Quantifying Rift Valley fever virus transmission efficiency in a lamb-mosquito-lamb model

Rift Valley fever virus (RVFV) is a (re)emerging mosquito-borne pathogen impacting human and animal health. How RVFV spreads through a population depends on population-level and individual-level interactions between vector, host and pathogen. Here, we estimated the probability for RVFV to transmit to naive animals by experimentally exposing lambs to a bite of an infectious mosquito, and assessed if and how RVFV infection subsequently developed in the exposed animal. Aedes aegypti mosquitoes, previously infected via feeding on a viremic lamb, were used to expose naive lambs to the virus. Aedes aegypti colony mosquitoes were used as they are easy to maintain and readily feed in captivity. Other mosquito spp. could be examined with similar methodology. Lambs were exposed to either 1-3 (low exposure) or 7-9 (high exposure) infectious mosquitoes. All lambs in the high exposure group became viremic and showed characteristic signs of Rift Valley fever within 2-4 days post exposure. In contrast, 3 out of 12 lambs in the low exposure group developed viremia and disease, with similar peak-levels of viremia as the high exposure group but with some heterogeneity in the onset of viremia. These results suggest that the likelihood for successful infection of a ruminant host is affected by the number of infectious mosquitoes biting, but also highlights that a single bite of an infectious mosquito can result in disease. The per bite mosquito-to-host transmission efficiency was estimated at 28% (95% confidence interval: 15 - 47%). We subsequently combined this transmission efficiency with estimates for life traits of Aedes aegypti or related mosquitoes into a Ross-McDonald mathematical model to illustrate scenarios under which major RVFV outbreaks could occur in naïve populations (i.e., R0 >1). The model revealed that relatively high vector-to-host ratios as well as mosquitoes feeding preferably on competent hosts are required for R0 to exceed 1. Altogether, this study highlights the importance of experiments that mimic natural exposure to RVFV. The experiments facilitate a better understanding of the natural progression of disease and a direct way to obtain epidemiological parameters for mathematical models.

Evaluating spatial and temporal patterns of tick exposure in the United States using community science data submitted through a smartphone application

Research initiatives that engage the public (i.e., community science or citizen science) increasingly provide insights into tick exposures in the United States. However, these data have important caveats, particularly with respect to reported travel history and tick identification. Here, we assessed whether a smartphone application, The Tick App, provides reliable and novel insights into tick exposures across three domains - travel history, broad spatial and temporal patterns of species-specific encounters, and tick identification. During 2019-2021, we received 11,424 tick encounter submissions from across the United States, with nearly all generated in the Midwest and Northeast regions. Encounters were predominantly with human hosts (71%); although one-fourth of ticks were found on animals. Half of the encounters (51%) consisted of self-reported peri‑domestic exposures, while 37% consisted of self-reported recreational exposures. Using phone-based location services, we detected differences in travel history outside of the users' county of residence along an urbanicity gradient. Approximately 75% of users from large metropolitan and rural counties had travel out-of-county in the four days prior to tick detection, whereas an estimated 50-60% of users from smaller metropolitan areas did. Furthermore, we generated tick encounter maps for Dermacentor variabilis and Ixodes scapularis that partially accounted for travel history and overall mirrored previously published species distributions. Finally, we evaluated whether a streamlined three-question sequence (on tick size, feeding status, and color) would inform a simple algorithm to optimize image-based tick identification. Visual aides of tick coloration and size engaged and guided users towards species and life stage classification moderately well, with 56% of one-time submitters correctly selecting photos of D. variabilis adults and 76% of frequent-submitters correctly selecting photos of D. variabilis adults. Together, these results indicate the importance of bolstering the use of smartphone applications to engage community scientists and complement other active and passive tick surveillance systems.

Fleas from common rodent species are an unlikely source of plague (Yersinia pestis) in managed forests of northwestern Oregon, USA

Anthropogenic environmental change can alter the susceptibility of wildlife hosts to pathogens and provide an opportunity for disease emergence. We explored Yersinia pestis prevalence in fleas from three rodent species inhabiting intensively managed forests in Oregon, USA. Y. pestis was not detected in the 145 fleas (3 families and 9 species) collected. Our results suggest a low public health threat from plague in this anthropogenically altered landscape and contribute to regional Y. pestis monitoring efforts.

