1. United States Department of Agriculture, Agriculture Research Service, Avian Disease and Oncology Laboratory, East Lansing, Michigan.
2. Department of Pathobiology, University of Guelph, Guelph, Ontario, Canada.
3. Department of Statistics and Probability, Michigan State University, East Lansing, Michigan.
4. D.I. Ivanovski Institute of Virology, Moscow, Russia.
5. Department of Poultry Science, Texas A&M University, College Station, Texas.