[1] Univ Vet Sci, Inst Virol, A-1210 Vienna, Austria
[2] Univ Vet Sci, Inst Fish & Bee Dis, A-1210 Vienna, Austria
[3] Fed Off & Res Ctr Agr, Inst Apiculture, A-1226 Vienna, Austria
[4] Inst Anim Hlth, Dept Bee Pathol, D-79108 Freiburg, Germany
[5] Univ Surrey, Sch Biol Sci, Surrey GU2 7XH, England
[6] Univ Western Cape, Dept Microbiol, ZA-7535 Bellville, South Africa
[7] Fed Off & Res Ctr Agr, Inst Apiculture, A-3293 Lunz, Austria
[8] Univ Bonn, Inst Apiculture, D-53127 Bonn, Germany