Acute neuropathogenicity with experimental infection of equine herpesvirus 9 in common marmosets (Callithrix jacchus)

Correlation of Immunomodulatory Cytokine Expression with Histopathological Changes and Viral Antigen in a Hamster Model of Equine Herpesvirus-9 Encephalitis

A group of hamsters (n = 25) was intranasally infected with equine herpesvirus-9 (EHV-9) and mRNA transcription levels of several proinflammatory (IFN-γ, TNF-α and IL-6) and anti-inflammatory (IL-4, IL-10 and TGF-β) cytokines were investigated in brain tissue using RT-qPCR. These levels were correlated with the severity of sequential histopathological changes and intensity of immunohistochemical labelling of virus antigen in brain. Early and progressive upregulation of all the proinflammatory and anti-inflammatory cytokines investigated (P < 0.05) was correlated with increasing severity of encephalitis and viral antigen expression from 2 days post infection (dpi) with a peak at 4-5 dpi (P <0.05).

Time Course-Dependent Study on Equine Herpes Virus 9-Induced Abortion in Syrian Hamsters

Simple Summary

Equine herpesvirus 9 (EHV-9) is a virus belonging to the family of equine herpesviruses. EHV-9 has been isolated from natural infections of different wild and zoo animals. In addition, it has been associated with encephalitis and abortion in several animal species. However, the host range and pathogenesis of this virus are still unknown. Herein, we investigated the underlying pathogenesis of EHV-9-induced abortion in relation to the gestation period in either early or late trimester infection. We noticed that the late trimester infection of EHV-9 was associated with more severe death and both placental and fetal tissue localization of the virus. Also, early stage infection was accompanied by band necrotic changes within the placenta, which usually led to abortion.

Abstract

This study aimed to follow the time-course pathogenesis of EHV-9 abortion in early and late trimesters. Twenty-seven pregnant hamster dams were divided into three groups: (G1) control, (G2) EHV-9-inoculated on the 5th day (early trimester), and (G3) EHV-9-inoculated on the 10th day of gestation (late trimester). Dams were sacrificed at different time points during gestation and examined for viremia and viral DNA in different fetal and maternal tissues and pathological changes in fetal tissue, placenta, and cytokines. Animals in G3 showed a marked increase in the number of dead fetuses than those in G2. Histopathological findings of G2 showed early band coagulative necrosis of maternal spaces and stromal decidual cells. Necrotic changes were observed within the decidua basalis, spongiotrophoblast layer, and labyrinth. First, the virus was localized within mononuclear leukocytes in the decidua capsularis and basalis, and within the necrotic chorionic villi and cervical epithelium. G3 demonstrated degenerative changes within the chorionic villi and trophospongium. The virus antigen was observed within the chorionic villi, trophoblasts, mononuclear cells, and fetal tissues. In conclusion, EHV-9 induced abortion mostly occurs through necrosis of the chorionic villi and cannot cross through the capsular placenta in the early trimester but can through the developed decidual placentation.

Comparative Neuropathogenesis of Equine Herpesvirus 9 and its Mutant Clone (SP21) Inoculated Intranasally in a Hamster Model

The neuropathogenesis of equine herpesvirus 9 (EHV-9), a neurotropic herpesvirus, and its mutant clone (SP21) was studied experimentally in a hamster model. EHV-9-infected hamsters showed clinical signs of infection at 3 days post infection (dpi), while infection with SP21 resulted in clinical signs at 4 dpi. Clinical signs were more severe in the EHV-9-infected group than in the SP21-infected group. There was a significant difference in the time of anterograde transmission of EHV-9 and SP21 inside the brain. Viraemia was detected in the EHV-9-infected group at 4-5 dpi, while no viraemia was detected in the SP21-infected group. The serum concentration of tumour necrosis factor-α was significantly higher in EHV-9-infected animals than in those infected by SP21 group at 4-5 dpi, but there was no difference in the serum concentration of interferon-γ. The spatiotemporal profiles of viral replication and virus-associated histopathology were remarkably similar, were high in the olfactory bulb and cerebral hemispheres, and decreased progressively towards the medulla oblongata. The mean group scores of the histopathological changes for the entire brain were significantly higher in the EHV-9 group than in the SP21 group at all time points, starting from 3 dpi. These results suggest that the gene products of the open reading frame (ORF)19 and ORF14 play essential roles in the neuropathogenesis of EHV-9, as the two point-mutations detected in SP21 significantly altered the neuropathogenesis of the virus.

