1. Department of Epidemiology, University of Nebraska Medical Center, Omaha, NE 68198, USA
2. Aklilu Lemma Institute of Pathobiology, Addis Ababa University, Addis Ababa P.O. Box 1176, Ethiopia
3. Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, NE 68198, USA
4. Department of Biostatistics, University of Nebraska Medical Center, Omaha, NE 68198, USA
5. Department of Environmental, Agricultural & Occupational Health, University of Nebraska Medical Center, Omaha, NE 68198, USA
6. Department of Virology, Parasitology and Immunology, Ghent University, 9820 Merelbeke, Belgium