Variant rabbit hemorrhagic disease virus in young rabbits, Spain

Abstract

Outbreaks of rabbit hemorrhagic disease have occurred recently in young rabbits on farms on the Iberian Peninsula where rabbits were previously vaccinated. Investigation identified a rabbit hemorrhagic disease virus variant genetically related to apathogenic rabbit caliciviruses. Improved antivirus strategies are needed to slow the spread of this pathogen.

Figure 1

Evolutionary relationships of rabbit hemorrhagic disease virus (RHDV) and related viruses. A total of 38 nt sequences were analyzed: the isolate from this study, designated RHDV-N11 (GenBank accession no. JX133161); 18 classical RHDV and 12 RHDVa isolates; 6 rabbit calicivirus (RCV)–like isolates; and European brown hare syndrome virus (GenBank accession no. Z69620) as an outlier. Evolutionary history was inferred by using the neighbor-joining method; optimal tree with the sum of branch length = 1.33075964 is shown. The tree is drawn to scale, with branch lengths in the same units as those of the evolutionary distances used to infer the phylogenetic tree. Evolutionary distances were computed by using the p-distance method (14) and are in the units of the number of base differences per site. Codon positions included were 1st + 2nd + 3rd + Noncoding. All ambiguous positions were removed for each sequence pair; the final dataset consisted of 646 positions. Evolutionary analyses were conducted in MEGA5 (15). RHDV genetic groups are indicated. GenBank accession numbers of the sequences were: RCV-like strains: EU871528, GU368915, X96868, EF558587, AM268419, GQ166866; RHDV strains; AJ006019, AJ535094, Y15424, Y15426, Y15441, EF363035, Y15427, AF402614, RHU54983, AF295785, Z49271, L48547, Y15440, RHU49726, Z29514, M67473, X87607, FR823355; RHDVa strains: DQ069280, DQ280493, DQ069282, AY269825, DQ841708, DQ205345, AF258618, DQ069281, AJ969628, AF453761, EF558584, Y15442.

Figure 2

Results of immunohistochemical staining using monoclonal antibody 6G2 and the ABC complex technique of liver and intestine samples from young rabbits infected with rabbit hemorrhagic disease virus (RHDV) isolate RHDV-N11 and control rabbits. A) Liver of RHDV-N11–infected rabbit. Hepatocytes show intense 6G2-specific immunolabeling. Scale bar = 50 µm. B) Intestinal villi in small intestine of RHDV-N11–infected rabbit. Areas of focal necrosis and epithelial cells show strong immunolabeling. Scale bar = 20 µm. C) Liver of control rabbit. Hepatocytes do not show positive immunolabeling. Scale bar = 50 µm. D) Epithelial cells of intestinal villi of control rabbit do not show positive results on staining. Scale bar = 100 µm.