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USGS2024

Linking avian malaria parasitemia estimates from quantitative PCR and microscopy reveals new infection patterns in Hawai'i

Plasmodium parasites infect thousands of species and provide an exceptional system for studying host-pathogen dynamics, especially for multi-host pathogens. However, understanding these interactions requires an accurate assay of infection. Assessing Plasmodium infections using microscopy on blood smears often misses infections with low parasitemias (the fractions of cells infected), and biases in malaria prevalence estimates will differ among hosts that differ in mean parasitemias. We examined Plasmodium relictum infection and parasitemia using both microscopy of blood smears and quantitative polymerase chain reaction (qPCR) on 299 samples from multiple bird species in Hawai'i and fit models to predict parasitemias from qPCR cycle threshold (Ct) values. We used these models to quantify the extent to which microscopy underestimated infection prevalence and to more accurately estimate infection patterns for each species for a large historical study done by microscopy. We found that most qPCR-positive wild-caught birds in Hawaii had low parasitemias (Ct scores ≥35), which were rarely detected by microscopy. The fraction of infections missed by microscopy differed substantially among eight species due to differences in species’ parasitemia levels. Infection prevalence was likely 4–5-fold higher than previous microscopy estimates for three introduced species, including Zosterops japonicus , Hawaii’s most abundant forest bird, which had low average parasitemias. In contrast, prevalence was likely only 1.5–2.3-fold higher than previous estimates for Himatione sanguinea and Chlorodrepanis virens , two native species with high average parasitemias. Our results indicate that relative patterns of infection among species differ substantially from those observed in previous microscopy studies, and that differences depend on variation in parasitemias among species. Although microscopy of blood smears is useful for estimating the frequency of different Plasmodium stages and host attributes, more sensitive quantitative methods, including qPCR, are needed to accurately estimate and compare infection prevalence among host species.

Hawai'i↗

USGS2013

Evaluation of blood and muscle tissues for molecular detection and characterization of hematozoa infections in northern pintails ( Anas acuta ) wintering in California

Information on the molecular detection of hematozoa from different tissue types and multiple years would be useful to inform sample collection efforts and interpret results of meta-analyses or investigations spanning multiple seasons. In this study, we tested blood and muscle tissue collected from northern pintails ( Anas acuta ) during autumn and winter of different years to evaluate prevalence and genetic diversity of Leucocytozoon , Haemoproteus , and Plasmodium infections in this abundant waterfowl species of the Central Valley of California. We first compared results for paired blood and wing muscle samples to assess the utility of different tissue types for molecular investigations of haemosporidian parasites. Second, we explored inter-annual variability of hematozoa infection in Central Valley northern pintails and investigated possible effects of age, sex, and sub-region of sample collection on estimated parasite detection probability and prevalence. We found limited evidence for differences between tissue types in detection probability and prevalence of Leucocytozoon , Haemoproteus , and Plasmodium parasites, which supports the utility of both sample types for obtaining information on hematozoan infections. However, we detected 11 haemosporidian mtDNA cyt b haplotypes in blood samples vs. six in wing muscle tissue collected during the same sample year suggesting an advantage to using blood samples for investigations of genetic diversity. Estimated prevalence of Leucocytozoon parasites was greater during 2006–2007 as compared to 2011–2012 and four unique haemosporidian mtDNA cyt b haplotypes were detected in the former sample year but not in the latter. Seven of 15 mtDNA cyt b haplotypes detected in northern pintails had 100% identity with previously reported hematozoa lineages detected in waterfowl ( Haemoproteus and Leucocytozoon ) or other avian taxa ( Plasmodium ) providing support for lack of host specificity for some parasite lineages.

California↗

USGS2013

Using occupancy models to investigate the prevalence of ectoparasitic vectors on hosts: an example with fleas on prairie dogs

