Biology subjects

Gilbert, A. T.

Publications and source records attributed to Gilbert, A. T..

6 recordsLinked to original sources

bioRxiv2026

Ethyl-iophenoxic acid as a serum biomarker for marsupial species in oral bait trials

Ethyl-iophenoxic acid (Et-IPA) is widely recognized as a useful biomarker to confirm oral bait consumption in eutherian species. In historical studies on marsupials, Et-IPA was rapidly eliminated from brushtail possums (Trichosurus vulpecula) and swamp wallabies (Wallabia bicolor) suggesting limited use for marsupial species. However, a 1 mg oral dose of Et-IPA was detectable in the marsupial Tasmanian devils (Sarcophilus harrisii) for [≥] 56 days suggesting the biomarker can be used in a devil bait vaccine program. To assess Et-IPA marking in off-target marsupials that may consume baits, we administered 1 mg oral doses of Et-IPA to brushtail possums, forester kangaroos (Macropus giganteus tasmaniensis), spotted-tailed quolls (Dasyurus maculatus) and eastern quolls (Dasyurus viverrinus). Liquid chromatography with tandem mass spectrometry was used to detect and quantify serum Et-IPA. Et-IPA was detected in the serum on day 2 but was not detected by day 14 in any of the species tested, including the two quoll species which are in the same carnivorous Dasyuridae family as the devils. The rapid elimination of Et-IPA in the marsupials included in this study suggests it is not useful as a biomarker for these species. Furthermore, rapid elimination in the kangaroos and possums suggests that Et-IPA is unlikely to accumulate in the food chain following distribution of Et-IPA-marked oral bait vaccines for Tasmanian devils. Short summary for non-expertsA recent study in Tasmanian devils (Sarcophilus harrisii) challenged the concept that ethyl iophenoxic acid (Et-IPA) is not a useful serum biomarker for marsupials. Using the same sensitive liquid chromatography-tandem mass spectrometry method we detected serum Et-IPA in four marsupial species on day two post-ingestion but by day 14, serum Et-IPA was undetectable. These findings indicate that Et-IPA is an unsuitable biomarker for these species and suggest that Et-IPA from devil bait vaccines is unlikely to bioaccumulate in the Tasmanian environment.

zoology↗

bioRxiv2023

Spatiotemporal overlap and contact rates among small Indian mongooses and free-roaming domestic dogs in Puerto Rico: Implications for rabies virus transmission

Small Indian mongooses (Urva auropunctata) are the primary terrestrial wildlife rabies reservoir on Puerto Rico, the Dominican Republic, Cuba and Grenada, where they represent a risk to public health through direct human exposure and through transmission of rabies virus to domestic animals that have close association with humans. Historically rabies virus was introduced via domestic dogs and then later shifted into mongoose populations on Puerto Rico and other islands, yet domestic dog-mongoose ecological interactions have been understudied throughout the Caribbean. In this study, we derived daily activity patterns from baited camera traps, and investigated the use of proximity and GPS tracking data acquired concomitantly from mongooses and free-ranging domestic dogs (FRDD) to characterise intra- and interspecific contacts and estimate contact rates. Our results highlight that although mongooses and FRDD are both relatively active in late afternoon, close interspecific contacts only occurred among 4% of collared mongoose-dog dyads, were infrequent (range: 0 - 0.19; median = 0 contacts per day), and were spatially restricted to road and forest edges. Mongooses were only documented to contact feral FRDD, whereas no mongoose contacts with stray FRDD were detected. The space use by stray FRDD and association to humans may play a role in limiting direct contacts with mongooses and the associated risks of rabies virus cross-species transmission. Intraspecific contacts were documented among 11% of collared mongoose-mongoose dyads, occurred at a rate ranging between 0 - 0.57 (median = 0) contacts per day, and took place within wildlands. Intraspecific contacts were documented among 30% of collared dog dyads, at rates ranging between 0 - 3.37 (median = 0) contacts per day, which was more frequent contact than observed for collared mongooses ({chi}2 = 8.84; DF =2; P = 0.012). All dog-dog contacts occurred in proximity to human residential development and involved both stray-stray and stray-feral FRDD collared dyads. Feral FRDD may represent a rabies virus vector between mongooses and FRDD living close to humans. Home range overlap was a significant predictor of contact rates (P < 0.001) among intra- and interspecific dyads of both species and may represent a useful proxy for contact between species that also overlap in daily activity patterns. Transitional areas between wildlands and human residential development could represent hotspots for infectious disease transmission between mongooses and feral FRDDs. Characterization and quantification of contact rates in mongooses and FRDDs across the wildland-urban gradient across wet and dry seasons could help to inform animal rabies control strategies on Puerto Rico and other Caribbean islands with enzootic mongoose rabies.

