Research articleDiversity and stability of Aleutian mink disease virus during bottleneck transitions resulting from eradication in domestic mink in Denmark
Introduction
Aleutian mink disease virus (AMDV) is the only member species of the genus Amdovirus of the family Parvoviridae. The host range of AMDV comprises the mustelids, raccoons, and skunks (Kenyon et al., 1978, Porter et al., 1982, Oie et al., 1996, Manãs et al., 2001, Fournier-Chambrillon et al., 2004) and rare cases of human infections have also been reported (Chapman and Jimenez, 1963, Helmbolt et al., 1965, Jepsen et al., 2009). AMDV can cause a variety of disease complexes in domestic mink (Neovison vison) among which is pneumonia in kits of non-immune females with mortalities close to 100%. Older mink can develop a chronic immune complex-mediated disease with increased mortality and reduced fertility (Bloom et al., 1988). On a global scale, AMDV is a major infectious cause of economical losses in mink farming.
AMDV in Denmark has been subject to a control campaign since 1976, and eradication has been supported by legislation since 1999 where Aleutian disease became notifiable in Denmark (Anonymous, 1999). A combination of trade restrictions imposed on infected farms and subsidies for sanitation has resulted in a stamping out practice where nearly all infected farms are pelting all mink in consecutive seasons. In 2001 only 5% of Danish mink farms were still infected. All infected mink farms with few exceptions were located in the northernmost tip of the peninsula of Jutland (Vendsyssel) separated from the rest of the peninsula by a coast-to-coast spanning fiord, Limfjorden. This has remained the situation from 2001 to 2010 with the exception of a feed-borne introduction of a strain, Sole/DEN/02, and transient presence of this strain in farms in southern parts of Jutland and the island of Funen in 2002 (Willadsen, 2006). The national surveillance program comprises serological screening of 15% of all breeding animals during November–January, prior to mating, as well as all barren females during May–June. Control zones of a radius of 5 km are established around infected farms and intensified testing is carried out in these zones.
Only few attempts of molecular epidemiological studies on AMDV have been conducted (Gottschalck et al., 1994, Olofsson et al., 1999, Knuuttila et al., 2009). It was found that AMDV exhibits a large genetic diversity with incidental presence in single mink of multiple variants and it was suggested that there is no geographical or temporal clustering of AMDV strains. The situation today in Denmark is so different from that in other parts of the world since AMDV-free farms and areas are predominant and evolutionary bottlenecks might have been imposed on the AMDV population due to the progression of the eradication campaign.
The tip of northern Jutland, Vendsyssel, is a 3000 km2 area with the highest density of mink farms in Denmark. In this area AMDV has resisted the attempts of control that were found successful in all other regions of Denmark leading to speculations if new strains of AMDV with increased ability of spread, possibly by airborne routes, had been introduced to this area. The present epidemiological study is the first one, focusing on two consecutive seasons. The aims were to reveal the population dynamics of AMDV strains, the origin of AMDV strains circulating in northern Jutland and the identification of significant risk factors associated with the recurrent infections at mink farms.
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Virus isolates
Included in the study were 162 AMDV isolates from 79 of 98 farms with sero-positive mink found in 2004 and 112 AMDV isolates from 51 of 57 farms with sero-positive mink found in 2005. The number of isolates from single farms varied from one to five. All farms were located in northern Jutland. Additionally, 50 isolates were included which had been collected from 32 infected farms located in other parts of Denmark during 1998–2003, including five representative isolates of strain Sole/DEN/02
Results
The number of mink farms in northern Jutland, Vendsyssel, by January 2004 was approximately 350. The number of farms found infected with AMDV as a result of the national screening program was 157 in 2004 and 65 in 2005 (Willadsen, 2006). The location of non-infected and infected farms in 2004 and 2005 is shown in Fig. 1. AMDV was detected in sample material from 98 farms in 2004 and 57 farms in 2005. An appropriate quality of PCR products made characterization of AMDV isolates by sequencing
Discussion
AMDV has been reported to exhibit an unusual high variability or genetic diversity (Gottschalck et al., 1991, Olofsson et al., 1999) and it was suggested that spatiotemporal clustering was non-existing for this virus (Knuuttila et al., 2009). Possibly disencouraged by similar findings in other laboratories, only few molecular epidemiological studies on AMDV have been published. The present study takes advantage of the relative success of the eradication program in Denmark resulting in (i)
Acknowledgements
Dr. C.M. Willadsen, Danish Fur Breeder's Laboratory, Langagervej 74, DK-2600 Glostrup, is acknowledged for providing organ material for the analyses, for many fruitful discussions and critically reviewing our conclusions and suggestions. Analyses for the presence of AMDV by PCR and sequencing of PCR products were carried out at the National Veterinary Laboratory, Department of Virology, Lindholm, DK-4771 Kalvehave. The authors thank Birthe Elise Jensen, Lindholm, for expert technical
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2015, Virus ResearchCitation Excerpt :By contrast, there is no information about AMDV prevalence in Estonia. Earlier phylogenetic analyses suggested that, globally, mink AMDV strains can be divided into three to five major groups (Olofsson et al., 1999; Knuuttila et al., 2009; Christensen et al., 2011; Jensen et al., 2012; Sang et al., 2012; Nituch et al., 2012; Wang et al., 2014), and strains isolated from other species are divergent from mink strains (Oie et al., 1996; Murakami et al., 2001; Manas et al., 2001). AMDV strains do not seem to cluster based on pathogenicity (Schuierer et al., 1997; Olofsson et al., 1999; Knuuttila et al., 2009; Nituch et al., 2012), but grouping linked to geographical origin (Christensen et al., 2011; Jensen et al., 2012; Nituch et al., 2012; Sang et al., 2012) and free-ranging and farmed mink reservoirs (Jensen et al., 2012; Nituch et al., 2012) has been shown in some countries.