Airborne Transmission of a Novel Tembusu Virus in Ducks

Abstract

The routes of transmission of a newly emerged Tembusu virus (TMUV, Flavivirus) in ducks in China remain unclear. Our epidemiological data show that TMUV is spread in winter, when mosquitos are inactive, which suggests that nonvector transmission routes are involved in the spread of TMUV. Furthermore, in vivo studies indicate that TMUV can be transmitted efficiently among ducks by both direct contact and aerosol transmission. This finding has important implications for the control of infection with this novel TMUV in the field. In April 2010, a novel Tembusu virus (TMUV)-associated disease, characterized by retarded growth, high fever, loss of appetite, decline in egg production, and death, emerged in ducks in China (1-5). Since then, TMUV has continuously infected ducks and caused significant economic loss in China. TMUV is a member of the Ntaya virus group in the genus Flavivirus of the family Flaviviridae (6, 7). TMUV was first isolated from mosquitoes in Kuala Lumpur, Malaysia, in 1955; since then, TMUV has been isolated from Culex species mosquitos in Malaysia and Thailand (6, 7). However, the natural reservoir, transmission route, and epidemic situation of TMUV in China remain unclear. To better understand the prevalence and potential transmission route of TMUV in China, we conducted active surveillance of TMUV in ducks at different time points in China.A total of 1,200 serum samples were collected randomly from 53 duck farms in Shandong and Hebei Provinces. Samples were collected from 27-to 380-day-old ducks from 25 farms in the fall (October to December 2011) and 53 farms in the late winter (February and March 2012), respectively. The farms investigated in winter included all of the fall sites (except one farm in Laiwu) (see Fig. S1 in the supplemental material). The presence of TMUVspecific antibody was determined by a blocking enzyme-linked immunosorbent assay (ELISA) based on monoclonal antibody (MAb) 1F5, which is a neutralizing MAb that binds specifically to the E protein of TMUV. A blocking ELISA based on this MAb was developed for the detection of neutralization-related antibodies against TMUV (8). TMUV antibody titers are expressed as percent inhibition (PI) of blocking of MAb 1F5 at a test serum dilution of 1:10. The selected cutoff PI value for positive serum was 18.4%. All serum samples were prepared and tested as described previously (8). In October and December 2011, only 11.8% of the farms investigated (2/17) were TMUV seropositive in Shandong Province, and none of the 8 farms investigated in Hebei Province were seropositive (Fig. 1A). Surprisingly, 3 to 4 months later (February and March 2012), 53.7% (22/41) and 50.0% (6/12) of the farms investigated in Shandong and Hebei Provinces became TMUV seropositive. During October and December 2011, the mean rates of seropositivity of the serum samples collected were 11.7 and 0% in Shandong and Hebei Provinces, respectively, which increased to 41.0 and 54.5% during February and March 2012. At most (78.1%) of the TMUV-positive farms, the seropositivi...

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