Diseases of lagomorphs

Diseases of Lagomorphs antonio lavazza and brian d. cooke Diseases in the European rabbit (Oryctolagus cuniculus) have always been of wide interest, largely because of the rabbit’s importance as a domestic species and its use for meat and fur production. It is also a common laboratory animal and increasingly used as a model for exploring human diseases (Duranthon et al. 2012), especially with the development of transgenic tools that enable enhanced gene expression or silencing. Rosell (2000) lists and discusses a wide range of naturally occurring diseases in domestic European rabbits, including dietary deficiencies; bacterial respiratory, reproductive, and enteric diseases; parasites; and viral diseases. Some of these diseases, in particular, those caused by viruses, are confined to a single host species within the order Lagomorpha, whereas there are other multi- host diseases, like tularemia, that affect not only many lagomorph species, but a wide range of other taxa as well. With the exclusion of multifactorial conditioned diseases, many of these same diseases and conditions also afflict wild lagomorphs, but are often neglected in terms of their impacts on natural populations. Nevertheless, in this chapter the aim is not to produce an exhaustive list of all diseases of wild lagomorphs, but rather to give some basic information on select diseases and to suggest precautionary procedures for carefully managing their inadvertent introduction and spread that could compromise lagomorph management and conservation. Some lagomorph diseases are well studied because lethal viruses such as myxoma virus (MYXV) have been deliberately used to reduce numbers of introduced European rabbits where they have become serious pests. However, the introduction of MYXV within the European rabbit’s native range (Spain, Portugal, and France) in the mid- 1950s also caused intense conservation concern (Angulo and Bárcena 2007; Ross and Tittensor 1986) and, on becoming endemic in wild rabbits, have recurrent annual impacts on rabbit meat farms. Other viruses such as rabbit hemorrhagic disease virus (RHDV) and European brown hare syndrome virus (EBHSV) have apparently emerged spontaneously within Asia and Europe, respectively, and RHDV has been used as a biological control agent in Australia as well. When MYXV was introduced into Australia more than 60 years ago, research by Fenner in particular (Fenner and Fantini 1999; Fenner and Ratcliffe 1965) not only showed why a relatively benign MYXV from a South American lagomorph (the tapetí Sylvilagus brasiliensis sensu stricto) caused lethal disease on transfer into European rabbits, but also tracked the course of evolution of subsequent disease resistance in rabbits. This work has since become the foundation for wider theory and has been fundamental in understanding subsequent diseases such as rabbit hemorrhagic disease (RHD). RHD and European brown hare syndrome (EBHS) are similar diseases caused by two highly related but phylogenetically distinct RNA viruses belonging to the genus Lagovirus of the family Caliciviridae. RHD and EBHS have restricted host specificity both naturally and experimen1709048_int_cc2015.indd 18 15/9/2017 15:59 Diseases of Lagomorphs 19 tally (Bergin et al. 2009; Lavazza et al. 1996; Lenghaus et al. 1994). In fact, they were initially considered genus- specific, the former infecting only wild and domestic European rabbits and the latter mainly European hares (Lepus europaeus). Nevertheless, there is increasing evidence that lagoviruses such as RHDV are rapidly co- evolving to match increased disease resistance in rabbits. A new virus serotype (RHDV2) has emerged (Le Gall- Reculé et al. 2011; Le Gall- Reculé et al. 2013), and it is apparently replacing those strains (RHDV and RHDVa) that initially spread. The origin of RHDV2 is still under study, but the preliminary results indicate that it could not have evolved from RHDV, but it rather represents a new viral emergence from an unknown source (Le Gall- Reculé et al. 2013); the hypothesis of a species jump has also been proposed (Esteves et al. 2015). The genomic and antigenic profiles of RHDV2 are quite different from those of RHDV, to such an extent that it could be considered a distinct serotype, even able to infect rabbits with specific immunity against classical RHDV. This advantage enabled RHDV2 to rapidly spread in Europe, causing significant losses in farmed and wild rabbits. This finding has wider implications, not simply in terms of the need for improved vaccines to protect domestic rabbits, but also because RHDV2 is not confined to European rabbits and has shown a capacity to cause disease in other lagomorphs, notably Cape hares (L. capensis mediterraneus; Puggioni et al. 2013), and, more sporadically, as a probable result of spillover events, Corsican hares.