Human influenza A virus H1N1 in marine mammals in California, 2019

Acknowledgements: We acknowledge Jesierose Poblacion, Carlos Rios, Christine Fontaine, Barbie Halaska, and the veterinary staff at TMMC, who conducted marine mammal sampling and provided swabs and serum under NOAA permit 18786–04. We thank Wendy Puryear, Nichola Hill, and Jonathan Runstadler at Tufts University, who provided HI protocols, and Randy Albrecht at the Icahn School of Medicine at Mount Sinai, who provided control sera for HI assays. Hon Ip at the National Wildlife Health Center provided the IAV H3N8 isolate. We are grateful to all authors from the originating laboratories responsible for obtaining the human specimens, as well as the submitting laboratories where the genome data were generated and shared via GISAID.
Funder: UC Davis School of Veterinary Medicine Endowment Fund
From 2011-2018, we conducted surveillance in marine mammals along the California coast for influenza A virus (IAV), frequently detecting anti-influenza antibodies and intermittently detecting IAV. In spring 2019, this pattern changed. Despite no change in surveillance intensity, we detected IAV RNA in 10 samples in March and April, mostly in nasal and rectal swabs from northern elephant seals (Mirounga angustirostris). Although virus isolation was unsuccessful, IAV sequenced from one northern elephant seal nasal swab showed close genetic identity with pandemic H1N1 IAV subclade 6B.1A.1 that was concurrently circulating in humans in the 2018/19 influenza season. This represents the first report of human A(H1N1)pdm09 IAV in northern elephant seals since 2010, suggesting IAV continues to spill over from humans to pinnipeds.