Ectoparasites are often difficult to detect in the field. We developed a method that can be used with occupancy models to estimate the prevalence of ectoparasites on hosts, and to investigate factors that influence rates of ectoparasite occupancy while accounting for imperfect detection. We describe the approach using a study of fleas (Siphonaptera) on black-tailed prairie dogs ( Cynomys ludovicianus ). During each primary occasion (monthly trapping events), we combed a prairie dog three consecutive times to detect fleas (15 s/combing). We used robust design occupancy modeling to evaluate hypotheses for factors that might correlate with the occurrence of fleas on prairie dogs, and factors that might influence the rate at which prairie dogs are colonized by fleas. Our combing method was highly effective; dislodged fleas fell into a tub of water and could not escape, and there was an estimated 99.3% probability of detecting a flea on an occupied host when using three combings. While overall detection was high, the probability of detection was always <1.00 during each primary combing occasion, highlighting the importance of considering imperfect detection. The combing method (removal of fleas) caused a decline in detection during primary occasions, and we accounted for that decline to avoid inflated estimates of occupancy. Regarding prairie dogs, flea occupancy was heightened in old/natural colonies of prairie dogs, and on hosts that were in poor condition. Occupancy was initially low in plots with high densities of prairie dogs, but, as the study progressed, the rate of flea colonization increased in plots with high densities of prairie dogs in particular. Our methodology can be used to improve studies of ectoparasites, especially when the probability of detection is low. Moreover, the method can be modified to investigate the co-occurrence of ectoparasite species, and community level factors such as species richness and interspecific interactions.

International Journal for Parasitology: Parasites ↗

USGS2015

Evidence for intercontinental parasite exchange through molecular detection and characterization of haematozoa in northern pintails ( Anas acuta ) sampled throughout the North Pacific Basin

Empirical evidence supports wild birds as playing a role in the interhemispheric exchange of bacteria and viruses; however, data supporting the redistribution of parasites among continents are limited. In this study, the hypothesis that migratory birds contribute to the redistribution of parasites between continents was tested by sampling northern pintails (Anas acuta) at locations throughout the North Pacific Basin in North America and East Asia for haemosporidian infections and assessing the genetic evidence for parasite exchange. Of 878 samples collected from birds in Alaska (USA), California (USA), and Hokkaido (Japan) during August 2011 - May 2012 and screened for parasitic infections using molecular techniques, Leucocytozoon, Haemoproteus, and Plasmodium parasites were detected in 555 (63%), 44 (5%), and 52 (6%) samples, respectively. Using an occupancy modeling approach, the probability of detecting parasites via replicate genetic tests was estimated to be high (p ≥ 0.95). Multi-model inference supported variation of Leucocytozoon parasite prevalence by northern pintail age class and geographic location of sampling in contrast to Haemoproteus and Plasmodium parasites for which there was only support for variation in parasite prevalence by sampling location. Thirty-one unique mitochondrial DNA haplotypes were detected among haematozoa infecting northern pintails including seven lineages shared between samples from North America and Japan. The finding of identical parasite haplotypes at widely distributed geographic locations and general lack of genetic structuring by continent in phylogenies for Leucocytozoon and Plasmodium provides evidence for intercontinental genetic exchange of haemosporidian parasites. Results suggest that migratory birds, including waterfowl, could therefore facilitate the introduction of avian malaria and other haemosporidia to novel hosts and spatially distant regions.

Alaska, California↗

USGS2015

Prevalence and genetic diversity of haematozoa in South American waterfowl and evidence for intercontinental redistribution of parasites by migratory birds

To understand the role of migratory birds in the movement and transmission of haematozoa within and between continental regions, we examined 804 blood samples collected from eleven endemic species of South American waterfowl in Peru and Argentina for infection by Haemoproteus , Plasmodium , and/or Leucocytozono blood parasites. Infections were detected in 25 individuals of six species for an overall apparent prevalence rate of 3.1%. Analysis of haematozoa mitochondrial DNA revealed twelve distinct parasite haplotypes infecting South American waterfowl, four of which were identical to lineages previously observed infecting ducks and swans sampled in North America. Analysis of parasite mitochondrial DNA sequences revealed close phylogenetic relationships between lineages originating from waterfowl samples regardless of continental affiliation. In contrast, more distant phylogenetic relationships were observed between parasite lineages from waterfowl and passerines sampled in South America for Haemoproteus and Leucocytozoon , suggesting some level of host specificity for parasites of these genera. The detection of identical parasite lineages in endemic, South American waterfowl and North American ducks and swans, paired with the close phylogenetic relationships of haematozoa infecting waterfowl on both continents, provides evidence for parasite redistribution between these regions by migratory birds.

