Biological Control of Rabbits in Australia: Myxomatosis and RHD

Australia's war against the European rabbit (Oryctolagus cuniculus)—introduced 1859, reaching plague proportions by 1900—has relied on two deliberate viral introductions that constitute history's largest vertebrate biocontrol program.

Myxomatosis (Myxoma Virus) — 1950

• Origin: South American rabbit virus; tested in Australia 1930s-40s
• Release: December 1950, Murray-Darling Basin; spread naturally via mosquitoes, fleas
• Initial impact: 99% mortality in naive populations; ~500M rabbits killed in 2 years
• Mechanism: Myxomatous lesions (skin tumors), conjunctivitis, immunosuppression → secondary pneumonia
• Coevolution: Rabbits developed resistance (innate, acquired); virus attenuated (less lethal strains favored). Mortality dropped to 40-60%
• Vectors: Mosquitoes (primary), rabbit fleas (Spanish flea introduced 1960s for arid zones)

Rabbit Haemorrhagic Disease (RHDV/RHDV2) — 1995/2015

• RHDV1 (Czech CAPM-V351): Released 1995 (Wardang Island SA → mainland). Calicivirus; acute hepatic necrosis; death in 12-36 hrs
• Initial impact: 90%+ mortality in susceptible populations; arid zones most affected
• Limitations: Less effective in cool/wet regions; benign calicivirus (RCV-A1) gave cross-immunity
• RHDV2 (GI.2): Detected 2015 (likely accidental/natural arrival). Broader host range (hares, juveniles), overcomes RHDV1 immunity
• K5 strain (Korean RHDV1): Released 2017 nationally to boost efficacy in cool/wet areas

Combined Impact

• Population suppression: Rabbits reduced from ~600M (1950) to ~150-200M (current est.)
• Economic benefit: $70B+ cumulative agricultural savings (ABARES)
• Ecological recovery: Native vegetation regeneration; reduced erosion; predator release (foxes, cats switch prey)
• Ongoing management: Viruses + conventional (warren ripping, fumigation, shooting, fencing, new toxins)

Ethical and Ecological Debates

• Welfare: Myxomatosis causes suffering (days-weeks); RHD quicker but still distressing
• Non-target effects: RHDV2 infects European brown hare; minimal other impacts documented
• Resistance management: Monitoring genetic resistance; rotating/stacking viruses
• Predator-prey dynamics: Rabbit suppression → mesopredator release (foxes/cats eat natives)

Future Directions

• Genetic biocontrol (gene drive, immunocontraception)—research stage
• RHDV variants surveillance (recombinants emerging)
• Integrated pest management: viruses + landscape-scale conventional control
• Climate change: Range shifts, vector dynamics, virulence evolution

Australia's rabbit biocontrol remains a global case study in long-term host-pathogen coevolution, demonstrating both the power and limits of viral control for invasive vertebrates.