seasonal decline in the proportion of recently infected mosquitoes. This trend was not observed in 2002 because infection rates indicated a high likelihood of more than 1 infected mosquito per pool at the peak of transmission. Unlike a previous study, the 95% confidence intervals of infection rates based on the 2 detection methods did not always overlap. The highest infection rates occurred in 2002 when mean monthly temperatures were above average. AuthorsNovak, Robert J., LAMPMAN, RICHARD L., KRASAVIN, NINA M. and SZYSKA, MICHAEL Year Published2006 PublicationJournal of the American Mosquito Control Association LocationsDOI10.2987/8756-971X(2006)22[76:ACOTWN]2.0.CO;2 Additional Information:http://www.ncbi.nlm.nih.gov/pubmed/16646326 |
| A Live Attenuated West Nile Virus Strain as a Potential Veterinary Vaccine | LUSTIG, SHLOMO | 2000 |
KeywordsWNV AbstractThis article reviews the development of two attenuated West Nile virus (WNV) variants, WNI-25 and WNI-25A. These variants have lost the neuroinvasion trait of the parental virus. Attenuation was achieved through serial passages in mosquito cells and neutralization escape from WNV-specific monoclonal antibody. Genetic analysis reveals amino acid changes between the parental and each of the variants. The attenuated variants preserve the ability to replicate in mice and geese and to induce a protective immune response. WNI-25A was found to be a genetically stable virus. This variant was successfully used as a live vaccine to protect geese against a wild-type virulent WNV field isolate that closely resembles the WNV isolated during the 1999 New York epidemic. AuthorsLUSTIG, SHLOMO, OLSHEVSKY, UDY, BEN-NATHAN, DAVID, LACHMI, BAT-EL, MALKINSON, MERTYN, KOBILER, DAVID and HALEVY, MENACHEM Year Published2000 PublicationViral Immunology LocationsDOI10.1089/vim.2000.13.401 |
| A Method to Increase Efficiency in Testing Pooled Field-Collected Mosquitoes | Chisenhall, Daniel M. | 2008 |
KeywordsWest Nile virus, mosquito pool, quantitative reverse transcriptase polymerase chain reaction, arbovirus testing, surveillance, WNV AbstractTesting field-caught mosquito collections can result in thousands of pools, and testing pools of 50 mosquitoes each can be both time consuming and cost prohibitive. Consequently, we have developed an alternative approach to testing mosquito pools for arboviruses, utilizing a superpool strategy. When mosquito samples are processed for extraction of viral RNA and subsequent virus testing via quantitative real-time polymerase chain reaction, each pool is tested individually. Using the method described here, 0.025 ml from each of 10 pools is combined into a superpool for RNA extraction and testing. When a virus-positive superpool sample is found, each of the original 10 pools that constitute this sample is tested individually in order to find the specific positive sample. By retesting the original samples after the initial superpool screen, we are still able to obtain reliable estimates for minimum infection rates or maximum likelihood estimations. To test this principle, we created controlled mosquito pools of known titer and subjected them to our superpool process. We were able to detect our entire range of laboratory-created pools as being West Nile virus (WNV) positive. In 2005, field surveillance efforts from our laboratory resulted in over 4,000 mosquito pools tested, with 8 resulting WNV-positive samples. We found that all of these field samples were detected as WNV positive using the superpool method and contained calculated virus titers from <0.1 to 4.1 log10 plaque-forming units/ml WNV, indicating that the limit of superpool detection of WNV is below this point. These results reveal that the superpool method could be accurately used to detect WNV in field-collected specimens. AuthorsChisenhall, Daniel M., Vitek, Christopher J., Richards, Stephanie L. and Mores, Christopher N. Year Published2008 PublicationJournal of the American Mosquito Control Association LocationsDOI10.2987/5671.1 Additional Information:http://www.ncbi.nlm.nih.gov/pubmed/18666541 |
| A MULTIPLE CAGE–HOLDING, WIND-SENSITIVE VANE DESIGN FOR USE IN GROUND ADULTICIDING EFFICACY TESTING IN HARRIS COUNTY, TEXAS | VESSEY, NATHAN Y. | 2007 |
KeywordsWind-sensitive vane apparatus, treatment cages, ground ultra-low volume testing, WNV AbstractA wind-sensitive vane apparatus was designed and implemented specifically to accommodate the attachment of otherwise unidirectional insecticide treatment cages used in ground ultra-low volume mosquito adulticide field tests. This cage support system is useful in keeping the potential West Nile virus and St. Louis encephalitis vector Culex quinquefasciatus caged mosquitoes oriented into the wind during field efficacy tests. Testing capacity for resistance surveillance was tripled during the 2005 season, and more reliable results were achieved as a consequence. AuthorsBueno, Rudy, VESSEY, NATHAN Y., STARK, PAMELA M. and FLATT, KYLE L. Year Published2007 PublicationJournal of the American Mosquito Control Association LocationsDOI10.2987/8756-971X(2007)23[237:AMCWVD]2.0.CO;2 Additional Information:http://www.ncbi.nlm.nih.gov/pubmed/17847862 |
| A TWO-YEAR EVALUATION OF ELEVATED CANOPY TRAPPING FOR CULEX MOSQUITOES AND WEST NILE VIRUS IN AN OPERATIONAL SURVEILLANCE PROGRAM IN THE NORTHEASTERN UNITED STATES | Andreadis, Theodore G. | 2007 |
