Herpesvirus in a captive Australian Krefft's river turtle (Emydura macquarii krefftii)

Herpesviruses in Reptiles

Since the 1970s, several species of herpesviruses have been identified and associated with significant diseases in reptiles. Earlier discoveries placed these viruses into different taxonomic groups on the basis of morphological and biological characteristics, while advancements in molecular methods have led to more recent descriptions of novel reptilian herpesviruses, as well as providing insight into the phylogenetic relationship of these viruses. Herpesvirus infections in reptiles are often characterised by non-pathognomonic signs including stomatitis, encephalitis, conjunctivitis, hepatitis and proliferative lesions. With the exception of fibropapillomatosis in marine turtles, the absence of specific clinical signs has fostered misdiagnosis and underreporting of the actual disease burden in reptilian populations and hampered potential investigations that could lead to the effective control of these diseases. In addition, complex life histories, sampling bias and poor monitoring systems have limited the assessment of the impact of herpesvirus infections in wild populations and captive collections. Here we review the current published knowledge of the taxonomy, pathogenesis, pathology and epidemiology of reptilian herpesviruses.

EPIDEMIOLOGY OF EMYDOIDEA HERPESVIRUS 1 IN FREE-RANGING BLANDING'S TURTLES (EMYDOIDEA BLANDINGII) FROM ILLINOIS

Herpesvirus infections have been associated with high morbidity and mortality in populations of captive emydid chelonians worldwide, but novel herpesviruses have also recently been identified in apparently healthy free-ranging emydid populations. Blanding's turtle (Emydoidea blandingii), an endangered species in Illinois, has experienced range-wide declines because of habitat loss, degradation, and fragmentation. A novel herpesvirus, Emydoidea herpesvirus 1 (EBHV1), was identified in Blanding's turtles in DuPage County, IL, in 2015. Combined oral-cloacal swabs were collected from radio transmitter-fitted and trapped (n = 54) turtles multiple times over the 2016 activity season. In addition, swabs were collected at a single time point from trapped and incidentally captured (n = 84) Blanding's turtles in DuPage (n = 33) and Lake (n = 51) counties over the same field season. Each sample was tested for EBHV1 using quantitative polymerase chain reaction (qPCR). EBHV1 was detected in 15 adult females for an overall prevalence of 10.8% (n = 15/138; 95% confidence interval [CI]: 6.2-17.3%). In radio transmitter-fitted females, there was a significantly higher prevalence of EBHV1 DNA in May (23.8%, n = 10/42) than June (3.6%, n = 1/28), July (0%, n = 0/42), August (0%, n = 0/47), or September (7.7%, n = 3/39) (odds ratio: 12.19; 95% CI: 3.60-41.30). The peak in May corresponds to the onset of nesting and may be associated with increased physiologic demands. Furthermore, all positive turtles were qPCR negative in subsequent months. There were no clinical signs associated with EBHV1 detection. This investigation is the critical first step to characterizing the implications of EBHV1 for Blanding's turtle population health and identifying management changes that may improve sustainability.

Development and validation of a quantitative PCR assay for detection of Terrapene herpesvirus 2 in eastern box turtles (Terrapene carolina carolina)

Herpesviruses are associated with disease in many chelonian species, resulting in pathology such as respiratory tract infection, stomatitis, conjunctivitis, hepatitis, and papillomatosis. Herpesvirus-associated fibropapillomas cause significant morbidity and mortality in marine turtles, and have been identified in an eastern box turtle (Terrapene carolina carolina) infected with Terrapene herpesvirus 2 (TerHV2). Further investigation is necessary to understand the impact of carcinogenic herpesviruses on chelonian health; however, reliable and specific methods for detection and quantitation of herpesviral load are lacking. The purpose of this study was to develop and validate a quantitative PCR assay for detection of TerHV2 in box turtles. TaqMan primer-probes were developed targeting the DNA polymerase gene. Inter- and intra-assay variability, linear range of detection, limit of detection, and specificity were assessed. The assay was highly specific for TerHV2, failing to amplify seven closely-related chelonian herpesviruses. It performed with high efficiency (slope = -3.52, R² = 1, efficiency = 92.29 %), low intra-assay variability and low inter-assay variability (coefficient of variation ≤ 1.25 % at all standard dilutions). Reaction efficiency was not impacted in the presence of box turtle DNA from combined oral/cloacal swabs or whole blood. This qPCR assay has a linear range of detection from 10⁷ to 10¹ viral copies per reaction and provides a valuable tool in the surveillance and characterization of TerHV2 in box turtles.

