I was recently doing some reading on the biological control program run in Australia to manage the feral rabbit population and learnt a few things. First off; in 2015 we released a second variant of the rabbit haemorrhagic disease virus (RHDV, aka calicivirus) due to increasing immunity in the rabbit population to the first virus that was released in 1996. Secondly, and more interestingly, there is a benign virus (RCV-A1) that is prevalent in wetter areas of Australia that gives immunity to the lethal bio-control agents.
Previously I’d heard that calicivirus was really effective in the drier areas of Australia, but rabbits that lived in the wetter areas of the country tended to recover quite quickly from the initial population drop (i.e. the rabbits that survived the virus doing what rabbits do best and quickly rising in numbers once more). I’d put this down to the higher rainfall and increased plant growth providing the bunnies with more food, but apparently there was another reason; RCV-A1 is prevalent in these wetter areas. Thus the rabbits that lived in these areas had higher immunity to calicivirus, which, of course, got me thinking about smallpox and a certain Edward Jenner.
Jenner was an English doctor and scientist who lived in the 18th century, at a time when smallpox was a huge problem for humanity; killing hundreds of thousands each year. He noticed that farmers who had contracted cowpox (a much milder disease, closely related to smallpox) were immune to getting smallpox. Jenner thought that by deliberately giving people cowpox they would be immune to the more lethal disease. His initial experiments were successful and thus the world’s first vaccine was born; eventually leading to the worldwide eradication of smallpox in 1980. (Wiki also mentions that several other people were conducting similar experiments at around the same time or earlier, but Jenner is the one responsible for widespread implementation, and thus mostly gets the credit for it).
Back to the rabbits – in this case RCV-A1 is acting like cowpox and protecting feral rabbits from contracting the more lethal calicivirus. The problem here is the environmental harm that rabbits cause to the Australian environment due to grazing and out-competing native fauna. Biological control can be a cheap and very effective means to reduce feral rabbit populations, but it is important to remember that it isn’t a silver bullet solution. Ongoing monitoring of rabbit populations and other control programs need to be continued to aid conservation of our unique and beautiful landscape.
If you want more information, please see the links below.
https://www.environment.gov.au/system/files/resources/bf9352c2-35ae-4a80-8828-96de630731a9/files/tap-rabbit-background-2016.pdf
https://en.wikipedia.org/wiki/Edward_Jenner
https://en.wikipedia.org/wiki/Benjamin_Jesty
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