Lymphoproliferative Disease Virus and Reticuloendotheliosis Virus Detection and Disease in Wild Turkeys (Meleagris gallopavo)

Lymphoproliferative disease virus (LPDV) and reticuloendotheliosis virus (REV) are oncogenic retroviruses that can cause disease in wild and domestic fowl. Lymphoproliferative disease virus infections are common and widespread in Wild Turkeys (Meleagris gallopavo) in the US and east-central Canada, while REV has been detected worldwide in numerous avian host species. We tested tissues (spleen, liver, and/or bone marrow, plus neoplastic tissue, if present) from 172 Wild Turkeys that underwent necropsy from December 2018 through October 2021 for both viruses using PCR. We evaluated demographic, geographic, temporal, and seasonal data by chi-square test of independence and logistic regression for turkeys infected with LPDV and/or REV. At least one of these retroviruses was detected in 80.8% (139/172) of Wild Turkeys from 15 US states, with significantly more turkeys being positive for LPDV (72.1%, 124/172) versus REV (43.6%, 75/172; P<0.001). Both viruses (coinfections) were detected in 34.9% (60/172) of turkeys. Among LPDV-infected turkeys (including coinfections), bone marrow had the highest detection rate (38/58, 65.5%), significantly higher than spleen (30/58, 51.7%) and liver (20/58, 34.5%; P<0.001). In REV-infected turkeys, bone marrow had the highest detection rate (24/58, 41.4%). All three tissues (spleen, liver, bone marrow) concurrently tested positive in most (15/25, 60%) REV-infected turkeys. These results suggest LPDV tissue tropism for bone marrow, whereas REV may have broader tissue tropism. Histopathology consistent with lymphoid proliferation and/or neoplasia characteristic of lymphoproliferative disease was evident in 29/172 (16.9%) turkeys assessed, including two REV-only-infected turkeys. Season was significantly associated with LPDV prevalence (highest in winter); year and season were both significantly associated with REV prevalence (highest in 2020 and winter). These data contribute to optimizing diagnostic strategies that may aid in pathogen monitoring and improve detections to increase our understanding of the potential impacts of these viruses on Wild Turkey populations.

Whole genome assessment of a declining game bird reveals cryptic genetic structure and insights for population management

Population genomics applied to game species conservation can help delineate management units, ensure appropriate harvest levels and identify populations needing genetic rescue to safeguard their adaptive potential. The ruffed grouse (Bonasa umbellus) is rapidly declining in much of the eastern USA due to a combination of forest maturation and habitat fragmentation. More recently, mortality from West Nile Virus may have affected connectivity of local populations; however, genetic approaches have never explicitly investigated this issue. In this study, we sequenced 54 individual low-coverage (~5X) grouse genomes to characterize population structure, assess migration rates across the landscape to detect potential barriers to gene flow and identify genomic regions with high differentiation. We identified two genomic clusters with no clear geographic correlation, with large blocks of genomic differentiation associated with chromosomes 4 and 20, likely due to chromosomal inversions. After excluding these putative inversions from the data set, we found weak but nonsignificant signals of population subdivision. Estimated gene flow revealed reduced rates of migration in areas with extensive habitat fragmentation and increased genetic connectivity in areas with less habitat fragmentation. Our findings provide a benchmark for wildlife managers to compare and scale the genetic diversity and structure of ruffed grouse populations in Pennsylvania and across the eastern USA, and we also reveal structural variation in the grouse genome that requires further study to understand its possible effects on individual fitness and population distribution.

Comparison of Pathology and Immunohistochemistry in Natural and Experimental West Nile Virus Infections in Ruffed Grouse (Bonasa umbellus)

Ruffed Grouse (Bonasa umbellus) populations have declined in much of the eastern US in recent decades. Research suggests that West Nile virus (WNV) contributed to these declines, based on decreasing population indices temporally correlated to WNV introduction into North America, high morbidity and mortality in experimentally infected Ruffed Grouse, and relatively low statewide seroprevalence concurrent with high WNV vector indices. We describe lesions and relevant diagnostic findings in six, free-ranging Ruffed Grouse that directly or indirectly died of natural WNV infection and compare results to experimentally infected Ruffed Grouse. All naturally infected grouse were found moribund or dead from August to December 2015-18 in the northeastern US; 4/6 grouse were subadults. Necropsy, histopathology, immunohistochemistry, and/or ancillary tests contributed to the diagnosis of WNV-associated disease in all cases. The most common lesions in naturally infected grouse were myocardial inflammation, degeneration, and/or necrosis, consistent with lesions in experimentally infected grouse. Evidence of trauma in 6/6 naturally infected grouse suggests the possibility of WNV-associated morbidity as a predisposing factor. Diagnostic findings in 3/6 naturally infected grouse were consistent with experimentally infected grouse with severe disease 7-8 d postinoculation; the remaining naturally infected birds had similar findings to experimentally infected subclinical grouse. Our results further support the notion that WNV contributes to mortality of free-ranging Ruffed Grouse and may be used to improve surveillance strategies and population-level management approaches.