Projecting vaccine demand and impact for emerging zoonotic pathogens

BACKGROUND

Despite large outbreaks in humans seeming improbable for a number of zoonotic pathogens, several pose a concern due to their epidemiological characteristics and evolutionary potential. To enable effective responses to these pathogens in the event that they undergo future emergence, the Coalition for Epidemic Preparedness Innovations is advancing the development of vaccines for several pathogens prioritized by the World Health Organization. A major challenge in this pursuit is anticipating demand for a vaccine stockpile to support outbreak response.

METHODS

We developed a modeling framework for outbreak response for emerging zoonoses under three reactive vaccination strategies to assess sustainable vaccine manufacturing needs, vaccine stockpile requirements, and the potential impact of the outbreak response. This framework incorporates geographically variable zoonotic spillover rates, human-to-human transmission, and the implementation of reactive vaccination campaigns in response to disease outbreaks. As proof of concept, we applied the framework to four priority pathogens: Lassa virus, Nipah virus, MERS coronavirus, and Rift Valley virus.

RESULTS

Annual vaccine regimen requirements for a population-wide strategy ranged from > 670,000 (95% prediction interval 0-3,630,000) regimens for Lassa virus to 1,190,000 (95% PrI 0-8,480,000) regimens for Rift Valley fever virus, while the regimens required for ring vaccination or targeting healthcare workers (HCWs) were several orders of magnitude lower (between 1/25 and 1/700) than those required by a population-wide strategy. For each pathogen and vaccination strategy, reactive vaccination typically prevented fewer than 10% of cases, because of their presently low R₀ values. Targeting HCWs had a higher per-regimen impact than population-wide vaccination.

CONCLUSIONS

Our framework provides a flexible methodology for estimating vaccine stockpile needs and the geographic distribution of demand under a range of outbreak response scenarios. Uncertainties in our model estimates highlight several knowledge gaps that need to be addressed to target vulnerable populations more accurately. These include surveillance gaps that mask the true geographic distribution of each pathogen, details of key routes of spillover from animal reservoirs to humans, and the role of human-to-human transmission outside of healthcare settings. In addition, our estimates are based on the current epidemiology of each pathogen, but pathogen evolution could alter vaccine stockpile requirements.

Outdoor Activity Associated with Higher Self-Reported Emotional Well-Being During COVID-19

Shifts in activity patterns during the COVID-19 pandemic might have impacted the benefits of outdoor activities for mental health. By leveraging an existing mobile application, we collected self-reported data on daily outdoor activities, emotional well-being, and the influence of COVID-19 on participant's outdoor activity levels during April-July 2020. Individuals reporting outdoor activities, in greenspaces or in their residence, had higher well-being scores and this effect increased with age. Self-reported impacts of COVID-19 on emotional well-being were associated with lower well-being scores. This work suggests that outdoor activities may have improved mental health during the COVID-19 pandemic.

Knowledge, attitudes, and behaviors regarding tick-borne disease prevention in Lyme disease-endemic areas of the Upper Midwest, United States

Lyme disease and other tick-borne diseases are a major public health threat in the Upper Midwestern United States, including Michigan, Minnesota, and Wisconsin. To prevent tick bites and tick-borne diseases, public health officials commonly recommend personal protective measures and property management techniques. Adoption of tick-borne disease prevention behaviors and practices by individuals are, however, highly variable. We aimed to characterize current tick-borne disease knowledge, attitudes, and prevention behaviors (KAB) practiced by the public in these states, as well as their willingness to use specific tick control methods. We conducted a population-based survey in summer 2019 in 48 high-risk counties (those having a five-year average (2013-2017) Lyme disease incidence of ≥ 10 cases per 100,000 persons per year), in Michigan, Minnesota, and Wisconsin. A total of 2713 surveys were analyzed; survey weights were used to account for household selection probability and post-stratified to match county-level joint age and sex population distributions in population-level inference. An estimated 98% of the population had heard of Lyme disease, with most perceiving it as very or extremely serious (91%); however, only an estimated 25% perceived tick-borne diseases as very or extremely common in their community. Among those who spent time in places with ticks from April through October, an estimated 68% check themselves thoroughly for ticks most of the time or always and 43% use bug repellent on skin or clothing most of the time or always. An estimated 13% of the population had ever treated their property with a pesticide to kill ticks, and 3% had ever used devices that apply pesticide to rodents to kill ticks on their property. Willingness to practice tick bite prevention behaviors, however, was estimated to be much higher; with 82% being willing to perform tick checks at least once a day, and more than 60% willing to use bug repellent, tick control products on pets, or to bathe within two hours of being outdoors. We found that residents would likely be willing to support a county-wide tick control program to reduce the risk of tick-borne disease in their community (81%) or to apply tick control products to their property to reduce the risk of tick-borne disease in their household (79%). Tick checks were more likely to be practiced among participants who perceived tick-borne diseases to be highly prevalent in their community, if they or a household member had been previously diagnosed with a tick-borne disease?, or if they perceived tick exposure to be likely around their home, cabin, or vacation home. In addition, property-based tick control methods were associated with perceived risk of encountering ticks around the home, cabin, or vacation home. Participants who had seen information from state health departments were also more likely to practice preventive measures. The most common reported barriers to using any of these methods were forgetfulness, safety concerns, and lack of awareness. Our survey findings shed light on how residents from these Upper Midwest states may adopt tick control and tick bite prevention measures and how public health outreach may be most effective for this population.

