Elsevier

Veterinary Microbiology

Volume 139, Issues 3–4, 18 November 2009, Pages 262-269
Veterinary Microbiology

Alphaherpesvirus infections in semidomesticated reindeer: A cross-sectional serological study

https://doi.org/10.1016/j.vetmic.2009.06.013Get rights and content

Abstract

Alphaherpesviruses infect a wide range of animal species and cause diseases. Cervid herpesvirus 2 (CvHV-2) was originally isolated from reindeer in Finland but the impact of CvHV-2 infections on reindeer remains unclear. CvHV-2 infection could be partly responsible for calf losses as there are indications that it is associated with abortions and neonatal diseases. Previous serosurveys of reindeer (Rangifer tarandus tarandus) have shown that an alphaherpesvirus is circulating among reindeer in Norway. The aim of the present study was to determine the prevalence of CvHV-2 infection among reindeer in various herding districts in Finnmark, the largest reindeer area in Norway, and to identify factors associated with becoming infected with CvHV-2. A total of 3062 serum samples were tested using an ELISA and a sub-set of samples was further tested using a seroneutralization test. The ELISA revealed that 49% of samples were positive. Extrapolation of the results to the total population (111,350 animals; 66% of the Finnmark reindeer population) showed that the seroprevalence in the population was 48%. Seroprevalence varied from 7.6% to 90.7% between districts and was affected by age, weight and population density. ELISA-positive samples neutralized CvHV-2 at serum dilutions greater than those required for neutralization of bovine herpesvirus type 1. It is concluded that CvHV-2 is endemic throughout the reindeer herding districts of northern Norway.

Introduction

There are several alphaherpesviruses that infect ruminants and cause disease. As the infections are easily transmitted in animal populations with high densities and may have substantial economic consequences, they have been targeted by eradication campaigns (Ackermann and Engels, 2006). Bovine herpesvirus type 1 (BoHV-1) is the best characterized ruminant alphaherpesvirus. It is associated with diseases of the respiratory and genital tracts (infectious bovine rhinotracheitis, infectious pustular vulvovaginitis and pustular balanoposthitis), abortion and meningoencephalitis (Muylkens et al., 2007).

Several alphaherpesviruses that are antigenically related to BoHV-1 (Thiry et al., 2006) have been isolated from ruminant species such as goats (Capra aegagrus hircus; caprine herpesvirus 1; CpHV-1) (Keuser et al., 2004), North American elk (Cervus elaphus nelsoni; Elk herpesvirus 1; ElkHV-1) (Deregt et al., 2000), red deer (Cervus elaphus elaphus; cervid herpesvirus 1; CvHV-1) (Inglis et al., 1983) and reindeer (Rangifer tarandus tarandus; cervid herpesvirus 2; CvHV-2) (Ek-Kommonen et al., 1986, Rockborn et al., 1990).

Cross-species infections among ruminant alphaherpesviruses have been documented (Thiry et al., 2006). Experimental infections have demonstrated that CvHV-2 can infect cattle and that BoHV-1 can infect reindeer, but neither of the infections could be reactivated, indicating that latency was not established (Thiry et al., 2001), unlike in the case of ElkHV-1 infection and latency in cattle (Deregt et al., 2005).

Isolation of CvHV-2 has only been achieved as a result of experimental reactivation in Finland and Sweden (Ek-Kommonen et al., 1986, Rockborn et al., 1990). Serological screenings have demonstrated alphaherpesvirus seropositivity in Grant's caribou (Rangifer tarandus granti) in Alaska (39% seroprevalence) (Dieterich, 1980), barren-ground caribou (Rangifer tarandus groenlandicus) in Greenland (37% seroprevalence) (Anonymous, 1999), woodland caribou (Rangifer tarandus caribou) in Canada (52% seroprevalence) (Tessaro et al., 2005) and in semidomesticated reindeer (Rangifer tarandus tarandus) in Finland (23–64% seroprevalence) (Ek-Kommonen et al., 1982, Nettleton et al., 1988), Sweden (11–28% seroprevalence) (Rehbinder et al., 1992, Rockborn et al., 1990) and Norway (13–30% seroprevalence) (Stuen et al., 1993, Tryland et al., 2005). Antibodies against an alphaherpesvirus have thus been detected in all reindeer subspecies investigated except for the Svalbard reindeer subspecies (Rangifer tarandus platyrhynchus) in the Svalbard high arctic archipelago (Stuen et al., 1993).

