Evidence of Ranavirus Infections among Sympatric Larval Amphibians and Box Turtles

Ranavirus (Frog Virus 3) Infection in Free-Living Three-Toed Box Turtles (Terrapene mexicana triunguis) in Missouri, USA

Frog virus 3 (FV3) and related ranaviruses are emerging infectious disease threats to ectothermic vertebrate species globally. Although the impact of these viruses on amphibian health is relatively well studied, less is understood about their effects on reptile health. We report two cases of FV3 infection, 11 mo apart, in three-toed box turtles (Terrapene mexicana triunguis) from a wildlife rehabilitation center. Case 1 had upper respiratory signs upon intake but had no clinical signs at the time of euthanasia 1 mo later. Case 2 presented for vehicular trauma, had ulcerative pharyngitis and glossitis, and died overnight. In case 1, we detected FV3 nucleic acid with qPCR in oral swabs, kidney, liver, spleen, and tongue. In case 2, we detected FV3 in an oral swab, an oral plaque, heart, kidney, lung, liver, spleen, and tongue. We also detected FV3 nucleic acid with in situ hybridization for case 2. For both cases, FV3 was isolated in cell culture and identified with DNA sequencing. Histopathologic examination of postmortem tissue from case 1 was unremarkable, whereas acute hemorrhagic pneumonia and splenic necrosis were noted in case 2. The difference in clinical signs between the two cases may have been due to differences in the temporal course of FV3 disease at the time of necropsy. Failure to detect this infection previously in Missouri reptiles may be due to lack of surveillance, although cases may also represent a novel spillover to box turtles in Missouri. Our findings reiterate previous suggestions that the range of FV3 infection may be greater than previously documented and that infection may occur in host species yet to be tested.

Divergent impacts of warming weather on wildlife disease risk across climates

Disease outbreaks among wildlife have surged in recent decades alongside climate change, although it remains unclear how climate change alters disease dynamics across different geographic regions. We amassed a global, spatiotemporal dataset describing parasite prevalence across 7346 wildlife populations and 2021 host-parasite combinations, compiling local weather and climate records at each location. We found that hosts from cool and warm climates experienced increased disease risk at abnormally warm and cool temperatures, respectively, as predicted by the thermal mismatch hypothesis. This effect was greatest in ectothermic hosts and similar in terrestrial and freshwater systems. Projections based on climate change models indicate that ectothermic wildlife hosts from temperate and tropical zones may experience sharp increases and moderate reductions in disease risk, respectively, though the magnitude of these changes depends on parasite identity.

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.

Optimizing, validating, and field testing a multiplex qPCR for the detection of amphibian pathogens

Amphibian populations worldwide are facing numerous threats, including the emergence and spread of infectious diseases. In the past 2 decades, Batrachochytrium dendrobatidis (Bd), a parasitic fungus, and a group of viruses comprising the genus Ranavirus have become widespread and resulted in mass mortality events and extirpations worldwide. In 2013, another novel fungus, B. salamandrivorans (Bsal), was attributed to dramatic declines in populations of fire salamander Salamandra salamandra in the Netherlands. Experimental infections demonstrated that Bsal is highly pathogenic to numerous salamander genera. In an effort to prevent the introduction of Bsal to North America, the US Fish and Wildlife Service (USFWS) listed 201 salamander species as injurious wildlife under the Lacey Act. To determine infection status and accurately assess amphibian health, the development of a sensitive and specific diagnostic assay was needed. We describe the optimization and validation of a multiplex quantitative polymerase chain reaction (qPCR) protocol for the simultaneous detection of Bd, Bsal, and frog virus 3-like ranaviruses. A synthetic genome template (gBlock®) containing the target genes from all 3 pathogens served as the positive control and allowed accurate quantification of pathogen genes. The assay was validated in the field using an established non-lethal swabbing technique to survey local amphibian populations throughout a range of habitats. This multiplex qPCR demonstrates high reproducibility, sensitivity, and was capable of detecting both Bd and ranavirus in numerous locations, species, and life stages. Bsal was not detected at any point during these sampling efforts.

