Effect of age and inoculation route on the infection of duck Tembusu virus in Goslings.

Duck Tembusu virus (TMUV) is an emerging flavivirus that has caused variable levels of outbreaks in poultry in recent years. In order to study the effect of age and inoculation routes on the TMUV infection, one hundred healthy domestic 5-day-old and 20-day-old goslings were equally divided into five groups and four experimental groups of goslings were infected with the TMUV-SDSG strain by intravenous and intranasal routes, respectively. Severe clinical signs were observed in goslings infected at 5 days of age, including listlessness, growth retardation, severe neurological dysfunction and even death. However, goslings infected at 20 days of age showed mild symptoms and no mortality. The severity of gross lesions gradually reduced as goslings matured. The severe histopathological changes were observed in 5-day-old infected goslings, including cerebral edema, viral encephalitis, myocardial necrosis, hepatic steatosis, spleen lymphoid cell depletion, pancreatic epithelial cell shedding and interstitial hemorrhage. However, 20-day-old infected goslings showed mild histopathological changes. Viral loads in different tissues were detected by the SYBR Green I real-time PCR assay. The level of viral loads in most of tissues 5-day-old infected goslings was higher than that of 20-day-old infected goslings, correlating with the severity of clinical symptoms and lesions in these tissues. 20-day-old infected goslings developed significantly higher serum neutralizing antibody titers than 5-day-old infected goslings. Furthermore, goslings infected with TMUV intravenously demonstrated more severe clinical signs, lesions and higher viral loads in tissues than those of goslings infected with TMUV intranasally. Therefore, age and inoculation routes can affect the pathogenicity of TMUV in geese and younger geese are more susceptible to the virus. Age and inoculation route factors should be considered in study of the pathogenicity, pathogenesis, folumation of prevention and therapy strategies of TMUV infection in geese.