Cloacal and tracheal swabs were collected from 1389 hunter-killed ducks in Cameron Parish, Louisiana, during the 1986 and 1987 waterfowl seasons. Twenty-eight avian influenza viruses (AIVs) were isolated from 605 blue-winged teal (Anas discors), 75 mottled ducks (A. fulvigula), 375 gadwalls (A. stepera) and 334 green-winged teal (A. crecca). Prevalence estimates of AIV in ducks sampled during September, November, and December through January were 3.1%, 2.0%, and 0.4%, respectively. Differences in prevalence were detected by season (P = 0.044) and age class (P = 0.036). Two isolations from resident mottled ducks document transmission of AIV on these wintering areas. Much subtype diversity was present, with nine of 13 hemagglutinin (HA) and nine of nine neuraminidase (NA) subtypes recovered. Predominant HA and NA subtypes were typical of AIVs commonly associated with waterfowl. Results indicate that AIVs are transmitted in the wintering areas, and, although prevalence is low, these viruses continue to circulate within these duck populations during winter.

Isolation-reared mallards (Anas platyrhynchos) were placed on ponds in turkey-rearing areas in Minnesota, and their cloacae were periodically swabbed to attempt isolating virus from embryonated chicken eggs. Nearby turkeys were sampled by taking cloacal and tracheal swabs as well as blood samples. Hemagglutinating viruses were identified at the National Veterinary Services Laboratory, U.S. Department of Agriculture, Ames, Iowa. During this two-year study, the weekly influenza virus-isolation rate from ducks varied from 0 to 24.4%. A total of 213 influenza viruses were isolated from the ducks. Twenty-six influenza virus subtypes were detected. Ninety-seven flocks of turkeys were diagnosed as having influenza by virus isolation and/or serology. Eight influenza virus subtypes were involved in the turkey outbreaks, and seven of these were also detected in the ducks and/or other avian species. The weekly infection rate of the sentinel ducks correlated directly with observations of wild ducks at the monitoring sites. Influenza virus was isolated from water samples collected near the sentinel duck sites during the study.

Five 34-wk-old turkey breeder layer flocks in separate houses of 2550 birds each in a single farm in Ohio experienced a drop in egg production from late January to early February 2004. Tracheal swabs (n = 60), cloacal swabs (n = 50), and convalescent sera (n = 110) from the flocks were submitted to the laboratory for diagnostics. Virus isolation was attempted in specific-pathogen free embryonating chicken eggs and Vero and MDCK cells. Virus characterization was performed using agar gel immunodiffusion, the hemagglutination test, the hemagglutination inhibition test, the virus neutralization test, reverse transcription-polymerase chain reaction, sequencing, and phylogenetic analysis. A presumptive influenza virus was successfully propagated and isolated on the first passage in MDCK cells, but initially not in Vero cells or specific-pathogen free chicken embryos. After two passages in MDCK cells, it was possible to propagate the isolate in specific-pathogen free chicken embryos. Preliminary sequence analysis of the isolated virus confirmed that it was influenza A virus with almost 100% (235/236) identity with the matrix gene of a swine influenza A virus, A/Swine/Illinois/100084/01 (H1N2). However, it was not possible to subtype the virus using conventional serotyping methods. The results of genetic characterization of the isolated virus showed that it was the H3N2 subtype and was designated as A/Turkey/OH/313053/04 (H3N2). Phylogenetic analysis of the eight gene segments of the virus showed that A/Turkey/OH/313053/04 (H3N2) isolate was most closely related to the triple-reassortant H3N2 swine viruses [A/Swine/WI/14094/99 (H3N2)] that have been circulating among pigs in the United States since 1998, which contains gene segments from avian, swine, and human viruses. The A/Turkey/OH/313053/04 (H3N2) isolated from turkeys in this study was classified as a low pathogenic avian influenza A virus because it only caused a drop in egg production with minor other clinical signs and no mortality.

In 2001, all 109 retail live-bird markets (LBMs) in New York and New Jersey were surveyed for the presence of avian influenza virus (AIV) by a real time reverse transcriptase/polymer chain reaction assay (RRT/PCR) and results compared to virus isolation (VI) in embryonating chicken eggs. The RRT/PCR had a 91.9% sensitivity and 97.9% specificity in detecting presence of AIV at the market level. However, the sensitivity at the sample level is 65.87%. The RRT/PCR is a reliable method to identify AIV at the market level. In addition, a cross-sectional epidemiologic study of the LBMs showed that, during the past 12 months, markets that were open 7 days per week and those that also sold rabbits had the highest risk for being positive for AIV. Markets that were closed one or more days per week and those that performed daily cleaning and disinfecting had the lowest risk for being AIV positive.

Influenza A viruses (subtype H1N1), recently isolated from turkeys in different areas of the United States, were determined to be closely related to strains typically associated with pigs. This conclusion was based on comparisons of H1N1 isolates from pigs, humans, ducks, and turkeys with polyclonal and monoclonal antibodies, RNA-RNA competitive hybridization, and replication studies. One of the H1N1 isolates from turkeys caused influenza in a laboratory technician, who displayed fever, respiratory illness, virus shedding, and seroconversion. These results suggest that turkeys as well as pigs are involved in the maintenance of these viruses and their transmission to humans.