Enhancing Eastern Equine Encephalitis Virus Surveillance in New Jersey: Optimized Collection of Culiseta Melanura

Eastern equine encephalitis virus (EEEV) causes the most clinically severe neuroinvasive arboviral disease in the United States. The virus is endemic in eastern and Gulf Coast states and the Great Lakes region, causing cases annually. To detect EEEV circulation in its enzootic cycle before the virus infects humans and other mammals, mosquito control agencies in New Jersey have conducted mosquito surveillance using a series of permanent wooden resting box sites since 1975. We conducted 2 field studies, 1 evaluating resting traps and 1 evaluating efficacy of CO2 lures, to optimize collection of Culiseta melanura, the primary enzootic vector of EEEV. Resulting mosquito samples were subjected to molecular analysis to determine EEEV infection rates. Corrugated plastic boxes trapped more bloodfed Cs. melanura than other resting trap types (resting boxes, Centers for Disease Control and Prevention [CDC] resting traps, or fiber pots) and were similar to resting boxes in total number of female Cs. melanura caught. Further, non-baited CDC light traps were more successful in trapping host-seeking Cs. melanura than those baited with dry ice, a CO2 lure. The EEEV RNA was identified in Cs. melanura, Aedes vexans, Anopheles quadrimaculatus, and Uranotaenia sapphirina. Our findings indicate that corrugated plastic boxes and non-CO2 baited traps could improve detection of Cs. melanura. Mosquito control agencies are encouraged to periodically assess their surveillance strategy for EEEV.

Field-Collected Ticks From Benton County, Arkansas, and Prevalence of Associated Pathogens

The recovery of a Haemaphysalis longicornis Neumann (Acari: Ixodidae) tick from a dog in Benton County, Arkansas, in 2018 triggered a significant environmental sampling effort in Hobbs State Park Conservation Area. The objective of the investigation was to assess the tick population density and diversity, as well as identify potential tick-borne pathogens that could pose a risk to public health. During a week-long sampling period in August of 2018, a total of 6,154 ticks were collected, with the majority identified as Amblyomma americanum (L), (Acari: Ixodidae) commonly known as the lone star tick. No H. longicornis ticks were found despite the initial detection of this species in the area. This discrepancy highlights the importance of continued monitoring efforts to understand the dynamics of tick populations and their movements. The investigation also focused on pathogen detection, with ticks being pooled by species, age, and sex before being processed with various bioassays. The results revealed the presence of several tick-borne pathogens, including agents associated with ehrlichiosis (n = 12), tularemia (n = 2), and Bourbon virus (BRBV) disease (n = 1), as well as nonpathogenic rickettsial and anaplasmosis organisms. These findings emphasize the importance of public health messaging to raise awareness of the risks associated with exposure to tick-borne pathogens. Prevention measures, such as wearing protective clothing, using insect repellent, and conducting regular tick checks, should be emphasized to reduce the risk of tick-borne diseases. Continued surveillance efforts and research are also essential to improve our understanding of tick-borne disease epidemiology and develop effective control strategies.

Predicted reduction in transmission from deployment of ivermectin-treated birdfeeders for local control of West Nile virus

Ivermectin (IVM)-treated birds provide the potential for targeted control of Culex mosquitoes to reduce West Nile virus (WNV) transmission. Ingestion of IVM increases mosquito mortality, which could reduce WNV transmission from birds to humans and in enzootic maintenance cycles affecting predominantly bird-feeding mosquitoes and from birds to humans. This strategy might also provide an alternative method for WNV control that is less hampered by insecticide resistance and the logistics of large-scale pesticide applications. Through a combination of field studies and modeling, we assessed the feasibility and impact of deploying IVM-treated birdfeed in residential neighborhoods to reduce WNV transmission. We first tracked 105 birds using radio telemetry and radio frequency identification to monitor their feeder usage and locations of nocturnal roosts in relation to five feeder sites in a neighborhood in Fort Collins, Colorado. Using these results, we then modified a compartmental model of WNV transmission to account for the impact of IVM on mosquito mortality and spatial movement of birds and mosquitoes on the neighborhood level. We found that, while the number of treated lots in a neighborhood strongly influenced the total transmission potential, the arrangement of treated lots in a neighborhood had little effect. Increasing the proportion of treated birds, regardless of the WNV competency status, resulted in a larger reduction in infection dynamics than only treating competent birds. Taken together, model results indicate that deployment of IVM-treated feeders could reduce local transmission throughout the WNV season, including reducing the enzootic transmission prior to the onset of human infections, with high spatial coverage and rates of IVM-induced mortality in mosquitoes. To improve predictions, more work is needed to refine estimates of daily mosquito movement in urban areas and rates of IVM-induced mortality. Our results can guide future field trials of this control strategy.

Exposure of Egyptian Rousette Bats (Rousettus aegyptiacus) and a Little Free-Tailed Bat (Chaerephon pumilus) to Alphaviruses in Uganda

The reservoir for zoonotic o'nyong-nyong virus (ONNV) has remained unknown since this virus was first recognized in Uganda in 1959. Building on existing evidence for mosquito blood-feeding on various frugivorous bat species in Uganda, and seroprevalence for arboviruses among bats in Uganda, we sought to assess if serum samples collected from bats in Uganda demonstrated evidence of exposure to ONNV or the closely related zoonotic chikungunya virus (CHIKV). In total, 652 serum samples collected from six bat species were tested by plaque reduction neutralization test (PRNT) for neutralizing antibodies against ONNV and CHIKV. Forty out of 303 (13.2%) Egyptian rousettes from Maramagambo Forest and 1/13 (8%) little free-tailed bats from Banga Nakiwogo, Entebbe contained neutralizing antibodies against ONNV. In addition, 2/303 (0.7%) of these Egyptian rousettes contained neutralizing antibodies to CHIKV, and 8/303 (2.6%) contained neutralizing antibodies that were nonspecifically reactive to alphaviruses. These data support the interepidemic circulation of ONNV and CHIKV in Uganda, although Egyptian rousette bats are unlikely to serve as reservoirs for these viruses given the inconsistent occurrence of antibody-positive bats.