Identification of public submitted tick images: A neural network approach

Ticks and tick-borne diseases represent a growing public health threat in North America and Europe. The number of ticks, their geographical distribution, and the incidence of tick-borne diseases, like Lyme disease, are all on the rise. Accurate, real-time tick-image identification through a smartphone app or similar platform could help mitigate this threat by informing users of the risks associated with encountered ticks and by providing researchers and public health agencies with additional data on tick activity and geographic range. Here we outline the requirements for such a system, present a model that meets those requirements, and discuss remaining challenges and frontiers in automated tick identification. We compiled a user-generated dataset of more than 12,000 images of the three most common tick species found on humans in the U.S.: Amblyomma americanum, Dermacentor variabilis, and Ixodes scapularis. We used image augmentation to further increase the size of our dataset to more than 90,000 images. Here we report the development and validation of a convolutional neural network which we call "TickIDNet," that scores an 87.8% identification accuracy across all three species, outperforming the accuracy of identifications done by a member of the general public or healthcare professionals. However, the model fails to match the performance of experts with formal entomological training. We find that image quality, particularly the size of the tick in the image (measured in pixels), plays a significant role in the network's ability to correctly identify an image: images where the tick is small are less likely to be correctly identified because of the small object detection problem in deep learning. TickIDNet's performance can be increased by using confidence thresholds to introduce an "unsure" class and building image submission pipelines that encourage better quality photos. Our findings suggest that deep learning represents a promising frontier for tick identification that should be further explored and deployed as part of the toolkit for addressing the public health consequences of tick-borne diseases.

Integrated Tick Management in South Central Wisconsin: Impact of Invasive Vegetation Removal and Host-Targeted Acaricides on the Density of Questing Ixodes scapularis (Acari: Ixodidae) Nymphs

As tick-borne disease incidence increases and pathogens expand into new areas, the need for effective tick management strategies is paramount. In this 5-yr study (2014-2018) conducted in south central Wisconsin, we assessed whether an integrated tick management approach, deployed during peak tick activity (May-August), was more effective at reducing black-legged ticks (Ixodes scapularis Say (Ixodida: Ixodidae)), than individual interventions. Using a factorial design, invasive vegetation removal (Amur honeysuckle, Lonicera maackii Ruprecht (Dipsacales: Caprifoliaceae) and common buckthorn, Rhamnus cathartica Linnaeus (Rosales: Rhamnaceae)) was coupled with deployments of permethrin-treated cotton nesting materials (tick tubes) that target the white-footed mouse (Peromyscus leucopus Rafinesque (Rodentia: Cricetidae)). Results show that the probability of encountering a larval tick by drag sampling was unaffected by treatments at the cumulative 5-yr level. However, vegetation removal significantly reduced larval encounters in 2014, 2015, and 2018, by 33%, 57%, and 61% respectively, and reduced the density of questing nymphal (DON) ticks by 45% in 2015 compared to controls. Despite the limited effect on DON, vegetation removal significantly reduced the cumulative 5-yr density of Borrelia burgdorferi sensu stricto infected nymphs (DIN) (70%) compared to controls as a result of decreased nymphal infection prevalence. Sites treated with tick tubes had lower DIN (66%) and DON (54%) across the study and nymphs were reduced every year following the initial year of deployment compared to controls. Combining treatments did not further reduce DIN or DONs. We conclude that long-term integration of tick tubes with invasive vegetation removal does not provide additional benefit over individual treatments alone.

