1. Department of Veterinary Clinical Studies, Universiti Pertanian Malaysia, Serdang, Selangor, Malaysia
2. Department of Veterinary Microbiology and Immunology, Univercity of California, Davis, California 95616, USA
3. California Veterinary Diagnostic Laboratory, P.O. Box 1770, University of California, Davis, California 95616, USA
4. Present address: Animal Diagnostic Laboratory, Department of Veterinary Science, Penn State University, University Park, Pennsylvania 16802, USA