Mosquito Control Activities during Local Transmission of Zika Virus, Miami-Dade County, Florida, USA, 2016

In 2016, four clusters of local mosquitoborne Zika virus transmission were identified in Miami-Dade County, Florida, USA, generating "red zones" (areas into which pregnant women were advised against traveling). The Miami-Dade County Mosquito Control Division initiated intensive control activities, including property inspections, community education, and handheld sprayer applications of larvicides and adulticides. For the first time, the Mosquito Control Division used a combination of areawide ultralow-volume adulticide and low-volume larvicide spraying to effectively control Aedes aegypti mosquitoes, the primary Zika virus vector within the county. The number of mosquitoes rapidly decreased, and Zika virus transmission was interrupted within the red zones immediately after the combination of adulticide and larvicide spraying.

Bourbon Virus in Wild and Domestic Animals, Missouri, USA, 2012-2013

Since its recent discovery, Bourbon virus has been isolated from a human and ticks. To assess exposure of potential vertebrate reservoirs, we assayed banked serum and plasma samples from wildlife and domestic animals in Missouri, USA, for Bourbon virus–neutralizing antibodies. We detected high seroprevalence in raccoons (50%) and white-tailed deer (86%).

Focal amplification and suppression of West Nile virus transmission associated with communal bird roosts in northern Colorado

To explain the patchy distribution of West Nile virus (WNV), we propose that avian immunity encountered by Culex vectors regulates WNV transmission, particularly at communal bird roosts. To test this hypothesis, we selected two test sites with communally roosting American robins (Turdus migratorius) and two control sites that lacked communal roosts. The density of vector-vertebrate contacts, represented by engorged Culex pipiens, was 23-fold greater at test sites compared to control sites, and the density of blood-engorged Cx. pipiens measured in resting mosquito traps correlated positively with the presence of robins and negatively with the presence of other birds, confirming an attraction to robins for blood feeding. WNV transmission was alternately up-regulated (amplification) and down-regulated (suppression) at both test sites. At one test site, infection in resting Cx. pipiens surged from zero to 37.2 per thousand within four weeks, and robin immunity rose from 8.4% to 64% before reducing to 33%. At this site, ten potentially infectious contacts between vector and vertebrates (including nine robins and a mourning dove [Zenaida macroura]) were documented. Infectious vector-vertebrate contacts were absent from control sites. The use of infectious vector-vertebrate contacts, rather than infected mosquitoes, to evaluate a transmission focus is novel.

Flanders hapavirus in western North America

Flanders virus (FLAV; family Rhabdoviridae) is a mosquito-borne hapavirus with no known pathology that is frequently isolated during arbovirus surveillance programs. Here, we document the presence of FLAV in Culex tarsalis mosquitoes and a Canada goose (Branta canadensis) collected in western North America, outside of the currently recognized range of FLAV. Until now, FLAV-like viruses detected in the western United States were assumed to be Hart Park virus (HPV, family Rhabdoviridae), a closely related congener. A re-examination of archived viral isolates revealed that FLAV was circulating in California as early as 1963. FLAV also was isolated in Nebraska, Colorado, South Dakota, North Dakota, and Saskatchewan, Canada. Phylogenetic analysis of the U1 pseudogene for 117 taxa and eight nuclear genes for 15 taxa demonstrated no distinct clustering between western FLAV isolates. Assuming the range of FLAV has been expanding west, these results indicate that FLAV likely spread west following multiple invasion events. However, it remains to be determined if the detection of FLAV in western North America is due to expansion or is a result of enhanced arbovirus surveillance or diagnostic techniques. Currently, the impact of FLAV infection remains unknown.

Surveillance for Heartland and Bourbon Viruses in Eastern Kansas, June 2016

In June 2016, we continued surveillance for tick-borne viruses in eastern Kansas following upon a larger surveillance program initiated in 2015 in response to a fatal human case of Bourbon virus (BRBV) (Family Orthomyxoviridae: Genus Thogotovirus). In 4 d, we collected 14,193 ticks representing four species from four sites. Amblyomma americanum (L.) (Acari: Ixodidae) accounted for nearly all ticks collected (n = 14,116, 99.5%), and the only other species identified were Amblyomma maculatum Koch (Acari: Ixodidae), Dermacentor variabilis (Say) (Acari: Ixodidae) and Ixodes scapularis Say (Acari: Ixodidae). All ticks were tested for both BRBV and Heartland virus (Family Bunyaviridae: Genus Phlebovirus) in 964 pools. Five Heartland virus positive tick pools were detected and confirmed by real-time reverse transcription PCR (rRT-PCR), while all pools tested negative for BRBV. Each Heartland positive pool was composed of 25 A. americanum nymphs with positive pools collected at three different sites in Bourbon County. A. americanum is believed to be the primary vector of both Heartland and BRBVs to humans based upon multiple detections of virus in field-collected ticks, its abundance, and its aggressive feeding behavior on mammals including humans. However, it is possible that A. americanum encounters viremic vertebrate hosts of BRBV less frequently than viremic hosts of Heartland virus, or that BRBV is less efficiently passed among ticks by co-feeding, or less efficiently passed vertically from infected female ticks to their offspring resulting in lower field infection rates.

