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

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ABSTRACT

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.

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Histopathology (Grevy’s zebra, CG3) showing non-suppurative encephalitis represented by mononuclear perivascular cuffs in the gray matter of the cerebral cortex (a) and forebrain (b); Hematoxilin–eosine (HE) staining. Meningeal perivascular infiltration of inflammatory cells (arrows) (c); HE staining.
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viruses-08-00262-f001: Histopathology (Grevy’s zebra, CG3) showing non-suppurative encephalitis represented by mononuclear perivascular cuffs in the gray matter of the cerebral cortex (a) and forebrain (b); Hematoxilin–eosine (HE) staining. Meningeal perivascular infiltration of inflammatory cells (arrows) (c); HE staining.

Mentions: Gross lesions in respiratory or nervous tissue were not observed at necropsy. The clinical observations for the EHV-positive animals are described in Table 1. The captive zebra (CP4) exhibited ataxia and tremors without improvement after a course of medication. Microscopic examination revealed diffuse alveolar edema in lung tissue. The EHV-9-positive zebra (CG3) exhibited central nervous disorders with ataxia and restlessness; the animal collapsed and was subsequently euthanized. Non-suppurative encephalitis associated with perivascular cuffing in the internal granular layer (IV) of the frontal part of the cerebral cortex (forebrain) and gray matter of the cerebral cortex was observed (Figure 1a,b). Meningeal perivascular inflammation with mainly lymphocytes and macrophages was also observed (Figure 1c). Mild neuronal degeneration and glial reactions were found in the central nervous system, mainly in the cerebrum and olfactory bulb, but not in the cerebellum (Figure 2a,b). Intra-nuclear inclusion bodies were not detected. Additionally, over-dilatation of lung alveoli with congestion in intra-alveolar blood vessels was observed.


Zebra Alphaherpesviruses (EHV-1 and EHV-9): Genetic Diversity, Latency and Co-Infections
Histopathology (Grevy’s zebra, CG3) showing non-suppurative encephalitis represented by mononuclear perivascular cuffs in the gray matter of the cerebral cortex (a) and forebrain (b); Hematoxilin–eosine (HE) staining. Meningeal perivascular infiltration of inflammatory cells (arrows) (c); HE staining.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5035975&req=5

viruses-08-00262-f001: Histopathology (Grevy’s zebra, CG3) showing non-suppurative encephalitis represented by mononuclear perivascular cuffs in the gray matter of the cerebral cortex (a) and forebrain (b); Hematoxilin–eosine (HE) staining. Meningeal perivascular infiltration of inflammatory cells (arrows) (c); HE staining.
Mentions: Gross lesions in respiratory or nervous tissue were not observed at necropsy. The clinical observations for the EHV-positive animals are described in Table 1. The captive zebra (CP4) exhibited ataxia and tremors without improvement after a course of medication. Microscopic examination revealed diffuse alveolar edema in lung tissue. The EHV-9-positive zebra (CG3) exhibited central nervous disorders with ataxia and restlessness; the animal collapsed and was subsequently euthanized. Non-suppurative encephalitis associated with perivascular cuffing in the internal granular layer (IV) of the frontal part of the cerebral cortex (forebrain) and gray matter of the cerebral cortex was observed (Figure 1a,b). Meningeal perivascular inflammation with mainly lymphocytes and macrophages was also observed (Figure 1c). Mild neuronal degeneration and glial reactions were found in the central nervous system, mainly in the cerebrum and olfactory bulb, but not in the cerebellum (Figure 2a,b). Intra-nuclear inclusion bodies were not detected. Additionally, over-dilatation of lung alveoli with congestion in intra-alveolar blood vessels was observed.

View Article: PubMed Central - PubMed

ABSTRACT

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.

No MeSH data available.


Related in: MedlinePlus