SG33 Myxoma Virus and Field Recombination | CDC EID

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Volume 17, Number 4–April 2011
Research
Genome Sequence of SG33 Strain and Recombination between Wild-Type and Vaccine Myxoma Viruses
Christelle Camus-Bouclainville, Magalie Gretillat, Robert Py, Jacqueline Gelfi, Jean-Luc Guérin, and Stéphane Bertagnoli

Author affiliations: French National Institute for Agricultural Research, Toulouse, France; and Université de Toulouse, École Nationale Vétérinaire, Toulouse


Suggested citation for this article

Abstract
Myxomatosis in Europe is the result of the release of a South America strain of myxoma virus in 1952. Several attenuated strains with origins in South America or California have since been used as vaccines in the rabbit industry. We sequenced the genome of the SG33 myxoma virus vaccine strain and compared it with those of other myxoma virus strains. We show that SG33 genome carries a large deletion in its right end. Furthermore, our data strongly suggest that the virus isolate from which SG33 is derived results from an in vivo recombination between a wild-type South America (Lausanne) strain and a California MSD-derived strain. These findings raise questions about the use of insufficiently attenuated virus in vaccination.

Myxoma virus is a member of the family Poxviridae and the genus Leporipoxvirus (1). It causes a benign infection in American rabbits (Sylvilagus spp.) but is responsible for myxomatosis in the European rabbit (Oryctolagus cuniculus). This systemic and lethal infection is characterized by a large myxoma at the inoculation site, a leonine facies caused by edema, and numerous secondary myxomas (2).

Distinct myxoma virus (MYXV) strains from South America and California have been identified; virulence of California MSW strain is higher than that of South America strains in European rabbits (3). In contrast, the California MSD strain is reported to be less pathogenic (3) and has thus been used as a basis for the generation of vaccine strains on several occasions.

MYXV was introduced in France in 1952 as a means to control wild rabbit populations (2), and it has since spread widely throughout Europe. The strain used had been derived from a virulent South America strain (4) and has been called Lausanne since 1957 (5). Although MYXV was introduced to control wild rabbit populations, it rapidly spread to domestic rabbits, and by 1954, 30%–40% of the rabbit industry in France had been destroyed (2). Shope fibroma virus (SFV) was first used as a vaccine (6,7) but was only moderately effective. Limited trials were performed (2) by using an MSD-derived vaccine strain developed in California by Saito et al. (8), but this strain was later shown to cause myxomatosis symptoms in rabbits (9,10). Further attempts to attenuate the Saito strain were made (9). Some of the vaccine strains used throughout Europe today, such as Borghi (11) and MAV (12), are derived from the Saito strain.

In France, another attenuated vaccine was developed by Saurat et al. (13) in the École Nationale Vétérinaire de Toulouse virology laboratory. MYXV SG33 strain was obtained in 1977 by serial passages on a rabbit kidney cell line and chicken embryo cells at 33°C from an isolate obtained from a wild rabbit killed in the Toulouse area in 1973 (13). It has since been widely used as a vaccine against myxomatosis in rabbits in France and other countries in Europe.

Preliminary analyses of the SG33 genome showed a large deletion near the right end of the genome (14,15). Cavadini et al. recently performed a partial analysis of the SG33 sequence (16). They amplified and sequenced 200-bp to 10,000-bp fragments from 15 genomic locations, spanning 35 MYXV genes, and demonstrated that it was highly (97%–100% identity) similar to Lausanne. However, they reported somewhat lower similarities between both strains for M138L-M139R (GenBank accession no. HM104692) and M142R-M144R (GenBank accession no. HM104702) sequences, with 84% and 89% identity, respectively. They observed 100% identity between their M138L-M139R sequence and the only available MSD sequence, a partial sequence of M138L (GenBank accession no. AF030894) (17). We present the analysis of the genome sequence of MYXV SG33 vaccine strain, which confirms the presence of a large right-end deletion and shows evidence of a field recombination between a wild-type and a vaccine strain.


full-text:
SG33 Myxoma Virus and Field Recombination | CDC EID


Suggested Citation for this Article
Camus-Bouclainville C, Gretillat M, Py R, Gelfi J, Guérin J-L, Bertagnoli S. Genome sequence of SG33 strain and recombination between wild-type and vaccine myxoma viruses. Emerg Infect Dis [serial on the Internet]. 2011 Apr [date cited].
http://www.cdc.gov/EID/content/17/4/633.htm


DOI: 10.3201/eid1704.101146


Comments to the Authors
Please use the form below to submit correspondence to the authors or contact them at the following address:

Christelle Camus-Bouclainville, UMR INRA-ENVT 1225, 23 Chemin des Capelles, BP 87614, F-31076 Toulouse CEDEX 3, France; email: c.camus@envt.fr