Elsevier

Virus Research

Volume 145, Issue 2, November 2009, Pages 321-328
Virus Research

Cervid herpesvirus 2 experimentally reactivated in reindeer can produce generalized viremia and abortion

https://doi.org/10.1016/j.virusres.2009.08.002Get rights and content

Abstract

Cervid herpesvirus 2 (CvHV2) has never been isolated from reindeer in Norway, but serological data and investigations by PCR indicate that the virus is endemic in the country, with horizontal and vertical transmission, systemic spread, and latency in the trigeminal ganglion. In this study two seropositive reindeer, one of which was pregnant, were administered dexamethasone, to reactivate CvHV2 latent infection. One control animal received sterile water. All animals including the control reactivated, as shown by amplification of CvHV2 DNA from nasal swabs. The pregnant animal showed lesions in the lip mucosa 10 days after the first dexamethasone injection and CvHV2 was visualized by electron microscopy and isolated from those lesions, as well as from nasal and vaginal swabs. On day 13 she aborted and CvHV2 was isolated from both the aborted calf and the mother. CvHV2 was isolated from the other animal administered dexamethasone. Despite amplification of viral DNA in the control animal, it was never possible to isolate the virus. Molecular characterization of the new isolates confirmed these to be CvHV2, and similar to the previous known strain Salla82.

Present results represent the first isolation of CvHV2 in Norway and reconfirm that this virus can cause systemic infections in reindeer even after reactivation episodes, and infect the fetus in utero despite a prompt immune response. While it is not possible to atribute the abortion to CvHV2 alone, present data together with previous reports of vertical transmission of CvHV2 and neonatal death, point to an abortogenic potential, which should be further investigated.

Introduction

Cervid herpesvirus 2 (CvHV2) belongs to the genus Varicellovirus in the subfamily Alphaherpesvirinae, family Herpesviridae, order Herpesvirales (Davison et al., 2009). Varicelloviruses infect and cause disease in a wide variety of mammals, have a fast replication cycle and establish latency in regional neural ganglia (Roizmann et al., 1992). Several viruses of ruminants belong to the genus Varicellovirus, of which bovine herpesvirus 1 (BoHV1) causing bovine rhinotracheitis (IBR) and infectious pustular vulvovaginitis (IPV) as well as encephalitis and abortion in bovines is the most studied (Engels and Ackermann, 1996, Pastoret et al., 1982).

Ruminant varicelloviruses have been shown to be genetically closely related, as demonstrated by the DNA sequences of the UL27 gene encoding glycoprotein B, with a 92% homology between BoHV1 and CvHV2 (Thiry et al., 2007). Serological cross-reactions between viruses of this genus have also been shown (Deregt et al., 2005, Lyaku et al., 1992, Martin et al., 1990, Rimstad et al., 1992). The latter may affect the efficiency and feasibility of IBR/IPV eradication or surveillance programs (Thiry et al., 2008).

In the last 30 years several serosurveys have shown high prevalence of CvHV2 infections in different populations of wild and semi-domesticated reindeer (Rangifer tarandus tarandus) in Norway (Lillehaug et al., 2003, Stuen et al., 1993), Sweden (Rehbinder et al., 1992) and Finland (Ek-Kommonen et al., 1982); in barren-ground caribou (Rangifer tarandus groenlandicus) in Greenland (Anonymous, 1999); and in Grant's caribou (Rangifer tarandus granti) in Alaska (Dieterich, 1981).

Reindeer husbandry is of major economical and cultural importance, especially for local indigenous communities throughout the Arctic, with more than three million animals being herded in Europe, Asia and Northern America. In Norway, there were more than 275,000 reindeer in 2006/07, of which almost 90% are semi-domesticated. The mortality of semi-domesticated reindeer in Norway in 2006 reached 37% during the herding year (April 1, 2005–March 31, 2006; Anonymous, 2007). Predators cause the majority of the mortality, but approximately 11% of the losses are of unresolved etiology. The impact of abortions in mortality is difficult to confirm as birth takes place unattended by people, and since aborted materials are quickly consumed by scavengers.

