Publications by authors named "Amy T Gilbert"

43 Publications

Evidence of Arctic Fox Survival following Exposure to Rabies Virus.

J Wildl Dis 2021 Nov 23. Epub 2021 Nov 23.

US Department of Agriculture, National Wildlife Research Center, 4101 Laporte Avenue, Fort Collins, Colorado 80521, USA.

The arctic fox variant of the rabies virus (RABV) is enzootic in the circumpolar north. Reports of abortive RABV exposures motivated a retrospective analysis of sera from 41 arctic foxes captured at Karrak Lake in Nunavut, Canada, during 2011-2015. Estimated RABV antibody prevalence among foxes was 14% (95% confidence interval, 7-28%).
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http://dx.doi.org/10.7589/JWD-D-21-00071DOI Listing
November 2021

Data-Driven Management-A Dynamic Occupancy Approach to Enhanced Rabies Surveillance Prioritization.

Viruses 2021 Sep 9;13(9). Epub 2021 Sep 9.

National Wildlife Research Center, Wildlife Services, Animal and Plant Health Inspection Service, United States Department of Agriculture, Fort Collins, CO 80521, USA.

Rabies lyssavirus (RABV) is enzootic in raccoons across the eastern United States. Intensive management of RABV by oral rabies vaccination (ORV) has prevented its spread westward and shown evidence of local elimination in raccoon populations of the northeastern US. The USDA, Wildlife Services, National Rabies Management Program (NRMP) collaborates with other agencies to implement broad-scale ORV and conducts extensive monitoring to measure the effectiveness of the management. Enhanced Rabies Surveillance (ERS) was initiated during 2005 and updated in 2016 to direct surveillance efforts toward higher-value specimens by assigning points to different methods of encountering specimens for collection (strange-acting, roadkill, surveillance-trapped, etc.; specimen point values ranged from 1 to 15). We used the 2016-2019 data to re-evaluate the point values using a dynamic occupancy model. Additionally, we used ERS data from 2012-2015 and 2016-2019 to examine the impact that the point system had on surveillance data. Implementation of a point system increased positivity rates among specimens by 64%, indicating a substantial increase in the efficiency of the ERS to detect wildlife rabies. Our re-evaluation found that most points accurately reflect the value of the surveillance specimens. The notable exception was that samples from animals found dead were considerably more valuable for rabies detection than originally considered (original points = 5, new points = 20). This work demonstrates how specimen prioritization strategies can be used to refine and improve ERS in support of wildlife rabies management.
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http://dx.doi.org/10.3390/v13091795DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8472164PMC
September 2021

Rabies post-exposure healthcare-seeking behaviors and perceptions: Results from a knowledge, attitudes, and practices survey, Uganda, 2013.

PLoS One 2021 2;16(6):e0251702. Epub 2021 Jun 2.

Poxvirus and Rabies Branch, Division of High-Consequence Pathogens and Pathology, National Center of Emerging and Zoonotic Infectious Diseases, United States Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America.

Background: Rabies is a viral disease of animals and people causing fatal encephalomyelitis if left untreated. Although effective pre- and post-exposure vaccines exist, they are not widely available in many endemic countries within Africa. Since many individuals in these countries remain at risk of infection, post-exposure healthcare-seeking behaviors are crucial in preventing infection and warrant examination.

Methodology: A rabies knowledge, attitudes, and practices survey was conducted at 24 geographically diverse sites in Uganda during 2013 to capture information on knowledge concerning the disease, response to potential exposure events, and vaccination practices. Characteristics of the surveyed population and of the canine-bite victim sub-population were described. Post-exposure healthcare-seeking behaviors of canine-bite victims were examined and compared to the related healthcare-seeking attitudes of non-bite victim respondents. Wealth scores were calculated for each household, rabies knowledge was scored for each non-bitten survey respondent, and rabies exposure risk was scored for each bite victim. Logistic regression was used to determine the independent associations between different variables and healthcare-seeking behaviors among canine-bite victims as well as attitudes of non-bitten study respondents.

Results: A total of 798 households were interviewed, capturing 100 canine-bite victims and a bite incidence of 2.3 per 100 person-years. Over half of bite victims actively sought medical treatment (56%), though very few received rabies post-exposure prophylaxis (3%). Bite victims who did not know or report the closest location where PEP could be received were less likely to seek medical care (p = 0.05). Respondents who did not report having been bitten by a dog with higher knowledge scores were more likely to respond that they would both seek medical care (p = 0.00) and receive PEP (p = 0.06) after a potential rabies exposure event.

Conclusions: There was varying discordance between what respondents who did not report having been bitten by a dog said they would do if bitten by a dog when compared to the behaviors exhibited by canine-bite victims captured in the KAP survey. Bite victims seldom elected to wash their wound or receive PEP. Having lower rabies knowledge was a barrier to theoretically seeking care and receiving PEP among not bitten respondents, indicating a need for effective and robust educational programs in the country.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0251702PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8171952PMC
November 2021

Oral Rabies Vaccination of Small Indian Mongooses () with ONRAB via Ultralite Baits.

Viruses 2021 04 23;13(5). Epub 2021 Apr 23.

United States Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services, National Wildlife Research Center, 4101 LaPorte Ave., Fort Collins, CO 80521, USA.

The Ontario Rabies Vaccine (ONRAB) is a human adenovirus rabies glycoprotein recombinant oral vaccine immunogenic for small Indian mongooses when delivered by direct instillation into the oral cavity. We offered Ultralite baits containing ~1.8 mL 10 TCID ONRAB oral rabies vaccine to 18 mongooses, while 6 mongooses were offered identical baits in placebo form. We collected sera from individual mongooses at days 0, 14 and 30 post vaccination (pv) and quantified rabies virus neutralizing antibodies (RVNA) using the rapid fluorescent focus inhibition test, with titers greater than or equal to 0.1 IU/mL considered positive. All study subjects were RVNA negative prior to bait offering. Bait consumption was variable: all 6 sham and 13 of 18 (72%) treatment animals consumed/punctured the baits offered. By day 30 pv, RVNA were detected among 11 of 13 (84.6%) of treatment mongooses that consumed/punctured baits, whereas sham-vaccinated mongooses remained RVNA negative throughout the study. We conclude ONRAB is immunogenic for mongooses by Ultralite bait delivery, although the bait design may need further optimization.
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http://dx.doi.org/10.3390/v13050734DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8144982PMC
April 2021

Modeling Mongoose Rabies in the Caribbean: A Model-Guided Fieldwork Approach to Identify Research Priorities.

