1. Department of Pathobiological Sciences; School of Veterinary Medicine; Louisiana State University; Baton Rouge Louisiana 70803 USA
2. Microscopy Center; Comparative Biomedical Sciences; School of Veterinary Medicine; Louisiana State University; Baton Rouge Louisiana 70803 USA
3. Department of Infectious Diseases and Pathology; College of Veterinary Medicine; University of Florida; Gainesville Florida 32611 USA