Evidence for Vertical Transmission of Babesia odocoilei (Piroplasmida: Babesiidae) in Ixodes scapularis (Acari: Ixodidae)

Limited evidence suggests that the cervid parasite, Babesia odocoilei, is transovarially transmitted from adult female Ixodes scapularis Say to offspring. The prevalence of B. odocoilei in unfed larval I. scapularis and whether vertical transmission is crucial to pathogen maintenance are currently unknown. To investigate these questions, 275 unfed larvae from two Wisconsin counties were tested for B. odocoilei genetic material. Sixteen of 29 pools were positive for the parasite. The maximum likelihood estimation for overall larval infection prevalence was 7.8% (95% confidence interval: 4.7-12). This vertically acquired infection appears to be sustained transstadially in nymphal ticks the following year; however, our relatively small sample and replicate size warrants additional evaluation. Our study revealed further evidence of vertical transmission, a low and consistent infection prevalence in larvae, and the potential importance of vertical transmission in B. odocoilei maintenance.

Coinfection of Ixodes scapularis (Acari: Ixodidae) Nymphs With Babesia spp. (Piroplasmida: Babesiidae) and Borrelia burgdorferi (Spirochaetales: Spirochaetaceae) in Wisconsin

Borrelia burgdorferi, the spirochete that causes Lyme disease, is endemic and widespread in Wisconsin. Research in the northeastern United States has revealed a positive association between Babesia microti, the main pathogen that causes babesiosis in humans, and Bo. burgdorferi in humans and in ticks. This study was conducted to examine associations between the disease agents in the Upper midwestern United States. Ixodes scapularis Say nymphs (N = 2,858) collected between 2015 and 2017 from nine locations in Wisconsin were tested for Babesia spp. and Borrelia spp. using real-time PCR. Two species of Babesia were detected; Ba. microti and Babesia odocoilei (a parasite of members of the family Cervidae). Prevalence of infection at the nine locations ranged from 0 to 13% for Ba. microti, 11 to 31% for Bo. burgdorferi sensu stricto, and 5.7 to 26% for Ba. odocoilei. Coinfection of nymphs with Bo. burgdorferi and Ba. odocoilei was detected in eight of the nine locations and significant positive associations were observed in two of the eight locations. The prevalence of nymphal coinfection with both and Bo. burgdorferi and Ba. microti ranged from 0.81 to 6.5%. These two pathogens were significantly positively associated in one of the five locations where both pathogens were detected. In the other four locations, the observed prevalence of coinfection was higher than expected in all but one site-year. Clinics and healthcare providers should be aware of the association between Ba. microti and Bo. burgdorferi pathogens when treating patients who report tick bites.

Sin Nombre virus prevalence from 2014-2017 in wild deer mice, Peromyscus maniculatus, on five of the California Channel Islands

Sin Nombre virus (SNV) is a zoonotic virus that is highly pathogenic to humans. The deer mouse, Peromyscus maniculatus, is the primary host of SNV, and SNV prevalence in P. maniculatus is an important indicator of human disease risk. Because the California Channel Islands contain permanent human settlements, receive hundreds of thousands of visitors each year, and can have extremely high densities of P. maniculatus, surveillance for SNV in island P. maniculatus is important for understanding the human risk of zoonotic disease. Despite the importance of surveillance on these heavily utilized islands, SNV prevalence (i.e. the proportion of P. maniculatus that test positive to antibodies to SNV) has not been examined in the last 13-27 years. We present data on 1,610 mice sampled for four consecutive years (2014-2017) on five of the California Channel Islands: East Anacapa, Santa Barbara, Santa Catalina, San Nicolas, and San Clemente. Despite historical data indicating SNV-positive mice on San Clemente and Santa Catalina, we detected no SNV-positive mice on these islands, suggesting very low prevalence or possible loss of SNV. Islands historically free of SNV (East Anacapa, Santa Barbara, and San Nicolas) remained free of SNV, suggesting that rates of pathogen introduction from other islands and/or the mainland are low. Although continued surveillance is warranted to determine whether SNV establishes on these islands, our work helps inform current human disease risk in these locations and suggests that SNV prevalence on these islands is currently very low.

