MARINE MAMMAL SCIENCE, 22(1): 214–221 ( January 2006) C  2006 by the Society for Marine Mammalogy SEROLOGIC INVESTIGATION OF INFLUENZA A VIRUS INFECTION IN CETACEANS FROM THE WESTERN NORTH PACIFIC AND THE SOUTHERN OCEANS KAZUE OHISHI TADASHI MARUYAMA Research Program for Marine Biology and Ecology, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Natsushima 2-15, Yokosuka, 237-0061, Japan E-mail: oishik@jamstec.go.jp AI NINOMIYA HIROSHI KIDA Graduate School of Veterinary Medicine, Hokkaido University, Kita-ku, Sapporo, Hokkaido 060-0818, Japan RYOKO ZENITANI TAKEHARU BANDO YOSHIHIRO FUJISE Institute of Cetacean Research, Toyomi-cho, Tokyo 104-0055, Japan KEN NAKAMATSU NOBUYUKI MIYAZAKI Ocean Research Institute, University of Tokyo, Nakano-ku, Tokyo 164-863, Japan ANDREI N. BOLTUNOV All-Russian Research Institute for Nature Protection, Moscow, Russia Influenza A viruses infect a variety of birds and mammals. Wild waterfowl are the primary reservoirs for all influenza A virus strains that have been introduced into mammals including humans (Webster et al . 1992, Murphy and Webster 1996). Interspecies transmission of influenza plays an important role in its evolution and ecology (Webster et al . 1992, Kida et al . 1994, Murphy and Webster 1996). It is important to monitor the distribution of the influenza in various wild animal species including marine mammals in order to understand the maintenance and evolution of the virus in an ever-broadening range of host animals with the ultimate goal of predicting the emergence of new pandemic strains. Influenza A viruses are classified into subtypes based on antigenetic differences in their two surface glycoproteins, namely hemagglutinin (H) and neuraminidase (N). Fifteen H subtypes and nine N subtypes are presently recognized (Webster et al . 1992, Murphy and Webster 1996). In the past few decades, influenza A virus infection 214