Bourbon Virus in Field-Collected Ticks, Missouri, USA

Bourbon virus (BRBV) was first isolated in 2014 from a resident of Bourbon County, Kansas, USA, who died of the infection. In 2015, an ill Payne County, Oklahoma, resident tested positive for antibodies to BRBV, before fully recovering. We retrospectively tested for BRBV in 39,096 ticks from northwestern Missouri, located 240 km from Bourbon County, Kansas. We detected BRBV in 3 pools of Amblyomma americanum (L.) ticks: 1 pool of male adults and 2 pools of nymphs. Detection of BRBV in A. americanum, a species that is aggressive, feeds on humans, and is abundant in Kansas and Oklahoma, supports the premise that A. americanum is a vector of BRBV to humans. BRBV has not been detected in nonhuman vertebrates, and its natural history remains largely unknown.

Surveillance for Tick-Borne Viruses Near the Location of a Fatal Human Case of Bourbon Virus (Family Orthomyxoviridae: Genus Thogotovirus) in Eastern Kansas, 2015

Bourbon virus (Family Orthomyxoviridae: Genus Thogotovirus) was first isolated from a human case-patient residing in Bourbon County, Kansas, who subsequently died. Before becoming ill in late spring of 2014, the patient reported several tick bites. In response, we initiated tick surveillance in Bourbon County and adjacent southern Linn County during spring and summer of 2015. We collected 20,639 host-seeking ticks representing four species from 12 sites. Amblyomma americanum (L.) (Acari: Ixodidae) and Dermacentor variabilis (Say) (Acari: Ixodidae) accounted for nearly all ticks collected (99.99%). Three tick pools, all composed of adult A. americanum ticks collected in Bourbon County, were virus positive. Two pools were Heartland virus (Family Bunyaviridae: Genus Phlebovirus) positive, and one was Bourbon virus positive. The Bourbon virus positive tick pool was composed of five adult females collected on a private recreational property on June 5. Detection of Bourbon virus in the abundant and aggressive human-biting tick A. americanum in Bourbon County supports the contention that A. americanum is a vector of Bourbon virus to humans. The current data combined with virus detections in Missouri suggest that Bourbon virus is transmitted to humans by A. americanum ticks, including both the nymphal and adult stages, that ticks of this species become infected as either larvae, nymphs or both, perhaps by feeding on viremic vertebrate hosts, by cofeeding with infected ticks, or both, and that Bourbon virus is transstadially transmitted. Multiple detections of Heartland virus and Bourbon virus in A. americanum ticks suggest that these viruses share important components of their transmission cycles.

Neutralizing antibodies against flaviviruses, Babanki virus, and Rift Valley fever virus in Ugandan bats

Introduction: A number of arboviruses have previously been isolated from naturally-infected East African bats, however the role of bats in arbovirus maintenance is poorly understood. The aim of this study was to investigate the exposure history of Ugandan bats to a panel of arboviruses.

Materials and methods: Insectivorous and fruit bats were captured from multiple locations throughout Uganda during 2009 and 2011–2013. All serum samples were tested for neutralizing antibodies against West Nile virus (WNV), yellow fever virus (YFV), dengue 2 virus (DENV-2), Zika virus (ZIKV), Babanki virus (BBKV), and Rift Valley fever virus (RVFV) by plaque reduction neutralization test (PRNT). Sera from up to 626 bats were screened for antibodies against each virus.

Results and Discussion: Key findings include the presence of neutralizing antibodies against RVFV in 5/52 (9.6%) of little epauletted fruit bats (Epomophorus labiatus) captured from Kawuku and 3/54 (5.6%) Egyptian rousette bats from Kasokero cave. Antibodies reactive to flaviviruses were widespread across bat taxa and sampling locations.

Conclusion: The data presented demonstrate the widespread exposure of bats in Uganda to arboviruses, and highlight particular virus-bat associations that warrant further investigation.

Surveillance for Heartland Virus (Bunyaviridae: Phlebovirus) in Missouri During 2013: First Detection of Virus in Adults of Amblyomma americanum (Acari: Ixodidae)

During 2013, we collected and tested ticks for Heartland virus (HRTV), a recently described human pathogen in the genus Phlebovirus (Bunyaviridae), from six sites in northwestern Missouri. Five sites were properties owned by HRTV patients, and the sixth was a conservation area that yielded virus in ticks during 2012. We collected 39,096 ticks representing five species; however, two species, Amblyomma americanum (L.) (97.6%) and Dermacentor variabilis (Say) (2.3%), accounted for nearly all ticks collected. We detected 60 HRTV-positive tick pools and all were composed of A americanum: 53 pools of nymphs, six pools of male adults, and one pool of female adults. This is the first record of HRTV in adult ticks. Virus was detected at five properties that yielded A. americanum ticks, including properties owned by four of five patients. Virus was detected at two sites that yielded virus in 2012. Detection of virus in multiple years indicates that the virus persists in ticks within a relatively small geographic area, although infection rates (IR) may vary greatly among sites and between years at a site. IR per 1,000 A. americanum in northwestern Missouri during the April-July 2013 study period were as follows: all adults, IR = 1.13; adult females, IR = 0.33; adult males, IR = 1.90; and nymphs, IR = 1.79. The IR in nymphs, the stage with the largest data set, corresponds to 1/559 infected ticks. Having robust estimates of IR in various stages for A. americanum should lead to more accurate public health messaging and a better understanding of virus transmission.

Serological investigation of heartland virus (Bunyaviridae: Phlebovirus) exposure in wild and domestic animals adjacent to human case sites in Missouri 2012-2013

Heartland virus (HRTV; Bunyaviridae: Phlebovirus) has recently emerged as a causative agent of human disease characterized by thrombocytopenia and leukopenia in the United States. The lone star tick (Amblyomma americanum L.) has been implicated as a vector. To identify candidate vertebrate amplification hosts associated with enzootic maintenance of the virus, sera and ticks were sampled from 160 mammals (8 species) and 139 birds (26 species) captured near 2 human case residences in Andrew and Nodaway Counties in northwest Missouri. HRTV-specific neutralizing antibodies were identified in northern raccoons (42.6%), horses (17.4%), white-tailed deer (14.3%), dogs (7.7%), and Virginia opossums (3.8%), but not in birds. Virus isolation attempts from sera and ticks failed to detect HRTV. The high antibody prevalence coupled with local abundance of white-tailed deer and raccoons identifies these species as candidate amplification hosts.

