Eastern equine encephalitis virus (EEEV) is a deadly arboviral pathogen with 30% severe case fatality. EEEV exhibits pronounced 2-3 year cyclical outbreak patterns in the northeastern United States, linked to shifts in mosquito feeding preferences between hatch-year and adult avians. We developed an age-structured vector-host model incorporating differential feeding patterns of Culiseta melanura mosquitoes on European Starlings and American Robins. Global sensitivity analysis revealed mosquito biting rate (a) as the dominant driver in transmission, with avian infectivity (delta) and exposure (alpha) playing secondary roles. Pairing tree-based machine learning algorithms with SHAP analysis on 100,000 parameter set simulations identified parameter hierarchies that govern cyclic transmission. Adult avian mortality (mu A) was identified as the key parameter underlying unstable cyclic and stable transmission patterns. SHAP further revealed these patterns to be grounded on opposite sides of the same epidemiological mechanism. Stable endemics emerge from demographic stability paired with transmission optimization, while unstable cyclic endemics emerge from demographic instability paired with minimal transmission optimization. Numerical simulations illustrated critical threshold dynamics at 0.2 <= alpha <= 0.4, where heightened hatch-year exposure triggers demographic instability responsible for observed 2-3 year cycles, while balanced exposure (alpha approximate to 0.5) leads to stable endemics. These mechanisms provide a foundation for targeted surveillance and control interventions.

The Eastern equine encephalitis virus (EEEV) is a neurological mosquito-borne disease that spans the northeastern coast of the United States and Canada. Prior studies have focused on how mosquitoes prefer to take blood meals from hatch-year avian hosts rather than adult avian hosts to determine the rate at which the virus is spread between the Black-Tailed Mosquito (Culiseta melanura) and select avian species. In these studies, it was found that mosquito blood meal preference correlated well with avian brooding seasons for certain avian species such as the European Starling (Sturnus vulgaris) and the American Robin (Turdus migratorius). In this study, a host stage-structured model is developed where the avian host group is split into two categories: adult avians and hatch-year avians. The system of ordinary differential equations (ODEs) used to create this model are analyzed to better understand the transmission dynamics of EEEV between the two host classes. The extent to which fluctuations occurred in transmission rates according to host/vector abundances, mosquito biting rate, and host stage was explored. By utilizing the model, it was found that when hatch-year avians are more exposed to the virus, a cyclic outbreak can be observed. Since hatch-year avians lack defensive mechanisms, unlike their adult counterpart, they are more readily exposed to the mosquito vector. ### Competing Interest Statement The authors have declared no competing interest.

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.

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.

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.

Mayaro virus (MAYV, Togaviridae) and Oropouche orthobunyavirus (OROV, Peribunyaviridae) are emerging enzootic arboviruses in Latin America. Outbreaks of febrile illness associated with MAYV and OROV have been reported among humans mainly in the northern region of Brazil since the 1980s, and recent data suggest these viruses have circulated also in more populated areas of western Brazil. MAYV shares mosquito vectors with yellow fever virus and it has been historically detected during yellow fever epidemics. Aiming to investigate the transmission of OROV and MAYV at the human-animal interface during a yellow fever, chikungunya and Zika outbreaks in Brazil, we conducted a retrospective molecular investigation in 810 wild and domestic animals, 106 febrile patients, and 22.931 vectors collected from 2016 to 2018 in Cuiaba and Campo Grande metropolitan regions, western Brazil. All samples tested negative for OROV and MAYV RNA by RT-qPCR. Findings presented here suggest no active circulation of MAYV and OROV in the sampled hosts. Active surveillance and retrospective investigations are instrumental approaches for the detection of cryptic and subclinical activity of enzootic arboviruses and together serve as a warning system to implement appropriate actions to prevent outbreaks.

