VN October 2023

Oktober 2023 33 RABBIT HAEMORRHAGIC DISEASE Aetiology Epidemiology Diagnosis Prevention and Control References https://www.woah.org/fileadmin/Home/eng/Animal_Health_in_the_ World/docs/pdf/Disease_cards/RHD.pdf This article is sponsored by V-Tech AETIOLOGY Classification of the causative agent Family Caliciviridae, Genus Lagovirus , Rabbit haemorrhagic disease virus (RHDV) RHDV was identified in 1984 as the agent of a highly contagious, acute and fatal disease of rabbits (RHD). Rabbit lagoviruses consist of pathogenic viruses (RHDVs) and non-pathogenic viruses (RCVs), related but genetically divergent. Phylogenetic analyses of pathogenic RHDV strains indicate the existence of three distinct groups: the “classic RHDV” with the genogroups G1–G5 isolated from 1984 onwards, the antigenic variant RHDVa/G6 identified in 1996, and RHDV2 identified in 2010. The RHDV and RHDVa are phylogenetically related and their capsid protein (VP60) differs in nucleotide diversity from RHDV2 by more than 15%. RHDV2 was first identified in France on 2010, and since then has spread throughout Europe, replacing the circulating RHDV/RHDVa strains in most European countries. The available data (see below) suggest that RHDV2 is a newly emerged virus of unknown origin. Its antigenic profile is quite different from that of RHDV, to such an extent that it could be considered a distinct serotype. The provisional name RHDV2 therefore seems more appropriate than RHDVb, which is used by some authors. In addition to RHDV, RCVs have been identified, both in commercial and wild rabbits, that are genetically related to RHDV to varying degrees. Among these RCVs, those most closely genetically related to RHDV (identified in several European rabbit farms) induce a good level of cross-protection towards RHD. Other RCVs genetically less related to RHDV have been identified in Australian wild rabbit populations, and infected rabbits showed a very limited degree of protection, if any, when challenged with RHDV. A similar disease termed European brown hare syndrome (EBHS) has been described mainly in the brown hare ( Lepus europaeus ) since 1970–80. The aetiological agent (EBHSV) is a lagovirus genetically and antigenically related to the RHDV. However, RHDV and EBHSV, in spite of their almost contemporaneous identification but in different geographical areas, represent two viral species with non-overlapping host ranges. Resistance to physical and chemical action The following characteristics were ascertained for RHDV/RHDVa, but have yet to be formally confirmed for RHDV2. Temperature: Survives heat of 50°C for 1 hour, and freeze–thaw cycles. pH: Stable at pH 4.5–10.5. Survives pH 3.0 but inactivated at pH >12. Chemicals: Inactivated with sodium hydroxide (1%) or formalin (1–2%). OIE Terrestrial Animal Health Code recommends formalin (3%) for disinfecting pelts. Treatment with 1.0–1.4% formaldehyde or 0.2–0.5% beta-propiolactone at 4°C inactivates the virus but does not reduce its immunogenicity and is therefore indicated for the production of vaccines. Disinfectants: Other suggested disinfectants include substituted phenolics (e.g. 2%One-stroke Environ®) and 0.5% sodium hypochlorite. Viral infectivity is not reduced by ether or chloroform and trypsin. Survival: RHDV and EBHSV are very resistant to inactivation, particularly when protected by organic material. Virus may persist in chilled or frozen rabbit meat, as well as in decomposing carcasses in the environment, for months. It is protected within tissues, and can survive >7 months in organ suspensions stored at 4°C, at least 3 months in the dried state on cloth at room temperature, for up to 20 days at 22°C in decomposing rabbit carcasses and at least 2 days at 60°C in an organ suspension and the dried state. EPIDEMIOLOGY RHD is an extremely contagious and fatal viral hepatitis of adult domesticated and wild rabbits belonging to the Oryctolagus cuniculus species. Young rabbits (less than 6–8 weeks old) are subclinically infected, developing a specific humoral response. Severe losses are common in unvaccinated animals, and in intensive farms a variable proportion of rabbits may die according to the type of virus. Technical I Article >>> 34