First report of ranavirus mortality in a common snapping turtle Chelydra serpentina

Trace Amounts of Ranavirus Detected in Common Musk Turtles (Sternotherus odoratus) at a Site Where the Pathogen Was Previously Common

Ranaviruses are global multi-host pathogens that infect ectothermic vertebrates and cause mass mortality events in some species. In 2021-2022, we surveyed two species of aquatic turtles in a Virginia site where previous research found ranavirus in lizards (Sceloporus undulatus) and turtles (Chrysemys picta picta and Terrapene carolina carolina). We sampled tissues from 206 turtles and tested 249 samples (including recaptures) for ranavirus using qPCR. We detected trace amounts of ranavirus DNA in 2.8% of Common Musk Turtles (Sternotherus odoratus). We did not detect the virus in Eastern Painted Turtles (C. p. picta). The Ct values from animals carrying ranavirus corresponded to positive controls with a concentration of one copy of ranavirus DNA per microliter and likely reflect DNA in the environment rather than ranavirus infection in turtles. Turtles carrying ranavirus DNA came from only one pond in one year. The amount of ranavirus in our study site, as indicated by tissue samples from turtles, appears to have dropped dramatically since previous research conducted over a decade ago. This study represents the first report of ranavirus detected in S. odoratus and contributes to the scarce literature on longitudinal surveys of ranavirus in wild chelonians. We emphasize the need for large sample sizes and multi-year sampling to detect this pathogen in wild populations.

Non-Lethal Detection of Ranavirus in Fish

Emergent infectious diseases have an increasing impact on both farmed animals and wildlife. The ability to screen for pathogens is critical for understanding host-pathogen dynamics and informing better management. Ranavirus is a pathogen of concern, associated with disease outbreaks worldwide, affecting a broad range of fish, amphibian, and reptile hosts, but research has been limited. The traditional screening of internal tissues, such as the liver, has been regarded as the most effective for detecting and quantifying Ranavirus. However, such methodology imposes several limitations from ethical and conservation standpoints. Non-lethal sampling methods of viral detection were explored by comparing the efficacy of both buccal swabbing and fin clipping. The study was conducted on two Iberian, threatened freshwater fish (Iberochondrostoma lusitanicum and Cobitis paludica), and all samples were screened using qPCR. While for C. paludica both methods were reliable in detecting Ranavirus, on I. lusitanicum, there was a significantly higher detection rate in buccal swabs than in fin tissue. This study, therefore, reports that fin clipping may yield false Ranavirus negatives when in small-bodied freshwater fish. Overall, buccal swabbing is found to be good as an alternative to more invasive procedures, which is of extreme relevance, particularly when dealing with a threatened species.

Influence of Herbicide Exposure and Ranavirus Infection on Growth and Survival of Juvenile Red-Eared Slider Turtles (Trachemys scripta elegans)

Ranaviruses are an important wildlife pathogen of fish, amphibians, and reptiles. Previous studies have shown that susceptibility and severity of infection can vary with age, host species, virus strain, temperature, population density, and presence of environmental stressors. Experiments are limited with respect to interactions between this pathogen and environmental stressors in reptiles. In this study, we exposed hatchling red-eared slider turtles (Trachemys scripta elegans) to herbicide and ranavirus treatments to examine direct effects and interactions on growth, morbidity, and mortality. Turtles were assigned to one of three herbicide treatments or a control group. Turtles were exposed to atrazine, Roundup ProMax®, or Rodeo® via water bath during the first 3 weeks of the experiment. After 1 week, turtles were exposed to either a control (cell culture medium) or ranavirus-infected cell lysate via injection into the pectoral muscles. Necropsies were performed upon death or upon euthanasia after 5 weeks. Tissues were collected for histopathology and detection of ranavirus DNA via quantitative PCR. Only 57.5% of turtles exposed to ranavirus tested positive for ranaviral DNA at the time of death. Turtles exposed to ranavirus died sooner and lost more mass and carapace length, but not plastron length, than did controls. Exposure to environmentally relevant concentrations of herbicides did not impact infection rate, morbidity, or mortality of hatchling turtles due to ranavirus exposure. We also found no direct effects of herbicide or interactions with ranavirus exposure on growth or survival time. Results of this study should be interpreted in the context of the modest ranavirus infection rate achieved, the general lack of growth, and the unplanned presence of an additional pathogen in our study.

