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United States Articles found through PubMed 2000-2012

Description

West Nile Virus (WNV) is a mosquito-borne virus that can infect humans. Originally known in East Africa, WNV has now spread throughout the world. The first case of WNV in the western hemisphere was identified in New York in 1999, and within 5 years the disease had spread throughout the United States and into Canada, Latin America, and the Caribbean. While most of WNV infections cause no symptoms, the remaining cases show flu-like symptoms, and can lead to neurological disease or death.

latest article added on November 2013

ArticleFirst AuthorPublished
Bird-Baited Traps for Surveillance of West Nile Mosquito Vectors: Effect of Bird Species, Trap Height, and Mosquito Escape RatesDarbro, Jonathan M.2006

Bird-Baited Traps for Surveillance of West Nile Mosquito Vectors: Effect of Bird Species, Trap Height, and Mosquito Escape Rates

Keywords

West Nile virus, house sparrow, chicken, Culex p. pipiens, Culex restuans, WNV

Abstract

Host-seeking mosquitoes were sampled in bird-baited traps at four sites in New York state in 2003–2004. Trap placement and efficacy of chickens, Gallus gallus domesticus L., as bait compared with house sparrows, Passer domesticus L., an important reservoir of West Nile virus (family Flaviviridae, genus Flavivirus, WNV), was evaluated. Each site had a chicken-baited trap near ground level (≈1.5 m) and in the tree canopy (≈9 m), and a house sparrow-baited trap at ground level and canopy level. Each trap allowed mosquito access to birds on one end, and an inner mesh screen blocked bird access on the other end. The two most abundant mosquitoes, Culex restuans Theobald and Culex pipiens pipiens L., were differentiated using molecular characters. In 2003, Cx. restuans and Cx. p. pipiens made up 88% of total mosquito catch. In 2004, Cx. restuans comprised 43% of total catch and Cx. p. pipiens comprised 33%. The remaining species representing at least 1% of total catch were Ochlerotatus trivittatus (Coquillett), Coquilletidia perturbans (Walker), and Culiseta morsitans (Theobald). Capture rates were similar for chicken and house sparrow-baited traps; however, significantly more mosquitoes were captured in the canopy for both bird species. Cx. restuans preferred canopy traps, whereas equal numbers of Cx. p. pipiens were captured at ground and canopy levels. Mosquitoes were more likely to escape (74%) when excluded from birds than when allowed free access to birds (54%). Sentinel bird surveillance for WNV can be improved by trapping in the tree canopy in addition to ground level to capture the most important avian vectors.

Authors

Darbro, Jonathan M. and Harrington, Laura C.

Year Published

2006

Publication

Journal of Medical Entomology

Locations
DOI

10.1603/0022-2585(2006)043[0083:BTFSOW]2.0.CO;2

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/16506452

Importance of Vertical and Horizontal Transmission of West Nile Virus by Culex pipiens in the Northeastern United States Anderson, John F.2006

Importance of Vertical and Horizontal Transmission of West Nile Virus by Culex pipiens in the Northeastern United States

Keywords

WNV

Abstract

West Nile virus (WNV) has become established in the northeastern United States, where mosquitoes are inactive during winter. There have been no documented studies to explain how this virus survives winter and reinitiates infection in spring. We report that WNV was vertically transmitted to 2 F1 female Culex pipiens from a naturally infected female collected in Stratford, Connecticut. One vertically infected F1 female, which was 168 days old, fed on a hamster that died 8 days later of West Nile disease. This suggests that WNV survives winter in unfed, vertically infected C. pipiens with amplification initiated in spring by horizontal transmission

Authors

Anderson, John F. and Main, Andy J.