animal behavior and cognition↗

bioRxiv2022

Evaluation of oral baits and distribution methods for Tasmanian devils (Sarcophilus harrisii)

ContextDiseases are increasingly contributing to wildlife population declines. Tasmanian devil (Sarcophilus harrisii) populations have locally declined by 82% largely due to the morbidity and mortality associated with two independent transmissible devil facial tumours (DFT1 and DFT2). Toxic baits are often used as a management tool for controlling vertebrate pest populations in Australia, but in other areas of the world oral baits are also used to deliver vaccines or pharmaceuticals to wildlife. Oral vaccine bait products have been distributed for more than 50 years at a landscape scale to protect wildlife from rabies virus and contributed to the elimination of fox rabies from more than ten European nations. An oral bait vaccine to protect against devil facial tumours has been proposed as a management tool to improve the population health, resiliency and fitness of wild Tasmanian devils. AimOur goal was to evaluate the potential use of edible baits as vehicles for vaccine delivery to Tasmanian devils. MethodWe tested placebo versions of baits that are already used in Australia. Key resultsCaptive devils consumed all types of placebo baits but exhibited a preference for ruminant- and fish-based baits. Captive devils also consumed inert capsules inserted into placebo baits. Bait fate trials in the field revealed that baits were generally removed within 24 hours. Tasmanian pademelons (Thylogale billardierii), brushtail possums (Trichosurus vulpecula), and Eastern quolls (Dasyurus viverrinus) were the most common nontarget bait competitors at six private properties in southern Tasmania; wild devils removed approximately 5% of ground baits at these sites. We also evaluated an automated bait dispenser, which reduced nontarget uptake and resulted in over 50% of the baits being removed by devils. ConclusionsThis study demonstrates that captive and wild devils will accept and consume placebo versions of commercial baits. Bait dispensers or modified baits or baiting strategies are needed to increase bait uptake by devils. ImplicationsBait dispensers can be used at a regional scale to deliver baits to Tasmanian devils. These could act as vehicles for preventive or therapeutic vaccines to mitigate the impacts of disease on devil populations. Short summaryThis study aimed to test oral baits as potential vaccine delivery vehicles for Tasmanian devils. Captive and wild devils consumed placebo versions of commercial baits used on mainland Australia. Abundant non-target species, such as brushtail possums, Tasmanian pademelons, and eastern quolls consumed most baits in the wild. Implementation of automated bait dispensers increased bait uptake by devils to over 50% at the same regional field sites.

zoology↗

bioRxiv2021

Ethyl-Iophenoxic acid as a serum marker for oral baiting of carnivorous marsupials

ContextEthyl-Iophenoxic acid (Et-IPA) has been widely used as a bait biomarker to determine oral bait consumption by vertebrate wildlife species. Oral bait vaccines have been delivered to numerous wildlife species to protect them from disease. The Tasmanian devil (Sarcophilis harrisii), the largest extant carnivorous marsupial species, is threatened by the transmissible cancers known as devil facial tumour disease (DFTD). Development of a protective DFTD vaccine is underway, and an oral bait has been proposed to deliver the vaccine in the wild. The bait delivery system requires a biomarker that can be detected for several months post-consumption in Tasmanian devils. AimTo determine the suitability of Et-IPA as a bait biomarker in the Tasmanian devil. MethodTwo Tasmanian devils were fed 50 mg Et-IPA (4.5 to 7.1 mg Et-IPA/kg bodyweight). Liquid chromatography with tandem mass spectrometry (LC-MS/-MS) was used to directly measure Et-IPA in baseline serum samples and samples collected on days 1, 14, 26 and 56 post-baiting. Key resultBoth devils retained serum Et-IPA concentrations at two orders of magnitude above negative control sera when this study concluded. ConclusionsEt-IPA is a useful bait biomarker for Tasmanian devils and can be included in future DFTD bait vaccine field trials to determine bait vaccine uptake.