Investigation of multiple mortality events in eastern box turtles (Terrapene carolina carolina)

Wildlife mortality investigations are important for conservation, food safety, and public health; but they are infrequently reported for cryptic chelonian species. Eastern box turtles (Terrapene carolina carolina) are declining due to anthropogenic factors and disease, and while mortality investigations have been reported for captive and translocated individuals, few descriptions exist for free-living populations. We report the results of four natural mortality event investigations conducted during routine health surveillance of three Illinois box turtle populations in 2011, 2013, 2014, and 2015. In April 2011, over 50 box turtles were found dead and a polymicrobial necrotizing bacterial infection was diagnosed in five survivors using histopathology and aerobic/anaerobic culture. This represents the first reported occurrence of necrotizing bacterial infection in box turtles. In August 2013, paired histopathology and qPCR ranavirus detection in nine turtles was significantly associated with occupation of moist microhabitats, identification of oral plaques and nasal discharge on physical exam, and increases in the heterophil count and heterophil to lymphocyte ratio (p < 0.05). In July 2014 and 2015, ranavirus outbreaks reoccurred within a 0.2km radius of highly-disturbed habitat containing ephemeral ponds used by amphibians for breeding. qPCR ranavirus detection in five individuals each year was significantly associated with use of moist microhabitats (p < 0.05). Detection of single and co-pathogens (Terrapene herpesvirus 1, adenovirus, and Mycoplasma sp.) was common before, during, and after mortality events, but improved sample size would be necessary to determine the impacts of these pathogens on the occurrence and outcome of mortality events. This study provides novel information about the causes and predictors of natural box turtle mortality events. Continued investigation of health, disease, and death in free-living box turtles will improve baseline knowledge of morbidity and mortality, identify threats to survival, and promote the formation of effective conservation strategies.

RANAVIRUS CAUSES MASS DIE-OFFS OF ALPINE AMPHIBIANS IN THE SOUTHWESTERN ALPS, FRANCE

Pathogenic fungi and viruses cause mortality outbreaks in wild amphibians worldwide. In the summer of 2012, dead tadpoles and adults of the European common frog Rana temporaria were reported in alpine lakes in the southwestern Alps (Mercantour National Park, France). A preliminary investigation using molecular diagnostic techniques identified a Ranavirus as the potential pathogenic agent. Three mortality events were recorded in the park, and samples were collected. The amphibian chytrid fungus Batrachochytrium dendrobatidis was not detected in any of the dead adult and juvenile frogs sampled (n=16) whereas all specimens were positive for a Ranavirus. The genome sequence of this Ranavirus was identical to previously published sequences of the common midwife toad virus (CMTV), a Ranavirus that has been associated with amphibian mortalities throughout Europe. We cultured virus from the organs of the dead common frogs and infecting adult male common frogs collected in another alpine region where no frog mortality had been observed. The experimentally infected frogs suffered 100% mortality (n=10). The alpine die-off is the first CMTV outbreak associated with mass mortality in wild amphibians in France. We describe the lesions observed and summarize amphibian populations affected by Ranaviruses in Europe. In addition, we discuss the ecologic specificities of mountain amphibians that may contribute to increasing their risk of exposure to and transmission of Ranaviruses.

Co-Infection by Chytrid Fungus and Ranaviruses in Wild and Harvested Frogs in the Tropical Andes

While global amphibian declines are associated with the spread of Batrachochytrium dendrobatidis (Bd), undetected concurrent co-infection by other pathogens may be little recognized threats to amphibians. Emerging viruses in the genus Ranavirus (Rv) also cause die-offs of amphibians and other ectotherms, but the extent of their distribution globally, or how co-infections with Bd impact amphibians are poorly understood. We provide the first report of Bd and Rv co-infection in South America, and the first report of Rv infections in the amphibian biodiversity hotspot of the Peruvian Andes, where Bd is associated with extinctions. Using these data, we tested the hypothesis that Bd or Rv parasites facilitate co-infection, as assessed by parasite abundance or infection intensity within individual adult frogs. Co-infection occurred in 30% of stream-dwelling frogs; 65% were infected by Bd and 40% by Rv. Among terrestrial, direct-developing Pristimantis frogs 40% were infected by Bd, 35% by Rv, and 20% co-infected. In Telmatobius frogs harvested for the live-trade 49% were co-infected, 92% were infected by Bd, and 53% by Rv. Median Bd and Rv loads were similar in both wild (Bd = 10^1.2 Ze, Rv = 10^2.3 viral copies) and harvested frogs (Bd = 10^3.1 Ze, Rv = 10^2.7 viral copies). While neither parasite abundance nor infection intensity were associated with co-infection patterns in adults, these data did not include the most susceptible larval and metamorphic life stages. These findings suggest Rv distribution is global and that co-infection among these parasites may be common. These results raise conservation concerns, but greater testing is necessary to determine if parasite interactions increase amphibian vulnerability to secondary infections across differing life stages, and constitute a previously undetected threat to declining populations. Greater surveillance of parasite interactions may increase our capacity to contain and mitigate the impacts of these and other wildlife diseases.