Herpesvirus associated dermal papillomatosis in Williams' mud turtle Pelusios williamsi with effects of autogenous vaccine therapy

An adult female of Williams’ mud turtle, Pelusios williamsi long-term captive, that was allegedly caught wild in Kenya was found to have developed papilloma-like skin lesions. Excised tumors were examined histologically after routine processing with hematoxylin and eosin (H & E) stained slides, examined for the presence of viral particles by electron microscopy employing negative staining, and examined for the presence of viral DNA by PCR. Microscopic features in pre-treatment biopsies were fully diagnostic and consistent with multifocal squamous cell papilloma. Viral-type inclusion bodies were not identified. Turtle was found to be infected by reptilian herpesvirus. Association with herpesvirus and vast multiplicity of tumors thwarted surgical solution. An autogenous vaccine was prepared using 5 g of excised fresh tissue, aseptically ground, treated with diluted formalin, centrifuged to obtain a supernatant, and subsequently exposed to UV light. Autogenous vaccine induced substantial areas of necrosis of the papillomatous lesions noted by the loss of cytological architecture, nuclear loss, and by edema. The outer edges of the healing biopsies appeared to be regenerating. Therefore, our vaccine application could be considered as effective. It is difficult to treat and eliminate herpesvirus infection because of its cryptic presence and sudden onset of disease. Successful application of autogenous vaccine could be a potentially promising strategy, which deserves further testing.

Development and validation of a quantitative PCR assay for detection of Emydoidea herpesvirus 1 in free-ranging Blanding's turtles (Emydoidea blandingii)

Blanding's turtles (Emydoidea blandingii), an endangered species in Illinois, have experienced range-wide declines because of habitat degradation and fragmentation, predation, and road mortality. While ongoing studies are crucial to a thorough understanding of the natural history and demographics in these disjointed Illinois populations, infectious disease threats have been largely unevaluated. Herpesvirus outbreaks have been associated with high morbidity and mortality in populations of captive tortoises and turtles worldwide, including the family Emydidae (pond and box turtles). However, novel herpesviruses including Terrapene herpesvirus 1, Emydid herpesvirus 1 and 2, and Glyptemys herpesvirus 1 and 2, have recently been identified in apparently healthy free-ranging freshwater turtles. In 2015, 20 free-ranging Blanding's turtles in DuPage County, Illinois were screened for a herpesvirus using consensus PCR. A novel herpesvirus species (Emydoidea herpesvirus 1; EBHV1) was identified in two animals and shared a high degree of sequence homology to other freshwater turtle herpesviruses. Two quantitative real-time PCR assays, using EBHV1 primer-1 and primer-2, were developed to target an EBHV1-specific segment of the DNA-dependent DNA polymerase gene and validated. Both assays performed with high efficiency (slope = -3.2; R² = 1), low intra-assay variability, and low inter-assay variability (coefficient of variation <2% at all dilutions). However, EBHV1 primer-2 displayed less variation and was selected to test clinical samples and five closely related herpesvirus control samples. Results indicate that this assay is specific for EBHV1, has a linear range of detection from 10⁸ to 10¹ viral copies per reaction, and can categorically detect as few as 1 viral copy per reaction. This qPCR assay provides a valuable diagnostic tool for future characterization of EBHV1 epidemiology.