Year Published

2006

Publication

The Journal of Infectious Diseases

Locations
DOI

10.1086/508754

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/17083043

West Nile Virus Epidemics in North America Are Driven by Shifts in Mosquito Feeding BehaviorKilpatrick, A. Marm2006

West Nile Virus Epidemics in North America Are Driven by Shifts in Mosquito Feeding Behavior

Keywords

WNV

Abstract

West Nile virus (WNV) has caused repeated large-scale human epidemics in North America since it was first detected in 1999 and is now the dominant vector-borne disease in this continent. Understanding the factors that determine the intensity of the spillover of this zoonotic pathogen from birds to humans (via mosquitoes) is a prerequisite for predicting and preventing human epidemics. We integrated mosquito feeding behavior with data on the population dynamics and WNV epidemiology of mosquitoes, birds, and humans. We show that Culex pipiens, the dominant enzootic (bird-to-bird) and bridge (bird-to-human) vector of WNV in urbanized areas in the northeast and north-central United States, shifted its feeding preferences from birds to humans by 7-fold during late summer and early fall, coinciding with the dispersal of its preferred host (American robins, Turdus migratorius) and the rise in human WNV infections. We also show that feeding shifts in Cx. tarsalis amplify human WNV epidemics in Colorado and California and occur during periods of robin dispersal and migration. Our results provide a direct explanation for the timing and intensity of human WNV epidemics. Shifts in feeding from competent avian hosts early in an epidemic to incompetent humans after mosquito infection prevalences are high result in synergistic effects that greatly amplify the number of human infections of this and other pathogens. Our results underscore the dramatic effects of vector behavior in driving the transmission of zoonotic pathogens to humans.

Authors

Kramer, Laura D., Kilpatrick, A. Marm, Jones, Matthew J., Marra, Peter P. and Daszak, Peter

Year Published

2006

Publication

PLoS Biology

Locations
DOI

10.1371/journal.pbio.0040082

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/16494532

Oviposition Activity Patterns and West Nile Virus Infection Rates for Members of the Culex pipiens Complex at Different Habitat Types within the Hybrid Zone, Shelby County, TN, 2002 (Diptera: Culicidae)Savage, Harry M.2006

Oviposition Activity Patterns and West Nile Virus Infection Rates for Members of the Culex pipiens Complex at Different Habitat Types within the Hybrid Zone, Shelby County, TN, 2002 (Diptera: Culicidae)

Keywords

Culex pipiens complex, oviposition activity period, West Nile virus, pipiens, hybrid zone, WNV

Abstract

Oviposition activity and West Nile virus (family Flaviviridae, genus Flavivirus, WNV) infection rates were assessed for members of the Culex pipiens complex from July through December 2002 by using gravid traps placed at four ecologically different sites in the southern portion of the hybrid zone in Shelby County, TN. Molecular assays identified three members of the Cx. pipiens complex: Cx. pipiens pipiens L., Cx. p. quinquefasciatus Say, and Cx. p. pipiens–Cx. p. quinquefasciatus hybrids (hybrids). The Cx. pipiens complex accounted for 90% of mosquitoes collected in gravid traps. All 285 WNV-positive mosquitoes were Culex mosquitoes, and 277 (97%) were Cx. pipiens complex mosquitoes. Infection rates among members of the Cx. pipiens complex were not significantly different. Infection rates were significantly higher at two urban sites than at a rural site, and WNV was not detected at a forested site. At urban sites, abundances of members of the Cx. pipiens complex corresponded to a simple latitude model of the hybrid zone. Cx. p. quinquefasciatus was most abundant (46.4%), followed by hybrids (34.1%) and Cx. p. pipiens (19.5%). The relative abundances at a rural site were reversed with Cx. p. pipiens (48.4%) being most abundant. This demonstrates that spatial habitat variation may profoundly influence the distribution of members of the Cx. pipiens complex within the hybrid zone. Members of the Cx. pipiens complex did not display different oviposition patterns. However, oviposition patterns assessed hourly at urban and rural sites were significantly different. At urban sites, oviposition activity of Cx. pipiens complex mosquitoes was bimodal with an evening peak associated with sunset and a morning peak associated with sunrise. At the rural site, the evening peak was pronounced and the morning peak weak and similar to nighttime activity.

