Monitoring of Rabbit Hemorrhagic Disease Virus in European Wild Rabbit (Oryctolagus cuniculus) Populations by PCR Analysis of Rabbit Fecal Pellets.

European rabbits (Oryctolagus cuniculus) are affected by rabbit hemorrhagic disease (RHD), which is caused by a lagovirus responsible for significant mortality in European wild rabbit populations. Our study aimed to evaluate the potential for detecting viral RNA by duplex real-time PCR in rabbit fecal pellets collected in the field, as a noninvasive method to monitor RHD virus circulation in wild populations. To do this, monthly discoveries of rabbits that died from RHD and detection of viral RNA in fecal pellets were recorded in two enclosed populations of wild rabbits throughout a year. The results suggested a low performance of this procedure to monitor viral infection incidence and a weak concordance with monthly discoveries of rabbits that died from RHD. This poor association was probably due to the low amount of viral RNA in feces, the prolonged time of excretion after infection, and that the number of rabbits found dead from RHD does not necessarily correlate with RHD incidence. Nevertheless, this procedure may be a complementary noninvasive method to assist in determining the presence of RHD viruses in populations. Additional research is needed to determine the suitability of this methodology to perform epidemiologic surveys on wild populations of European rabbits and, especially, other European or North American lagomorph species affected by lagoviruses.

Changes in European wild rabbit population dynamics and the epidemiology of rabbit haemorrhagic disease in response to artificially increased viral transmission.

European wild rabbit (Oryctolagus cuniculus) populations are severely affected by rabbit haemorrhagic disease (RHD), currently aggravated by the spread of the new lagovirus serotype RHDV2 that replaced the classical RHDV strains (RHDV/RHDVa). This virus causes high mortality in both adult and young rabbits and to date, there is no management tool to effectively reduce its impact on wild rabbit populations. This hinders the success of common strategies, such as habitat management or restocking, in areas where rabbits are native. However, the present study, conducted on enclosed wild rabbit populations, showed that spreading RHDV2 on baits during breeding periods induced infection of young rabbits, reducing mortality rates, presumably due to maternal antibody protection. This reduced the young rabbit mortality hazard by a third, and more juvenile rabbits immune to RHDV2 were recruited into the adult breeding population. Young rabbits from populations in which the force of infection of RHDV2 was increased, however, exhibited considerably higher susceptibility to infection by RHDV than those from non-treated control populations. Since co-circulation of classical RHDVs was ruled out, differences in the type and degree of immunization, the level of cross-protection and/or other unknown factors, such as the circulation of undetected non-pathogenic lagoviruses, arose as possible explanations. This meant that although the present study demonstrated the possibility of successfully modulating the impact of RHD in wild populations, the epidemiological complexity of the situation where several lagoviruses circulate requires additional research to determine final applicability of the proposed method.

Infectivity of rabbit haemorrhagic disease virus excreted in rabbit faecal pellets.

Rabbit haemorrhagic disease (RHD) is caused by a lagovirus affecting European rabbits (Oryctolagus cuniculus). Viral RNA is detected in tissues or faeces of convalescent rabbits, suggesting persistent infections; however, this RNA has not been shown to be related to infective viruses to date. In the present work, seven laboratory rabbits were challenged with the RHDV2/b virus variant. Viral RNA was individually detected by duplex qPCR in faeces collected for four weeks after infection, and the infective capacity of viral RNA excreted in the faeces of surviving rabbits was tested by challenging new rabbits with faecal inocula. As results, viral RNA was detected in faeces until the end of the assay. Viral RNA detected in the fourth week was infective only in the case of one rabbit that did not exhibit clear seroconversion, suggesting persistent infection as a result of an impaired immune response. Since the surviving rabbits were apparently healthy individuals, the importance of detecting carriers and the correct management of faeces to control RHD outbreaks in rabbitries are highlighted.

Detection of Rabbit Hemorrhagic Disease Virus GI.2/RHDV2/b in the Mediterranean Pine Vole ( Microtus duodecimcostatus) and White-Toothed Shrew ( Crocidura russula).

The European wild rabbit ( Oryctolagus cuniculus) is a key prey species on the Iberian Peninsula, and several predator species that are at risk of extinction are dependent on them as prey. A new rabbit hemorrhagic disease (RHD) virus genotype (GI.2/RHDV2/b) emerged in 2010 and posed a threat to wild rabbit populations. During a survey aimed at investigating RHD epidemiology in wild rabbits, GI.2/RHDV2/b was detected by duplex real-time PCR in carcasses of one Mediterranean pine vole ( Microtus duodecimcostatus) and two white-toothed shrews ( Crocidura russula). Laboratory New Zealand white rabbits that were challenged with inocula obtained from the liver of the small mammals died showing RHD lesions, confirming the infectiousness of the isolates. Phylogenetic analysis of the VP60 gene nucleotide sequences showed complete homology between the isolates from the two small mammal species and a high degree of similarity, but not complete homology, to GI.2/RHDV2/b sequences from wild rabbits. The GI.2/RHDV2/b genotype has not been reported in species outside the order Lagomorpha.

Rabbit haemorrhagic disease: Cross-protection and comparative pathogenicity of GI.2/RHDV2/b and GI.1b/RHDV lagoviruses in a challenge trial.

European rabbits (Oryctolagus cuniculus) are severely affected by rabbit haemorrhagic disease (RHD). Caused by a lagovirus, the disease leads to losses in the rabbit industry and has implications for wildlife conservation. Past RHD outbreaks have been caused by GI.1/RHDV genotype viruses. A new virus belonging to the GI.2/RHDV2/b genotype emerged in 2010, quickly spreading and replacing the former in several countries; however, limited data are available on its pathogenicity and epidemiological factors. The present work extends these issues and evaluates cross-protection between both genotypes. Ninety-four and 88 domestic rabbits were challenged with GI.2/RHDV2/b and GI.1b/RHDV variant isolates, respectively. Cross-protection was determined by a second challenge on survivors with the corresponding strain. Mortality by GI.2/RHDV2/b was highly variable due to unknown individual factors, whereas mortality by GI.1b/RHDV was associated with age. Mortality in rabbits < 4 weeks old was 84%, higher than previously reported. Cross-protection was not identical between the two viruses because the ratio of mortality rate ratios for the first and second challenges was 3.80 ±â€¯2.68 times higher for GI.2/RHDV2/b than it was for GI.1b/RHDV. Rabbit susceptibility to GI.2/RHDV2/b varied greatly and appeared to be modulated by the innate functionality of the immune response and/or its prompt activation by other pathogens. GI.1b/RHDV pathogenicity appeared to be associated with undetermined age-related factors. These results suggest that GI.2/RHDV2/b may interact with other pathogens at the population level but does not satisfactorily explain the GI.1b/RHDV virus's quick replacement.