J. Comp. Path. 2000, Vol. 122, 115–122 doi:10.1053/jcpa.1999.0346, available online at http://www.idealibrary.com on The Efficacy of Two Vaccination Schemes Against Experimental Infection with a Virulent Amyxomatous or a Virulent Nodular Myxoma Virus Strain D. Marlier, J. Mainil*, C. Boucraut-Baralon†, A. Linden* and H. Vindevogel Department of Bird and Rabbit Medicine, Faculty of Veterinary Medicine, University of Lie `ge, Bld de Colonster 20, Bat B42, Sart-Tilman, B4000, Lie `ge, *Department of Bacteriology, Faculty of Veterinary Medicine, University of Lie `ge, Bld de Colonster 20, Bat B43, Sart-Tilman, B4000, Lie `ge, Belgium and †Laboratoire Associe ´ INRA-ENVT de Microbiologie Mole ´culaire, Ecole Nationale Ve ´te ´rinaire de Toulouse, 23 Chemin des Capelles, 31076 Toulouse Cedex, France Summary Two types of myxomatosis vaccine are available commercially, namely, vaccine prepared from the Shope fibroma virus (SFV) and that prepared from an attenuated myxoma virus (MV) strain, e.g., SG33. An experiment was designed to compare two vaccination schemes for their ability to protect rabbits against challenge with either a virulent amyxomatous MV strain or a virulent nodular MV strain. Apart from a difference in the cutaneous expression of the disease, the two challenge strains resembled each other in respect of mortality rate, naso-conjunctival shedding of virus, and tissue infection. Vaccination with SFV alone failed to prevent clinical signs, naso-conjunctival shedding or tissue infection. Vaccination with SFV followed by a booster inoculation with SG33 protected rabbits against the development of clinical signs and significantly reduced both viral shedding in naso-conjunctival exudates and viral infection of eyelids, lungs and testes; virus was, however, isolated from testes of some surviving animals.  2000 Harcourt Publishers Ltd and homologous) are available commercially Introduction (Vautherot et al., 1997). Heterologous live vaccines Myxomatosis is a specific disease of European rab- are based on the close antigenic relationship be- bits (Oryctolagus cuniculus) due to a virus belonging tween myxoma virus (MV) and another Le- to the genus Leporipoxvirus. Two forms of the disease poripoxvirus, the Shope fibroma virus (SFV). (nodular and amyxomatous) have been identified Homologous live vaccines contain an attenuated to date (Brun et al. , 1981; Joubert et al., 1982). MV strain such as SG33 (Saurat et al. , 1978) or Prevention of myxomatosis, a matter of great Borghi (Cancellotti, 1995). Both types of vaccine importance to rabbit breeders, is usually achieved have their advantages and drawbacks. Thus, het- by controlling vectors (mosquitoes, fleas), by lim- erologous vaccines are weakly immunogenic and iting direct or indirect contact with wild rabbits provide only short-term protection; homologous and by vaccination (Okerman, 1994). Because the vaccines, on the other hand, may be immuno- sanitary measures are usually inefficient, myx- suppressive, especially in young animals (Vautherot omatosis prophylaxis must be based on effective et al., 1997). No inactivated vaccine against myx- omatosis is currently available. vaccination. Two types of live vaccine (heterologous 0021–9975/00/020115+08 $35·00  2000 Harcourt Publishers Ltd