by Dolores Gavier-Widén and Aleksija Neimanis

Rabbit hemorrhagic disease virus (RHDV) (genus Lagovirus, Caliciviridae) affects wild and domestic European rabbits (Oryctolagus cuniculus). The disease emerged in Europe in the 1980s causing epidemics of high mortality in rabbits. The host range of RHDV is restricted to Oryctolagus cuniculus and high mortality (70-100%) has been observed in adult rabbits. From the 5th week of age, young rabbits become partially susceptible to develop disease and by the 8th week they are fully susceptible. The disease is characterized by acute severe necrotizing hepatitis and hemorrhagic disease. A highly related but phylogenetically distinct Lagovirus causes a similar disease in European brown hares (Lepus europaeus) called “European brown hare syndrome”.

Mortality caused by Lagoviruses has contributed to the decline of wild rabbit and European brown hare populations throughout Europe, which has had a major ecological impact since these lagomorphs are key species in the ecosystems. The widespread epizootics of RHD in the late 80s and early 1990s in Western Europe resulted in a drastic reduction (50% to 80%) and fragmentation of populations of wild rabbits (Virgos et al, 2007), which had an important impact on conservation. In Mediterranean ecosystems the European wild rabbit is a keystone-species, it is the main prey for at least 29 predators, including rabbit-specialists such as the Spanish Imperial Eagle (Aquila adalberti) and the Iberian lynx (Lynx pardinus) (Delibes et al, 1981, Ferrer and Negro, 2004). Sharp population decline of wild rabbits caused by RHD resulted in a shift of distribution of rabbit-consuming species with consequent changes in their breeding and population dynamics. Bonelli’s eagles (Aquila fasciata), a threatened bird of prey in Europe, bases its diet on rabbits and scarcity of wild rabbits due to RHD-mortality has been identified as one of the main threats for the eagles. Costly conservation programmes have been conducted in the Mediterranean region for the recovery of rabbit–specialist predators (Cortés-Avizanda, et al, 2015).

A new pathogenic Lagovirus, designated RHDV2 (also named RHDVb), emerged in France in 2010 (Le Gall-Reculè et al., 2011, Le Gall-Reculè et al., 2013). This new virus differs phylogenetically from other lagoviruses, including classic RHDV, and also presents a unique antigenic profile. RVHD2 partially escapes immunity conferred by previous exposure to classic RHDV resulting in re-emergence of disease, mortality and epidemics in wild and domestic rabbits. RHDV2 has rapidly spread throughout Europe and to date, has been reported in France, Italy, Spain, Portugal, Germany, Azores islands and the UK, and most recently in Sweden. In large parts of Europe the new lagovirus has largely replaced the classic RHDV.

The emergent new lagovirus, RVHD2, has different epidemiological characteristics than classic RHDV, namely, i) its host range is broader causing disease not only in rabbits but also in Cape Hares (L. capensis subsp. mediterraneus) (Puggioni et al., 2013) and Italian hares (L. corsicanus) (Camarda et al., 2015); ii) it causes mortality in young rabbits (under 30 days of age) and iii) it has lower and more variable mortality rates.

The origin of lagoviruses, including the recently emerged RHDV2, is not yet clear, and the emergence of this new lagovirus together with its impact on wild rabbit populations are of concern. Moreover, the rapid spread of RHDV2 and its potential to affect other Lagomorphs species in sympatry with populations of wild rabbits in Europe constitutes a threat not only to lagomorphs, but also to species that feed on them.

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