Viruses 2021 02 20;13(2). Epub 2021 Feb 20.

Epidemiology of Zoonoses and Public Health Research Group (GREZOSP), Faculty of Veterinary Medicine, Université de Montréal, 3190 Rue Sicotte, Saint-Hyacinthe, QC J2S 2M2, Canada.

We applied the model-guided fieldwork framework to the Caribbean mongoose rabies system by parametrizing a spatially-explicit, individual-based model, and by performing an uncertainty analysis designed to identify parameters for which additional empirical data are most needed. Our analysis revealed important variation in output variables characterizing rabies dynamics, namely rabies persistence, exposure level, spatiotemporal distribution, and prevalence. Among epidemiological parameters, rabies transmission rate was the most influential, followed by rabies mortality and location, and size of the initial infection. The most influential landscape parameters included habitat-specific carrying capacities, landscape heterogeneity, and the level of resistance to dispersal associated with topography. Movement variables, including juvenile dispersal, adult fine-scale movement distances, and home range size, as well as life history traits such as age of independence, birth seasonality, and age- and sex-specific mortality were other important drivers of rabies dynamics. We discuss results in the context of mongoose ecology and its influence on disease transmission dynamics. Finally, we suggest empirical approaches and study design specificities that would provide optimal contributing data addressing the knowledge gaps identified by our approach, and would increase our potential to use epidemiological models to guide mongoose rabies control and management in the Caribbean.
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http://dx.doi.org/10.3390/v13020323DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7923793PMC
February 2021

Serological Responses of Raccoons and Striped Skunks to Ontario Rabies Vaccine Bait in West Virginia during 2012-2016.

Viruses 2021 01 22;13(2). Epub 2021 Jan 22.

USDA/APHIS/WS/National Rabies Management Program, 59 Chenell Dr., Concord, NH 03301, USA.

Since the 1990s, oral rabies vaccination (ORV) has been used successfully to halt the westward spread of the raccoon rabies virus (RV) variant from the eastern continental USA. Elimination of raccoon RV from the eastern USA has proven challenging across targeted raccoon () and striped skunk () populations impacted by raccoon RV. Field trial evaluations of the Ontario Rabies Vaccine Bait (ONRAB) were initiated to expand ORV products available to meet the rabies management goal of raccoon RV elimination. This study describes the continuation of a 2011 trial in West Virginia. Our objective was to evaluate raccoon and skunk response to ORV occurring in West Virginia for an additional two years (2012-2013) at 75 baits/km followed by three years (2014-2016) of evaluation at 300 baits/km. We measured the change in rabies virus-neutralizing antibody (RVNA) seroprevalence in targeted wildlife populations by comparing levels pre- and post-ORV during each year of study. The increase in bait density from 75/km to 300/km corresponded to an increase in average post-ORV seroprevalence for raccoon and skunk populations. Raccoon population RVNA levels increased from 53% (300/565, 95% CI: 50-57%) to 82.0% (596/727, 95% CI: 79-85%) during this study, and skunk population RVNA levels increased from 11% (8/72, 95% CI: 6-20%) to 39% (51/130, 95% CI: 31-48%). The RVNA seroprevalence pre-ORV demonstrated an increasing trend across study years for both bait densities and species, indicating that multiple years of ORV may be necessary to achieve and maintain RVNA seroprevalence in target wildlife populations for the control and elimination of raccoon RV in the eastern USA.
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http://dx.doi.org/10.3390/v13020157DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7912576PMC
January 2021

Contextualizing bats as viral reservoirs.

Science 2020 10;370(6513):172-173

U.S. Department of Agriculture, Animal and Plant Health Inspection Service, National Wildlife Research Center, Fort Collins, CO, USA.

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http://dx.doi.org/10.1126/science.abd4559DOI Listing
October 2020

Possibility for reverse zoonotic transmission of SARS-CoV-2 to free-ranging wildlife: A case study of bats.

PLoS Pathog 2020 09 3;16(9):e1008758. Epub 2020 Sep 3.

US Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America.

The COVID-19 pandemic highlights the substantial public health, economic, and societal consequences of virus spillover from a wildlife reservoir. Widespread human transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) also presents a new set of challenges when considering viral spillover from people to naïve wildlife and other animal populations. The establishment of new wildlife reservoirs for SARS-CoV-2 would further complicate public health control measures and could lead to wildlife health and conservation impacts. Given the likely bat origin of SARS-CoV-2 and related beta-coronaviruses (β-CoVs), free-ranging bats are a key group of concern for spillover from humans back to wildlife. Here, we review the diversity and natural host range of β-CoVs in bats and examine the risk of humans inadvertently infecting free-ranging bats with SARS-CoV-2. Our review of the global distribution and host range of β-CoV evolutionary lineages suggests that 40+ species of temperate-zone North American bats could be immunologically naïve and susceptible to infection by SARS-CoV-2. We highlight an urgent need to proactively connect the wellbeing of human and wildlife health during the current pandemic and to implement new tools to continue wildlife research while avoiding potentially severe health and conservation impacts of SARS-CoV-2 "spilling back" into free-ranging bat populations.
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http://dx.doi.org/10.1371/journal.ppat.1008758DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7470399PMC
September 2020

Variation in host home range size decreases rabies vaccination effectiveness by increasing the spatial spread of rabies virus.

J Anim Ecol 2020 06 15;89(6):1375-1386. Epub 2020 Feb 15.

United States Department of Agriculture, Animal and Plant Health Inspection Service, National Wildlife Research Center, Fort Collins, CO, USA.

