Genetic clustering of Borna disease virus natural animal isolates, laboratory and vaccine strains strongly reflects their regional geographical origin

Abstract

The aim of this study was to gain more detailed insights into the genetic evolution and variability of Borna disease virus (BDV). Phylogenetic analyses were performed on field viruses originating from naturally infected animals, the BDV vaccine strain ‘Dessau’, four widely used laboratory strains and the novel BDV subtype No/98. Four regions of the BDV genome were analysed: the complete p40, p10 and p24 genes and the 5′-untranslated region of the X/P transcript. BDV isolates from the same geographical area exhibited a clearly higher degree of identity to each other than to BDV isolates from other regions, independent of host species and year of isolation. Five different clusters could be established within endemic areas, corresponding to the geographical regions from which the viruses originated: (i) a Swiss, Austrian and Liechtenstein Rhine valley group, related closely to the geographically bordering Baden-Wurttemberg and Bavaria II group (ii) in the western part of Germany; (iii) a third group, called Bavaria I group, limited in occurrence to Bavaria; (iv) a southern Saxony-Anhalt and bordering northern Saxony group, bound to the territories of these federal states in the eastern part of Germany; and (v) a mixed group, consisting of samples from different areas of Germany; however, these were mainly from the federal states of Thuringia and Lower Saxony. The laboratory strains and the vaccine strain clustered within these groups according to their geographical origins. All field and laboratory strains, as well as the vaccine strain, clearly segregated from the recently described and highly divergent BDV strain No/98, which originated from an area in Austria where Borna disease is not endemic.

Epidemiology and host spectrum of Borna disease virus infections

“…This finding indicates that additional BDV variants with distinct features may be present, but probably escape detection with primers and probes designed to amplify the known strains. Even the most similar central European BDV strains present with minor differences according to their geographical, but not host species, origin (Kolodziejek et al, 2005). Recently, a BDV-related novel virus species, ABV, was found by a pan-viral microarray screening method (Kistler et al, 2008) and, based on the established ABV-detection methods, another distinct bornavirus lineage was revealed in goose and swan (Delnatte et al, 2011;Payne et al, 2011).…”

“…Secondly, focal BDV epidemics are observed independently of the region and species at 2-to 5-year intervals (Zwick et al, 1927;reviewed by Dürrwald & Ludwig, 1997;Dürrwald et al, 2006a), which could be related to fluctuation in wild rodent numbers. Thirdly, BDV strains cluster geographically rather than according to the species or year of isolation, suggesting that transmission within a domestic species is uncommon (Kolodziejek et al, 2005). Furthermore, BDV is transmitted in rodents: vertically in mice (Okamoto et al, 2003) and horizontally in rats via urine (Sauder & Staeheli, 2003).…”

“…Rigorous vaccination was compulsory in the former German Democratic Republic in 1962-1992, but the campaign proved ineffective. Nowadays, infections caused by these unsuccessful vaccinations possibly contribute to the fact that the incidence of clinical BD is still highest in horses in Germany (reviewed by Dürrwald et al, 2006a;; the same is implied by BDV molecular epidemiology (Kolodziejek et al, 2005). No vaccination against this persistent infection has since been recommended, although new recombinant vaccine candidates expressing BDV N mediate protection from the disease (but not from infection) in mice (Hausmann et al, 2005).…”

“…BD cases in even the most common victims, sheep and horses, are mainly sporadic (Danner, 1978;Priestnall et al, 2011;Vahlenkamp et al, 2002), and transmission within or between the domestic species occurs rarely, if ever (Kolodziejek et al, 2005;Metzler et al, 1979). Furthermore, the endemic areas have not essentially changed with human travelling and animal trading.…”

First Serological Evidence of Borna Disease Virus in Healthy Horses from Yucatan, Mexico

“…Strain H1766 has 95% -98% homology with strains V and He/80, and only 81% with Borna No/98. Other minor variants have been reported as avian Bornavirus [2]. BDV infection causes disease in the central nervous system (CNS) of many vertebrate species, which is frequently manifested by behavioural abnormalities and even fatalities [3].…”