Authors

Savage, Harry M., Anderson, Michael, Gordon, Emily, McMillen, Larry, Colton, Leah, Charnetzky, Dawn, Delorey, Mark, Aspen, Stephen, Burkhalter, Kristen, Biggerstaff, Brad J. and Godsey, Marvin

Year Published

2006

Publication

Journal of Medical Entomology

Locations
DOI

10.1603/0022-2585(2006)43[1227:OAPAWN]2.0.CO;2

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/17162958

WEST NILE VIRUS IN RAPTORS FROM VIRGINIA DURING 2003: CLINICAL, DIAGNOSTIC, AND EPIDEMIOLOGIC FINDINGSJoyner, Priscilla H.2006

WEST NILE VIRUS IN RAPTORS FROM VIRGINIA DURING 2003: CLINICAL, DIAGNOSTIC, AND EPIDEMIOLOGIC FINDINGS

Keywords

Bubo virginianus, Buteo jamaicensis, epidemiology, great horned owl, hematology, raptors, red-tailed hawk, surveillance, West Nile virus, WNV

Abstract

Sixty-one birds of prey admitted to The Wildlife Center of Virginia (WCV; Waynesboro, Virginia, USA) from June to November 2003 were tested for West Nile virus (WNV) infection. Choanal and/or cloacal swabs were obtained and submitted to Virginia's Division of Consolidated Laboratory Services (Richmond, Virginia, USA) for analysis with real-time reverse transcriptase polymerase chain reaction (RT-PCR). Forty birds of prey were positive for WNV by RT-PCR. Five avian families and nine species of raptors were represented, with great horned owls (Bubo virginianus) and red-tailed hawks (Buteo jamaicensis) most frequently affected. Presenting clinical signs were consistent with previous reports of WNV infection in raptors; however, these differed between species. Of WNV positive birds, nonspecific signs of illness were the most common clinical findings, particularly in red-tailed hawks; signs included dehydration (n=20), emaciation (n=18), and depression (n=15). Neurologic abnormalities were frequently identified, especially in great horned owls, and included head tremors (n=17), ataxia (n=13), head incoordination (n=7), torticollis (n=3), nystagmus (n=3), and head tilt (n=3). Great horned owls exhibited anemia and leukocytosis with heterophilia, eosinophilia, and monocytosis consistent with chronic inflammation. Red-tailed hawks were anemic with a heterophilic leukocytosis and regenerative left shift. The majority of WNV cases occurred during August and September; there was a marked increase in the number of raptors admittedto WCV during these months followed by a marked decrease during October, November, and December. This pattern differed from mean monthly admissions during the previous 10 years and suggests a negative impact on local raptor populations. The effects of WNV on avian populations are largely unknown; however, because of their ecological importance, further investigation of the effects of WNV on raptor populations is warranted.

Authors

Joyner, Priscilla H., Kelly, Sean, Shreve, Allison A., Snead, Sarah E., Sleeman, Jonathan M. and Pettit, Denise A.

Year Published

2006

Publication

Journal of Wildlife Diseases

Locations
DOI

10.7589/0090-3558-42.2.335

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/16870856

Culex Population Dynamics and West Nile Virus Transmission in East-Central IllinoisLampman, Richard2006

Culex Population Dynamics and West Nile Virus Transmission in East-Central Illinois

Keywords

Diptera, Culicidae, Culex pipiens, Culex restuans, West Nile virus, infection rate, crossover, WNV

Abstract

Temporal changes in the abundance Culex restuans and Culex pipiens were monitored in east-central Illinois for over a decade using infusion-baited oviposition traps. The 2 species typically exhibited a seasonal shift in relative abundance with a mean crossover date (when the proportion of egg rafts from both species is equal) of August 10 or 11, depending on leap year, with a 95% confidence interval of ±10.7 days. The date of crossover was linearly related to the date of last spring frost and occurred on average about 123 days after the last spring frost. Despite the predictability of crossover, the weekly pattern in the proportion of Cx. pipiens before and after crossover varied considerably, even between years with similar crossover dates. After West Nile virus became established in our area, we found that transmission based on Culex from gravid traps did not increase until Cx. pipiens abundance increased in oviposition traps. Infection rates peaked within the half-month period after crossover. The peak in Cx. pipiens abundance in oviposition traps during this 3-year period was between the 2nd half of August and the end of September. A higher magnitude of transmission in 2002 coincided with warmer temperatures during July and August and an extended period in which the 2 Culex species were in relatively equal abundance.