International Journal for Parasitology: Parasites ↗

USGS2015

Enhanced understanding of ectoparasite: host trophic linkages on coral reefs through stable isotope analysis

Parasitism, although the most common type of ecological interaction, is usually ignored in food web models and studies of trophic connectivity. Stable isotope analysis is widely used in assessing the flow of energy in ecological communities and thus is a potentially valuable tool in understanding the cryptic trophic relationships mediated by parasites. In an effort to assess the utility of stable isotope analysis in understanding the role of parasites in complex coral-reef trophic systems, we performed stable isotope analysis on three common Caribbean reef fish hosts and two kinds of ectoparasitic isopods: temporarily parasitic gnathiids ( Gnathia marleyi ) and permanently parasitic cymothoids ( Anilocra ) . To further track the transfer of fish-derived carbon (energy) from parasites to parasite consumers, gnathiids from host fish were also fed to captive Pederson shrimp ( Ancylomenes pedersoni ) for at least 1 month. Parasitic isopods had δ 13 C and δ 15 N values similar to their host, comparable with results from the small number of other host–parasite studies that have employed stable isotopes. Adult gnathiids were enriched in 15 N and depleted in 13 C relative to juvenile gnathiids, providing insights into the potential isotopic fractionation associated with blood-meal assimilation and subsequent metamorphosis. Gnathiid-fed Pedersen shrimp also had δ 13 C values consistent with their food source and enriched in 15 N as predicted due to trophic fractionation. These results further indicate that stable isotopes can be an effective tool in deciphering cryptic feeding relationships involving parasites and their consumers, and the role of parasites and cleaners in carbon transfer in coral-reef ecosystems specifically.

Lameshur Bay, St. John, Virgin Islands↗

USGS2015

Sea otter health: challenging a pet hypothesis

A recent series of studies on tagged sea otters ( Enhydra lutris nereis ) challenges the hypothesis that sea otters are sentinels of a dirty ocean, in particular, that pet cats are the main source of exposure to Toxoplasma gondii in central California. Counter to expectations, sea otters from unpopulated stretches of coastline are less healthy and more exposed to parasites than city-associated otters. Ironically, now it seems that spillover from wildlife, not pets, dominates spatial patterns of disease transmission.

International Journal for Parasitology: Parasites ↗

USGS2016

Ectoparasitism on deep-sea fishes in the western North Atlantic: In situ observations from ROV surveys

A complete understanding of how parasites influence marine ecosystem functioning requires characterizing a broad range of parasite-host interactions while determining the effects of parasitism in a variety of habitats. In deep-sea fishes, the prevalence of parasitism remains poorly understood. Knowledge of ectoparasitism, in particular, is limited because collection methods often cause dislodgment of ectoparasites from their hosts. High-definition video collected during 43 remotely operated vehicle surveys (2013–2014) provided the opportunity to examine ectoparasitism on fishes across habitats (open slope, canyon, seamount, cold seep) and depths (494–4689 m) off the northeastern U.S., while providing high-resolution images and valuable observations of fish behavior. Only 9% (n = 125 individuals) of all observed fishes (25 species) were confirmed with ectoparasites, but higher percentages (&sim;33%) were observed for some of the most abundant fish species (e.g., Antimora rostrata) . Ectoparasites included two copepod families (Lernaeopodidae, Sphyriidae) that infected four host species, two isopod families (Cymothoidae, Aegidae) that infected three host species, and one isopod family (Gnathiidae) that infected 19 host species. Hyperparasitism was also observed. As host diversity declined with depth, ectoparasite diversity declined; only gnathiids were observed at depths down to 3260 m. Thus, gnathiids appear to be the most successful group to infect a diversity of fishes across a broad depth range in the deep sea. For three dominant fishes ( A. rostrata , Nezumia bairdii , Synaphobranchus spp.), the abundance and intensity of ectoparasitism peaked in different depths and habitats depending on the host species examined. Notably, gnathiid infections were most intense on A. rostrata , particularly in submarine canyons, suggesting that these habitats may increase ectoparasite infections. Although ectoparasitism is often overlooked in deep-sea benthic communities, our results demonstrate that it occurs widely across a variety of habitats, depths, and locations and is a significant component of deep-sea biodiversity.

