1. School of Veterinary Science; The University of Queensland; Brisbane 4072 Australia
2. The Animal Referral Hospital; 250 Parramatta Road, Homebush New South Wales Australia
3. Centre for Veterinary Education, B22; The University of Sydney; New South Wales Australia
4. Faculty of Veterinary Science; the University of Sydney; New South Wales Australia
5. “Gameford”; 336 Palmyra Avenue, Shanes Park New South Wales 2747 Australia
6. Epidemiology Unit; Queensland Institute of Medical Research; Herston Brisbane 4006 Australia