Rabbitpox virus (RPXV) is highly virulent for rabbits and it has long been suspected to be a close relative of vaccinia virus. To explore these questions, the complete coding region of the rabbitpox virus genome was sequenced to permit comparison with sequenced strains of vaccinia virus and other orthopoxviruses. The genome of RPXV strain Utrecht (RPXV-UTR) is 197 731 nucleotides long, excluding the terminal hairpin structures at each end of the genome. The RPXV-UTR genome has 66?5 % A+T content, 184 putative functional genes and 12 fragmented ORF regions that are intact in other orthopoxviruses. The sequence of the RPXV-UTR genome reveals that two RPXV-UTR genes have orthologues in variola virus (VARV; the causative agent of smallpox), but not in vaccinia virus (VACV) strains. These genes are a zinc RING finger protein gene (RPXV-UTR-008) and an ankyrin repeat family protein gene (RPXV-UTR-180). A third gene, encoding a chemokine-binding protein (RPXV-UTR-001/184), is complete in VARV but functional only in some VACV strains. Examination of the evolutionary relationship between RPXV and other orthopoxviruses was carried out using the central 143 kb DNA sequence conserved among all completely sequenced orthopoxviruses and also the protein sequences of 49 gene products present in all completely sequenced chordopoxviruses. The results of these analyses both confirm that RPXV-UTR is most closely related to VACV and suggest that RPXV has not evolved directly from any of the sequenced VACV strains, since RPXV contains a 719 bp region not previously identified in any VACV. INTRODUCTIONPoxviruses are large double-stranded DNA viruses; they have genomes ranging from 130 to 380 kb and replicate in the cytoplasm of cells of their hosts, which include both vertebrates and insects (Esposito & Fenner, 2001;Moss, 2001). Two of the most important members of the Poxviridae are variola virus (VARV), the causative agent of smallpox, and the closely related vaccinia virus (VACV) that was successfully used as the live vaccine for smallpox. VARV and VACV belong to the genus Orthopoxvirus of the Chordopoxvirinae. While VARV no longer circulates naturally in the human population, it remains a serious bioterrorism concern as does monkeypox virus (MPXV), which occasionally produces serious zoonotic infections of humans (Ligon, 2004;Reynolds et al., 2004). The origins of VACV are complicated and confused because of the many sources of vaccine material and methods of propagation and distribution during the centuries of its use (Bazin, 2000). A comparison of the recently sequenced horsepox virus genome with other orthopoxviruses (OPVs) found the highest degree of similarity with genomes of several VACV strains, leading to the suggestion that VACV is possibly a natural horse pathogen (D. L. Rock, personal communication). It is also interesting that VACV strains closely related to those employed as vaccines in the smallpox eradication programme have maintained natural infection cycles in 3These authors contributed equally to this paper. (Gr...

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A nonlinear diversity combining scheme using the Viterbi ratio-threshold technique is discussed. The performances of the ratio-threshold diversity combiner in fast frequency hop spread spectrum systems with M-ary frequency shift keying modulation (FFHIMFSK) under band multitone jamming without and with the additive white Guassian noise are analyzed. The exact bit error probabilities are computed by using an average computation model. The performances under band multitone jamming and under partial band noise jamming are compared. For binary FSK modulation, the performances under the two types of jamming are almost the same, but for 8-ary F-SK modulation, tone jamming is more effective against communications. The structure of the combiner is very simple. Another merit of this combiner is that its output can be directly fed to a soft-decision FEC decoder.