Hepatitis associated with herpes viral infection in the tortoise (Testudo horsfieldii)

A testudinid herpesvirus 1 (TeHV1)-associated disease outbreak in a group of Horsfield's tortoises (Testudo horsfieldii)

In spring 2020, a severe disease outbreak with high morbidity and mortality was observed in a collection of 15 Horsfield's tortoises (Testudo horsfieldii). Affected tortoises showed upper respiratory- and gastrointestinal tract signs, including rhinitis and stomatitis. Testudinid herpesvirus 1 (TeHV1) and Mycoplasma spp. were detected by PCR in oral swabs of affected animals. Histological examination of one deceased animal showed intranuclear inclusion bodies typical for herpesvirus infections in liver, spleen and oesophagus. The virus was likely introduced into the collection 2 years earlier by a clinically healthy Horsfield's tortoise that was tested positive for TeHV1 by PCR.

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.

CHARACTERIZING THE EPIDEMIOLOGY OF HISTORIC AND NOVEL PATHOGENS IN BLANDING'S TURTLES (EMYDOIDEA BLANDINGII)

Pathogens such as herpesviruses, Mycoplasma spp., and frog virus 3-like ranavirus have contributed to morbidity and mortality in many species of free-living and zoo-maintained chelonians. However, their prevalence is understudied in Blanding's turtles (Emydoidea blandingii) across North America. To assess the presence of these pathogens, Blanding's turtles were sampled in Lake County, Illinois, in 2017 (N = 213) and 2018 (N = 160). DNA from cloacal-oral swabs was assayed for four ranaviruses, three Mycoplasma spp., two Salmonella spp., Emydoidea herpesvirus 1 (EBHV1), and tortoise intranuclear coccidiosis (TINC) using a multiplex quantitative polymerase chain reaction (qPCR). Pathogens were most frequently detected in adult turtles (n = 25) and rarely in subadults (n = 2) or juveniles (n = 1). EBHV1 was detected in 22 individuals with no clinical signs of illness, most (n = 20) occurring in the month of May (P < 0.0001). EBHV1 cases at one study site significantly clustered within the same 0.64-km area from 17 to 22 May 2017 (P < 0.0001) and 14 to 15 May 2018 (P = 0.0006). Individuals were rarely positive for Salmonella typhimurium (n = 6). A novel Mycoplasma sp. sharing high homology with other emydid Mycoplasma spp. was detected in one turtle with nasal discharge. Neither TINC nor any ranaviruses were detected. Continued monitoring of this population and habitat may facilitate identification of risk factors for pathogen occurrence and clarify the impact of infectious diseases on Blanding's turtle conservation outcomes.

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.

Hematological and pathological features of massive hepatic necrosis in two radiated tortoises (Astrochelys radiata)

Two radiated tortoises (Astrochelys radiata) exhibited anorexia and hypokinesia. In both cases, hematological and serum biochemical examinations revealed high alkaline phosphatase levels, moderately high aspartate aminotransferase levels and white blood cell counts approximately within the normal range. Despite being treated, the tortoises died 9 and 43 days after the first clinical examination. Gross pathological examinations revealed that the livers of both animals were extremely swollen and contained pale yellow necrotic tissue. Histopathological assessment revealed that the livers contained a massive area of hepatic necrosis surrounded by migration of macrophages and multinucleated giant cells. In one of the cases, severe fibrosis was observed. The present study provides reference information for similar cases in the future.

PREVALENCE OF TERRAPENE HERPESVIRUS 1 IN FREE-RANGING EASTERN BOX TURTLES (TERRAPENE CAROLINA CAROLINA) IN TENNESSEE AND ILLINOIS, USA

Diseases affecting the upper respiratory tract, such as herpesviruses, are well described in captive chelonians worldwide, but their importance in free-ranging populations is less well known. To characterize the disease epidemiology of terrapene herpesvirus 1 (TerHV1), 409 free-ranging eastern box turtles ( Terrapene carolina carolina) in Tennessee and Illinois, US were tested for TerHV1 in 2013 and 2014 using TaqMan quantitative PCR. Whole blood and swabs of the oral mucosa were collected from 365 adults (154 females, 195 males, 16 unknown sex) and 44 juveniles. The prevalence of detection was 31.3% (n=128). Turtles were more likely to be positive for TerHV1 in July (50%; n=67) compared to September (38%; n=44) and May (11%; n=17). Turtles sampled in 2014 had a significantly higher prevalence (50%; n=98) than in 2013 (14%; n=30). In a multivariate model, only season, year, and the interaction between season and year were maintained; turtles were most likely to be positive in July (odds ratio: 30.5) and September (odds ratio: 41.8) 2014 compared to May 2013. The prevalence was not statistically different by state of collection, sex, or age class. Packed cell volume (25.5%) and total solids (4.8 mg/dL) in positive turtles were significantly higher than in negative turtles (23.0%; 4.3 mg/dL). Positive turtles had increased eosinophil concentrations, fewer lymphocytes, and fewer monocytes. No clinical sign was associated with detection of herpesvirus. Widespread DNA evidence of TerHV1 infection was detected in eastern box turtles, and knowledge of the epidemiology of this virus may aid in management of free-ranging and captive individuals.

