1. Institute for Genome Sciences, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
2. Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
3. Department of Epidemiology and Public Health, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
4. Department of Biological Sciences, University of Idaho, Moscow, ID 83844, USA.
5. Institute for Bioinformatics and Evolutionary Studies, University of Idaho, Moscow, ID 83844, USA.
6. Department of Mathematics, University of Idaho, Moscow, ID 83844, USA.
7. Department of Statistics, University of Idaho, Moscow, ID 83844, USA.