WEST NILE VIRUS EXPOSURE AND INFECTION AMONG HUNTER-HARVESTED RUFFED GROUSE COHORTS IN A STABLE POPULATION

West Nile virus (WNV) was introduced to North America two decades ago, but for many species, including Ruffed Grouse (Bonasa umbellus), the effects of WNV on individuals and populations remain poorly understood. Recent studies suggest the effect of WNV on Ruffed Grouse might vary among geographic regions, depending on habitat conditions. We studied WNV in Minnesota, US, during 2018-19, in a region known to have abundant Ruffed Grouse habitat and a population cycling around a stable long-term average. We worked with cooperating hunters to collect hearts, feathers, and blood on filter strips from birds harvested in the fall to examine exposure to the virus. We detected antibodies to WNV or a flavivirus (probably WNV) in 12.5% and 12.3% of birds in 2018 and 2019, respectively. However, we did not isolate the virus from any heart samples, indicating that exposed birds were not experiencing an active infection of WNV at the time of harvest. Our findings indicate that, although Minnesota Ruffed Grouse are exposed to WNV, some birds mount a successful immune response and survive. However, our sampling approach did not account for birds that might have become infected over the summer and died, so it is unknown how much WNV mortality occurred before the fall harvest. Birds lost to WNV over the summer could reduce the number of birds that hunters see in the fall, thus reducing the quality of their hunting experiences. Management options for mitigating WNV impacts and other stressors consist primarily of providing high-quality Ruffed Grouse habitat that produces birds in good condition that are more likely to recover from infection.

A proposed framework for the development and qualitative evaluation of West Nile virus models and their application to local public health decision-making

West Nile virus (WNV) is a globally distributed mosquito-borne virus of great public health concern. The number of WNV human cases and mosquito infection patterns vary in space and time. Many statistical models have been developed to understand and predict WNV geographic and temporal dynamics. However, these modeling efforts have been disjointed with little model comparison and inconsistent validation. In this paper, we describe a framework to unify and standardize WNV modeling efforts nationwide. WNV risk, detection, or warning models for this review were solicited from active research groups working in different regions of the United States. A total of 13 models were selected and described. The spatial and temporal scales of each model were compared to guide the timing and the locations for mosquito and virus surveillance, to support mosquito vector control decisions, and to assist in conducting public health outreach campaigns at multiple scales of decision-making. Our overarching goal is to bridge the existing gap between model development, which is usually conducted as an academic exercise, and practical model applications, which occur at state, tribal, local, or territorial public health and mosquito control agency levels. The proposed model assessment and comparison framework helps clarify the value of individual models for decision-making and identifies the appropriate temporal and spatial scope of each model. This qualitative evaluation clearly identifies gaps in linking models to applied decisions and sets the stage for a quantitative comparison of models. Specifically, whereas many coarse-grained models (county resolution or greater) have been developed, the greatest need is for fine-grained, short-term planning models (m-km, days-weeks) that remain scarce. We further recommend quantifying the value of information for each decision to identify decisions that would benefit most from model input.

WEST NILE VIRUS INFECTION IN RUFFED GROUSE (BONASA UMBELLUS) IN PENNSYLVANIA, USA: A MULTI-YEAR COMPARISON OF STATEWIDE SEROSURVEYS AND VECTOR INDICES

Eastern populations of Ruffed Grouse (Bonasa umbellus) have been in a decades-long decline across the mid-Atlantic and southern Appalachian Mountains of the US. West Nile virus (WNV), which first arrived in the US in 1999, is suspected to have contributed to these declines based on decreased population indices since the arrival of WNV in Pennsylvania as well as on high, experimentally induced WNV-associated morbidity rates. A 3-yr statewide survey was conducted across Pennsylvania to measure flavivirus (i.e., WNV) seroprevalence among hunter-harvested grouse. The overall seroprevalence from 2015-17 was 14.4% (81/563); annual seroprevalence ranged from 2.8% (4/145) in the 2017 hunt year to 22.6% (52/230) in 2016-17. We analyzed the effects of numerous variables (i.e., Ruffed Grouse age and sex, hunt year, WNV vector index [VI], and region of Pennsylvania) on WNV serostatus by logistic regression. While there was no significant difference in WNV seroprevalence between sex and age group, there was significant variation in seroprevalence between geographic regions of Pennsylvania and across hunt years. Additionally, there was a negative correlation between WNV seroprevalence and VI. Low seroprevalence rates among Ruffed Grouse corresponded to years with a high VI, supporting experimental findings that Ruffed Grouse may be highly susceptible to WNV-associated disease. Additional strategic research efforts are essential to more effectively measure the effects of WNV on Ruffed Grouse and other vulnerable avian species.