High Proportion of Unfed Larval Blacklegged Ticks, Ixodes scapularis (Acari: Ixodidae), Collected From Modified Nest Boxes for Mice

The blacklegged tick, Ixodes scapularis Say, is the primary vector of several tick-borne pathogens, including those causing Lyme disease and babesiosis, in the eastern United States and active collection methods for this species include dragging or wild animal sampling. Nest boxes targeting mice may be an alternative strategy for the surveillance and collection of immature I. scapularis feeding on these hosts and would be much safer for animals compared to small mammal trapping. We constructed double-walled insulated nest boxes (DWINs) with collection tubes mounted below the nesting chamber and deployed eleven in southern Wisconsin from June until September of 2020. The DWINs were occupied by Peromyscus spp. and birds (wren species, Troglodytidae family). We collected 192 ticks from collection tubes, all of which were identified as either I. scapularis (95%) or Dermacentor variabilis Say (Acari: Ixodidae) (5%). Only 12% (21/182) and 20% (2/10) of I. scapularis and D. variabilis were blood-fed, respectively. The high proportion of unfed ticks found in collection tubes may be due to grooming by hosts inside the nest boxes. Alternatively, immature ticks may have climbed trees and entered the DWIN seeking a host. Results suggest that nest boxes could be a tool for finding ticks in areas of low density or at the leading edge of invasion, when small mammal trapping or drag sampling is not feasible.

Do-It-Yourself Tick Control: Granular Gamma-Cyhalothrin Reduces Ixodes scapularis (Acari: Ixodidae) Nymphs in Residential Backyards

Lyme disease is the most common vector-borne disease in the United States with hotspots in the Northeast and Midwest. Integrated vector control for mosquito-borne disease prevention is often organized at the community level, but tick control is primarily coordinated at the household and individual level. Management of the blacklegged tick, Ixodes scapularis (Say), the vector of the causative agent of Lyme disease in the Midwest and eastern United States in peridomestic environments may be critical as many tick encounters are reported to occur in the yard. Therefore, we assessed the effectiveness of a widely available and low-cost pesticide that targets common lawn pests and is labeled for use against ticks. In June 2019, we evaluated a granular form of gamma-cyhalothrin in a placebo-controlled residential backyard study (n = 90) in two communities in Wisconsin. The product applied by the research team reduced nymphal blacklegged ticks in plots established in the lawn part of the ecotone by 97% one week after application at both communities and by 89-97% three to four weeks postapplication. The proportion of homes with at least one nymphal tick postapplication was significantly lower at acaricide-treated homes and ranged from 4.2 to 29.2% compared with placebo homes where at least one nymphal tick was found at 50-81.5% of homes. These results support the efficacy of a low-cost do-it-yourself strategy for homeowners seeking to reduce blacklegged ticks in the yard.

Assessing Recognition of the Vector of Lyme Disease Using Resin-Embedded Specimens in a Lyme Endemic Area

Lyme disease (LD) is the most common vector-borne disease in the United States. To assess whether a tick bite puts someone at risk for LD, adequate tick identification skills are needed. We surveyed residents of a high LD-incidence state, Wisconsin, on their ability to distinguish ticks from insects and to identify the specimens that could transmit the LD causative agent. Surveys were conducted using resin blocks with four insects and four tick specimens embedded. About half of the participants (64 of 130) recognized all of the ticks, and 60% of those individuals chose only ticks and no insects. Younger participants (18- to 44-yr old) were more likely to identify ticks correctly compared with those 45 yr and older. Participants who agreed strongly with the statement 'I know a lot about ticks` were also likelier to correctly identify ticks. When asked to identify which specimens could transmit LD, less than 25% of participants chose both the Ixodes scapularis Say adult female and nymph and about half of those (15% of participants) picked only those two and no other specimens. Although the relatively small convenience sample was biased toward younger participants who consider themselves 'outdoorsy', results showed that further assessments of tick recognition skills are needed to understand what determines whether people can recognize medically important ticks and to evaluate the potential benefits of enhanced education. In addition to the value of the resin blocks as research tools, the blocks may be useful as training tools to improve tick check efficacy.