Lesions and Distribution of Viral Antigen in the Brain of Hamsters Infected With Equine Herpesvirus (EHV)–9, EHV-1 Strain Ab4p, and Zebra-Borne EHV-1

Encephalitis in hamsters, which was induced by equine herpesvirus (EHV)–9, EHV-1 strain Ab4p, and zebra-borne EHV-1, was investigated and compared to assess viral kinetics and identify the progression and severity of neuropathological findings. Hamsters were inoculated with EHV-9, EHV-1 strain Ab4p, and zebra-borne EHV-1 via the nasal route and euthanized at 24, 48, 72, 96, 120, 144, and 168 hours postinoculation (HPI). The inoculated hamsters had mild to severe neurological signs at 60 to 72, 96, and 120 HPI, and the mortality rate was 75%, 0%, and 0% for animals inoculated with EHV-9, EHV-1 strain Ab4p, and zebra-borne EHV-1 viruses, respectively. Inoculated hamsters had varying degrees of rhinitis and lymphoplasmacytic meningoencephalitis, as well as differences in the severity and distribution of cerebral lesions. Furthermore, the cellular distribution of viral antigen depended on the inoculated virus. Neuronal necrosis was widely detected in animals inoculated with EHV-9, while marked perivascular cuffs of infiltrating inflammatory cells and gliosis were detected in animals inoculated with EHV-1 strain Ab4p and zebra-borne EHV-1. In the present study, 3 viruses belonging to the herpesvirus family induced encephalitis after initial propagation in the nasal cavity. These viruses might travel to the brain via the olfactory pathway and/or trigeminal nerve, showing different distributions and severities of neuropathological changes.

How Host Specific Are Herpesviruses? Lessons from Herpesviruses Infecting Wild and Endangered Mammals

Herpesviruses are ubiquitous and can cause disease in all classes of vertebrates but also in animals of lower taxa, including molluscs. It is generally accepted that herpesviruses are primarily species specific, although a species can be infected by different herpesviruses. Species specificity is thought to result from host-virus coevolutionary processes over the long term. Even with this general concept in mind, investigators have recognized interspecies transmission of several members of the Herpesviridae family, often with fatal outcomes in non-definitive hosts-that is, animals that have no or only a limited role in virus transmission. We here summarize herpesvirus infections in wild mammals that in many cases are endangered, in both natural and captive settings. Some infections result from herpesviruses that are endemic in the species that is primarily affected, and some result from herpesviruses that cause fatal disease after infection of non-definitive hosts. We discuss the challenges of such infections in several endangered species in the absence of efficient immunization or therapeutic options.

Effect of a single point mutation on equine herpes virus 9 (EHV-9) neuropathogenicity after intranasal inoculation in a hamster model

This study aimed to investigate the neuropathogenesis of equine herpes virus 9 (EHV-9) by studying the effects of a single point mutation introduced in two different EHV-9 genes. The two EHV-9 mutants, 14R and 19R, were generated carrying a point mutation in two separate EHV-9 genes. These mutants, along with the wild-type EHV-9, were used to infect a hamster model. The EHV-9- and 19R-infected groups showed earlier and more severe clinical signs of infection than the 14R-infected group. The white blood cells (WBCs) count was significantly increased in both EHV-9- and 19R-infected groups compared to the 14R-infected group at the 4th day post infection (DPI). Viremia was also detected earlier in both EHV-9- and 19R-infected groups than 14R-infected group. There were differences in the anterograde transmission pattern of both EHV-9 and 19R compared to 14R inside the brain. Serum TNF-α, IL-6 and IFN-γ levels were significantly increased in both EHV-9- and 19R-infected groups compared to the 14R-infected group. Histopathological and immunohistochemical analyses revealed that the mean group scores for the entire brain were significantly higher in both EHV-9- and 19R- infected groups than 14R-infected group. Collectively, these results confirm that the gene product of Open Reading Frame 19 (ORF19) plays an important role in EHV-9 neuropathogenicity and that the mutation in ORF19 is responsible for the attenuation of EHV-9.