Serologic screening of semi-domesticated reindeer in Norway have confirmed that CvHV2 is endemic in the reindeer population (Das Neves et al., 2009a, Das Neves et al., 2009b) with an overall seroprevalence of approximately 47% (Das Neves et al., in press). The presence of CvHV2 in fetuses (Das Neves et al., 2009a) indicates that CvHV2 might have an impact on reproductive success, as is the case with varicellaviruses in other ruminant species that cause abortions and increased offspring mortality (Muylkens et al., 2007, Smith, 1997, Thiry et al., 2006).

In bovines, BoHV1 reactivation episodes may lead to virus excretion at the original port of entry, though many times without any clinical signs (Engels and Ackermann, 1996). A previous CvHV2 reactivation study concluded that the main impact of this infection in reindeer was the development of mucosal lesions, which served as the port of entry for secondary bacterial infections (Rockborn et al., 1990). Studies of the time course of acquired humoral immune response, viral spread in the body and the pathogenicity of reactivations are lacking for CvHV2 infection in reindeer. It is also unknown if the CvHV2 circulating today in the reindeer population in Norway is identical to the original Finnish isolate from more than 25 years ago (CvHV2 Salla 82, Ek-Kommonen et al., 1986).

Given the high seroprevalence of CvHV2 in reindeer in Norway, and the limited knowledge about the virus and its impact on reindeer health, an experimental reactivation study in naturally infected reindeer was carried out. CvHV2 was isolated, characterization was initialized, and the pathogenicity, including possible transmission to fetuses, was studied.

Section snippets

Cells and viruses

Madin–Darby bovine kidney cells (MDBK; ATCC CCL22) were used for virus isolation and propagation. Cells were maintained in Eagle's minimum essential medium (EMEM) supplemented with 10% of horse serum (LGC Standards, Teddington, UK).

The isolates obtained in this study as well as strains CvHV2 Salla 82 (Ek-Kommonen et al., 1986), CvHV1 Banffshire 82 (Inglis et al., 1983) and BoHV1 Iowa (Miller and van der Maaten, 1984) were propagated in MDBK cells with EMEM with 2% of horse serum and 2%

Clinical observations

Animals D1 and D3 showed no abnormal behaviours or clinical signs throughout the experiment. Animal D2 presented several superficial skin erosions with serous exudate of the upper and lower lips on day 10 (Fig. 1), which increased in size and number. On day 11 a biopsy and swab of a skin lesion were taken. On day 13 an aborted calf (D2a) was found and the mother (D2) had uterus prolapse. After sedation the prolapsed tissues were washed, examined and the prolapse was resolved. Two intra-vaginal

Discussion

In this work we describe the first isolation of CvHV2 from reindeer in Norway. Lesions on the lips were found 11 days after the onset of administration of dexamethasone and were similar to those previously reported (Rockborn et al., 1990). Reactivation of the latent infection induced a prompt increase of specific antibody titres and thereafter CvHV2 could no longer be isolated.

Electron microscopy revealed the presence of viral particles in the lip lesions, with ultrastructure and size

Conclusion

The present study reports the first isolation of CvHV2 in reindeer in Norway. The virus was found to be almost identical to a CvHV2 Finnish isolate from 1982. Excretion of virus occurred after reactivation followed by an immune response that prevented further excretion of viral particles. The presence of CvHV2 in several organs of an aborted fetus could indicate the involvement of CvHV2 in abortions, and its impact on the reproduction of reindeer should be further investigated. Reindeer

Acknowledgments

For help during the experimental infection, we would like to acknowledge Kjetil Åsbakk PhD, Kristin Prestrud DVM PhD, Renate Sjølie DVM and Andrea Balboni DVM, as well as the University of Tromsø and BioForsk for technical and logistical support. We would like to acknowledge the help in the lab of Eva Breines and Ellinor Hareide as well as of Randi Olsen at the Department of Electronic Microscopy of the University of Tromsø.

This project was partly funded by The Norwegian Reindeer Development

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