Animal movement influences the spatial spread of directly transmitted wildlife disease through host-host contact structure. Wildlife disease hosts vary in home range-associated foraging and social behaviours, which may increase the spread and intensity of disease outbreaks. The consequences of variation in host home range movement and space use on wildlife disease dynamics are poorly understood, but could help to predict disease spread and determine more effective disease management strategies. We developed a spatially explicit individual-based model to examine the effect of spatiotemporal variation in host home range size on the spatial spread rate, persistence and incidence of rabies virus (RABV) in raccoons (Procyon lotor). We tested the hypothesis that variation in home range size increases RABV spread and decreases vaccination effectiveness in host populations following pathogen invasion into a vaccination zone. We simulated raccoon demography and RABV dynamics across a range of magnitudes and variances in weekly home range size for raccoons. We examined how variable home range size influenced the relative effectiveness of three components of oral rabies vaccination (ORV) programmes targeting raccoons-timing and frequency of bait delivery, width of the ORV zone and proportion of hosts immunized. Variability in weekly home range size increased RABV spread rates by 1.2-fold to 5.2-fold compared to simulations that assumed a fixed home range size. More variable host home range sizes decreased relative vaccination effectiveness by 71% compared to less variable host home range sizes under conventional vaccination conditions. We found that vaccination timing was more influential for vaccination effectiveness than vaccination frequency or vaccination zone width. Our results suggest that variation in wildlife home range movement behaviour increases the spatial spread and incidence of RABV. Our vaccination results underscore the importance of prioritizing individual-level space use and movement data collection to understand wildlife disease dynamics and plan their effective control and elimination.
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http://dx.doi.org/10.1111/1365-2656.13176DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7317853PMC
June 2020

SAFETY, IMMUNOGENICITY, AND EFFICACY OF INTRAMUSCULAR AND ORAL DELIVERY OF ERA-G333 RECOMBINANT RABIES VIRUS VACCINE TO BIG BROWN BATS ().

J Wildl Dis 2020 07 2;56(3):620-630. Epub 2020 Jan 2.

LYSSA LLC, 309 Pirkle Ferry Rd., Suite D300, Cumming, Georgia 30040, USA.

Attenuated strains of rabies virus (RABV) have been used for oral vaccination of wild carnivores in Europe and North America. However, some RABV vaccines caused clinical rabies in target animals. To improve the safety of attenuated RABV as an oral vaccine for field use, strategies using selection of escape mutants under monoclonal antibody neutralization pressure and reverse genetics-defined mutations have been used. We tested the safety, immunogenicity, and efficacy of one RABV construct, ERA-g333, developed with reverse genetics by intramuscular (IM) or oral (PO) routes in big brown bats (). Twenty-five bats received 5×10 mouse intracerebral median lethal doses (MICLD) of ERA-g333 by IM route, 10 received 5×10 MICLD of ERA-g333 by PO route, and 22 bats served as unvaccinated controls. Twenty-one days after vaccination, 44 bats were infected by IM route with 10 MICLD of RABV. We report both the immunogenicity and efficacy of ERA-g333 delivered by the IM route; no induction of humoral immunity was detected in bats vaccinated by the PO route. Two subsets of bats vaccinated IM (=5) and PO (=3) were not challenged, and none developed clinical rabies from ERA-g333. Scarce reports exist on the evaluation of oral rabies vaccines in insectivorous bats, although the strategy evaluated here may be feasible for future application to these important RABV reservoirs.
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http://dx.doi.org/10.7589/2019-04-108DOI Listing
July 2020

Volatile metabolomic signatures of rabies immunization in two mesocarnivore species.

PLoS Negl Trop Dis 2019 12 2;13(12):e0007911. Epub 2019 Dec 2.

USDA-APHIS-WS-NWRC, Fort Collins, Colorado, United States of America.

Rabies is a zoonotic disease caused by infection with rabies virus, which circulates naturally in several wild carnivore and bat reservoirs in the United States (US). The most important reservoir in the US from an animal and public health perspective is the raccoon (Procyon lotor). To prevent the westward expansion of a significant raccoon rabies epizootic along the eastern seaboard, an operational control program implementing oral rabies vaccination (ORV) has existed in the US since the 1990s. Recently, two vaccine efficacy studies conducted with raccoons and striped skunks (Mephitis mephitis) provided the opportunity to determine if volatile fecal metabolites might be used to non-invasively monitor ORV programs and/or predict virus protection for these species. The volatile metabolome is a rich source of information that may significantly contribute to our understanding of disease and infection. Fecal samples were collected at multiple time points from raccoons and striped skunks subjected to oral treatment with rabies vaccine (or sham). Intramuscular challenge with a lethal dose of rabies virus was used to determine protection status at six (raccoons) and 11 (skunks) months post-vaccination. In addition to fecal samples, blood was collected at various time points to permit quantitative assessment of rabies antibody responses arising from immunization. Feces were analyzed by headspace gas chromatography with mass spectrometric detection and the chromatographic responses were grouped according to cluster analysis. Cluster scores were subjected to multivariate analyses of variance (MANOVA) to determine if fecal volatiles may hold a signal of immunization status. Multiple regression was then used to build models of the measured immune responses based on the metabolomic data. MANOVA results identified one cluster associated with protective status of skunks and one cluster associated with protective status of raccoons. Regression models demonstrated considerably greater success in predicting rabies antibody responses in both species. This is the first study to link volatile compounds with measures of adaptive immunity and provides further evidence that the volatile metabolome holds great promise for contributing to our understanding of disease and infections. The volatile metabolome may be an important resource for monitoring rabies immunization in raccoons and striped skunks.
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http://dx.doi.org/10.1371/journal.pntd.0007911DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6907841PMC
December 2019

Placebo Oral Rabies Vaccine Bait Uptake by Small Indian Mongooses () in Southwestern Puerto Rico.

J Wildl Dis 2020 04 21;56(2):452-456. Epub 2019 Nov 21.

US Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services, National Wildlife Research Center, 4101 LaPorte Ave., Fort Collins, Colorado 80521, USA.