Studies on the feeding behavior of hematophagous insects, particularly those of medical importance, are relevant for tracking possible pathogen transmission routes and identifying biases in the choice of vertebrates. We evaluated host selection of blood-feeding mosquitoes in a disturbed forest in the Magdalena Medio valley in Colombia from March 2017 to April 2018, after the introduction of Zika virus to the Americas from the 2015-2016 outbreak. We estimated vertebrate diversity and collected blood-engorged female mosquitoes. Mosquito genomic DNA/RNA was extracted for vertebrate host identification and pathogen detection. We performed conventional PCR and sequencing, using universal primers targeting vertebrate regions of the eukaryotic mitochondrial genome to determine bloodmeal host. Additionally, we tested for the presence of flaviviruses in all mosquito samples with RT-PCR. Based on the identity and quantity of detected bloodmeals, we performed mosquito-vertebrate interaction network analysis and estimated topology metrics. In total, we collected 292 engorged female mosquitoes representing 20 different species. Bloodmeal analyses identified 26 vertebrate species, the majority of which were mammals (N=16; 61.5%). No flavivirus infection was confirmed. Although feeding patterns varied, network analyses showed a high degree of specialization by mosquitoes and revealed ecological and phylogenetic relationships among the host community. We conclude that host selection or preference by mosquitoes is species specific.

ABSTRACT IMPACT: Successful implementation of this control strategy will result in a commercially available ivermectin-treated birdfeed that the public can use to protect themselves from infection with West Nile virus (WNV) by reducing mosquito survival and thereby suppressing WNV transmission around their homes. OBJECTIVES/GOALS: We assessed the efficacy and feasibility of ivermectin (IVM)-treated birds as a mosquito control strategy for local reduction of West Nile virus (WNV) transmission. We conducted a randomized field trial in backyard chickens and developed a mathematical model informed by field data to predict the impact of treated wild birds on transmission. METHODS/STUDY POPULATION: We placed 48 chickens in four treated and four untreated control flocks in backyards coops across Davis, CA and administered IVM daily in feed to treated flocks (Jul-Sep 2019). We assessed entomological indices weekly (i.e. Culex mosquito abundance, WNV infection prevalence, and parity rate) around each coop, monitored serum IVM levels in treated chickens, and tested for WNV antibodies in all chickens. Shifting our focus to wild birds, we developed a spatially-implicit mathematical model of WNV transmission near IVM-treated birdfeeders. Model parameters for bird movement were based on our telemetry of 27 birds in Fort Collins, CO (Aug-Sep 2020). Using the model, we predicted optimal deployment of treated feeders to provide local WNV control. RESULTS/ANTICIPATED RESULTS: WNV seroconversions were reduced in treated vs. untreated flocks, indicating a reduction in WNV transmission intensity at treated coops (P = 0.03). A sustained, but insignificant reduction in number of infected mosquitoes was observed near treated coops (P = 0.59); small sample sizes and below normal WNV prevalence in the study area limited our power. We anticipate that optimal spacing and number of IVM-treated birdfeeders required for effective WNV control in neighborhoods will depend on feeder usage rates by common bird species irrespective of WNV competence; broad availability of IVM-treated bloodmeals to mosquitoes will be more effective in reducing transmission than targeting the few species responsible for viral amplification. DISCUSSION/SIGNIFICANCE OF FINDINGS: IVM is a novel method for controlling zoonotic pathogens in the US and has the potential for targeted mosquito control to reduce pesticide usage. Evaluating spatial deployment of IVM-treated bird feed for local reduction in WNV transmission is a stepping stone to commercial deployment of this WNV control strategy.