An enigmatic mass mortality event of Blanding’s Turtles (Emydoidea blandingii) in a protected area

Mass mortality events (MMEs) can remove up to 90% of individuals in a population and are especially damaging to population viability of long-lived species with slow life histories. Our goal was to elucidate the cause(s) of a MME of 53 Blanding’s Turtles (Emydoidea blandingii (Holbrook, 1838)), a globally endangered species, in a protected area. We investigated disease, winter-kill, and depredation as potential causes of the mortality. The turtle carcasses lacked soft tissue to test for disease, so we examined tissue from co-occurring live Leopard Frogs (Lithobates pipiens (Schreber, 1782)) and found no evidence of ranavirus, indicating that the disease was not present at our study site. Water temperature and dissolved aquatic oxygen at known overwintering sites and sites which yielded carcasses did not differ, suggesting that winter-kill did not cause the MME. Carcass condition, comparisons with descriptions of turtle depredation events in the literature, and trail cameras paired with turtle decoys identified potential predators within the study site and suggested that mass depredation, enabled by low water levels and a concomitant reduction in aquatic habitat, was the most likely cause of mortality. Our study can inform conservation of the study population and the management of MMEs of long-lived species elsewhere.

Plasma complement activation mechanisms differ in ornate (Terrapene ornata ornata) and eastern box turtles (Terrapene carolina carolina)

Eastern (Terrapene carolina carolina) and ornate (Terrapene ornata ornata) box turtles have robust plasma antibacterial activity, however, the mechanism behind this activity is unknown. We used sheep red blood cell (SRBC) hemolysis assays, mannan-affinity chromatography, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) to explore the mechanisms of complement activity in box turtles. Plasma from both species demonstrated volume, time, and temperature-dependent SRBC hemolysis, with significantly greater hemolytic activity in ornate box turtle plasma. Hemolytic activity was highly attenuated following treatment with heat, EDTA, and salicylaldoxime in both species, but was unchanged after treatment with methylamine and ammonium hydroxide. Two abundant mannan-binding proteins (presumed C-type lectins) were identified in eastern box turtle plasma using SDS-PAGE and MALDI-TOF, but ornate box turtles did not express either protein. Eastern box turtles appear to rely on the lectin pathway of complement activation while ornate box turtles utilize the alternative pathway. This study provides further evidence that mechanisms underlying immune function are not always conserved between closely related species. This finding may have important implications for explaining species differences in susceptibility to emerging threats such as disease, toxicants, and climate change.

Emerging Infectious Diseases of Chelonians: An Update

Chelonians are increasingly challenged by anthropogenic threats and disease. This article summarizes recent literature and clinical experiences regarding 4 emerging infectious diseases in turtles and tortoises: ranaviruses, cryptosporidiosis, intranuclear coccodiosis of Testudines, and Emydomyces testavorans.

High prevalence of subclinical frog virus 3 infection in freshwater turtles of Ontario, Canada

Ranaviruses have been associated with chelonian mortality. In Canada, the first two cases of ranavirus were detected in turtles in 2018 in Ontario, although a subsequent survey of its prevalence failed to detect additional positive cases. To confirm the prevalence of ranavirus in turtles in Ontario, we used a more sensitive method to investigate if lower level persistent infection was present in the population. Here we report results via a combination of qPCR, PCR, Sanger sequencing and genome sequencing from turtles from across Ontario, with no clinical signs of illness. We found 2 positives with high viral load and 5 positives with low viral load. Histopathology found subtle histological changes. DNA sequences identified two types of frog virus 3 (FV3), and genome sequencing identified a ranavirus similar to wild-type FV3. Our results show that the virus has been present in Ontario's turtles as subclinical infections.