Effect of Mouse Strain on Equine Herpesvirus 9 Infection

The infectivity of equine herpesvirus (EHV)-9 has been studied in different animal models including immunocompromised animals. The current study focused on the infectivity of EHV-9 in different mouse strains (C3H, C57BL, DBA, BALB/c-nu/nu, BALB/c and ICR) by intranasal inoculation of 2 × 10⁶ plaque forming units (PFU). Various organs, including head and lungs, were collected 7 days post infection (dpi) to investigate microscopical lesions and the distribution of EHV-9 antigen. Immunopositivity of tissue sections was scored using ImageJ software. Open reading frame (ORF) 30 expression in lung tissues was quantified using quantitative reverse transcriptase polymerase chain reaction. Pathological examination revealed different degrees of rhinitis in the different mouse strains. Severe rhinitis was detected in C3H and BALB/c-nu/nu strains, moderate rhinitis was observed in C57BL and DBA strains and no lesions were detected in BALB/c mice. Immunopositivity for EHV-9 antigens was detected in the olfactory epithelium of C3H and BALB/c-nu/nu strains. Compared with C57BL, DBA, BALB/c-nu/nu, ICR and BALB/c strains, the C3H strain showed greater expression of EHV-9 antigens in the brain. The proportion of areas with high positive to positive immunoreactivity for EHV-9 were 7.57, 3.42, 3.12, 2.51, 1.79 and 0.03% for C3H, C57BL, DBA, BALB/c-nu/nu, ICR and BALB/c strains, respectively. The proportions of areas with low positive to negative immunoreactivity were 92.42, 96.70, 96.87, 97.48, 98.16 and 99.96%, respectively. The highest relative expression levels for EHV-9 ORF30 in the lungs were in C3H mice. No significant differences in the expression of ORF30 were observed in other strains. In conclusion, of the strains examined, C3H, C57BL, DBA, BALB/c-nu/nu and ICR were the most susceptible to EHV-9 infection, and the BALB/c strain was less susceptible.

Zebra-borne neurotropic equid herpesvirus 1 meningoencephalitis in a Thomson’s gazelle (Eudorcas thomsonii)

We describe the histopathologic, immunohistochemical, and molecular features of a case of meningoencephalitis in a Thomson’s gazelle ( Eudorcas thomsonii) naturally infected with zebra-borne equid herpesvirus 1 (EHV-1) and the implications for the molecular detection of zebra-borne EHV-1. A 4-y-old female Thomson’s gazelle was submitted for postmortem examination; no gross abnormalities were noted except for meningeal congestion. Microscopic evaluation demonstrated multifocal nonsuppurative meningoencephalitis with intranuclear eosinophilic and amphophilic inclusion bodies and EHV-9 antigen in neurons. PCR demonstrated the presence of a herpesvirus with a nucleotide sequence 99–100% identical to the corresponding sequences of zebra-borne EHV-1 and of EHV-9 strains. To determine whether EHV-1 or EHV-9 was involved, a PCR with a specific primer set for EHV-9 ORF59/60 was used. The sequence was identical to that of 3 recognized zebra-borne EHV-1 strains and 91% similar to that of EHV-9. This isolate was designated as strain LM2014. The partial glycoprotein G ( gG) gene sequence of LM2014 was also identical to the sequence of 2 zebra-borne EHV-1 strains (T-529 isolated from an onager, 94-137 from a Thomson’s gazelle). The histologic lesions of encephalitis and antigen localization in this gazelle indicate prominent viral neurotropism, and lesions were very similar to those seen in EHV-1– and EHV-9–infected non-equid species. Histologic lesions caused by EHV-9 and zebra-borne EHV-1 are therefore indistinguishable.

A SEROLOGIC AND POLYMERASE CHAIN REACTION SURVEY OF EQUINE HERPESVIRUS IN BURCHELL'S ZEBRAS (EQUUS QUAGGA), HARTMANN'S MOUNTAIN ZEBRAS (EQUUS ZEBRA HARTMANNAE), AND THOMSON'S GAZELLES (EUDORCAS THOMSONII) IN A MIXED SPECIES SAVANNAH EXHIBIT