The small Indian mongoose () is a rabies reservoir in areas of the Caribbean including Puerto Rico, but no rabies vaccination program targeting this host exists. We used two derivatives of iophenoxic acid (IPA) to evaluate placebo oral rabies vaccine bait uptake by mongooses in southwestern Puerto Rico. We hand-distributed baits at an application rate of 200 baits/km at three, 400 ha, sites during autumn 2016 and spring 2017. Each site contained 90-100 cage traps in a 100 ha central trapping area. We used ethyl-IPA as a biological marker during the autumn and methyl-IPA during the spring. We live captured mongooses for 10 consecutive days, beginning 1 wk following bait application. We obtained a serum sample from captured mongooses and analyzed the sera for ethyl- and methyl-IPA by liquid chromatography-mass spectrometry. During autumn 2016, 63% (55/87) mongooses sampled were positive for ethyl-IPA. In spring 2017, 69% (85/123) of mongooses were positive for methyl-IPA. Pooling seasons, accounting for recaptures between years, and disregarding marker type, 74% (133/179) unique mongooses were positive for IPA biomarker, indicating bait consumption during either the autumn, spring, or both trials. We conclude that distributing baits at an application rate of 200 baits/km is sufficient to reach over 60% of the target mongoose population in dry forest habitats of Puerto Rico.
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April 2020

Rabies Surveillance Identifies Potential Risk Corridors and Enables Management Evaluation.

Viruses 2019 10 31;11(11). Epub 2019 Oct 31.

National Wildlife Research Center, United States Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services, Fort Collins, CO 80521, USA.

Intensive efforts are being made to eliminate the raccoon variant of rabies virus (RABV) from the eastern United States and Canada. The United States Department of Agriculture (USDA) Wildlife Services National Rabies Management Program has implemented enhanced rabies surveillance (ERS) to improve case detection across the extent of the raccoon oral rabies vaccination (ORV) management area. We evaluated ERS and public health surveillance data from 2006 to 2017 in three northeastern USA states using a dynamic occupancy modeling approach. Our objectives were to examine potential risk corridors for RABV incursion from the U.S. into Canada, evaluate the effectiveness of ORV management strategies, and identify surveillance gaps. ORV management has resulted in a decrease in RABV cases over time within vaccination zones (from ( ψ ¯ ) of 0.60 standard error (SE) = 0.03 in the spring of 2006 to ψ ¯ of 0.33 SE = 0.10 in the spring 2017). RABV cases also reduced in the enzootic area (from ψ ¯ of 0.60 SE = 0.03 in the spring of 2006 to ψ ¯ of 0.45 SE = 0.05 in the spring 2017). Although RABV occurrence was related to habitat type, greater impacts were associated with ORV and trap-vaccinate-release (TVR) campaigns, in addition to seasonal and yearly trends. Reductions in RABV occupancy were more pronounced in areas treated with Ontario Rabies Vaccine Bait (ONRAB) compared to RABORAL V-RG. Our approach tracked changes in RABV occurrence across space and time, identified risk corridors for potential incursions into Canada, and highlighted surveillance gaps, while evaluating the impacts of management actions. Using this approach, we are able to provide guidance for future RABV management.
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http://dx.doi.org/10.3390/v11111006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6893774PMC
October 2019

Immunogenicity of Ontario Rabies Vaccine for Small Indian Mongooses ().

J Wildl Dis 2020 01 30;56(1):224-228. Epub 2019 Sep 30.

US Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services, National Wildlife Research Center, 4101 LaPorte Ave., Fort Collins, Colorado 80521, USA.

Oral rabies vaccination is the principal strategy used to control rabies in wildlife. No oral rabies vaccine is licensed for small Indian mongooses (). The Ontario Rabies Vaccine Bait (ONRAB) is a human adenovirus type-5 rabies glycoprotein recombinant vaccine licensed for rabies control in striped skunks () in Canada and is under experimental evaluation in the US. We evaluated varying doses of ONRAB vaccine by direct instillation into the oral cavity with three groups of 10 mongooses: Group 1 received 10 TCID, group 2 received 10 TCID, and group 3 received 10 TCID of vaccine. Six control mongooses were sham-vaccinated with culture media. We collected a serum sample prior to vaccination and on days 14 and 30 postvaccination (PV). We quantified the level of rabies virus neutralizing antibodies (RVNA) from mongoose sera and compared titers among vaccinated groups and time points PV, where values greater than or equal to 0.1 IU/mL were considered positive. On day 14 PV, 87% (26 of 30, 95% confidence interval 70-95%) of vaccinates had seroconverted, whereas all vaccinates demonstrated RVNA by day 30 PV. There was a marginal effect of vaccine dose on group means of log-transformed RVNA titers at day 14 PV (=2.5, =0.099), but not day 30 PV. Sham-vaccinated animals were seronegative during all time points.
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January 2020

Analysis of Iophenoxic Acid Analogues in Small Indian Mongoose (Herpestes Auropunctatus) Sera for Use as an Oral Rabies Vaccination Biological Marker.

J Vis Exp 2019 05 31(147). Epub 2019 May 31.

US Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services, National Wildlife Research Center.

The small Indian mongoose (Herpestes auropunctatus) is a reservoir of rabies virus (RABV) in Puerto Rico and comprises over 70% of animal rabies cases reported annually. The control of RABV circulation in wildlife reservoirs is typically accomplished by a strategy of oral rabies vaccination (ORV). Currently no wildlife ORV program exists in Puerto Rico. Research into oral rabies vaccines and various bait types for mongooses has been conducted with promising results. Monitoring the success of ORV relies on estimating bait uptake by target species, which typically involves evaluating a change in RABV neutralizing antibodies (RVNA) post vaccination. This strategy may be difficult to interpret in areas with an active wildlife ORV program or in areas where RABV is enzootic and background levels of RVNA are present in reservoir species. In such situations, a biomarker incorporated with the vaccine or the bait matrix may be useful. We offered 16 captive mongooses placebo ORV baits containing ethyl-iophenoxic acid (et-IPA) in concentrations of 0.4% and 1% inside the bait and 0.14% in the external bait matrix. We also offered 12 captive mongooses ORV baits containing methyl-iophenoxic acid (me-IPA) in concentrations of 0.035%, 0.07% and 0.14% in the external bait matrix. We collected a serum sample prior to bait offering and then weekly for up to eight weeks post offering. We extracted Iophenoxic acids from sera into acetonitrile and quantified using liquid chromatography/mass spectrometry. We analyzed sera for et-IPA or me-IPA by liquid chromatography-mass spectrometry. We found adequate marking ability for at least eight and four weeks for et- and me-IPA, respectively. Both IPA derivatives could be suitable for field evaluation of ORV bait uptake in mongooses. Due to the longevity of the marker in mongoose sera, care must be taken to not confound results by using the same IPA derivative during consecutive evaluations.
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http://dx.doi.org/10.3791/59373DOI Listing
May 2019

Discovery and Characterization of Bukakata orbivirus (), a Novel Virus from a Ugandan Bat.

