[1] Wildlife Conservat Soc, 2300 Southern Blvd, Bronx, NY 10460 USA
[2] Univ Glasgow, Coll Med Vet & Life Sci, Boyd Orr Ctr Populat & Ecosyst Hlth, Glasgow G12 8QQ, Lanark, Scotland
[3] Erasmus MC, Dept Virosci, NL-3015 GE Rotterdam, Netherlands
[4] Univ Cambridge, Dept Zool, Cambridge CB2 3EJ, England