New England Seamount Chain↗

USGS2016

Helminth community structure in two species of arctic-breeding waterfowl

Climate change is occurring rapidly at high latitudes, and subsequent changes in parasite communities may have implications for hosts including wildlife and humans. Waterfowl, in particular, harbor numerous parasites and may facilitate parasite movement across broad geographic areas due to migratory movements. However, little is known about helminth community structure of waterfowl at northern latitudes. We investigated the helminth communities of two avian herbivores that breed at high latitudes, Pacific black brant ( Branta bernicla nigricans ), and greater white-fronted geese ( Anser albifrons ), to examine effects of species, geographic area, age, and sex on helminth species richness, aggregation, prevalence, and intensity. We collected 83 and 58 black brant and white-fronted geese, respectively, from Arctic and Subarctic Alaska July-August 2014. We identified 10 known helminth species ( Amidostomum anseris , Amidostomum spatulatum , Drepanidotaenia lanceolata , Epomidiostomum crami , Heterakis dispar , Notocotylus attenuatus , Tetrameres striata , Trichostrongylus tenuis , Tschertkovilepis setigera , and Wardoides nyrocae ) and 1 previously undescribed trematode. All geese sampled were infected with at least one helminth species. All helminth species identified were present in both age classes and species, providing evidence of transmission at high latitudes and suggesting broad host susceptibility. Also, all but one helminth species were present at both sites, suggesting conditions are suitable for transmission across a large latitudinal/environmental gradient. Our study provides important baseline information on avian parasites that can be used to evaluate the effects of a changing climate on host-parasite distributions.

Alaska↗

USGS2021

Plague transforms positive effects of precipitation on prairie dogs to negative effects

Rodents characteristically benefit from increased precipitation, especially in typically dry habitats; “good years” of high precipitation improve their forage and water balance. However, Yersinia pestis (plague), a flea-borne pathogen of mammals that was introduced to western North America, has the greatest negative impact on at least some species of rodents during years of above-average precipitation. In the absence of plague mitigation, negative effects of plague in wet years might overwhelm the otherwise beneficial effects of increased moisture. In Montana and Utah, USA, where plague now occurs enzootically, we investigated the influence of precipitation on finite rates of annual population change (2000–2005) for 3 species of prairie dogs ( Cynomys spp.) in replicated plots treated with deltamethrin dust and in non-treated plots for paired comparisons. There was a significant interaction between precipitation and treatment. When we reduced plague vector fleas, prairie dog visual counts tended to increase with increasing precipitation. Simultaneously, there was a negative relationship between counts and precipitation on paired plots where plague was not managed, suggesting that plague transformed and reversed the otherwise beneficial effect of increased precipitation. Are the good years gone for prairie dogs? Even if the good years are not gone, they are perhaps relatively scarce compared to historic times prior to the invasion of plague. This scenario might apply to other ecosystems and may pose broad conservation challenges in western North America.

Montana, Utah↗

USGS2021

Negligible evidence for detrimental effects of Leucocytozoon infections among Emperor Geese (Anser canagicus) breeding on the Yukon-Kuskokwim Delta, Alaska

Emperor Geese ( Anser canagicus ) are iconic waterfowl endemic to Alaska and adjacent areas of northeastern Russia that are considered to be near threatened by the International Union for Conservation. This species has been identified as harboring diverse viruses and parasites which have, at times, been associated with disease in other avian taxa. To better assess if disease represents a vulnerability for Emperor Geese breeding on the Yukon-Kuskokwim Delta, Alaska, we evaluated if haemosporidian parasites were associated with decreased mass or survival among adult female nesting birds captured during 2006–2016. Through molecular analyses, we detected genetically diverse Leucocytozoon , Haemoproteus , and Plasmodium parasites in 28%, 1%, and 1% of 607 blood samples screened in triplicate, respectively. Using regression analysis, we found evidence for a small effect of Leucocytozoon infection on the mass of incubating adult female Emperor Geese. The estimated mass of infected individuals was approximately 43 g (95% CI: 20–67 g), or approximately 2%, less than uninfected birds when captured during the second half of incubation (days 11–25). We did not, however, find support for an effect of Leucocytozoon infection on survival of adult female nesting Emperor Geese using a multi-state hidden Markov framework to analyze mark-resight and recapture data. Using parasite mitochondrial DNA cytochrome b sequences, we identified 23 haplotypes among infected Emperor Geese. Leucocytozoon haplotypes clustered into three phylogenetically supported clades designated as ‘ L. simondi clade A’, ‘ L. simondi clade B’, and ‘other Leucocytozoon ’. We did not find evidence that parasites assigned to any of these clades were associated with differential mass measures among nesting adult female Emperor Geese. Collectively, our results provide negligible evidence for Leucocytozoon parasites as causing detrimental effects to adult female Emperor Geese breeding on the Yukon-Kuskokwim Delta.