Context matters: Contrasting behavioral and residential risk factors for Lyme disease between high-incidence states in the Northeastern and Midwestern United States

The dynamics of zoonotic vector-borne diseases are determined by a complex set of parameters including human behavior that may vary with socio-ecological contexts. Lyme disease is the most common vector-borne disease in the United States. The Northeast and upper Midwest are the regions most affected - two areas with differing levels of urbanization and differing sociocultural settings. The probability of being infected with Lyme disease is related to the risk of encounters with Ixodes scapularis ticks infected with Borrelia burgdorferi sensu lato, which reflects both the environmental tick hazard and human behaviors. Herein, we compare behavioral and peridomestic risk factors perceived to influence the risk for human-tick encounters between two high-incidence states in the Northeast (New York and New Jersey) and one high-incidence state in the Midwest (Wisconsin). We used a smartphone application, The Tick App, as a novel survey tool, during spring and summer of 2018. Adaptive human behavior was identified in the relationship between outdoor activities and the use of methods to prevent tick bites. More frequent recreational outdoor activities and gardening (a peridomestic activity) were associated with a 1.4-2.3 times increased likelihood of using personal protective measures to prevent tick bites, when accounting for demographics and previous Lyme diagnosis. Most outdoor activities were more frequently reported by participants from the Midwest (n = 697), representing an older demographic, than the Northeast (n = 396). Participants from the Northeast were less likely to report use of personal protective measures to prevent tick bites, but a larger proportion of participants from the Northeast reported application of environmental pesticides targeting ticks or mosquitoes or other insects on their property (34 % of 279 versus 22 % of 616 participants) and interventions to reduce the presence of peridomestic deer compared to participants from the Midwest (e.g. 20 % of 278 versus 7% of 615 participants reported having a deer proof fence). Participants from the Midwest were more likely to kill rodents on their property (28 % versus 13 %). These differences illustrate the need for further assessment of personal behavior and tick exposure in these two Lyme disease-endemic regions to aid in targeted public health messaging to reduce tick-borne diseases.

An invasive disease, sylvatic plague, increases fragmentation of black-tailed prairie dog (Cynomys ludovicianus) colonies

Context

A disease can be a source of disturbance, causing population declines or extirpations, altering species interactions, and affecting habitat structure. This is particularly relevant for diseases that affect keystone species or ecosystem engineers, leading to potentially cascading effects on ecosystems.

Objective

We investigated the invasion of a non-native disease, plague, to a keystone species, prairie dogs, and documented the resulting extent of fragmentation and habitat loss in western grasslands. Specifically, we assessed how the arrival of plague in the Conata Basin, South Dakota, United States, affected the size, shape, and aggregation of prairie dog colonies, an animal species known to be highly susceptible to plague.

Methods

Colonies in the prairie dog complex were mapped every 1 to 3 years from 1993 to 2015. Plague was first confirmed in 2008 and we compared prairie dog complex and colony characteristics before and after the arrival of plague.

Results

As expected the colony complex and the patches in colonies became smaller and more fragmented after the arrival of plague; the total area of each colony and the mean area per patch within a colony decreased, the number of patches per colony increased, and mean contiguity of each patch decreased, leading to habitat fragmentation.

Conclusion

We demonstrate how an emerging infectious disease can act as a source of disturbance to natural systems and lead to potentially permanent alteration of habitat characteristics. While perhaps not traditionally thought of as a source of ecosystem disturbances, in recent years emerging infectious diseases have shown to be able to have large effects on ecosystems if they affect keystone species.

Immature Ixodes scapularis (Acari: Ixodidae) Collected From Peromyscus leucopus (Rodentia: Cricetidae) and Peromyscus maniculatus (Rodentia: Cricetidae) Nests in Northern Wisconsin

The blacklegged tick, Ixodes scapularis Say, is the primary Lyme disease vector in the eastern United States. Both immature stages of I. scapularis take blood meals from mice belonging to the genus Peromyscus. Mice are active during the night and spend the majority of diel periods in nests. Thus, immature I. scapularis have a greater opportunity to drop from Peromyscus hosts while in nests compared with the forest floor. Here, we collected 11 Peromyscus nests during a 3-mo period during which the immature I. scapularis are known to be active. We then examined nesting materials for the presence of I. scapularis. Immature I. scapularis were detected in 64% of Peromyscus nests examined. Additionally, 55% of the nests contained at least one Dermacentor variabilis Say larva. Eighty-seven percent of all larval ticks found within nests were blood-fed. Because Peromyscus spp. are highly competent reservoirs of numerous tick-borne pathogens, the ticks that detach in their nests may be important for the maintenance of tick-borne diseases. However, further studies are needed to determine the fate of the I. scapularis that detach in Peromyscus nests.