Viruses 2019 03 2;11(3). Epub 2019 Mar 2.

Department of Microbiology, Immunology, and Pathology, Colorado State University, Fort Collins, CO 80523, USA.

While serological and virological evidence documents the exposure of bats to medically-important arboviruses, their role as reservoirs or amplifying hosts is less well-characterized. We describe a novel orbivirus () isolated from an Egyptian fruit bat () trapped in 2013 in Uganda and named Bukakata orbivirus. This is the fifth orbivirus isolated from a bat, however genetic information had previously only been available for one bat-associated orbivirus. We performed whole-genome sequencing on Bukakata orbivirus and three other bat-associated orbiviruses (Fomede, Ife, and Japanaut) to assess their phylogenetic relationship within the genus and develop hypotheses regarding potential arthropod vectors. Replication kinetics were assessed for Bukakata orbivirus in three different vertebrate cell lines. Lastly, qRT-PCR and nested PCR were used to determine the prevalence of Bukakata orbivirus RNA in archived samples from three populations of Egyptian fruit bats and one population of cave-associated soft ticks in Uganda. Complete coding sequences were obtained for all ten segments of Fomede, Ife, and Japanaut orbiviruses and for nine of the ten segments for Bukakata orbivirus. Phylogenetic analysis placed Bukakata and Fomede in the tick-borne orbivirus clade and Ife and Japanaut within the /phlebotomine sandfly orbivirus clade. Further, Bukakata and Fomede appear to be serotypes of the species. Bukakata orbivirus replicated to high titers (10⁶⁻10⁷ PFU/mL) in Vero, BHK-21 [C-13], and R06E (Egyptian fruit bat) cells. Preliminary screening of archived bat and tick samples do not support Bukakata orbivirus presence in these collections, however additional testing is warranted given the phylogenetic associations observed. This study provided complete coding sequence for several bat-associated orbiviruses and in vitro characterization of a bat-associated orbivirus. Our results indicate that bats may play an important role in the epidemiology of viruses in the genus and further investigation is warranted into vector-host associations and ongoing surveillance efforts.
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http://dx.doi.org/10.3390/v11030209DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6466370PMC
March 2019

RACCOON () RESPONSE TO ONTARIO RABIES VACCINE BAITS (ONRAB) IN ST. LAWRENCE COUNTY, NEW YORK, USA.

J Wildl Dis 2019 07 8;55(3):645-653. Epub 2019 Jan 8.

2 US Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services, National Rabies Management Program, 59 Chenell Drive, Concord, New Hampshire 03301, USA.

Oral rabies vaccination (ORV) campaigns have been conducted annually in the US over the past two decades to prevent raccoon () rabies, which is enzootic along the eastern region of the country from southeastern Canada to Alabama. Because raccoon rabies has been eliminated from neighboring Canadian provinces, continued detection of the variant in the US is of concern due to the potential for infected raccoons to cross the border via the St. Lawrence River. Ontario Rabies Vaccine Baits (ONRAB) containing a live, recombinant human adenovirus expressing the rabies virus glycoprotein have been under experimental use in the US since 2011. We distributed ONRAB in St. Lawrence County, New York, from 2013 to 2015 as part of field trials to evaluate serologic responses in raccoons. Prior to ONRAB distribution, rabies virus neutralizing antibody (RVNA) seroprevalence in raccoons was 45.2% (183 of 405) and increased to 57.7% (165 of 286) after 3 yr of ONRAB baiting. Postbait RVNA seroprevalence increased each year, with a lower response observed in juvenile compared with adult raccoons. The pre-ONRAB seroprevalence detected in 2013 was relatively high and was likely impacted both by elevated rabies activity in the county and the use of ORV with a different vaccine bait for 14 consecutive years prior to our study. Tetracycline biomarker prevalence increased from 1.4% prior to ONRAB baiting to 51.3% from 2013 to 2015, demonstrating bait palatability to raccoons. These data complemented related field trials conducted in West Virginia and the northeastern US.
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http://dx.doi.org/10.7589/2018-09-216DOI Listing
July 2019

EFFECT OF HIGH-DENSITY ORAL RABIES VACCINE BAITING ON RABIES VIRUS NEUTRALIZING ANTIBODY RESPONSE IN RACCOONS ( PROCYON LOTOR).

J Wildl Dis 2019 04 3;55(2):399-409. Epub 2018 Dec 3.

3 US Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services, National Rabies Management Program, 59 Chenell Drive, Concord, New Hampshire 03301, USA.

From 2014 to 2016, we examined the effect of distributing oral rabies vaccine baits at high density (150 baits/km) in an area of Virginia, US that was naïve to oral rabies vaccination prior to the study. We also compared the effect of baiting at high density in a naïve area to baiting at standard density (75 baits/km) in an area that had been baited annually for 12 yr. Our results suggested that rabies virus seroconversion in raccoons ( Procyon lotor) gradually increased each year under the highdensity bait treatment. However, we did not detect a difference in seroconversion between bait density treatments. Virginia opossums ( Didelphis virginiana) were abundant in the study area and were a potentially important nontarget species that competed for oral rabies vaccine baits, but the ratio of opossums to raccoons in this study did not affect rabies virus neutralizing antibody response of the raccoon populations.
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http://dx.doi.org/10.7589/2018-05-138DOI Listing
April 2019

Raccoon () biomarker and rabies antibody response to varying oral rabies vaccine bait densities in northwestern Pennsylvania.