Detection of Mycoplasma spp., herpesviruses, topiviruses, and ferlaviruses in samples from chelonians in Europe

We tested samples from 1,015 chelonians in Europe for Mycoplasma spp., herpesviruses, ranaviruses, picornaviruses, and ferlaviruses by PCR. Mycoplasma spp. were detected in 42.1% and herpesviruses were detected in 8.0% of tested chelonians. Differentiation of the herpesviruses revealed that 46.9% of the detected chelonian viruses were testudinid herpesvirus 1 (TeHV-1) and 54.3% were TeHV-3, including co-detections of TeHV-1 and -3 in 3 tortoises. TeHV-4 was detected in a leopard tortoise ( Stigmochelys pardalis), and a herpesvirus that could not be further characterized was found in a pond slider ( Trachemys scripta). Picornaviruses (topiviruses) were detected in 2.2% of the tested animals; ferlaviruses were found in 0.6%; no ranaviruses were detected in any of the animals tested. Mycoplasma spp. were detected significantly more often in Horsfield’s tortoises ( Testudo horsfieldii), leopard tortoises, and Indian star tortoises ( Geochelone elegans) than in other species. Horsfield’s tortoises were also significantly more often positive for TeHV-1. Mycoplasma and TeHV-1 were co-detected in 3.0%, and mycoplasma and TeHV-3 in 2.3%. The TeHV-4–positive tortoise was also positive for mycoplasma. Mycoplasma and picornaviruses were co-detected in 1.2% of the tortoises. A spur-thighed tortoise ( Testudo graeca) was positive for mycoplasma and a ferlavirus. In some cases, >2 pathogens were detected. A significant correlation between mycoplasma and herpesvirus detection was found. Of all tested animals, 47.6% were positive for at least one pathogen, demonstrating the importance of pathogen detection in captive chelonians.

A Genomic Approach to Unravel Host-Pathogen Interaction in Chelonians: The Example of Testudinid Herpesvirus 3

We report the first de novo sequence assembly and analysis of the genome of Testudinid herpesvirus 3 (TeHV3), one of the most pathogenic chelonian herpesviruses. The genome of TeHV3 is at least 150,080 nucleotides long, is arranged in a type D configuration and comprises at least 102 open reading frames extensively co-linear with those of Human herpesvirus 1. Consistently, the phylogenetic analysis positions TeHV3 among the Alphaherpesvirinae, closely associated with Chelonid herpesvirus 5, a Scutavirus. To date, there has been limited genetic characterization of TeHVs and a resolution beyond the genotype was not feasible because of the lack of informative DNA sequences. To exemplify the potential benefits of the novel genomic information provided by this first whole genome analysis, we selected the glycoprotein B (gB) gene, for detailed comparison among different TeHV3 isolates. The rationale for selecting gB is that it encodes for a well-conserved protein among herpesviruses but is coupled with a relevant antigenicity and is consequently prone to accumulate single nucleotide polymorphisms. These features were considered critical for an ideal phylogenetic marker to investigate the potential existence of distinct TeHV3 genogroups and their associated pathology. Fifteen captive tortoises presumptively diagnosed to be infected with TeHVs or carrying compatible lesions on the basis of either the presence of intranuclear inclusions (presumptively infected) and/or diphtheronecrotic stomatitis-glossitis or pneumonia (compatible lesions) were selected for the study. Viral isolation, TeHV identification, phylogenetic analysis and pathological characterization of the associated lesions, were performed. Our results revealed 1) the existence of at least two distinct TeHV3 genogroups apparently associated with different pathologies in tortoises and 2) the first evidence for a putative homologous recombination event having occurred in a chelonian herpesvirus. This novel information is not only fundamental for the genetic characterization of this virus but is also critical to lay the groundwork for an improved understanding of host-pathogen interactions in chelonians and contribute to tortoise conservation.