. Possum disease is a protozoal disease. VERY different micro organism and not something against which you can develop a vaccine (very hard to vaccinate against protozoa) Flu viruses are well known for their ability to mutate freely - other viruses not so much. Rabies is a multi species disease but the vacine is very effective and has been for a very long time. Hendra is a paramyxovirus - related to distemper in dogs and measles in people. Both of which are very stable and against which we have had effective vaccines for a long time. Um..yes... Cos the healthy ones released will then get the virus from the currently infected ones you haven't trapped yet?? Or do you suggest we can catch EVERY bat in the area at one time and test? Are you going to hold them in a pen while their individual test results come back? Not to mention that you'd have to identify every one individually so you knew which results applied to which bat. Cos there's no pen side test. And then there's the issue of getting people prepared to handle the damn things knowing what they might be carrying... Culling also won't work real well as bats are quite migratory - cull out one colony and another will move into the space left behind. This dog has sero converted... he no longer appears to carry virus- he is not actively infected. You can learn a LOT from a dead animal - PM, tissue samples, virus isolation... the list goes on.