The Genome of a Tortoise Herpesvirus (Testudinid Herpesvirus 3) Has a Novel Structure and Contains a Large Region That Is Not Required for Replication In Vitro or Virulence In Vivo

Testudinid herpesvirus 3 (TeHV-3) is the causative agent of a lethal disease affecting several tortoise species. The threat that this virus poses to endangered animals is focusing efforts on characterizing its properties, in order to enable the development of prophylactic methods. We have sequenced the genomes of the two most studied TeHV-3 strains (1976 and 4295). TeHV-3 strain 1976 has a novel genome structure and is most closely related to a turtle herpesvirus, thus supporting its classification into genus Scutavirus, subfamily Alphaherpesvirinae, family Herpesviridae. The sequence of strain 1976 also revealed viral counterparts of cellular interleukin-10 and semaphorin, which have not been described previously in members of subfamily Alphaherpesvirinae. TeHV-3 strain 4295 is a mixture of three forms (m1, m2, and M), in which, in comparison to strain 1976, the genomes exhibit large, partially overlapping deletions of 12.5 to 22.4 kb. Viral subclones representing these forms were isolated by limiting dilution assays, and each replicated in cell culture comparably to strain 1976. With the goal of testing the potential of the three forms as attenuated vaccine candidates, strain 4295 was inoculated intranasally into Hermann's tortoises (Testudo hermanni). All inoculated subjects died, and PCR analyses demonstrated the ability of the m2 and M forms to spread and invade the brain. In contrast, the m1 form was detected in none of the organs tested, suggesting its potential as the basis of an attenuated vaccine candidate. Our findings represent a major step toward characterizing TeHV-3 and developing prophylactic methods against it.

IMPORTANCE

Testudinid herpesvirus 3 (TeHV-3) causes a lethal disease in tortoises, several species of which are endangered. We have characterized the viral genome and used this information to take steps toward developing an attenuated vaccine. We have sequenced the genomes of two strains (1976 and 4295), compared their growth in vitro, and investigated the pathogenesis of strain 4295, which consists of three deletion mutants. The major findings are that (i) TeHV-3 has a novel genome structure, (ii) its closest relative is a turtle herpesvirus, (iii) it contains interleukin-10 and semaphorin genes (the first time these have been reported in an alphaherpesvirus), (iv) a sizeable region of the genome is not required for viral replication in vitro or virulence in vivo, and (v) one of the components of strain 4295, which has a deletion of 22.4 kb, exhibits properties indicating that it may serve as the starting point for an attenuated vaccine.

A novel herpesvirus of the proposed genus Chelonivirus from an asymptomatic bowsprit tortoise (Chersina angulata)

A wild-caught Bowsprit tortoise (Chersina angulata) was received into quarantine and appeared clinically normal. Oral swabs for consensus herpesvirus polymerase chain reaction (PCR) and sequencing were obtained during routine quarantine, and a novel herpesvirus was identified. Comparative sequence analysis shows that this virus is a member of the subfamily Alphaherpesvirinae in the proposed genus Chelonivirus. Host/virus co-evolution appears to be common amongst herpesviruses and their hosts, and the most significant disease is typically seen when herpesviruses jump to related host species. Previous studies have found some diversity of herpesviruses in tortoises. This report expands the number of known herpesviruses of tortoises. It is reasonable to expect that there will be significantly different clinical consequences of different tortoise herpesviruses in different species, and that identification of host/virus relationships will aid in clinical management of tortoise collections. Further work is needed to determine the clinical implications of this and other tortoise herpesviruses in different tortoise species.

Two herpesviruses associated with disease in wild Atlantic loggerhead sea turtles (Caretta caretta)

Herpesviruses are associated with lung-eye-trachea disease and gray patch disease in maricultured green turtles (Chelonia mydas) and with fibropapillomatosis in wild sea turtles of several species. With the exception fibropapillomatosis, no other diseases of wild sea turtles of any species have been associated with herpesviral infection. In the present study, six necropsied Atlantic loggerhead sea turtles (Caretta caretta) had gross and histological evidence of viral infection, including oral, respiratory, cutaneous, and genital lesions characterized by necrosis, ulceration, syncytial cell formation, and intranuclear inclusion bodies. Nested polymerase chain reaction targeting a conserved region of the herpesvirus DNA-dependent-DNA polymerase gene yielded two unique herpesviral sequences referred to as loggerhead genital-respiratory herpesvirus and loggerhead orocutaneous herpesvirus. Phylogenetic analyses indicate that these viruses are related to and are monophyletic with other chelonian herpesviruses within the subfamily alpha-herpesvirinae. We propose the genus Chelonivirus for this monophyletic group of chelonian herpesviruses.

Identification of a novel herpesvirus from a California desert tortoise (Gopherus agassizii)

Herpesviruses are significant pathogens of tortoises, causing upper respiratory tract disease and necrotizing stomatitis, with infections often associated with high mortality rates. Herpesvirus infection in a captive California desert tortoise (Gopherus agassizii) was detected by light microscopic observation of intranuclear inclusion bodies in various tissues followed by transmission electron microscopic observation of herpesvirus-like particles, and amplification of herpesvirus nucleic acid sequences using polymerase chain reaction. Using an indirect enzyme linked immunosorbent assay, anti-tortoise herpesvirus antibodies were detected one month after initial onset of clinical signs. This novel herpesvirus is distinct from the previously described tortoise herpesvirus (tortoise herpesvirus-1, THV-1) sharing 83% sequence identity of 60 amino acids of a portion of the DNA polymerase gene and 79% sequence identity across 120 amino acids of a portion of the ribonucleotide reductase gene. Similar to THV-1, this novel herpesvirus, tortoise herpesvirus-2 (THV-2), also clusters with the alphaherpesviruses.