Heliyon 2018 Sep 6;4(9):e00754. Epub 2018 Sep 6.

U.S. Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services, National Wildlife Research Center, 4101 LaPorte Avenue, Fort Collins, CO 80521, USA.

Distribution of oral rabies vaccine baits has been used as a strategy for managing rabies in the United States since the 1990s. Since that time, efforts have been made to improve baiting strategies with a focus on bait density to maximize both efficiency and cost effectiveness. An optimal rabies management strategy includes a vaccine bait preferred by the target species that is distributed at the minimal density needed to achieve population immunity to prevent rabies spread. The purpose of our pilot study was to examine the effect of 75, 150, and 300 baits/km vaccine bait densities on rabies virus neutralizing antibody (RVNA) seroprevalence in raccoons (). Raboral V-RG® fishmeal polymer baits (Merial Inc. (now a part of Boehringer Ingelheim), Athens, Georgia) contain a tetracycline biomarker that was used to estimate bait consumption as another measure of intervention impact. Our results suggest that raccoon RVNA response increases as bait density increases, but the effect may not be sufficient to justify the cost except in the case of contingency actions or an epizootic. Non-target species, especially opossums () in certain areas, should be considered when determining an appropriate bait density to ensure sufficient baits are available for consumption by the target species.
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http://dx.doi.org/10.1016/j.heliyon.2018.e00754DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6129686PMC
September 2018

FIELD TRIALS OF ONTARIO RABIES VACCINE BAIT IN THE NORTHEASTERN USA, 2012-14.

J Wildl Dis 2018 10 24;54(4):790-801. Epub 2018 May 24.

2   US Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services, National Rabies Management Program, 59 Chenell Dr., Concord, New Hampshire 03301, USA.

In the US, rabies virus (RV) has been enzootic in raccoons ( Procyon lotor) since the late 1940s. Oral rabies vaccination (ORV) was implemented in the 1990s to halt the spread of raccoon RV and continues to be used as a wildlife management tool. Our objective was to evaluate a recombinant human adenovirus-rabies virus glycoprotein vaccine in northern New York, Vermont, and New Hampshire over a 3-yr period, using changes in RV neutralizing antibody (RVNA) seroprevalence in raccoon populations as an immunologic index of ORV impact. Vaccine baits were distributed at 75 baits/km and 750-m flight-line spacing in the study area. Animal sampling occurred during 10-d intervals pre- and post-ORV during 2012-14 within eight study cells: four northern cells had a history of ORV with a different vaccine for 3 or more years prior and four southern cells were ORV naive. Baseline raccoon RVNA seroprevalence was 27.3% ( n=1,079, 95% confidence interval [CI]: 24.8-30.1) before ORV in 2012. Raccoon RVNA seroprevalence averaged 68.5% ( n=1,551, 95% CI: 66.2-70.8) post-ORV during the 3-yr study. The RVNA seroprevalence levels in this study were considered to be adequate for stopping raccoon RV transmission and supported and expanded the results from a West Virginia field trial, as well as earlier evaluations along the Canada-US border.
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http://dx.doi.org/10.7589/2017-09-242DOI Listing
October 2018

Livestock abundance predicts vampire bat demography, immune profiles and bacterial infection risk.

Philos Trans R Soc Lond B Biol Sci 2018 05;373(1745)

Odum School of Ecology, University of Georgia, Athens, GA 30602, USA.

Human activities create novel food resources that can alter wildlife-pathogen interactions. If resources amplify or dampen, pathogen transmission probably depends on both host ecology and pathogen biology, but studies that measure responses to provisioning across both scales are rare. We tested these relationships with a 4-year study of 369 common vampire bats across 10 sites in Peru and Belize that differ in the abundance of livestock, an important anthropogenic food source. We quantified innate and adaptive immunity from bats and assessed infection with two common bacteria. We predicted that abundant livestock could reduce starvation and foraging effort, allowing for greater investments in immunity. Bats from high-livestock sites had higher microbicidal activity and proportions of neutrophils but lower immunoglobulin G and proportions of lymphocytes, suggesting more investment in innate relative to adaptive immunity and either greater chronic stress or pathogen exposure. This relationship was most pronounced in reproductive bats, which were also more common in high-livestock sites, suggesting feedbacks between demographic correlates of provisioning and immunity. Infection with both and haemoplasmas were correlated with similar immune profiles, and both pathogens tended to be less prevalent in high-livestock sites, although effects were weaker for haemoplasmas. These differing responses to provisioning might therefore reflect distinct transmission processes. Predicting how provisioning alters host-pathogen interactions requires considering how both within-host processes and transmission modes respond to resource shifts.This article is part of the theme issue 'Anthropogenic resource subsidies and host-parasite dynamics in wildlife'.
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http://dx.doi.org/10.1098/rstb.2017.0089DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5882995PMC
May 2018

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

Infect Ecol Epidemiol 2018 21;8(1):1439215. Epub 2018 Feb 21.

Division of Vector-borne Diseases, Arbovirus Diseases Branch, Centers for Disease Control and Prevention, Fort Collins, CO, USA.

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. 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.  Key findings include the presence of neutralizing antibodies against RVFV in 5/52 (9.6%) of little epauletted fruit bats () 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. The data presented demonstrate the widespread exposure of bats in Uganda to arboviruses, and highlight particular virus-bat associations that warrant further investigation.
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http://dx.doi.org/10.1080/20008686.2018.1439215DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5827769PMC
February 2018

Comparison of a Micro-Neutralization Test with the Rapid Fluorescent Focus Inhibition Test for Measuring Rabies Virus Neutralizing Antibodies.

Trop Med Infect Dis 2017 7;2(3). Epub 2017 Jul 7.

National Wildlife Research Center, US Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services, 4101 LaPorte Avenue, Fort Collins, Colorado, 80521, USA.