Methods for detection of West Nile virus antibodies in mosquito blood meals

We describe and compare 2 qualitative serologic techniques for detecting West Nile virus (WNV)-specific antibodies in mosquito blood meals. The techniques are the biotin microsphere immunoassay (b-MIA) and the inhibition platform of the VectorTest™ WNV antigen assay (VecTest-inhibition). To demonstrate the ability of these tests to detect WNV-neutralizing antibodies, we experimentally exposed feeding mosquitoes to blood containing 5 concentrations of 6B6C-1, a flavivirus-neutralizing monoclonal antibody. Antibody concentrations were quantified using the 90% plaque-reduction neutralization test (PRNT90). After 24 h of blood-meal digestion at 22.5°C, the threshold PRNT90 titer of detection was ≤18 for b-MIA and ≤50 for VecTest-inhibition. Both tests reliably detected antibodies in 3 of 3 blood meals that had been digested for up to 30 h, or were about 25% digested. The b-MIA was also applied to mosquitoes that had engorged on avian blood in Arizona following a WNV epidemic in 2010. There was no significant difference in the WNV antibody prevalence determined by b-MIA (52% of 71 avian blood meals) compared to the WNV-neutralizing antibody prevalence in birds determined by direct sampling (49% of 234 birds). VecTest-inhibition requires fewer resources and may be used in the field without a laboratory, but consumes the entire blood meal and relies on subjective interpretation of results. The b-MIA requires a laboratory and sophisticated equipment and reagents. Results for b-MIA are analyzed objectively and can be applied to mosquito blood meals with greater confidence than the VecTest-inhibition method and thus can contribute substantially to research and surveillance programs that would benefit from the detection of specific WNV antibodies in mosquito blood meals.

Experimental infection of Eurasian collared-dove (Streptopelia decaocto) with West Nile virus

The Eurasian collared-dove (Streptopelia decaocto) has recently experienced a population explosion in North America. It is frequently infected with West Nile virus (WNV). To test the hypothesis that the Eurasian collared-dove is competent to transmit WNV, we experimentally infected two cohorts of doves with two different strains of WNV, CO08, and NY99, respectively. Both virus strains induced a low-level viremia, capable of infecting a small fraction of vector mosquitoes. We suggest that the Eurasian collared-dove plays a relatively insignificant role as an amplifying host for WNV, but it may be important where it is locally abundant.

First detection of heartland virus (Bunyaviridae: Phlebovirus) from field collected arthropods

Heartland virus (HRTV), the first pathogenic Phlebovirus (Family: Bunyaviridae) discovered in the United States, was recently described from two Missouri farmers. In 2012, we collected 56,428 ticks representing three species at 12 sites including both patients' farms. Amblyomma americanum and Dermacentor variabilis accounted for nearly all ticks collected. Ten pools composed of deplete nymphs of A. americanum collected at a patient farm and a nearby conservation area were reverse transcription-polymerase chain reaction positive, and eight pools yielded viable viruses. Sequence data from the nonstructural protein of the Small segment indicates that tick strains and human strains are very similar, ≥ 97.6% sequence identity. This is the first study to isolate HRTV from field-collected arthropods and to implicate ticks as potential vectors. Amblyomma americanum likely becomes infected by feeding on viremic hosts during the larval stage, and transmission to humans occurs during the spring and early summer when nymphs are abundant and actively host seeking.

Avian hosts of West Nile virus in Arizona

West Nile virus (WNV) causes sporadic outbreaks of human encephalitis in Phoenix, Arizona. To identify amplifying hosts of WNV in the Phoenix area, we blood-sampled resident birds and measured antibody prevalence following an outbreak in the East Valley of metropolitan Phoenix during summer, 2010. House sparrow (Passer domesticus), house finch (Haemorhous mexicanus), great-tailed grackle (Quiscalus mexicanus), and mourning dove (Zenaida macroura) accounted for most WNV infections among locally resident birds. These species roost communally after early summer breeding. In September 2010, Culex vector-avian host contact was 3-fold greater at communal bird roosts compared with control sites, as determined by densities of resting mosquitoes with previous vertebrate contact (i.e., blood-engorged or gravid mosquitoes). Because of the low competence of mourning doves, these were considered weak amplifiers but potentially effective free-ranging sentinels. Highly competent sparrows, finches, and grackles were predicted to be key amplifying hosts for WNV in suburban Phoenix.

West Nile virus ecology in a tropical ecosystem in Guatemala

West Nile virus ecology has yet to be rigorously investigated in the Caribbean Basin. We identified a transmission focus in Puerto Barrios, Guatemala, and established systematic monitoring of avian abundance and infection, seroconversions in domestic poultry, and viral infections in mosquitoes. West Nile virus transmission was detected annually between May and October from 2005 to 2008. High temperature and low rainfall enhanced the probability of chicken seroconversions, which occurred in both urban and rural sites. West Nile virus was isolated from Culex quinquefasciatus and to a lesser extent, from Culex mollis/Culex inflictus, but not from the most abundant Culex mosquito, Culex nigripalpus. A calculation that combined avian abundance, seroprevalence, and vertebrate reservoir competence suggested that great-tailed grackle (Quiscalus mexicanus) is the major amplifying host in this ecosystem. West Nile virus transmission reached moderate levels in sentinel chickens during 2007, but less than that observed during outbreaks of human disease attributed to West Nile virus in the United States.