Alaska↗

USGS2021

Acute mortality in California tiger salamander (Ambystoma californiense) and Santa Cruz long-toed salamander (Ambystoma macrodactylum croceum) caused by Ribeiroia ondatrae (Class: Trematoda)

In early September 2019, a morbidity and mortality event affecting California tiger salamanders ( Ambystoma californiense ) and Santa Cruz long-toed salamanders ( Ambystoma macrodactylum croceum ) in late stages of metamorphosis was reported at a National Wildlife Refuge in Santa Cruz County, California, U.S.A. During the postmortem disease investigation, severe integumentary metacercarial (Class: Trematoda) infection, associated with widespread skin lesions, was observed. Planorbid snails collected from the ponds of the refuge within seven days of the mortality event were infected with Ribeiroia ondatrae, a digenetic trematode that can cause malformation and death in some amphibians. We suggest sustained seasonal high-water levels due to active habitat management along with several years of increased rainfall led to increased bird visitation, increased over-wintering of snails, and prolonged salamander metamorphosis, resulting in a confluence of conditions and cascading of host-parasite dynamics to create a hyper-parasitized state.

California↗

USGS2024

Diversity, distribution, and methodological considerations of haemosporidian infections among Galliformes in Alaska

Using samples spanning 10-degrees of latitude in Alaska, we provide the first comparative assessment of avian haemosporidia distribution of Arctic Alaska with subarctic host populations for four species of grouse and three species of ptarmigan (Galliformes). We found a high overall prevalence for at least one haemospordian genus (88%; N = 351/400), with spruce grouse ( Canachites canadensis ) showing the highest prevalence (100%; N = 54/54). Haemoproteus and Plasmodium lineages were only observed within grouse, while Leucocytozoon species were found within both grouse and ptarmigan. Further, different Leucocytozoon lineages were obtained from blood and tissue samples from the same individual, potentially due to the differential timing and duration of blood and tissue stages. Using different primer sets, we were able to identify different Leucocytozoon lineages within 55% (N = 44/80) of sequenced individuals, thereby detecting coinfections that may have otherwise gone undetected. The commonly used Haemoproteus / Plasmodium primers amplified Leucocytozoon for 90% (N = 103/115) of the products sequenced, highlighting the potential value of alternate primers to identify intra-genus coinfections and the importance of obtaining sequence information rather than relying solely on PCR amplification to assess parasite diversity. Overall, this dataset provides baseline information on parasite lineage distributions to assess the range expansion associated with climate change into Arctic regions and underscores methodological considerations for future studies.

Alaska↗

USGS2024

Prairie dog responses to vector control and vaccination during an initial Yersinia pestis invasion

We evaluated the invasion of plague bacteria Yersinia pestis into a population of black-tailed prairie dogs (Cynomys ludovicianus; BTPDs) in South Dakota. We aimed to ascertain if Y. pestis invaded slowly or rapidly, and to determine if vector (flea) control or vaccination of BTPDs assisted in increasing survival rates. We sampled BTPDs in 2007 (before Y. pestis documentation), 2008 (year of confirmed invasion), and 2009 (after invasion). We estimated annual BTPD re-encounter rates on three 9-ha plots treated annually with deltamethrin dust for flea control and three 9-ha plots lacking dust. In 2007 and 2008, approximately half the adult BTPDs live-trapped were injected subcutaneously with either an experimental plague vaccine (F1–V fusion protein) or placebo formulation; the remaining individuals were not inoculated. From 2007 to 2009, we sampled 1559 BTPDs on 2542 occasions. During 2007–2008, the prevalence and intensity of fleas on BTPDs were 69–97% lower on the dusted vs. no dust plots. From 2007 to 2008, the annual re-encounter rate of non-inoculated BTPDs was 150% higher on the dusted vs. no dust plots. During the same interval on the dusted plots, the re-encounter rate was 55% higher for vaccinated adult female BTPDs vs. nonvaccinated adult females, but the annual re-encounter rate was 19% lower for vaccinated adult males. By late August 2008, BTPDs were nearly extirpated from the no dust plots. During 2007–2008 and 2008–2009 on the dusted plots, which persisted, the BTPD re-encounter rate was 41% higher for vaccinated vs. non-vaccinated adult females but 35% lower for vaccinated adult males. Yersinia pestis erupted with vigor as it invaded. Flea control enhanced BTPD survival but did not offer full protection. Flea control and F1–V vaccination seemed to have additive, positive effects on adult females. Annual re-encounter rates were reduced for vaccinated adult males; additional experimentation is needed to further evaluate this trend.