zoology↗

bioRxiv2021

Accounting for animal movement improves vaccination strategies against wildlife disease in heterogeneous landscapes

Oral baiting is used to deliver vaccines to wildlife to prevent, control, and eliminate infectious diseases. A central challenge is how to spatially distribute baits to maximize encounters by target animal populations, particularly in urban and suburban areas where wildlife like raccoons (Procyon lotor) are abundant and baits are delivered along roads. Methods from movement ecology that quantify movement and habitat selection could help to optimize baiting strategies by more effectively targeting wildlife populations across space. We developed a spatially explicit, individual-based model of raccoon movement and oral rabies vaccine seroconversion to examine whether and when baiting strategies that match raccoon movement patterns perform better than currently employed baiting strategies in an oral rabies vaccination zone in greater Burlington, Vermont, USA. Habitat selection patterns estimated from locally radio-collared raccoons were used to parameterize movement simulations. We then used our simulations to estimate raccoon population rabies seroprevalence under currently used baiting strategies (actual baiting) relative to habitat selection-based baiting strategies (habitat baiting). We conducted simulations on the Burlington landscape and artificial landscapes that varied in heterogeneity relative to Burlington in the proportion and patch size of preferred habitats. We found that the benefits of habitat baiting strongly depended on the magnitude and variability of raccoon habitat selection and the degree of landscape heterogeneity within the baiting area. Habitat baiting improved seroprevalence over actual baiting for raccoons characterized as habitat specialists but not for raccoons that displayed weak habitat selection similar to radio-collared individuals--except when baits were delivered off roads where preferred habitat coverage and complexity was more pronounced. In contrast, in artificial landscapes with either more strongly juxtaposed favored habitats and/or higher proportions of favored habitats, habitat baiting performed better than actual baiting, even when raccoons displayed weak habitat preferences and where baiting was constrained to roads. Our results suggest that habitat selection-based baiting could increase raccoon population seroprevalence in urban-suburban areas, where practical, given the heterogeneity and availability of preferred habitat types in those areas. Our novel simulation approach provides a flexible framework to test alternative baiting strategies in multiclass landscapes to optimize bait distribution strategies.

ecology↗

bioRxiv2019

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

O_LIAnimal movement influences the spatial spread of wildlife infectious diseases through host-host contact structure and hence pathogen transmission. Wildlife disease hosts vary in characteristics related to pathogen transmission, which can increase the spread and intensity of disease outbreaks. The consequences of home range size variation on wildlife disease dynamics are poorly understood, but could help to predict disease spread and determine more effective disease management strategies.\nC_LIO_LIWe developed a spatially-explicit individual-based model to examine the effect of 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 host home range area variation decreases vaccination effectiveness in wildlife host populations following pathogen invasion into a vaccination zone.\nC_LIO_LIWe simulated raccoon demography and RABV dynamics across a range of magnitudes and variances in weekly home range radius distributions for raccoons, and compared results to conditions that assumed a fixed host home range area. We examined how variable host home range radius distributions influenced the relative effectiveness of three components of orally-baited raccoon RABV vaccination (ORV) programs--timing and frequency of bait delivery, width of the zone where ORV baits were delivered, and proportion of hosts immunized.\nC_LIO_LIVariability in home range radius distributions increased RABV spread rates by 1.2 - 5.2-fold compared to simulations with fixed radii. More variable host home range radius distributions decreased relative vaccination effectiveness by 71% compared to less variable host home range radius distributions under conventional vaccination conditions. We found that vaccination timing was more influential for vaccination effectiveness than vaccination frequency or vaccination zone width.\nC_LIO_LIOur results suggest that variation in wildlife home range exploration increases the spatial spread and incidence of wildlife disease. Our vaccination results underscore the importance of prioritizing individual-level space use data collection to understand the dynamics of wildlife diseases and plan their effective control and elimination.\nC_LI

ecology↗