In reindeer, CvHV-2 infection has usually been diagnosed as a subclinical genital infection as its clinical signs are mostly unknown (Ek-Kommonen et al., 1986, Thiry, 2007). However, oral ulcers, catarrhal enteritis and pulpy spleens have been observed after experimental reactivation of latent infection (Rockborn et al., 1990). Aborted or weak born offspring are common outcomes of BoHV-1 infection of bovines (Smith, 1997, Thiry, 2007), but the contribution of CvHV-2 infection to reproductive disorders remains unknown despite evidence of CvHV-2 vertical transmission in reindeer (Das Neves et al., 2009a).

Finnmark County is the largest reindeer herding area in Norway (Fig. 1) and had an estimated population of 167,811 reindeer in 2005/2006. Reindeer are kept under semi-nomadic husbandry conditions in Finnmark County. The animals are free-ranging but are herded within well-defined husbandry districts, with seasonal migrations occurring between coastal areas in summer and inland plateau areas in winter. Reindeer herding districts are usually demarcated by rivers, mountain ranges, fjords, or extensive man-made fences to prevent mixing of animals between herds and districts.

A serosurvey of reindeer in Finnmark in the early 1990s revealed an overall seroprevalence of 30% (15% in calves and 63% in adults) (Stuen et al., 1993). Reindeer mortality in Finnmark is high and reached 37% among calves during the 2005/2006 herding year (1st April 2005 to 31st March 2006). Although predators account for most mortalities, 11% of calf mortalities are of unknown aetiology (Anonymous, 2007). As the fecundity of semidomesticated reindeer is unknown (they usually give birth unattended while free-ranging), it is difficult to assess the contribution of abortion or weak calves to mortality (Tveraa et al., 2003), also because aborted materials are quickly taken by scavangers and rarely available for investigation.

The assumedly high prevalence of CvHV-2 infection in northern Norway prompted us to conduct a cross-sectional serological screening in various husbandry districts and to evaluate factors that might increase the chance for becoming infected with CvHV-2 (age, weight, animal density, geographical location and gender). It was anticipated that a study of this nature would provide information on the epidemiology of CvHV-2 seroprevalence in reindeer in Norway.

Section snippets

Sampling

Reindeer sera (n = 3062) from 14 summer herding districts were collected from 2004 to 2006 during the winter slaughtering period in Finnmark County, Norway. Sera were stored at −20 °C until testing.

Animal data

Information on gender, age, weight, district of origin and year of sampling were available from slaughter lists for 2576 animals. The animals were classified into four age classes by slaughter personnel based on weight, size of antlers and development of reproductive organs. As this classification

Overall results

According to the ELISA, 1502 of 3062 sera (49%) were positive for alphaherpesvirus, 1552 were negative, and 8 were classed as doubtful. Fig. 1 shows the distribution of the percentage competition values using kernel density estimation. Positive and negative results were clearly distinguishable and the positive results were concentrated above a competition percentage of 75%.

The overall seroprevalence at district level is shown in Table 1 and Fig. 2. Seroprevalence varied from 7.6% in district 6

Discussion

The high seroprevalence of CvHV-2 and the results of the seroneutralization test confirmed that CvHV-2 is widely prevalent among the reindeer population of Finnmark County, Norway. Weight, which also reflects age, and to a lesser extent animal density, were identified as factors associated with becoming infected, whereas gender, year of sampling and geographical location (east versus west) did not significantly affect seroprevalence. This may indicate that CvHV-2 infection is widespread among

Conclusion

CvHV-2 infection is endemic in the reindeer population of Finnmark County, Norway. Seroprevalence increases with increasing carcass weight, age and animal density, and CvHV-2 was found to be present throughout all Finnmark reindeer districts sampled on this serosurvey. Further investigations are needed to quantify the clinical impacts of this infection. Such information would be useful for reindeer husbandry, which plays a substantial economic and cultural role in local indigenous communities.

Acknowledgements

For irreplaceable help in the field, we acknowledge veterinary students Therese Berger, Anett Larsen, Trine Marhaug, Veronique Poulain, Ingebjørg Nymo, Matthieu Roger and Gina Petrovich, and guest researcher Federico Morandi. Cooperation with Rolf Ims and Rolf Rødven through the Ecosystem Finnmark project is acknowledged. We thank the staff at the Karasjok and Kautokeino slaughterhouses for their help and hospitality. We acknowledge the help of Lorène Dams at the Faculty of Veterinary Medicine

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