1. Department of Biotechnology, Royal Institute of Technology (KTH), 10691 Stockholm, Sweden.
2. Yunnan Laboratory of Molecular Biology of Domestic Animals, and Laboratory of Molecular Evolution and Genome Diversity, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650223, China.
3. Department of Virology, Swedish Institute for Infectious Disease Control, 17182 Solna, Sweden.