Authors

Lampman, Richard, Krasavin, Nina, Novak, Robert, Slamecka, Michael and Kunkel, Kenneth

Year Published

2006

Publication

Journal of the American Mosquito Control Association

Locations
DOI

10.2987/8756-971X(2006)22[390:CPDAWN]2.0.CO;2

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/17067036

Association of West Nile virus illness and urban landscapes in Chicago and DetroitRuiz, Marilyn O2007

Association of West Nile virus illness and urban landscapes in Chicago and Detroit

Keywords

WNV

Abstract

Background West Nile virus infection in humans in urban areas of the Midwestern United States has exhibited strong spatial clustering during epidemic years. We derived urban landscape classes from the physical and socio-economic factors hypothesized to be associated with West Nile Virus (WNV) transmission and compared those to human cases of illness in 2002 in Chicago and Detroit. The objectives were to improve understanding of human exposure to virus-infected mosquitoes in the urban context, and to assess the degree to which environmental factors found to be important in Chicago were also found in Detroit. Results Five urban classes that partitioned the urban space were developed for each city region. The classes had many similarities in the two settings. In both regions, the WNV case rate was considerably higher in the urban class associated with the Inner Suburbs, where 1940–1960 era housing dominates, vegetation cover is moderate, and population density is moderate. The land cover mapping approach played an important role in the successful and consistent classification of the urban areas. Conclusion The analysis demonstrates how urban form and past land use decisions can influence transmission of a vector-borne virus. In addition, the results are helpful to develop hypotheses regarding urban landscape features and WNV transmission, they provide a structured method to stratify the urban areas to locate representative field study sites specifically for WNV, and this analysis contributes to the question of how the urban environment affects human health.

Authors

Ruiz, Marilyn O, Walker, Edward D, Foster, Erik S, Haramis, Linn D and Kitron, Uriel D

Year Published

2007

Publication

International Journal of Health Geographics

Locations
DOI

10.1186/1476-072X-6-10

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/17352825

Environmental Predictors of Human West Nile Virus Infections, ColoradoPatnaik, Jennifer L.2007

Environmental Predictors of Human West Nile Virus Infections, Colorado

Keywords

WNV

Abstract

To determine whether environmental surveillance of West Nile virus–positive dead birds, mosquito pools, equines, and sentinel chickens helped predict human cases in metropolitan Denver, Colorado, during 2003, we analyzed human surveillance data and environmental data. Birds successfully predicted the highest proportion of human cases, followed by mosquito pools, and equines.

Authors

Patnaik, Jennifer L., Juliusson, Lara and Vogt, Richard L.

Year Published

2007

Publication

Emerging Infectious Diseases

Locations
DOI

10.3201/eid1311.070506

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/18217573

A TWO-YEAR EVALUATION OF ELEVATED CANOPY TRAPPING FOR CULEX MOSQUITOES AND WEST NILE VIRUS IN AN OPERATIONAL SURVEILLANCE PROGRAM IN THE NORTHEASTERN UNITED STATESAndreadis, Theodore G.2007

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

Keywords

West Nile virus, Culex pipiens, Culex restuans, Culex salinarius, surveillance, light trap, gravid trap, elevation, WNV

Abstract

The 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.

Authors

Andreadis, Theodore G. and ARMSTRONG, PHILIP M.

Year Published

2007

Publication

Journal of the American Mosquito Control Association

Locations
DOI

10.2987/8756-971X(2007)23[137:ATEOEC]2.0.CO;2

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/17847845

Larval habitats of potential mosquito vectors of West Nile virus in the Florida KeysHribar, Lawrence J.2007

Larval habitats of potential mosquito vectors of West Nile virus in the Florida Keys

Keywords

aquatic insects; Florida; mosquitoes; West Nile virus, WNV

Abstract

The occurrence of larvae of two potential vectors of West Nile virus, Culex nigripalpus and Culex quinquefasciatus, was examined in the Florida Keys. About half of the aquatic habitats examined contained larvae of either one or both of the species. Culex quinquefasciatus was the most frequently encountered species, whereas only 9% of habitats sampled contained Culex nigripalpus. Over half of those samples that contained Culex nigripalpus also contained Culex quinquefasciatus. The two species utilize similar larval habitats in the Florida Keys, Monroe County, Florida, USA.

Authors

Hribar, Lawrence J.

Year Published

2007

Publication

Journal of Water and Health

Locations
DOI

10.2166/wh.2006.053

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/17402282

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