1. Gunther F. Craun & Associates, 101 West Frederick Street, Suite 207, Staunton, VA 24401, USA
2. National Health & Environmental Effects Research Laboratory, Office of Research & Development, US Environmental Protection Agency, Research Triangle Park, NC 27711, USA
3. Division of Parasitic Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, GA 30341, USA