Intestinal B cells in the red-eared slider turtle, Trachemys scripta: Anatomical distribution and implications for ecological interactions with pathogenic microbes

Disease is a significant threat in the global decline of reptile species. Many aquatic reptiles live in habitats with high levels of opportunistic microbial pathogens, yet little is known about their immune system. Gut-associated lymphoid tissue is vital for protection against ingested pathogens and maintenance of normal gut microbiota. In mammals, gut mucosal immunity is well-characterized and mucosal surfaces are coated in protective antibodies. However, reptiles lack lymph nodes and Peyer's patches, which are the major sites of mammalian B cell responses. The presence or distribution of mucosal B cells in reptiles is unknown. In this study, we first set out to determine if B cells could be detected in intestinal tissues of red-eared slider turtles, Trachemys scripta. Using whole-mount immunochemistry and a primary antibody to turtle antibody light chains, we identified widely distributed B cell aggregates within the small intestine of hatchling turtles. These aggregates appeared similar to isolated lymphoid follicles (ILFs) in mammals and the frequency was much higher in distal intestinal sections than in proximal sections. To determine if these structures were inducible in the presence of microbes, we introduced an enteric Salmonella species through oral gavage. Analysis of intestinal tissues revealed that hatchlings exposed to Salmonella exhibited significantly more of these aggregates when compared with those that did not receive bacteria. These studies provide the first evidence for B cell-containing ILF-like structures in reptiles and provide novel information about gut immunity in nonmammalian vertebrates that could have important implications for ecological interactions with pathogens.

Evidence for low prevalence of ranaviruses in Ontario, Canada's freshwater turtle population

BACKGROUND

Ontario, Canada is home to eight native species of turtles; all eight are federally listed as Species At Risk, due to anthropogenic threats. However, until recently, reports of infectious disease have been lacking. Ranavirus is seen as an emerging threat for ectotherms globally, with mass die-offs most often reported in amphibians. Ranavirus has been detected in Ontario's amphibian populations, can be transmitted via water, and can be transmitted from amphibians to turtles. However, no studies on the prevalence of this virus in Ontario's turtles have previously been carried out. With recent reports of two confirmed positive case of ranavirus in turtles in Ontario, a knowledge of the ecology of ranavirus in Ontario's turtles has become even more important. This study estimates the prevalence of ranavirus in Ontario's turtles, and investigates the hypothesis that this is a newly emergent disease.

METHODS

Sixty-three samples were tested for ranavirus via PCR. These included a variety of turtle species, across their home range in Southern Ontario. Fifty-two of the samples originated from the liver and kidney of turtles who had succumbed to traumatic injuries after being admitted to the Ontario Turtle Conservation Centre; ten of the samples were taken from cloacal swabs, lesion swabs, or tail clips collected from live turtles showing signs of clinical disease. One of the live turtles was later euthanized for humane reasons and PCR was also carried out on the liver/kidney.

RESULTS

None of the 63 samples were found to be positive for ranavirus via PCR. The zero prevalence found in this study translates into a population prevalence estimate of less than 5%, with no change in prevalence from 2014-2018.

DISCUSSION

This is the first report on the prevalence of ranavirus in Ontario's turtles, and will help build an understanding of the ecology of this virus in Ontario. Ranavirus has historically been underreported in reptiles, but there has been an increase in global reports recently, most likely due to increased awareness. A carrier state is thought to exist in reptiles which makes surveillance in the population via random sampling a viable method of detection of prevalence. The first report of ranavirus in Ontario turtles occurred in 2018. This study suggests a continued low population prevalence for the years 2014-2018, however. Ongoing surveillance is necessary, as well as investigation of the eDNA presence in waterways as compared to the PCR of resident turtles, to further understand the sensitivity of these species to ranavirus infection. The utilization of qPCR would be helpful, to better quantify any positives encountered.