Myxomatosis and Rabbit Haemorrhagic Disease: A 30-Year Study of the Occurrence on Commercial Farms in Spain

SIMPLE SUMMARY: Myxomatosis has affected the European domestic rabbit in Spain since the end of 1953; and rabbit haemorrhagic disease (RHD) since mid-1988. In this study, we describe the occurrence of myxomatosis; and RHD; on commercial rabbitries visited in Spain; between 1988 and 2018. Annual occurrence of myxomatosis decreased over 30 years. Cases of myxomatosis were detected most frequently between August and March; more cases occurring in September and fewer in June. Two important RHD epidemics occurred; the first in 1988–1989 due to classic RHD virus (RHDV), and the second from 2011 to 2013 due to new calicivirus (RHDVb/RHDV2). Monthly occurrence of RHD in 2011–2018 was higher from April to August. Despite seasonal variations of these diseases; we recommend that young breeders and adults should be protected by vaccination all year round; and on-farm hygiene measures implemented ABSTRACT: In this retrospective study, we describe the relative occurrence of clinical myxomatosis, and rabbit haemorrhagic disease (RHD), on 1714 commercial farms visited in Spain, between 1988 and 2018. We determined the annual prevalence based on 817 visits to 394 farms affected by myxomatosis. Myxomatosis was more prevalent from August to March, being lowest in June (3%) and highest in September (8.9%). With regard to RHD, we assessed 253 visits to 156 affected farms. We analyzed mean annual and monthly incidence. Two important RHD epidemics occurred; the first in 1988–1989 due to RHDV GI.1 (also known as RHDV), and the second from 2011 to 2013 due to RHDV GI.2 (RHDV2 or RHDVb). These epidemics occurred at times when effective vaccination had not been carried out. Relative monthly incidence in 2011–2018 was higher from April to August (p < 0.001). The results we obtained from 1404 necropsies on 102 farms did not clearly relate serosanguinous nasal discharge in rabbits with disease caused by GI.2 infection. We also assessed vaccination schedules used on 200 doe farms visited from the end of 2014 to 2018; 95.5% vaccinated against myxomatosis and 97.5% against RHD. Both diseases remain prevalent; however, effective vaccination has produced a steady decline in myxomatosis and RHDV GI.1 and GI.2 on-farm detection. The maintenance of high hygienic standards will be needed to continue and improve this control. However, further studies are required to investigate the causes of sustained virus presence and vaccine breaks.