Table 1.
Virulence phenotype of Australian isolates of myxoma virus
| Virus | Year of virus isolation | Survival times (no. surviving)* | AST (normalized) | Inferred virulence grade† | Clinical syndromes observed (no. of rabbits)‡ | Genes disrupted/duplicated compared with SLS (known virulence genes, in bold) |
| Trial 1 | ||||||
| SLS | 1950 | 10.6–14.8 | 12.6 | 1 | A (6) | |
| KM13 | 1952 | 26–S (5) | na | 5 | D (6) | ΔM014 |
| Ur | 1953 | All S (6) | na | 5 | D (6) | ΔM005; ΔM014; ΔM134 |
| BD23 | 1999 | 11.2–24.5 | 13.3 | 2¶ | B (5) C (1) | ΔM147; ΔM009; Duplication M156; M154 |
| BRK 12/2/93 | 1993 | 11.9–24.5 | 13.5 | 2¶ | B (5) C (1) | ΔM009 |
| SWH 8/2/93 | 1993 | 11.1–20.5 | 14.3 | 2 | B (4) C (2) | ΔM009 |
| WS6 346 | 1995 | 12.2–29 | 15.8 | 2 | B (3) C (3) | ΔM005; ΔM009 |
| SWH1209 | 1996 | 13.3–32 | 19.1 | 3 | B (2) C (4) | ΔM009; duplication M156, M154 |
| Trial 2 | ||||||
| BRK 4/93 | 1993 | 10.6–12 | 11.4 | 1 | B (6) | ΔM009; ΔM036 |
| BD23 | 1999 | 10.6–12.6 | 11.85 | 1¶ | B (6) | ΔM147; ΔM009; duplication M156; M154 |
| BRK 12/2/93 | 1993 | 11.6–13.6 | 12.03 | 1¶ | B (6) | ΔM009 |
| BD44 | 1999 | 11.3–14.6 | 12.1 | 1 | B (6) | ΔM00.05; ΔM008.1; ΔM009 ΔM153; duplication M156, M154 |
| SWH 9/92 | 1992 | 10–23 | 12.2 | 1 | B (4) A (2) | ΔM009 |
| SWH 805 | 1993 | 12.6–28 | 14.4 | 2 | B (5) C (1) | ΔM009 |
| BRK 897 | 1995 | 12.6–28 | 16.4 | 3 | B (4) C (2) | ΔM009 |
| WS6 1071 | 1995 | 12.2–22.5 | 18.2 | 3 | B (2) C (4) | ΔM009; ΔM153 |
| Meby | 1991 | 10.6–S (1) | 16.9 | 3 | A-B§ (5) D (1) | ΔM009; ΔM153 |
| OB3 Y317 | 1994 | All S (6) | na | 5 | D (6) | ΔM009; ΔM012 |
A total of 16 isolates were assayed in groups of six laboratory rabbits in two trials. Two virus strains, BD23 and BRK 12/2/93, were tested in both trials. na, not applicable.
Survival times, unnormalized range. S, survived, with number surviving shown in brackets.
Grade 1, AST ≤13 d, CFR 100%; Grade 2, AST 14–16 d, CFR 95–99%; Grade 3, AST 17–28 d, CFR 70–95%; Grade 4, AST 29–50 d, CFR 50–70%; Grade 5, indeterminate AST, CFR <50%.
Syndrome A, typical cutaneous myxomatosis; B, acute collapse with little overt signs of myxomatosis; C, progressive “amyxomatous” myxomatosis in rabbits infected with viruses causing syndrome B but that did not suffer acute collapse; D, attenuated cutaneous myxomatosis (see SI Appendix for definitions).
BD23 and BRK 12/2/93 were graded as 2 in the first trial and as 1 in the repeat trial; the combined results are grade 1 for both strains.
Intermediate phenotype. Four animals died from acute collapse, and a fifth with bacterial infection associated with acute inflammation. All animals developed primary lesions consistent with typical cutaneous myxomatosis, but only two developed secondary lesions (SI Appendix, Table S1). The Meby strain is from Tasmania and has been isolated from viruses on continental Australia for at least 20 y.