Skip to main content

Biological controls

Myxo or RHDV, or both?
or wait for the future with gene drive technology?

In the past, the myxo virus has made a huge difference to the rabbit population. It continues to eliminate about 50% of rabbits that are infected. It was recognised in the past when rabbits eyes were affected by the virus. This might not happen today.

RHDV is a new class of virus that has been tried in recent years. The success rate is not always convincing - especially if the weather, environment, etc are not helping.

Gene drives will possibly happen in the future but for now they are not sufficiently tested and ready to go.

Note: much of our information comes from Rabbit Free Australia - thanks to them!

Learn about myxo, RDHV and gene drives:

A gene drive is a natural process and technology of genetic engineering that propagates a particular suite of genes throughout a population by altering the probability that a specific allele will be transmitted to offspring (instead of the Mendelian 50% probability). Gene drives can arise through a variety of mechanisms. They have been proposed to provide an effective means of genetically modifying specific populations and entire species.

gene drive image

And if you are keen to learn more about gene drives and the future:

Is myxo too old to be useful?

See what is explained on the Rabbit Free Australia site in an experts' forum by Brian COOKE [https://theconversation.com/profiles/brian-cooke-7527]

Hi Jarvis,

It is not inevitable that viruses like myxoma virus (MYXV) or rabbit haemorrhagic disease virus (RHDV) will eventually become less effective because they naturally become less virulent or because of increased resistance or immunity in rabbits.

This is because virulence is selectively adjusted, maximizing transmissibility, as the rabbit host develops greater resistance. The final outcome can depend on the genetic capacity of the virus to match or avoid host defences. In the case of myxoma virus, a large DNA virus, it has the capacity to supress the rabbit's immune system, hence it has been increasing in virulence as rabbits become more resistant. Today’s myxoma viruses appear to have kept pace with increases in rabbit resistance and still kill about 50% of wild rabbits just as they did 30 - 40 years ago.

On the other hand, RHDV, which is a small RNA virus, simply gets in and replicates rapidly before the rabbit’s immune system can react. It kills about 70% of infected rabbits. We think that, by killing rabbits, the chances of its spread by blowflies is increased. By contrast, non-pathogenic RCV-A1, although closely related to RHDV, effectively presents a small target by confining infection to a few gut cells. It causes no illness and does not strongly stimulate the rabbit's immune system. That way it can quietly replicate over a longer period and virus particles are excreted in rabbit faeces enabling the virus to spread. Presumably, rabbits stand on virus contaminated faeces and when they groom, which involves licking their paws, they ingest RCV-A1 viral particles.

The different ‘strategies’ for virus persistence that have evolved are varied and well understood but we can’t really predict what will happen in the long run. For example, contrary to what one might expect, highly lethal RHDV is thought to have evolved from a non-pathogenic precursor like RCV-A1. We can therefore say that it is not inevitable that viruses will always attenuate and become less effective.

Because myxomatosis has been effective in killing a substantial proportion of the rabbits it infects for over 70 years and RHDV has been around for 25 years (partly replaced by RHDV2) and causes even higher mortality, we can probably assume that both viruses will continue to be useful biological control agents for many years to come. 

From: https://rabbitfreeaustralia.org.au/rabbit-free-forum/