Avian Influenza Infection in Waterfowl Hunters and Wildlife Professionals

1. Average Age (yr) Age (range) Gender Exposure (yr) Age (yr) Hunting/Bird Exposure (yr) MN Titer HUNTER M 39 31 1:40 HUNTERS 34 17-61 19.8 DNR 1 M 52 27 1:10 DNR 47 24-68 21.5 DNR 2 M 53 30 1:10 Avian Influenza Infection in Waterfowl Hunters and Wildlife Professionals James S. Gill1, MD, PhD, Richard Webby2, PhD, Mary J.R. Gilchrist1, PhD, Gregory C. Gray3, MD, MPH 1University of Iowa Hygienic Laboratory, Iowa City, IA; 2St. Jude Children’s Research Hospital, Memphis, TN; 3University of Iowa Center for Emerging Infectious Diseases, Iowa City, IA; Results Discussion Introduction One 39 year-old duck hunter with 31 years of duck hunting experience and two Iowa DNR workers with 27 and 30 years of waterfowl exposure had elevated titers against avian influenza H11N9 by microneutralization assay and horse erythrocyte hemagglutination inhibition assay. The average age of the duck hunters and the Iowa DNR workers was 34 and 47 years, respectively, and the average number of years of waterfowl exposure of the two groups was 20 and 22 years, respectively. One-third of all participants routinely received influenza vaccination over the past three years. None of the subjects with elevated titers against H11N9 had been vaccinated against influenza. To our knowledge this is the first study to assess individuals with significant exposures to wild ducks and geese, the known reservoir of influenza A virus in nature. Virus transmission from wild waterfowl to humans is unknown. Even though our study subjects handled wild birds infected with avian influenza, they did not wear personal protective equipment. During the season when the banding of wild waterfowl occurs, it has been previously shown that 50-60% of hatch-year ducks (mallards) are infected with influenza A. In our study we provide serologic evidence using two different assays for past infection in humans with influenza H11, a subtype with an isolation frequency from wild ducks and shorebirds of 1% and 15.4%, respectively. Although the sample size was small, our study implies that the handling of wild ducks and geese is a risk factor for the transmission of avian influenza virus directly to humans. Wild ducks, geese, and shorebirds are the reservoir for influenza A virus in nature. All sixteen hemagglutinin (H) and nine neuraminidase (N) subtypes are found in these wild birds. Recently the rapid spread of the H5N1 influenza virus to new geographic regions by migrating birds has caused great concern among public health officials who fear the next great influenza pandemic. Until now serologic studies of the transmission of H5N1 and other highly pathogenic strains of avian influenza have focused on humans who have contact with infected domestic poultry. However, very little is known about transmission of influenza A virus from wild birds directly to humans. In this study we performed a cross-sectional seroprevalence study of individuals who are routinely, heavily exposed to wild ducks and geese through part of their duties of employment (bird banding) or through recreational activities (duck hunting). A B Materials & Methods • Sera collection • Serum samples were collected from 68 employees of the Iowa Department of Natural Resources (DNR) in February, 2005. Nearly all of these employees capture and band wild waterfowl as part of their duties of employment or hunt birds recreationally. • Serum samples were collected from 39 duck hunters at Lake Odessa Wildlife Management Area near Wapello, IA, in October, 2004. • Microneutralization Assay (MN) • MN assay, adapted per CDC protocol, was performed on all serum samples using avian influenza subtypes H1 through H12. Virus at 100 TCID50 per 50 l was incubated for 2 hr with heat-inactivated serum in 96-well plates. London MDCK cells, grown to 70-95% confluency and then trypsinized, were added at 2x105 cell per ml. The cells were acetone-fixed after 24 hr exposure to virus and ELISA was performed using a HRP-based test with specific mouse anti-influenza A antibody. OD was read at 490 nm. • Horse Erythrocyte Hemagglutination Inhibition Assay (HI) • HI assay, adapted per CDC protocol, using horse erythrocytes was performed on all hunter serum samples using avian influenza subtypes H1, H2, H3, and H11. Receptor destroying enzyme-treated serum was first heme-adsorbed with horse packed RBCs. Treated serum was incubated with virus at 8 hemagglutinin units per 50 l and then incubated with 1% horse RBC in 0.5% BSA in PBS for 1 hr in V-bottom plates, after which time the plates were read. Fig. 1. Histogram by age and group C Fig. 2. Histogram by age and seropositivity Table 1. Age and exposure by group Acknowledgements We thank Dale Garner, Bill Ohde, and other employees of the Iowa Department of Natural Resources for their assistance in this project. We thank Sharon Setterquist, Deb Wellman, Kelly Lesher, and Mohammad Ghazi for their technical expertise in performing the microneutralization assay and horse erythrocyte hemagglutination assay. We thank Ana Capuano. We also thank all volunteers who assisted with blood collecting. Table 2. Age, gender, exposure, and MN titer by individual