Studies on the feeding behavior of hematophagous insects, particularly those of medical importance, are relevant for tracking possible pathogen transmission routes and identifying biases in the choice of vertebrates. We evaluated host selection of blood-feeding mosquitoes in a disturbed forest in the Magdalena Medio valley in Colombia from March 2017 to April 2018, after the introduction of Zika virus to the Americas from the 2015–2016 outbreak. We estimated vertebrate diversity and collected blood-engorged female mosquitoes. Genomic DNA/RNA was extracted from the mosquito’s abdomen for vertebrate host identification and pathogen detection. We performed conventional PCR and sequencing, using universal primers targeting vertebrate regions of the eukaryotic mitochondrial genome to determine bloodmeal host. Additionally, we tested for the presence of flaviviruses in all mosquito samples with RT-PCR. Based on the identity and quantity of detected bloodmeals, we performed mosquito-vertebrate interaction network analysis and estimated topology metrics. In total, we collected 292 engorged female mosquitoes representing 20 different species. Bloodmeal analyses identified 26 vertebrate species, the majority of which were mammals (N = 16; 61.5%). No flaviviruses of medical importance were detected from the samples. Although feeding patterns varied, network analyses showed a high degree of specialization by mosquitoes and revealed ecological and phylogenetic relationships among the host community. We conclude that host selection or preference by mosquitoes is species specific.

IMPACT: Better understanding how clinicians make decisions about pain management, particularly since our prior research has demonstrated that opioids prescribed at discharge is the strongest predictor of opioids taken, is critical to decrease high-risk medication prescribing while preserving high-quality care. OBJECTIVES/GOALS: (1) Identify major biological, psychological, and social determinants of medical and surgical residents’ pain management decisions; (2) Determine salient themes regarding the experience of residents in the management of acute and chronic pain METHODS/STUDY POPULATION: Focus groups of internal medicine and general surgery residents at an academic, tertiary care training hospital located in an urban setting were conducted. Due to the COVID-19 pandemic, all focus groups were conducted virtually and occurred during required didactic sessions to facilitate participation. All interviews were recorded and transcribed. Two reviewers independently reviewed and coded the data following the principles of constructivist grounded theory. RESULTS/ANTICIPATED RESULTS: 42 residents participated in ten focus groups ranging in size from two to five individuals. Six themes emerged demonstrating salient BPS factors in pain management decisions: (1) patient and clinician expectations determine what is considered normal/acceptable; (2) inability of pain scales to reliably capture patient pain; (3) desire for more objective methods of pain assessment, while simultaneously recognizing that pain is an inherently subjective experience; (4) difficulty in determine when pain is 'real’ or 'legitimate'; (5) lack of education and protocols regarding pain management; (6) the importance of engaging other services such as acute pain service or nurse educators in complicated situations. Junior residents often expressed doubt in the appropriateness of their approaches and decisions. DISCUSSION/SIGNIFICANCE OF FINDINGS: Surgical and medical trainees routinely treat pain and may struggle, particularly in the early phases of training, to determine if pain levels are appropriate. There is also a lack of education and/or best practices for assessing and managing pain. These areas represent high-value, clinician-focused targets for future interventions to improve care. Education/Mentoring/Professional and Career Development

To the Editor —Bourbon virus (Thogotovirus, Orthomyxoviridae) was discovered in 2014 when a patient with history of multiple tick bites in Kansas died from an unknown infection [[1][1]]. Human infections from Bourbon virus have now been recognized in several states (i.e., Kansas, Oklahoma,

West Nile virus activity was evaluated within an island waterbird nesting colony with > 1,250 birds at Riverside Reservoir, Weld County, Colorado, USA. To avoid disturbance of nesting birds, blood-engorged mosquitoes (Culex tarsalis) were used to sample blood indirectly from birds rather than capturing, sampling, and releasing live birds. Local virus activity was confirmed by West Nile virus-positive feather samples from 26% of 46 carcasses collected during monthly visits to the colony from June to September 2009, including American White Pelican (Pelecanus erythrorhynchos; n = 7), California Gull (Larus californicus; n = 1), Snowy Egret (Egretta thula; n = 2), and Cattle Egret (Bubulcus ibis; n = 2). Of 22 blood-engorged mosquitoes collected and the blood meal host identified to species, one West Nile virus infection was detected (putatively from a Snowy Egret), and West Nile virus-specific antibodies were detected in eight samples: Snowy Egret (n = 5), Great Blue Heron (Ardea herodias; n = 2), and American White Pelican (n = 1). The engorgement rate of female Culex tarsalis at the nesting colony was 34%, sixfold higher than that at a nearby mainland site of 5.3%. The utilization of mosquitoes for sampling blood from wild animals may have broader application, and potentially reduce human disturbance of sensitive nesting bird species.