The rapid fluorescent focus inhibition test (RFFIT) is routinely used in the United States to measure rabies virus neutralizing antibodies (rVNA). RFFIT has a long history of reproducible and reliable results. The test has been modified over the years to use smaller volumes of reagents and samples, but requires a 50 μL minimum volume of test serum. To conduct pathogenesis studies, small laboratory animals such as mice are regularly tested for rVNA, but the minimum volume for a standard RFFIT may be impossible to obtain, particularly in scenarios of repeated sampling. To address this problem, a micro-neutralization test was developed previously. In the current study, the micro-neutralization test was compared to the RFFIT using 129 mouse serum samples from rabies vaccine studies. Using a cut-off value of 0.1 IU/mL, the sensitivity, specificity, and concordance of the micro-neutralization test were 100%, 97.5%, and 98%, respectively. The geometric mean titer of all samples above the cut-off was 2.0 IU/mL using RFFIT and 3.4 IU/mL using the micro-neutralization test, indicating that titers determined using the micro-neutralization test are not equivalent to RFFIT titers. Based on four rVNA-positive hamster serum samples, the intra-assay coefficient of variability was 24% and inter-assay coefficient of variability was 30.4 %. These results support continued use of the micro-neutralization test to determine rabies virus neutralizing antibody titers for low-volume serum samples.
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http://dx.doi.org/10.3390/tropicalmed2030024DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5568636PMC
July 2017

Predicting spatial spread of rabies in skunk populations using surveillance data reported by the public.

PLoS Negl Trop Dis 2017 Jul 31;11(7):e0005822. Epub 2017 Jul 31.

National Wildlife Research Center, United States Department of Agriculture, Wildlife Services, Fort Collins, Colorado, United States of America.

Background: Prevention and control of wildlife disease invasions relies on the ability to predict spatio-temporal dynamics and understand the role of factors driving spread rates, such as seasonality and transmission distance. Passive disease surveillance (i.e., case reports by public) is a common method of monitoring emergence of wildlife diseases, but can be challenging to interpret due to spatial biases and limitations in data quantity and quality.

Methodology/principal Findings: We obtained passive rabies surveillance data from dead striped skunks (Mephitis mephitis) in an epizootic in northern Colorado, USA. We developed a dynamic patch-occupancy model which predicts spatio-temporal spreading while accounting for heterogeneous sampling. We estimated the distance travelled per transmission event, direction of invasion, rate of spatial spread, and effects of infection density and season. We also estimated mean transmission distance and rates of spatial spread using a phylogeographic approach on a subsample of viral sequences from the same epizootic. Both the occupancy and phylogeographic approaches predicted similar rates of spatio-temporal spread. Estimated mean transmission distances were 2.3 km (95% Highest Posterior Density (HPD95): 0.02, 11.9; phylogeographic) and 3.9 km (95% credible intervals (CI95): 1.4, 11.3; occupancy). Estimated rates of spatial spread in km/year were: 29.8 (HPD95: 20.8, 39.8; phylogeographic, branch velocity, homogenous model), 22.6 (HPD95: 15.3, 29.7; phylogeographic, diffusion rate, homogenous model) and 21.1 (CI95: 16.7, 25.5; occupancy). Initial colonization probability was twice as high in spring relative to fall.

Conclusions/significance: Skunk-to-skunk transmission was primarily local (< 4 km) suggesting that if interventions were needed, they could be applied at the wave front. Slower viral invasions of skunk rabies in western USA compared to a similar epizootic in raccoons in the eastern USA implies host species or landscape factors underlie the dynamics of rabies invasions. Our framework provides a straightforward method for estimating rates of spatial spread of wildlife diseases.
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http://dx.doi.org/10.1371/journal.pntd.0005822DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5552346PMC
July 2017

Diversity and phylogenetic relationships among Bartonella strains from Thai bats.

PLoS One 2017 20;12(7):e0181696. Epub 2017 Jul 20.

Center for Global Health, Centers for Disease Control and Prevention, Atlanta, GA, United States of America.

Bartonellae are phylogenetically diverse, intracellular bacteria commonly found in mammals. Previous studies have demonstrated that bats have a high prevalence and diversity of Bartonella infections globally. Isolates (n = 42) were obtained from five bat species in four provinces of Thailand and analyzed using sequences of the citrate synthase gene (gltA). Sequences clustered into seven distinct genogroups; four of these genogroups displayed similarity with Bartonella spp. sequences from other bats in Southeast Asia, Africa, and Eastern Europe. Thirty of the isolates representing these seven genogroups were further characterized by sequencing four additional loci (ftsZ, nuoG, rpoB, and ITS) to clarify their evolutionary relationships with other Bartonella species and to assess patterns of diversity among strains. Among the seven genogroups, there were differences in the number of sequence variants, ranging from 1-5, and the amount of nucleotide divergence, ranging from 0.035-3.9%. Overall, these seven genogroups meet the criteria for distinction as novel Bartonella species, with sequence divergence among genogroups ranging from 6.4-15.8%. Evidence of intra- and intercontinental phylogenetic relationships and instances of homologous recombination among Bartonella genogroups in related bat species were found in Thai bats.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0181696PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5519213PMC
September 2017

Management and modeling approaches for controlling raccoon rabies: The road to elimination.

PLoS Negl Trop Dis 2017 03 16;11(3):e0005249. Epub 2017 Mar 16.

United States Department of Agriculture, National Wildlife Research Center, Fort Collins, Colorado, United States of America.

Rabies is an ancient viral disease that significantly impacts human and animal health throughout the world. In the developing parts of the world, dog bites represent the highest risk of rabies infection to people, livestock, and other animals. However, in North America, where several rabies virus variants currently circulate in wildlife, human contact with the raccoon rabies variant leads to the highest per capita population administration of post-exposure prophylaxis (PEP) annually. Previous rabies variant elimination in raccoons (Canada), foxes (Europe), and dogs and coyotes (United States) demonstrates that elimination of the raccoon variant from the eastern US is feasible, given an understanding of rabies control costs and benefits and the availability of proper tools. Also critical is a cooperatively produced strategic plan that emphasizes collaborative rabies management among agencies and organizations at the landscape scale. Common management strategies, alone or as part of an integrated approach, include the following: oral rabies vaccination (ORV), trap-vaccinate-release (TVR), and local population reduction. As a complement, mathematical and statistical modeling approaches can guide intervention planning, such as through contact networks, circuit theory, individual-based modeling, and others, which can be used to better understand and predict rabies dynamics through simulated interactions among the host, virus, environment, and control strategy. Strategies derived from this ecological lens can then be optimized to produce a management plan that balances the ecological needs and program financial resources. This paper discusses the management and modeling strategies that are currently used, or have been used in the past, and provides a platform of options for consideration while developing raccoon rabies virus elimination strategies in the US.
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http://dx.doi.org/10.1371/journal.pntd.0005249DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5354248PMC
March 2017

Exposure to Lyssaviruses in Bats of the Democratic Republic of the Congo.