Usability and Feasibility of a Smartphone App to Assess Human Behavioral Factors Associated with Tick Exposure (The Tick App): Quantitative and Qualitative Study

Background

Mobile health (mHealth) technology takes advantage of smartphone features to turn them into research tools, with the potential to reach a larger section of the population in a cost-effective manner, compared with traditional epidemiological methods. Although mHealth apps have been widely implemented in chronic diseases and psychology, their potential use in the research of vector-borne diseases has not yet been fully exploited.

Objective

This study aimed to assess the usability and feasibility of The Tick App, the first tick research–focused app in the United States.

Methods

The Tick App was designed as a survey tool to collect data on human behaviors and movements associated with tick exposure while engaging users in tick identification and reporting. It consists of an enrollment survey to identify general risk factors, daily surveys to collect data on human activities and tick encounters (Tick Diaries), a survey to enter the details of tick encounters coupled with tick identification services provided by the research team (Report a Tick), and educational material. Using quantitative and qualitative methods, we evaluated the enrollment strategy (passive vs active), the user profile, location, longitudinal use of its features, and users’ feedback.

Results

Between May and September 2018, 1468 adult users enrolled in the app. The Tick App users were equally represented across genders and evenly distributed across age groups. Most users owned a pet (65.94%, 962/1459; P<.001), did frequent outdoor activities (recreational or peridomestic; 75.24%, 1094/1454; P<.001 and 64.58%, 941/1457; P<.001, respectively), and lived in the Midwest (56.55%, 824/1457) and Northeast (33.0%, 481/1457) regions in the United States, more specifically in Wisconsin, southern New York, and New Jersey. Users lived more frequently in high-incidence counties for Lyme disease (incidence rate ratio [IRR] 3.5, 95% CI 1.8-7.2; P<.001) and in counties with cases recently increasing (IRR 1.8, 95% CI 1.1-3.2; P=.03). Recurring users (49.25%, 723/1468) had a similar demographic profile to all users but participated in outdoor activities more frequently (80.5%, 575/714; P<.01). The number of Tick Diaries submitted per user (median 2, interquartile range [IQR] 1-11) was higher for older age groups (aged >55 years; IRR 3.4, 95% CI 1.5-7.6; P<.001) and lower in the Northeast (IRR[NE] 0.4, 95% CI 0.3-0.7; P<.001), whereas the number of tick reports (median 1, IQR 1-2) increased with the frequency of outdoor activities (IRR 1.5, 95% CI 1.3-1.8; P<.001).

Conclusions

This assessment allowed us to identify what fraction of the population used The Tick App and how it was used during a pilot phase. This information will be used to improve future iterations of The Tick App and tailor potential tick prevention interventions to the users’ characteristics.

Plague-Positive Mouse Fleas on Mice Before Plague Induced Die-Offs in Black-Tailed and White-Tailed Prairie Dogs

Plague is a lethal zoonotic disease associated with rodents worldwide. In the western United States, plague outbreaks can decimate prairie dog (Cynomys spp.) colonies. However, it is unclear where the causative agent, Yersinia pestis, of this flea-borne disease is maintained between outbreaks, and what triggers plague-induced prairie dog die-offs. Less susceptible rodent hosts, such as mice, could serve to maintain the bacterium, transport infectious fleas across a colony, or introduce the pathogen to other colonies, possibly facilitating an outbreak. Here, we assess the potential role of two short-lived rodent species, North American deer mice (Peromyscus maniculatus) and Northern grasshopper mice (Onychomys leucogaster) in plague dynamics on prairie dog colonies. We live-trapped short-lived rodents and collected their fleas on black-tailed (Cynomys ludovicianus, Montana and South Dakota), white-tailed (Cynomys leucurus, Utah and Wyoming), and Utah prairie dog colonies (Cynomys parvidens, Utah) annually, from 2013 to 2016. Plague outbreaks occurred on colonies of all three species. In all study areas, deer mouse abundance was high the year before plague-induced prairie dog die-offs, but mouse abundance per colony was not predictive of plague die-offs in prairie dogs. We did not detect Y. pestis DNA in mouse fleas during prairie dog die-offs, but in three cases we found it beforehand. On one white-tailed prairie dog colony, we detected Y. pestis positive fleas on one grasshopper mouse and several prairie dogs live-trapped 10 days later, months before visible declines and plague-confirmed mortality of prairie dogs. On one black-tailed prairie dog colony, we detected Y. pestis positive fleas on two deer mice 3 months before evidence of plague was detected in prairie dogs or their fleas and also well before a plague-induced die-off. These observations of plague positive fleas on mice could represent early spillover events of Y. pestis from prairie dogs or an unknown reservoir, or possible movement of infectious fleas by mice.