The Centers for Disease Control and Prevention resting trap: a novel device for collecting resting mosquitoes

Commercially available wood-fiber pots used to collect resting mosquitoes were modified to improve sampling efficiency. The modified traps, called the Centers for Disease Control and Prevention resting traps, collected 16.0 and 5.2 times more adult Culex pipiens and Cx. tarsalis than the conventional wood-fiber pots. The resting trap increases the mean number of resting mosquitoes collected per trap-night and is useful for collecting blood-engorged mosquitoes.

Two new diterpene phenols from Calocedrus decurrans

Two new p-cymene based diphenols (1-2) were isolated from the heartwood of Calocedrus decurrans. Structures were elucidated by 1D and 2D NMR techniques and HRMS. Libocedroquinone (3) was also isolated as a natural product for the first time. A new system of nomenclature is proposed for description of such oligomeric p-cymene derivatives.

Two New Diterpene Phenols from Calocedrus decurrans

Two new p-cymene based diphenols (1-2) were isolated from the heartwood of Calocedrus decurrans. Structures were elucidated by 1D and 2D NMR techniques and HRMS. Libocedroquinone (3) was also isolated as a natural product for the first time. A new system of nomenclature is proposed for description of such oligomeric p-cymene derivatives.

Declining mortality in American crow (Corvus brachyrhynchos) following natural West Nile virus infection

Increased viremia and deaths in American Crows inoculated with a North American West Nile viral genotype indicate that viral genetic determinants enhance avian pathogenicity and increase transmission potential of WNV.

Crow deaths were observed after West Nile virus (WNV) was introduced into North America, and this phenomenon has subsequently been used to monitor the spread of the virus. To investigate potential differences in the crow virulence of different WNV strains, American Crows were inoculated with Old World strains of WNV from Kenya and Australia (Kunjin) and a North American (NY99) WNV genotype. Infection of crows with NY99 genotype resulted in high serum viremia levels and death; the Kenyan and Kunjin genotypes elicited low viremia levels and minimal deaths but resulted in the generation of neutralizing antibodies capable of providing 100% protection from infection with the NY99 strain. These results suggest that genetic alterations in NY99 WNV are responsible for the crow-virulent phenotype and that increased replication of this strain in crows could spread WNV in North America.

A single positively selected West Nile viral mutation confers increased virogenesis in American crows

West Nile virus (WNV), first recognized in North America in 1999, has been responsible for the largest arboviral epiornitic and epidemic of human encephalitis in recorded history. Despite the well-described epidemiological patterns of WNV in North America, the basis for the emergence of WNV-associated avian pathology, particularly in the American crow (AMCR) sentinel species, and the large scale of the North American epidemic and epiornitic is uncertain. We report here that the introduction of a T249P amino acid substitution in the NS3 helicase (found in North American WNV) in a low-virulence strain was sufficient to generate a phenotype highly virulent to AMCRs. Furthermore, comparative sequence analyses of full-length WNV genomes demonstrated that the same site (NS3-249) was subject to adaptive evolution. These phenotypic and evolutionary results provide compelling evidence for the positive selection of a mutation encoding increased viremia potential and virulence in the AMCR sentinel bird species.

DNA Vaccination of the American Crow (Corvus brachyrhynchos) Provides Partial Protection Against Lethal Challenge with West Nile Virus

The New York 1999 strain of West Nile virus (WNV) is nearly 100% fatal in the American crow (Corvus brachyrhynchos). We evaluated four WNV vaccine formulations in American crows, including intramuscular (i.m.) DNA vaccine, i.m. DNA vaccine with adjuvant, orally administered microencapsulated DNA vaccine, and i.m. killed vaccine. Neutralizing antibodies developed in approximately 80% of crows that received the DNA vaccine i.m. (with or without adjuvant), and in 44% that received the killed vaccine. However, no crows that received the oral microencapsulated DNA vaccine or the placebo developed WNV antibodies. All crows were challenged 10 wk after initial vaccination. No unvaccinated crows survived challenge, and survival rates were 44% (i.m. DNA vaccine), 60% (i.m. DNA vaccine with adjuvant), 0% (oral microencapsulated DNA vaccine), and 11% (killed vaccine). Peak viremia titers in the birds that survived were significantly lower as compared to titers in birds that died. Parenteral administration of a WNV DNA vaccine was associated with reduced mortality but did not provide sterile immunity.

Biocidal activity of three wood essential oils against Ixodes scapularis (Acari: Ixodidae), Xenopsylla cheopis (Siphonaptera: Pulicidae), and Aedes aegypti (Diptera: Culicidae)

The biocidal activity of three steam distilled wood essential oils-incense cedar, Calocedrus decurrens (Torr.) Florin; Port-Orford-cedar, Chamaecyparis lawsoniana (A. Murr.) Parl.; and western juniper, Juniperus occidentalis (Hook)--were evaluated against adult Aedes aegypti (L.) (Diptera: Culicidae) and Xenopsylla cheopis (Rothchild) (Siphonaptera: Pulicidae) and nymphal Ixodes scapularis Say (Acari: Ixodidae). In vitro laboratory bioassays were conducted to establish baseline dose-mortality data through 24 h. Incense cedar heartwood was the most toxic to all three vector species followed in order of activity by western juniper and Port-Orford-cedar based on LC50 and LC90 values. Ae. aegypti were substantially more susceptible to the oils than either I. scapularis or X. cheopis.

Rapid West Nile virus antigen detection

We compared the VecTest WNV antigen assay with standard methods of West Nile virus (WNV) detection in swabs from American Crows (Corvus brachyrhynchos) and House Sparrows (Passer domesticus). The VecTest detected WNV more frequently than the plaque assay and was comparable to a TaqMan reverse transcription–polymerase chain reaction.