Zika virus (ZIKV) was first discovered in 1947 in Uganda but was not considered a public health threat until 2007 when it found to be the source of epidemic activity in Asia. Epidemic activity spread to Brazil in 2014 and continued to spread throughout the tropical and subtropical regions of the Americas. Despite ZIKV being zoonotic in origin, information about transmission, or even exposure of non-human vertebrates and mosquitoes to ZIKV in the Americas, is lacking. Accordingly, from February 2017 to March 2018, we sought evidence of sylvatic ZIKV transmission by sampling whole blood from approximately 2000 domestic and wild vertebrates of over 100 species in West-Central Brazil within the active human ZIKV transmission area. In addition, we collected over 24,300 mosquitoes of at least 17 genera and 62 species. We screened whole blood samples and mosquito pools for ZIKV RNA using pan-flavivirus primers in a real-time reverse-transcription polymerase chain reaction (RT-PCR) in a SYBR Green platform. Positives were confirmed using ZIKV-specific envelope gene real-time RT-PCR and nucleotide sequencing. Of the 2068 vertebrates tested, none were ZIKV positive. Of the 23,315 non-engorged mosquitoes consolidated into 1503 pools tested, 22 (1.5%) with full data available showed some degree of homology to insect-specific flaviviruses. To identify previous exposure to ZIKV, 1498 plasma samples representing 62 species of domestic and sylvatic vertebrates were tested for ZIKV-neutralizing antibodies by plaque reduction neutralization test (PRNT90). From these, 23 (1.5%) of seven species were seropositive for ZIKV and negative for dengue virus serotype 2, yellow fever virus, and West Nile virus, suggesting potential monotypic reaction for ZIKV. Results presented here suggest no active transmission of ZIKV in non-human vertebrate populations or in alternative vector candidates, but suggest that vertebrates around human populations have indeed been exposed to ZIKV in West-Central Brazil.

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%).

St. Louis encephalitis virus (SLEV) and West Nile virus (WNV) have recently emerged in the southwestern United States. Surveillance for arboviruses in Las Vegas, NV, detected a surge of SLEV activity in the southern house mosquito (Culex quinquefasciatus Say) during 2016. To identify candidate avian amplifiers, we assessed the identification, viral infection, and immune status of vertebrate hosts for 195 blood-engorged Cx. quinquefasciatus mosquitoes collected in August and September 2016. Bloodmeals were identified from 164 engorged abdomens, representing 19 species of birds and three species of mammals. No SLEV or WNV viremia was detected, but one mosquito tested positive for Culex flavivirus. House finch (Haemorhous mexicanus) (Muller) was the most common bloodmeal, followed by domestic chicken (Gallus gallus) (Linnaeus), American robin (Turdus migratorius) L., house sparrow (Passer domesticus) (L.), great-tailed grackle (Quiscalus mexicanus) (Gmelin), northern mockingbird (Mimus polyglottos) (L.) and mourning dove (Zenaida macroura) (L.). SLEV-reactive antibodies were detected in six identified bloodmeals and WNV-reactive antibodies were detected in 33. House sparrow and house finch were the most likely hosts to show previous exposure to SLEV and WNV, respectively. Over-utilization by Cx. quinquefasciatus for bloodmeal hosts was observed primarily among robin, finch and sparrow, all species that roost communally. House finch stands out as a candidate important amplifier for both SLEV and WNV because of its preference by mosquito vectors, and high competence for closely related virus strains. While implicated in previous outbreaks as an important mosquito vector, Cx. quinquefasciatus feeds infrequently on mammals in Las Vegas, indicating a low risk for bridge transmission to humans.

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.