First Detection of Aedes albopictus (Diptera: Culicidae) and Expansion of Aedes japonicus japonicus in Wisconsin, United States

The 2015-2016 epidemic of Zika virus in the Americas raised concerns about the range of Aedes albopictus (Skuse) in the United States. In response, the University of Wisconsin Medical Entomology Laboratory coordinated with the Wisconsin Department of Health Services in 2016 to conduct Aedes spp. surveillance and set up an oviposition trap (ovitrap) network operated by local public health partners across southern and western Wisconsin. During 2016, 916 ovitrap events were processed, but only Aedes triseriatus Say (Diptera: Culicidae) and Aedes japonicus japonicus (Theobald) were detected. In 2017, a focused surveillance approach was employed to detect Ae. albopictus near sites with tires stored outdoors. Using this targeted approach, Ae. albopictus was detected from ovitraps in two out of seven counties surveyed during June, July, and August. This is the first record of Ae. albopictus in Wisconsin.

Impact of Sylvatic Plague Vaccine on Non-target Small Rodents in Grassland Ecosystems

Oral vaccination is an emerging management strategy to reduce the prevalence of high impact infectious diseases within wild animal populations. Plague is a flea-borne zoonosis of rodents that often decimates prairie dog (Cynomys spp.) colonies in the western USA. Recently, an oral sylvatic plague vaccine (SPV) was developed to protect prairie dogs from plague and aid recovery of the endangered black-footed ferret (Mustela nigripes). Although oral vaccination programs are targeted toward specific species, field distribution of vaccine-laden baits can result in vaccine uptake by non-target animals and unintended indirect effects. We assessed the impact of SPV on non-target rodents at paired vaccine and placebo-treated prairie dog colonies in four US states from 2013 to 2015. Bait consumption by non-target rodents was high (70.8%, n = 3113), but anti-plague antibody development on vaccine plots was low (23.7%, n = 266). In addition, no significant differences were noted in combined deer mice (Peromyscus maniculatus) and western harvest mouse (Reithrodontomys megalotis) abundance or community evenness and richness of non-target rodents between vaccine-treated and placebo plots. In our 3-year field study, we could not detect a significant positive or negative effect of SPV application on non-target rodents.

Evaluation of Yersinia pestis Transmission Pathways for Sylvatic Plague in Prairie Dog Populations in the Western U.S

Sylvatic plague, caused by the bacterium Yersinia pestis, is periodically responsible for large die-offs in rodent populations that can spillover and cause human mortalities. In the western US, prairie dog populations experience nearly 100% mortality during plague outbreaks, suggesting that multiple transmission pathways combine to amplify plague dynamics. Several alternate pathways in addition to flea vectors have been proposed, such as transmission via direct contact with bodily fluids or inhalation of infectious droplets, consumption of carcasses, and environmental sources of plague bacteria, such as contaminated soil. However, evidence supporting the ability of these proposed alternate pathways to trigger large-scale epizootics remains elusive. Here we present a short review of potential plague transmission pathways and use an ordinary differential equation model to assess the contribution of each pathway to resulting plague dynamics in black-tailed prairie dogs (Cynomys ludovicianus) and their fleas (Oropsylla hirsuta). Using our model, we found little evidence to suggest that soil contamination was capable of producing plague epizootics in prairie dogs. However, in the absence of flea transmission, direct transmission, i.e., contact with bodily fluids or inhalation of infectious droplets, could produce enzootic dynamics, and transmission via contact with or consumption of carcasses could produce epizootics. This suggests that these pathways warrant further investigation.