International Journal of Parasitology: Parasites a↗

USGS2024

Morbidity in California giant salamander (Dicamptodon ensatus Eschscholtz, 1833) caused by Euryhelmis sp. Poche, 1926 (Trematoda: Heterophyiidae)

In the fall of 2021, California Department of Fish and Wildlife reported larval and adult California giant salamanders ( Dicamptodon ensatus Eschscholtz, 1833) with skin lesions at multiple creeks in Santa Clara and Santa Cruz Counties, California, USA. Field signs in both stages included rough, lumpy textured skin, and larvae with tails that were disproportionately long, flat, wavy, and flaccid. Presence of large-bodied larvae suggested delayed metamorphosis, with some larvae having cloudy eyes and suspected blindness. To determine the cause of the disease, three first-of-the-year salamanders from one location were collected, euthanized with 20% benzocaine, and submitted for necropsy to the U.S. Geological Survey, National Wildlife Health Center. Upon gross examination, all salamanders were emaciated with no internal fat stores, and had multiple pinpoint to 1.5-mm diameter raised nodules in the skin over the body, including the head, gills, dorsum, ventrum, all four limbs, and the tail; one also had nodules in the oral cavity and tongue. Histologically all salamanders had multiple encysted metacercariae in the dermis, subcutis, and skeletal muscles of the head, body, and tail that were often associated with granulomatous and granulocytic inflammation and edema. A small number of encysted meta cercariae or empty cysts were present in the gills with minimal inflammation, and rarely in the kidney with no associated inflammation. Morphology of live metacercariae (Trematoda: Heterophyiidae), and sequencing of the 28S rRNA gene identified a species of Euryhelmis (Poche, 1926). Artificial digestion of a 1.65 g, decapitated, eviscerated carcass yielded 773 metacercariae, all of similar size and morphology as the live specimens. Based on these findings, the poor body condition of these salamanders was concluded to be due to heavy parasite burden. Environmental factors such as drought, increased temperature, and overcrowded conditions may be exacerbating parasite infections in these populations of salamander.

California↗

USGS2026

Contrasting haemosporidian infections in two ecologically distinct wading birds from breeding colonies in the southeastern United States

Wading birds may serve as ideal hosts for avian hemoparasites, as they are long-lived, undertake extensive movements, form dense breeding colonies, and inhabit water-associated environments that support vectors. Although previous studies have reported parasite species and prevalence in various wading bird species, little is known about their associations with bird behavior and life stage. To address this gap, we examined haemosporidian infections in two ecologically distinct species, white ibis ( Eudocimus albus ) and tricolored heron ( Egretta tricolor ), to explore differences in life stage and movement that may explain prevalence differences. We combined blood screening for hemoparasites with satellite tracking data describing birds’ movement patterns. We screened 95 white ibis (67 juveniles and 28 adults or subadults) and 69 tricolored herons (45 juveniles and 24 adults). We detected a single Haemoproteus plataleae lineage in both species, with higher infection prevalence in white ibis (42.1 %) than in tricolored herons (14.5 %). Among white ibis, adults showed a higher prevalence (67.9 %) than juveniles (31.3 %), whereas in tricolored herons, adults had a prevalence of 8.3 % and juveniles 17.8 %. Non-breeding season movement data showed that white ibis used both freshwater and saline habitats across the southeastern United States, which may also serve as habitats for vectors. In contrast, tricolored herons remained mainly along coastal areas, using saline habitats in the southeastern United States and wintering sites in Central America, which may be less favorable for vectors. Overall, white ibis may serve as major reservoirs and sources of reinfection for H. plataleae , whereas tricolored herons may facilitate parasite dispersal between breeding colonies along the coasts of the southeastern United States and wintering areas in Central America. This study presents the first direct comparison of hemoparasite infections in two ecologically distinct wading birds and highlights movement data as key to explaining infection differences, providing a baseline for future studies.