Reports of equine herpesvirus (EHV) 1 and EHV-9 causing clinical disease in a wide range of species have been well documented in the literature. It is thought that zebras are the natural hosts of EHV-9 both in the wild and in captive collections. Concerns about potential interspecies transmission of EHV-1 and EHV-9 in a mixed species savannah exhibit prompted serologic and polymerase chain reaction surveys. Eighteen Burchell's zebras ( Equus quagga ), 11 Hartmann's mountain zebras ( Equus zebra hartmannae), and 14 Thomson's gazelles ( Eudorcas thomsonii ) cohabitating the same exhibit were examined for EHV-1 virus neutralization titers, and evidence of virus via EHV 1-5 polymerase chain reactions. None of the animals had previous exposure to vaccination with EHV-1 or EHV-4. All tested zebras had positive EHV-1 titers, ranging from 4 to 384. All zebras and Thomson's gazelles had negative polymerase chain reaction results for all targeted equine herpesviruses. EHV-9-specific assays are not available but EHV-1, EHV-4, and EHV-9 cross-react serologically. Positive serology results indicate a potential latent equine herpesvirus in the zebra population, which prompted initiation of an equine herpesvirus vaccine protocol, changes in pregnant zebra mare management, and equine herpesvirus polymerase chain reaction screening prior to shipment to or from the study site.

Zebra Alphaherpesviruses (EHV-1 and EHV-9): Genetic Diversity, Latency and Co-Infections

Alphaherpesviruses are highly prevalent in equine populations and co-infections with more than one of these viruses’ strains frequently diagnosed. Lytic replication and latency with subsequent reactivation, along with new episodes of disease, can be influenced by genetic diversity generated by spontaneous mutation and recombination. Latency enhances virus survival by providing an epidemiological strategy for long-term maintenance of divergent strains in animal populations. The alphaherpesviruses equine herpesvirus 1 (EHV-1) and 9 (EHV-9) have recently been shown to cross species barriers, including a recombinant EHV-1 observed in fatal infections of a polar bear and Asian rhinoceros. Little is known about the latency and genetic diversity of EHV-1 and EHV-9, especially among zoo and wild equids. Here, we report evidence of limited genetic diversity in EHV-9 in zebras, whereas there is substantial genetic variability in EHV-1. We demonstrate that zebras can be lytically and latently infected with both viruses concurrently. Such a co-occurrence of infection in zebras suggests that even relatively slow-evolving viruses such as equine herpesviruses have the potential to diversify rapidly by recombination. This has potential consequences for the diagnosis of these viruses and their management in wild and captive equid populations.

An Ocular Infection Model Using Suckling Hamsters Inoculated With Equine Herpesvirus 9 (EHV-9)

By using a new member of the neurotropic equine herpesviruses, EHV-9, which induced encephalitis in various species via various routes, an ocular infection model was developed in suckling hamsters. The suckling hamsters were inoculated with EHV-9 via the conjunctival route and were sacrificed after 6, 12, 24, 36, 48, 72, 96, 120, and 144 hours (h) post inoculation (PI). Three horizontal sections of the brains, including the eyes and cranial cavity, were examined histologically to assess the viral kinetics and time-course neuropathological alterations using a panoramic view. At 6 to 24 h PI, there were various degrees of necrosis in the conjunctival epithelial cells, as well as frequent mononuclear cell infiltrations in the lamina propria and the tarsus of the eyelid, and frequent myositis of the eyelid muscles. At 96 h PI, encephalitis was observed in the brainstem at the level of the pons and cerebellum. EHV-9 antigen immunoreactivity was detected in the macrophages circulating in the eyelid and around the fine nerve endings supplying the eyelid, the nerves of the extraocular muscles, and the lacrimal glands from 6 h to 144 h PI. At 96 h PI, the viral antigen immunoreactivity was detected in the brainstem at the level of the pons and cerebellum. These results suggest that EHV-9 invaded the brain via the trigeminal nerve in addition to the abducent, oculomotor, and facial nerves. This conjunctival EHV-9 suckling hamster model may be useful in assessing the neuronal spread of neuropathogenic viruses via the eyes to the brain.

Cynomolgus monkeys (Macaca fascicularis) may not become infected with equine herpesvirus 9

BACKGROUND

It was suggested that Equine herpesvirus 9 (EHV-9) could be transmitted to higher non-human primates.

METHODS

Four cynomolgus monkeys (Macaca fascicularis) were inoculated with EHV-9 by the nasal route.

RESULTS

No abnormalities were observed pathologically, immunohistochemically, and genetically.

CONCLUSIONS

These findings indicate that cynomolgus monkeys are not susceptible to EHV-9.