Pathogenicity in six Australian reptile species following experimental inoculation with Bohle iridovirus

Ranaviruses are able to infect multiple species of fish, amphibian and reptile, and some strains are capable of interclass transmission. These numerous potential carriers and reservoir species compound efforts to control and contain infections in cultured and wild populations, and a comprehensive knowledge of susceptible species and life stage is necessary to inform such processes. Here we report on the challenge of 6 water-associated reptiles with Bohle iridovirus (BIV) to investigate its potential pathogenicity in common native reptiles of the aquatic and riparian fauna of northern Queensland, Australia. Adult tortoises Elseya latisternum and Emydura krefftii, snakes Boiga irregularis, Dendrelaphis punctulatus and Amphiesma mairii, and yearling crocodiles Crocodylus johnstoni were exposed via intracoelomic inoculation or co-habitation with infected con-specifics, but none were adversely affected by the challenge conditions applied here. Bohle iridovirus was found to be extremely virulent in hatchling tortoises E. latisternum and E. krefftii via intracoelomic challenge, as demonstrated by distinct lesions in multiple organs associated with specific immunohistochemistry staining and a lethal outcome (10/17) of the challenge. Virus was re-isolated from 2/5 E. latisternum, 4/12 E. krefftii and 1/3 brown tree snakes B. irregularis. Focal necrosis, haemorrhage and infiltration of granulocytes were frequently observed histologically in the pancreas, liver and sub-mucosa of the intestine of challenged tortoise hatchlings. Immunohistochemistry demonstrated the presence of ranavirus antigens in the necrotic lesions and in individual cells of the vascular endothelium, the connective tissue and in granulocytes associated with necrosis or present along serosal surfaces. The outcome of this study confirms hatchling tortoises are susceptible to BIV, thereby adding Australian reptiles to the host range of ranaviruses. Additionally, given that BIV was originally isolated from an amphibian, our study provides additional evidence that interclass transmission of ranavirus may occur in the wild.

Health assessment of free-living eastern box turtles (Terrapene carolina carolina) in and around the Maryland Zoo in Baltimore 1996-2011

Health data for free-living eastern box turtles (Terrapene carolina carolina) at the Maryland Zoo in Baltimore were analyzed. One hundred and eighteen turtles were captured on or near zoo grounds over the course of 15 yr (1996-2011), with recapture of many individuals leading to 208 total evaluations. Of the 118 individuals, 61 were male, 50 were female, and 7 were of undetermined sex. Of the 208 captures, 188 were healthy, and 20 were sick or injured. Complete health evaluations were performed on 30 turtles with physical examination records, complete blood counts (CBCs), and plasma biochemistry profiles. Eight animals were sampled more than once, yielding 40 total samples for complete health evaluations of these 30 individuals. The 40 samples were divided into healthy (N=29) and sick (N=11) groups based on clinical findings on physical examination. Samples from healthy animals were further divided into male (N=17) and female (N= 12) groups. CBC and biochemistry profile parameters were compared between sick and healthy groups and between healthy males and females. Sick turtles had lower albumin, globulin, total protein (TP), calcium, phosphorous, sodium, and potassium than healthy animals. Sick turtles also had higher heterophil to lymphocyte ratios. Healthy female turtles had higher leukocyte count, eosinophil count, total solids, TP, globulin, cholesterol, calcium, and phosphorous than healthy males. Banked plasma from all 40 samples was tested for antibodies to Mycoplasma agassizii and Mycoplasma testudineum via enzyme-linked immunosorbent assay. One sample from a clinically healthy female was antibody positive for M. agassizii; none were positive for M. testudineum. This study provides descriptive health data for eastern box turtles and CBC and biochemistry profile information for T. carolina carolina at and near the Maryland Zoo in Baltimore. It also reports low serologic evidence of exposure to mycoplasmosis.

First case of ranavirus and associated morbidity and mortality in an eastern mud turtle Kinosternon subrubrum in South Carolina

Ranaviruses are double-stranded DNA viruses that infect amphibians, fish, and reptiles, causing global epidemics in some amphibian populations. It is important to identify new species that may be susceptible to the disease, particularly if they reside in the same habitat as other at-risk species. On the Savannah River Site (SRS) in Aiken, South Carolina, USA, ranaviruses are present in several amphibian populations, but information is lacking on the presence, prevalence, and morbidity of the virus in reptile species. An eastern mud turtle Kinosternon subrubrum captured on the SRS in April 2014 exhibited clinical signs of a ranaviral infection, including oral plaque and conjunctivitis. Quantitative PCR analyses of DNA from liver tissue, ocular, oral, nasal, and cloacal swabs were all positive for ranavirus, and sequencing of the template confirmed infection with a FV3-like ranavirus. Histopathologic examination of postmortem tissue samples revealed ulceration of the oral and tracheal mucosa, intracytoplasmic epithelial inclusions in the oral mucosa and tongue sections, individualized and clusters of melanomacrophages in the liver, and bacterial rods located in the liver, kidney, heart, stomach, and small intestine. This is the first report of morbidity and mortality of a mud turtle with a systemic ranaviral infection.