There are several aspects to the use of RHDV as a "transmissible poison". And as usual most of them are not understood, or are dismissed as unimportant (or both).

LOSS OF VIRULENCE IN BAITS.

Prof Frank Griffin (University of Otago, Dunedin N.Z.) is an immunologist. He has been quite adamant about the potential (often apparently abundantly realised) for the virus coating on baits to be exposed to UV for considerable, but variable periods after distribution by air drop of whatever, before being ingested by a rabbit. The problem appears to be that in this very variable period - the fewer the rabbits and other bait takers, the longer the period is. The ordinary UV component of incoming solar radiation has the effect of attenuating the virus and so reducing its virulence. There are grounds for believing that being dosed with such attenuated virus, whilst not lethal still has the ability to be antigenic - promote the production of antibodies (which of course involves setting up a lineage of "memory cells") so that the resulting immunity will be of long duration. In parts of Otago it is clear that farmers spreading their "home brew" of the "kitchen whiz" variety were hardly A grade laboratory technicians, and the extent to which their handling of the virus may have initiated the attenuation process BEFORE dispersal is unknown. Then too it seems that dosages etc either in terms of amount per bait, and number of baits eaten per rabbit is entirely unknown. How much virus does it take to kill a rabbit? Is there a difference between rabbits with factor "x" (probably the benign RCV) and truly naive rabbits in the nature of the responses seems unknown. Then there are other problems about the persistence of the virus on baits under rainfall of differing intensities and durations. Originally most virus was spread on chopped carrots, or even sprayed onto the ground (and pasture?). Nowadays the commercial ZEN virus product is supposed to be incorporated onto oats baits, and any baits remaining after 48 hours are to be picked up and removed!!!!!!!!!!!!!!!!!!! Can you imagine a run-holder on his knees picking up oat grains?????????????????????? However, this condition which was imposed on the marketeers by our politically servile Pesticides Board. It may be taken as official recognition that leaving baits out exposed to the ameliorating effects of UV is a source of further difficulties through immunisation. I think we can say that officialdom recognises that UV irradiated baits are an embarrassing source of immunity through farmer-mediated immunisation.

HANDLING FARMER HOME BREWS AND WHIZ MIXTURES

It is very clear to those of us who have the slightest glimmerings of understanding about the risks of manipulating diseased tissues and extracts from them, that there are very real dangers in the process, and that sensible people will take sensible precautions as are usually required by law in any civilised country. Such measures typically aim not only to protect the operator from the pathogen known to be in the material to be handled, but also from the other pathogens that are or could be encountered in material of that origin. It seems to be a surprise to the naive that RHDV is not the only pathogen that might be expected to occur in such materials. Our local idiots didn't bother to think about this, and used their wive's kitchen food processors to "whiz up" mixtures of saline and rabbit offals in the kitchen, and then stored the resultant brews in the family fridge!!!!!!!! There was a special feature on the internet explaining how to do it, and this item was on a site maintained by out MAF (=Agriculture ministry). Of course anyone with any knowledge of disease transmission knows that the pulmonary route of infection is usually a most efficacious one. Remember the Nursery Rhyme about the Black Death -- Atishoo! Atishoo! we all fall down. Death from aerosols certainly spread the black death. We do not seem to have had any mortality from RHDV (or contaminants) dispersed in this fashion, but perhaps the Gods smiled. The risks are not to be ignored, and from a recent radio programme here it is clear that the making of home brews is continuing. So many who know not what they do charge ahead on the basis that if a little is good that lots more must be much better, and I'll just hope that nothing happens to my wife, or my kids. Me? I'm indestructible!

THE MYSTERY OF THE DISAPPEARING EARS

Garry Clark [of Invermay Animal Health Laboratory,NZ] recently gave us a short and tantalising paper on the diminishing rabbit ears. This raises a good few questions. Some that have occurred to me include: is the ear erosion phenomenon a result of an attenuated virus? Clark is certain that it is an RHD induced condition for the affected rabbits all die eventually from RHD. But it appeared from his photos of the progressive erosion of the ear pinnae [V-shaped notches appear at the tips of the ears) takes some time. About this time (when erosion starts)the cartilage in the median part of the lower ear undergoes a sort of hyperplasia of the cartilage cells in the middle of the ear to produce thickened longitudinal ribs in the ear. Typically, from his account, there is a major central rib, and usually a pair of lateral thickened ribs, one on either side of the central major rib. There appears to be little or no understanding of this phenomenon. I can make a few guesses, but you should understand this is only a "first guess." I suspect that the virus that causes "ear rot" is an attenuated variant of RHD, because as Clark reports these rabbits all die of RHDV eventually. The curious thing is that he did not comment on the time course of the disease. Clearly from the variety of slides of rabbits affected to various extents it takes some time for the ears to "rot" down to their stumps, and after that to die. This is quite different from the time course that we have all been dosed with, that the rabbits are all dead after 48 hours after a painless(?) infection. What has happened to the "ear rot" strain to slow the arrival of death? Could it be that the aetiology (development of the symptoms of the disease) relates in some way to the limited blood supply to the chondrocytes (cartilage cells) in the ear, which might be suspected of diminishing any access to antibodies for a time at least - pure speculation. There are so few data that there are also few restraints to the imagination, but the changed time-to-die seems to need an explanation.

I have no knowledge about whether the ear rot rabbits show signs of distress or pain. That's another unknown.

RISKS TO OTHER SPECIES

If the tests conducted by CSIRO suggested anything with much certainty about the host range of RHDV it was, in my opinion that it might generally be easier to infect birds than mammals. My feeling is that the tests were terminated as they became interesting - tsk tsk! Now if one puts out a large amount of virus on a bait that is attractive to other potential eaters, then one is in effect conducting a huge uncontrolled experiment to see if you can demonstrate that many other animals - anything that will eat the bait - oats, carrots or whatever will suffer any effects from these unknown doses. Further there is no way of limiting the dose given to individuals. Surely aerial dropped baits will look like the traditional manna from heaven, so it's fill up on it while there is a chance! Who will provide the funds to search for the cadavers of unintentional victims of this great experiment?

It seems to me that the little knowledge we have is contraindicative of any virus baiting programme. It seems that idiocy is a common condition in both Australia and New Zealand. It may be that with a bit of "luck" home brew biociding could serve to raise the IQ in both countries. That could be seen as a "public good", but whether it would off-set the side effects is open to doubt. From our experience of "biociding" the effects are of doubtful value. The risks of inadvertently immunising rabbits are real. The risks of increasing the host and reservoir range are unknown. Allowing, or encouraging the unskilled and the ill-equipped to process their own brews is very ill advised. (Are our workplace safety rules all a big con???)

All the best for success in the fight against the forces of darkness