Avian hosts for West Nile virus in St. Tammany Parish, Louisiana, 2002

West Nile virus (WNV) infections in free-ranging birds were studied in Slidell, St. Tammany Parish, Louisiana, after a human encephalitis outbreak peaked there in July 2002. Seroprevalence in resident, free-ranging wild birds in one suburban site was 25% and 24% in August and October, respectively, indicating that most transmission had ceased by early August. Mortality rates, seroprevalence rates, host competence, and crude population estimates were used in mathematical models to predict actual infection rates, population impacts, and importance as amplifying hosts for several common passerine birds. Northern cardinal (Cardinalis cardinalis) and house sparrow (Passer domesticus) were the principal amplifying hosts, but blue jay (Cyanocitta cristata) and northern mockingbird (Mimus polyglottos) also contributed. The blue jay population was reduced by an estimated 47%. A variety of passerine bird species combined to play an important role as amplifying hosts in the WNV transmission cycle.

Sentinel pigeon surveillance for West Nile virus by using lard-can traps at differing elevations and canopy cover classes

Sentinel pigeons, Columba livia, were installed in lard-can traps at heights of 1.5 m and 7.6-9.1 m within differing canopy cover classes in New York City. Adult mosquitoes were collected weekly from July to October 2002, as were serum samples from each pigeon. Culex pipiens L. and Culex restuans Theobald comprised 97% of mosquitoes collected and were most numerous in canopy-level, forested traps. The West Nile virus (family Flaviviridae, genus Flavivirus, WNV) seroconversion rate was significantly greater for pigeons in canopy-level traps, although seroconversions occurred concurrently with human cases in the city and were of little prognostic value to public health agencies. Our results indicate that sentinel pigeons were most effective for monitoring enzootic transmission of WNV when placed in single-sentinel caging 7.6-9.1 m above ground level.

Serologic Evidence of West Nile Virus Infection in Free-Ranging Mammals, Slidell, Louisiana, 2002

After an outbreak of West Nile virus (WNV) infections in Slidell, Louisiana, in 2002, we detected neutralizing antibodies to WNV in 13 of 120 mammals, representing five of six species sampled. Seroprevalence was measured in opossum, Didelphis virginiana (75%, n = 8), raccoons, Procyon lotor (60%, n = 5), black rats, Rattus rattus (6%, n = 36), hispid cotton rats, Sigmodon hispidus (4%, n = 24), and eastern gray squirrels, Sciurus carolinensis (2%, n = 43).

West Nile virus epizootiology in the southeastern United States, 2001

We investigated mosquito and bird involvement in West Nile virus (WNV) transmission in July 2001 in Jefferson County, FL, and Lowndes County, GA. We detected 16 WNV-infected pools from Culex quinquefasciatus, Cx. salinarius, Cx. nigripalpus, and Culiseta melanura. In Florida, 11% of 353 bird sera neutralized WNV. Antibody prevalence was greatest in northern cardinal (Cardinalis cardinalis, 75%), northern mockingbird (Mimus polyglottus, 50%), common ground-dove (Columbina passerina, 25%), common grackle (Quiscalus quiscula, 15%), domestic chicken (Gallus gallus, 16%), and house sparrow (Passer domesticus, 11%). Antibody-positive birds were detected in nine of 11 locations, among which prevalence in chickens ranged from 0% to 100%. Seropositive chickens were detected in Georgia as well. The primary transmission cycle of WNV in the southeastern United States apparently involves Culex mosquitoes and passerine birds. Chickens are frequently infected and may serve as effective sentinels in this region.

Use of novel compounds for pest control: insecticidal and acaricidal activity of essential oil components from heartwood of Alaska yellow cedar

Laboratory bioassays were conducted to determine the activity of 15 natural products isolated from essential oil components extracted from the heartwood of Alaska yellow cedar, Chamaecyparis nootkatensis (D. Don) Spach., against Ixodes scapularis Say nymphs, Xenopsylla cheopis (Rothchild), and Aedes aegypti (L.) adults. Four of the compounds from the essential oil have been identified as monoterpenes, five as eremophilane sesquiterpenes, five as eremophilane sesquiterpene derivatives from valencene and nootkatone, and one as a sesquiterpene outside the eremophilane parent group. Carvacrol was the only monoterpene that demonstrated biocidal activity against ticks, fleas, and mosquitoes with LC50 values after 24 h of 0.0068, 0.0059, and 0.0051% (wt:vol), respectively. Nootkatone from Alaska yellow cedar was the most effective of the eremophilane sesquiterpenes against ticks (LC50 = 0.0029%), whereas the nootkatone grapefruit extract exhibited the greatest biocidal activity against fleas (LC50 = 0.0029%). Mosquitoes were most susceptible to one of the derivatives of valencene, valencene-13-aldehyde (LC50 = 0.0024%), after 24 h. Bioassays to determine residual activity of the most effective products were conducted at 1, 2, 4, and 6 wk after initial treatment. Residual LC50 values for nootkatone did not differ significantly at 4 wk posttreatment from the observations made at the initial 24-h treatment. The ability of these natural products to kill arthropods at relatively low concentrations represents an alternative to the use of synthetic pesticides for control of disease vectors.

Bioecology and vectorial capacity of Aedes albopictus (Diptera: Culicidae) in Macao, China, in relation to dengue virus transmission

Until 2001, the Chinese Territory of Macao had not registered any autochthonous dengue cases, despite the abundance of Aedes albopictus (Skuse), a known vector. This work describes a bioecological characterization of the local Ae. albopictus adult population, with the purpose of estimating the receptivity of Macao to dengue introduction. In the wet seasons of 1997 and 1998 and the dry season of 1998, Ae. albopictus was the most abundant human-biting mosquito. Daily biting rates of 314 mosquitoes per person were recorded in the wet season with a reduction to 94 in the dry season. Ae. albopictus was mainly exophagic and exophilic and had a human blood index of 44%. The parity rate of field-collected mosquitoes was 57%. Daily survival rate ranged from 91 to 97%. Estimates of vectorial capacity ranged from 144 to 880, depending on what parameter values were used. These estimates indicated a great receptivity for the introduction of dengue viruses, as the 2001 outbreak came to prove.