Alabama↗

USGS2026

Edible baits for systemic flea control, plague mitigation, and wildlife conservation: Evaluation of four active ingredients with three rodent species in western North America

The flea-borne agent of plague, Yersinia pestis , is lethal to endangered black-footed ferrets ( Mustela nigripes , BFFs) and the prairie dogs ( Cynomys spp., PDs) on which BFFs depend for habitat and prey. We developed bait pellets containing insecticides for flea control with PDs. Individual baits contained 0.46, 0.91, 1.21, or 1.52 mg fipronil, 5.40 mg afoxolaner, 50.62 mg fluralaner, or 85.20 mg spinosad. From 2023 to 2025, we tested the baits with black-tailed PDs ( C. ludovicianus , BTPDs), Gunnison's PDs ( C. gunnisoni , GPDs), and Richardson's ground squirrels ( Urocitellus richardsonii , RGSs). We sampled hosts 2810 times and detected 8825 fleas across 2 U.S. States, 1 Canadian Province, 6 sites, 9 PD colonies, and 41 sampling plots. Over ∼12 mo across 5 replicates in South Dakota, USA, bait pellets with 0.91 or 1.52 mg fipronil, applied at a rate of 125 baits/ha, were more effective in reducing the abundance of fleas on BTPDs than 0.46 mg fipronil or the 3 other active ingredients; on 2 South Dakota replicates with data from 24 mo posttreatment, the effects of fipronil pellets on flea abundance had waned after ∼24 mo. Similarly, over ∼12 mo on 2 replicates in Arizona, USA, pellets with 1.52 mg fipronil were more effective in reducing the abundance of fleas on GPDs than pellets with 0.46 mg fipronil; on 1 replicate with available data from ∼2 yr posttreatment, the effects of fipronil pellets had waned after ∼24 mo. Over ∼8-11 mo across 2 replicates in Saskatchewan, Canada, baits with 1.21 mg fipronil/pellet were more effective in suppressing the abundance of fleas on BTPDs and RGSs when applied at 250 pellets/ha than 62 pellets/ha; flea control had waned after ∼20-23 mo. When applied annually at 125-250/ha, baits with 0.84-1.52 mg fipronil (FipBits) provided an effective, efficient, and affordable tool for flea control on PD colonies.

Arizona, Saskatchewan, South Dakota↗

USGS2026

Effects of fipronil bait pellets on two cricetid species: Potential implications for plague mitigation and wildlife conservation

We evaluated the effects of fipronil bait pellets on two cricetids that commonly occupy colonies of black-tailed prairie dogs ( Cynomys ludovicianus ; BTPDs): western deer mice ( Peromyscus sonoriensis ) and northern grasshopper mice ( Onychomys leucogaster ). In one experiment, bait pellets (0.96 mg fipronil/bait) were applied at 75 baits/ha to three 1.44-ha plots on a BTPD colony. Mouse abundance declined by 70% from before to 6-10 d after treatment. In a second experiment, bait pellets (0.46 or 1.52 mg fipronil/bait) were applied at 125 baits/ha to four plots (0.85-1.86 ha) on two BTPD colonies; two non-treated plots were baselines (1.09 and 2.06 ha). From before to 11-15 d after treatment, mouse abundance declined by 51%- 67% on the treated plots vs. a decline of 9% on the non-treated plots. Mouse survival from before to 11-15 d after treatment was 51% lower on the treated plots. In a third experiment, bait pellets (0.84 mg fipronil/bait) were applied at 125 baits/acre on two 1.44-ha plots on a BTPD colony; two 1.44-ha non-treated plots were baselines. Mouse survival from before to 30-44 d after treatment was 45% lower on the treated plots; the abundance of deer mice on the treated plots remained similar from before to 30-44 d after treatment, perhaps due to juvenile recruitment and/or immigration. In a laboratory experiment, 33 deer mice offered one bait pellet (0.86 mg fipronil/bait) consumed 27% of their bait, on average (range = 0-100%). Over 3 d, deer mouse mortality was estimated at 53%; mortality increased with fipronil dose, which averaged 11 mg fipronil/kg body mass (range = 3-46 mg/kg). Brain samples were available from 31 deer mice; all tested positive for fipronil sulfone, the primary mammalian metabolite of fipronil, at 19 to 61,205 ng fipronil sulfone/g. Additional experiments could determine if these findings scale up to larger landscapes.

South Dakota↗