Dissolved organic matter protects mosquito larvae from damaging solar UV radiation

Mosquitoes have increased in their abundance and geographic distribution in northeastern North America, coinciding with an increase in extreme precipitation events and up to a doubling of dissolved organic matter (DOM) concentrations in some inland waters. Increases in DOM can reduce exposure of mosquito larvae to solar ultraviolet (UV) radiation. Although mosquito larvae are most common in shaded habitats, almost nothing is known about their susceptibility to damage by solar UV radiation, or the ability of DOM to create a refuge from damaging UV in their shallow-water habitats. We hypothesize that 1) exposure to solar UV radiation is lethal to mosquito larvae, 2) larvae lack photo-enzymatic repair to fix UV-damaged DNA, and 3) DOM shades larvae from lethal solar UV radiation. We tested these hypotheses with experiments that manipulated UV radiation, the photo-repair radiation necessary for photo-enzymatic DNA repair, and DOM. Exposure to solar UV radiation significantly decreased larval survivorship, while DOM significantly increased it. There was no evidence of photo-enzymatic DNA repair. Our findings confirm that solar UV radiation decreases habitat suitability for mosquito larvae, but DOM provides a refuge from UV. This highlights the need for vector control managers to prioritize high DOM and shaded habitats in their efforts to reduce mosquito populations.

Climate change, ecosystems and abrupt change: science priorities

Ecologists have long studied patterns, directions and tempos of change, but there is a pressing need to extend current understanding to empirical observations of abrupt changes as climate warming accelerates. Abrupt changes in ecological systems (ACES)-changes that are fast in time or fast relative to their drivers-are ubiquitous and increasing in frequency. Powerful theoretical frameworks exist, yet applications in real-world landscapes to detect, explain and anticipate ACES have lagged. We highlight five insights emerging from empirical studies of ACES across diverse ecosystems: (i) ecological systems show ACES in some dimensions but not others; (ii) climate extremes may be more important than mean climate in generating ACES; (iii) interactions among multiple drivers often produce ACES; (iv) contingencies, such as ecological memory, frequency and sequence of disturbances, and spatial context are important; and (v) tipping points are often (but not always) associated with ACES. We suggest research priorities to advance understanding of ACES in the face of climate change. Progress in understanding ACES requires strong integration of scientific approaches (theory, observations, experiments and process-based models) and high-quality empirical data drawn from a diverse array of ecosystems. This article is part of the theme issue 'Climate change and ecosystems: threats, opportunities and solutions'.

Impact of West Nile Virus on Bird Populations: Limited Lasting Effects, Evidence for Recovery, and Gaps in Our Understanding of Impacts on Ecosystems

The introduction of West Nile virus to North America in 1999 had profound impacts on human and wildlife health. Here, we review studies of WNV impacts on bird populations and find that overall impacts have been less than initially anticipated, with few species showing sustained changes in population size or demographic rates across multiple regions. This raises four questions: 1) What is the evidence for WNV impact on bird populations and how can we strengthen future analyses? We argue that future studies of WNV impacts should explicitly incorporate temporal variation in WNV transmission intensity, integrate field data with laboratory experimental infection studies, and correct for multiple comparisons. 2) What mechanisms might explain the relatively modest impact of WNV on most bird populations? We suggest that spatial and temporal variation in WNV transmission moderates WNV impacts on species that occur in multiple habitats, some of which provide refugia from infection. 3) Have species recovered from the initial invasion of WNV? We find evidence that many species and populations have recovered from initial WNV impact, but a few have not. 4) Did WNV cause cascading effects on other species and ecosystems? Unfortunately, few studies have examined the cascading effects of WNV population declines, but evidence suggests that some species may have been released from predation or competition. We close by discussing potentially overlooked groups of birds that may have been affected by WNV, and one highlight species, the yellow-billed magpie (Pica nutalli Audubon, 1837 [Passeriformes: Corvidae]), that appears to have suffered the largest range-wide impact from WNV.