Serologic survey of cats and dogs during an epidemic of West Nile virus infection in humans

OBJECTIVE

To estimate West Nile virus (WNV) infection rates, assess environmental variables that correlated with seropositivity in dogs and cats, and assess whether pets should be considered as possible sentinels for WNV and therefore of potential human exposure.

DESIGN

Cross-sectional serosurvey.

ANIMALS

442 dogs and 138 cats.

PROCEDURE

Serum samples were screened for seropositivity against WNV by use of the plaque reduction neutralization test.

RESULTS

116 (26%) dogs and 13 (9%) cats yielded positive results. The odds of seropositivity against WNV for outdoor-only family dogs were almost 19 times as great as those for indoor-only family dogs and almost twice as great for stray dogs as for family dogs. Family dogs not receiving heartworm medication were 2.5 times as likely to yield positive results for antibodies against WNV as family dogs receiving heartworm medication.

CONCLUSIONS AND CLINICAL RELEVANCE

Seropositivity was greater for outdoor family dogs than for indoor family dogs. Further investigation of the potential use of stray dogs as sentinel indicators for WNV infection and the potential risk of human exposure is warranted.

Variation in virulence of West Nile virus strains for house sparrows (Passer domesticus)

The observation of avian mortality associated with West Nile virus (WNV) infection has become a hallmark epidemiologic feature in the recent emergence of this pathogen in Israel and North America. To determine if phenotypic differences exist among different WNV isolates, we exposed house sparrows (Passer domesticus) to low passage, lineage 1 WNV strains from North America (NY99), Kenya (KEN), and Australia (KUN; also known as Kunjin virus). House sparrows inoculated with the NY99 and KEN strains experienced similar mortality rates and viremia profiles. The KUN strain elicited significantly lower-titered viremia when compared with the other strains and induced no mortality. This study suggests that natural mortality in house sparrows due to Old World strains of WNV may be occurring where the KEN strain occurs.

Serologic evidence of West Nile virus infection in black bears (Ursus americanus) from New Jersey

Serum samples obtained from 51 free-ranging black bears (Ursus americanus) in northwestern New Jersey in February and March 2002 were analyzed for neutralizing antibodies to West Nile virus (WNV) and St. Louis encephalitis virus. Three (6%) of the black bears tested positive for WNV-neutralizing antibodies. One additional sample was positive for flavivirus-neutralizing antibodies but could not be differentiated for a specific virus type. This is the first report of WNV infection in black bears.

Serologic evidence for West Nile virus infection in birds in Staten Island, New York, after an outbreak in 2000

After an outbreak of West Nile virus (WNV) infections in people, horses, and wildlife in Staten Island, NY, during the summer of 2000, we surveyed the bird population of the island for evidence of infection. Neutralizing antibodies were detected in 59 of 257 (23.0%) resident birds and none of 96 transient (migrating) birds sampled in early October. Species with the greatest seroprevalence were northern cardinal (Cardinalis cardinalis) (69.2%) and rock dove (Columba livia) (54.5%). House sparrows (Passer domesticus) and chickens (Gallus gallus) had lower than expected seroprevalences, 8.6% and 5.5%, respectively. The geographic distribution of seropositivity suggested focal transmission at several locations on the island. The concentration of seropositive birds among resident bird populations on Staten Island supports the concept that many birds survive WNV infection and that some of these play an important role in the WNV-bird-mosquito transmission cycle.

Temporal abundance, parity, survival rates, and arbovirus isolation of field-collected container-inhabiting mosquitoes in eastern Tennessee

Surveillance of container-inhabiting mosquitoes was conducted from June 17 through November 9, 1998, at 2 1997 La Crosse virus (LAC) human case sites (Knox and Cocke counties, Tennessee). Mosquitoes were collected weekly with 2 dry ice-baited Centers for Disease Control miniature light traps, 2 omnidirectional Fay traps, and 40 oviposition traps at each site. A total of 8,408 mosquitoes, composed of Ochlerotatus triseriatus (n = 2,095) and Aedes albopictus (n = 6,313), were reared or collected and assayed for virus. The majority of host-seeking Ae. albopictus (n = 567) collected from July through October from both sites were dissected to determine parity status. Monthly parity rates ranged from 0.78 to 0.85 and 0.79 to 0.92 in Knox and Cocke counties, respectively. The high parity rates indicate that this population of Ae. albopictus has a high daily survival rate and may have a high vector potential. The temporal patterns in Ae. albopictus and Oc. triseriatus egg collections from both of the human case sites were significantly correlated, suggesting that the populations fluctuate in a similar manner across the eastern Tennessee region. Although LAC was not isolated from either species, one isolation of a California serogroup virus, most likely a subtype of Jamestown Canyon virus (JC), was recovered from a pool of 50 male Ae. albopictus reared from eggs collected at the Knox County site (minimum field infection rate of 1.89 per 1,000). This is the 1st report of a very closely related JC-like virus in Ae. albopictus and from Tennessee, as well as the 1st time this potential human pathogen has been isolated from transovarially infected field populations of Ae. albopictus.