J Wildl Dis 2017 04 2;53(2):408-410. Epub 2017 Feb 2.

2 Poxvirus and Rabies Branch, Division of High-Consequence Pathogens and Pathology, National Center for Emerging Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, 1600 Clifton Road NE, Atlanta, Georgia 30333, USA.

Lyssavirus infections in the Democratic Republic of Congo are poorly documented. We examined 218 bats. No lyssavirus antigens were detected but Lagos bat virus (LBV) neutralizing antibodies (VNA) were detected in Eidolon helvum and Myonycteris torquata . Four samples with LBV VNA reacted against Shimoni bat virus.
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http://dx.doi.org/10.7589/2016-06-122DOI Listing
April 2017

Ecological Potential for Rabies Virus Transmission via Scavenging of Dead Bats by Mesocarnivores.

J Wildl Dis 2017 04 17;53(2):382-385. Epub 2017 Jan 17.

3 US Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services, 8836 N 23 Avenue, Suite 2, Phoenix, Arizona 85021, USA.

Multiple species of bats are reservoirs of rabies virus in the Americas and are occasionally the source of spillover infections into mesocarnivore species. Although rabies transmission generally is assumed to occur via bite, laboratory studies have demonstrated the potential for rabies transmission via ingestion of rabid animals. We investigated the ecological potential for this mode of transmission by assessing mesocarnivore scavenging behavior of dead bats in suburban habitats of Flagstaff, Arizona, US. In autumn 2013, summer 2014, and autumn 2015, we placed 104 rabies-negative bat carcasses either near buildings, in wildland areas, or in residential yards and then monitored them with trail cameras for 5 d. Overall, 52 (50%) bat carcasses were scavenged, with 39 (75%) of those scavenged by striped skunks ( Mephitis mephitis ). Within our study area, striped skunks had a higher ecological potential to contract rabies via ingestion of bat carcasses compared to other mesocarnivore species, due both to a greater number of encounters and a higher probability of ingestion per encounter (91%), and they were significantly more likely to approach bat carcasses in yards than in wildland areas. Raccoons ( Procyon lotor ) and gray foxes ( Urocyon cinereoargenteus ) had fewer encounters (nine and 13, respectively) and lower probability of ingesting bats (33% and 8%, respectively).
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http://dx.doi.org/10.7589/2016-09-203DOI Listing
April 2017

Inferring infection hazard in wildlife populations by linking data across individual and population scales.

Ecol Lett 2017 03 16;20(3):275-292. Epub 2017 Jan 16.

Department of Ecology & Evolutionary Biology, UCLA, Los Angeles, CA, 90095, USA.

Our ability to infer unobservable disease-dynamic processes such as force of infection (infection hazard for susceptible hosts) has transformed our understanding of disease transmission mechanisms and capacity to predict disease dynamics. Conventional methods for inferring FOI estimate a time-averaged value and are based on population-level processes. Because many pathogens exhibit epidemic cycling and FOI is the result of processes acting across the scales of individuals and populations, a flexible framework that extends to epidemic dynamics and links within-host processes to FOI is needed. Specifically, within-host antibody kinetics in wildlife hosts can be short-lived and produce patterns that are repeatable across individuals, suggesting individual-level antibody concentrations could be used to infer time since infection and hence FOI. Using simulations and case studies (influenza A in lesser snow geese and Yersinia pestis in coyotes), we argue that with careful experimental and surveillance design, the population-level FOI signal can be recovered from individual-level antibody kinetics, despite substantial individual-level variation. In addition to improving inference, the cross-scale quantitative antibody approach we describe can reveal insights into drivers of individual-based variation in disease response, and the role of poorly understood processes such as secondary infections, in population-level dynamics of disease.
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http://dx.doi.org/10.1111/ele.12732DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7163542PMC
March 2017

Transmission or Within-Host Dynamics Driving Pulses of Zoonotic Viruses in Reservoir-Host Populations.

PLoS Negl Trop Dis 2016 Aug 4;10(8):e0004796. Epub 2016 Aug 4.

Disease Dynamics Unit, Department of Veterinary Medicine, University of Cambridge, Cambridge, United Kingdom.

Progress in combatting zoonoses that emerge from wildlife is often constrained by limited knowledge of the biology of pathogens within reservoir hosts. We focus on the host-pathogen dynamics of four emerging viruses associated with bats: Hendra, Nipah, Ebola, and Marburg viruses. Spillover of bat infections to humans and domestic animals often coincides with pulses of viral excretion within bat populations, but the mechanisms driving such pulses are unclear. Three hypotheses dominate current research on these emerging bat infections. First, pulses of viral excretion could reflect seasonal epidemic cycles driven by natural variations in population densities and contact rates among hosts. If lifelong immunity follows recovery, viruses may disappear locally but persist globally through migration; in either case, new outbreaks occur once births replenish the susceptible pool. Second, epidemic cycles could be the result of waning immunity within bats, allowing local circulation of viruses through oscillating herd immunity. Third, pulses could be generated by episodic shedding from persistently infected bats through a combination of physiological and ecological factors. The three scenarios can yield similar patterns in epidemiological surveys, but strategies to predict or manage spillover risk resulting from each scenario will be different. We outline an agenda for research on viruses emerging from bats that would allow for differentiation among the scenarios and inform development of evidence-based interventions to limit threats to human and animal health. These concepts and methods are applicable to a wide range of pathogens that affect humans, domestic animals, and wildlife.
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http://dx.doi.org/10.1371/journal.pntd.0004796DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4973921PMC
August 2016
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