Experimental intranasal infection of equine herpesvirus 9 (EHV-9) in suckling hamsters: kinetics of viral transmission and inflammation in the nasal cavity and brain

Equine herpesvirus 9 (EHV-9), the newest member of the equine herpesvirus family, is a highly neurotropic herpesvirus that induces encephalitis in a variety of animals. To access transmission of EHV-9 in the nasal cavity and brain, a suckling hamster model was developed so that precise sagittal sections of nasal and cranial cavities including the brain could be processed, which proved useful in detecting viral transmission as well as extension of pathological lesions. Suckling hamsters were inoculated intranasally with EHV-9, and were sacrificed at 6, 12, 18, 24, 36, 48, and 60 h post inoculation (PI). Sagittal sections of the entire head, including nasal and cranial cavities including the brain, were made to assess viral kinetics and identify the progress of the neuropathological lesions. At 12 to 24 h PI the virus attached to and propagated in the olfactory epithelium, and infected adjacent epithelial cells. At 48 h PI, immunohistochemistry for EHV-9 viral antigen showed that virus had extended from the site of infection into the olfactory bulb and olfactory nerve. These results indicate that EHV-9 rapidly invades the brain via the olfactory route after experimental intranasal infection.

Study on the infectivity of equine herpesvirus 9 (EHV-9) by different routes of inoculation in hamsters

The infectivity and pathology of equine herpesvirus 9 (EHV-9), a new neurotropic equine herpesvirus isolated from gazelles, was studied in hamsters experimentally infected via nasal, ocular, oral, intravenous (IV), or peritoneal routes. Clinically, all animals inoculated by the nasal route and ~25% inoculated by the oral and peritoneal routes showed neurological signs on days 3, 6, and 9 postinoculation (PI), respectively. Neurological signs were not observed in animals administered EHV-9 by the IV and ocular routes. With the exception of animals administered EHV-9 by the IV route, all infected animals had lymphocytic meningoencephalitis. Although there were a number of differences in the severity and distribution of the lesions depending on the route of inoculation, the basic features of lymphocytic meningoencephalitis caused by EHV-9 were common. Lesions consisted of neuronal necrosis, perivascular aggregates of lymphocytes, plasma cells, and neutrophils, gliosis, intranuclear inclusion bodies, and diffuse lymphocytic infiltrates in the meninges. Viral antigen was detected in degenerated neurons in infected animals inoculated by the nasal, ocular, oral, and peritoneal routes. The distribution of EHV-9 antigen was somewhat dependent on inoculation route. There were no microscopic abnormalities or viral antigen in animals treated by the IV route. This study provides new data about experimental EHV-9 infection in hamsters through routes other than the IV route. These results suggest that in the animals infected by the oral, ocular, and peritoneal routes, EHV-9 might travel to the brain through nerves, other than by the olfactory route, after initial propagation at the site of viral entry.

Meningoencephalitis in a Polar Bear Caused by Equine Herpesvirus 9 (EHV-9)

A 12-year-old female polar bear ( Ursus maritimus) developed a sudden onset of muscle tremors, erratic circling, increased blinking, head shaking, and ptyalism, which progressed to partial and generalized seizures. Ancillary diagnostic tests were inconclusive, and the only significant laboratory finding was nonsuppurative pleocytosis of cerebrospinal fluid. Euthanasia was elected. Microscopic evaluation demonstrated multifocal, random nonsuppurative meningoencephalitis involving most prominently the rostral cerebral cortex, as well as the thalamus, midbrain, and rostral medulla. Lesions consisted of inflammation, neuronal necrosis, gliosis, and both neuronal and glial basophilic intranuclear inclusion bodies. Immunohistochemistry with a polyclonal antibody reactive to several equine herpesviruses was positive within affected areas of the brain, and polymerase chain reaction conclusively demonstrated the presence of only equine herpesvirus 9. The clinical and morphologic features of this case resemble other fatal herpesvirus encephalitides derived from interspecies transmission and underscore the need for extreme caution when managing wild or captive equids.

New hosts for equine herpesvirus 9

Equine herpesvirus 9 was detected in a polar bear with progressive encephalitis; the source was traced to 2 members of a potential equid reservoir species, Grevy’s zebras. The virus was also found in an aborted Persian onager. Thus, the natural host range is extended to 6 species in 3 mammalian orders.