Detection of West Nile virus antigen in mosquitoes and avian tissues by a monoclonal antibody-based capture enzyme immunoassay

An antigen capture immunoassay to detect West Nile (WN) virus antigen in infected mosquitoes and avian tissues has been developed. With this assay purified WN virus was detected at a concentration of 32 pg/0.1 ml, and antigen in infected suckling mouse brain and laboratory-infected mosquito pools could be detected when the WN virus titer was 10(2.1) to 10(3.7) PFU/0.1 ml. In a blindly coded set of field-collected mosquito pools (n = 100), this assay detected WN virus antigen in 12 of 18 (66.7%) TaqMan-positive pools, whereas traditional reverse transcriptase PCR detected 10 of 18 (55.5%) positive pools. A sample set of 73 organ homogenates from naturally infected American crows was also examined by WN virus antigen capture immunoassay and TaqMan for the presence of WN virus. The antigen capture assay detected antigen in 30 of 34 (88.2%) TaqMan-positive tissues. Based upon a TaqMan-generated standard curve of infectious WN virus, the limit of detection in the antigen capture assay for avian tissue homogenates was approximately 10(3) PFU/0.1 ml. The recommended WN virus antigen capture protocol, which includes a capture assay followed by a confirmatory inhibition assay used to retest presumptive positive samples, could distinguish between the closely related WN and St. Louis encephalitis viruses in virus-infected mosquito pools and avian tissues. Therefore, this immunoassay demonstrates adequate sensitivity and specificity for surveillance of WN virus activity in mosquito vectors and avian hosts, and, in addition, it is easy to perform and relatively inexpensive compared with the TaqMan assay.

Arbovirus infection increases with group size

Buggy Creek (BCR) virus is an arthropod-borne alphavirus that is naturally transmitted to its vertebrate host the cliff swallow (Petrochelidon pyrrhonota) by an invertebrate vector, namely the cimicid swallow bug (Oeciacus vicarius). We examined how the prevalence of the virus varied with the group size of both its vector and host. The study was conducted in southwestern Nebraska where cliff swallows breed in colonies ranging from one to 3700 nests and the bug populations at a site vary directly with the cliff swallow colony size. The percentage of cliff swallow nests containing bugs infected with BCR virus increased significantly with colony size at a site in the current year and at the site in the previous year. This result could not be explained by differences in the bug sampling methods, date of sampling, sample size of the bugs, age structure of the bugs or the presence of an alternate host, the house sparrow (Passer domesticus). Colony sites that were reused by cliff swallows showed a positive autocorrelation in the percentage of nests with infected bugs between year t and year t+1, but the spatial autocorrelation broke down for year t+2. The increased prevalence of BCR virus at larger cliff swallow colonies probably reflects the larger bug populations there, which are less likely to decline in size and lead to virus extinction. To the authors' knowledge this is the first demonstration of arbovirus infection increasing with group size and one of the few known predictive ecological relationships between an arbovirus and its vectors/hosts. The results have implications for both understanding the fitness consequences of coloniality for cliff swallows and understanding the temporal and spatial variation in arboviral epidemics.

Serologic evidence for West Nile virus infection in birds in the New York City vicinity during an outbreak in 1999

As part of an investigation of an encephalitis outbreak in New York City, we sampled 430 birds, representing 18 species in four orders, during September 13-23, 1999, in Queens and surrounding counties. Overall, 33% were positive for West Nile (WN) virus-neutralizing antibodies, and 0.5% were positive for St. Louis encephalitis virus-neutralizing antibodies. By county, Queens had the most seropositive birds for WN virus (50%); species with the greatest seropositivity for WN virus (sample sizes were at least six) were Domestic Goose, Domestic Chicken, House Sparrow, Canada Goose, and Rock Dove. One sampled bird, a captive adult Domestic Goose, showed signs of illness; WN virus infection was confirmed. Our results support the concept that chickens and House Sparrows are good arbovirus sentinels. This study also implicates the House Sparrow as an important vertebrate reservoir host.

Comparative West Nile virus detection in organs of naturally infected American Crows (Corvus brachyrhynchos)

Widespread deaths of American Crows (Corvus brachyrhynchos)were associated with the 1999 outbreak of West Nile (WN) virus in the New York City region. We compared six organs from 20 crow carcasses as targets for WN virus detection. Half the carcasses had at least one positive test result for WN virus infection. The brain was the most sensitive test organ; it was the only positive organ for three of the positive crows. The sensitivity of crow organs as targets for WN virus detection makes crow death useful for WN virus surveillance.

Exposure of domestic mammals to West Nile virus during an outbreak of human encephalitis, New York City, 1999

We evaluated West Nile (WN) virus seroprevalence in healthy horses, dogs, and cats in New York City after an outbreak of human WN virus encephalitis in 1999. Two (3%) of 73 horses, 10 (5%) of 189 dogs, and none of 12 cats tested positive for WN virus-neutralizing antibodies. Domestic mammals should be evaluated as sentinels for local WN virus activity and predictors of the infection in humans.

First isolation of La Crosse virus from naturally infected Aedes albopictus

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.

Rapid detection of west nile virus from human clinical specimens, field-collected mosquitoes, and avian samples by a TaqMan reverse transcriptase-PCR assay

The authors report on the development and application of a rapid TaqMan assay for the detection of West Nile (WN) virus in a variety of human clinical specimens and field-collected specimens. Oligonucleotide primers and FAM- and TAMRA-labeled WN virus-specific probes were designed by using the nucleotide sequence of the New York 1999 WN virus isolate. The TaqMan assay was compared to a traditional reverse transcriptase (RT)-PCR assay and to virus isolation in Vero cells with a large number ( approximately 500) of specimens obtained from humans (serum, cerebrospinal fluid, and brain tissue), field-collected mosquitoes, and avian tissue samples. The TaqMan assay was specific for WN virus and demonstrated a greater sensitivity than the traditional RT-PCR method and correctly identified WN virus in 100% of the culture-positive mosquito pools and 98% of the culture-positive avian tissue samples. The assay should be of utility in the diagnostic laboratory to complement existing human diagnostic testing and as a tool to conduct WN virus surveillance in the United States.