KeywordsWest Nile virus, Culex pipiens, Culex restuans, Culex salinarius, surveillance, light trap, gravid trap, elevation, WNV AbstractThe effectiveness of CO2-baited Centers for Disease Control and Prevention miniature light traps elevated in the tree canopy (7.6 m) was compared with light traps placed at ground level (1.5 m) and grass-sod infused gravid traps for collecting Culex pipiens, Culex restuans, and Culex salinarius and detecting West Nile virus (WNV) activity in an operational surveillance program that encompassed 12 ecologically diverse sites in Connecticut in 2004 and 2005. More than twice as many Cx. pipiens were collected on average in light traps suspended in the tree canopy than in either light or gravid traps placed at ground level. This difference was generally restricted to those collection sites where markedly greater numbers of Cx. pipiens were collected with all trapping methods but was not associated with site-specific urbanization indices. Culex restuans was not preferentially attracted to light traps suspended in the tree canopy. No differences in the overall abundance of this species were recorded with either of the 2 trapping procedures, but both light traps were more effective than the gravid traps. Culex salinarius was significantly more attracted to ground-based light traps than traps suspended in the tree canopy, while gravid traps were ineffective at all sites regardless of the level of urbanization or any other specific land-use characteristic. CO2-baited light traps placed in the tree canopy were generally superior to ground-based light traps for detecting WNV in Cx. pipiens. West Nile virus–infected females were collected more regularly, and the frequency of infected pools was significantly greater. Twofold higher minimum field infection rates (maximum likelihood estimation [MLE] = 6.7 vs. 3.0 per 1,000 mosquitoes) were also recorded from canopy collections of this species, and virus was detected in canopy-collected females several weeks before it was detected in collections from light traps at ground level. We conclude that the use of CO2-baited light traps placed in the tree canopy for targeted trapping of Cx. pipiens and subsequent detection of WNV are likely to yield better overall results than light traps placed at ground level in this region of the northeastern United States. The virus isolation data obtained from Cx. pipiens collected in gravid traps compared favorably both temporally and spatially with results from canopy trap collections. There were no significant differences in the overall frequency of WNV-infected pools or MLEs for Cx. pipiens, but fewer total WNV isolations were made from Cx. pipiens collected in the gravid traps and virus was detected more infrequently. Results reaffirmed the utility of gravid traps as effective surveillance tools for detection of WNV in Cx. pipiens in the northeastern United States. However, findings also demonstrated that CO2-baited light traps placed in the tree canopy provided more consistent results where weekly detection of virus amplification is a critical objective. The comparative effectiveness of ground- and canopy-based light traps for detection of WNV-infected Cx. restuans and Cx. salinarius was inconclusive owing to the limited number of virus isolations that were made from these species during the 2 years of study. However, WNV virus isolations were made several weeks earlier and more frequently from Cx. restuans collected in traps placed in the canopy rather than at ground level in 2004. Results support the view that ground-based light traps are more effective for detection of WNV in Cx. salinarius. AuthorsAndreadis, Theodore G. and ARMSTRONG, PHILIP M. Year Published2007 PublicationJournal of the American Mosquito Control Association LocationsDOI10.2987/8756-971X(2007)23[137:ATEOEC]2.0.CO;2 Additional Information:http://www.ncbi.nlm.nih.gov/pubmed/17847845 |
| Abundance of West Nile virus mosquito vectors in relation to climate and landscape variables | Deichmeister, Jayne M. | 2011 |
KeywordsWNV AbstractIt is currently unclear if the potential for West Nile virus transmission by mosquito vectors in the eastern United States is related to landscape or climate factors or both. We compared abundance of vector species between urban and suburban neighborhoods of Henrico County, VA, in relation to the following factors: temperature, precipitation, canopy cover, building footprint, and proximity to drainage infrastructure. Mosquitoes were collected throughout the 2005, 2006, and 2007 seasons and tested for West Nile virus (WNV) in pools of 10-50. Test results of mosquito pools were compared to average site abundance from 37 sites in Henrico County, VA; abundance was then examined in relation to ecological variables. Urban infrastructure was positively correlated with the abundance of Culex pipiens L./Cx. restuans, and our findings implicate combined sewer overflow systems as large contributors to Culex vector populations. No measure of urbanization examined in our study was correlated with Aedes albopictus abundance. Our study showed that certain landscape variables identified using Geographic Information Systems are valuable for predicting primary WNV vector abundance in Virginia, and that temperature along with low precipitation are strong predictors of population growth. Our results support other regional studies that found WNV proliferates under drought conditions. AuthorsDeichmeister, Jayne M. and Telang, Aparna Year Published2011 PublicationJournal of Vector Ecology LocationsDOI10.1111/j.1948-7134.2011.00143.x Additional Information:http://www.ncbi.nlm.nih.gov/pubmed/21635644 |
