Pathogenicity Comparison Of Duck Tembusu Virus For Different Age Ducks

In April 2010,duck tembusu virus disease outbreak in China’s southeast coastal areas and it spread rapidly in almost all of the southeast provinces and most poultry farming provinces of China, including Jiangsu, Zhejiang, Anhui, Fujian,Shandong,Beijing, Hebei,Guangdong and Guangxi, in a very short period of time. Duck tembusu virus is one of most serious diseases still endangering our duck industry and it can epidemic throughout the year.Epidemiological survey shows all kinds of ducks susceptible to the disease. Clinical manifestations of inoculated ducks have significantly different due to ages.To study the pathogenicity of the novel duck Tembusu virus(DTMUV) in different ages Cherry Valley ducks, We chose eighty 10 days ducklings, 15 weeks young ducks and 55 weeks laying ducks as experimental animals, We inoculated intramuscularly ducks with DTMUV FX2010 strain to establish the animal model of infection, studying dynamically supervise clinical symptoms, pathological changes, tissue viral loads and immune responses of ducks. The results revealed that 10 days ducks showed loss of appetite, green loose stool,dyskinesia and other symptoms after 2dpi and some ducks acute death at 5-7dpi; 15-week-old ducks showed loss of appetite, green loose stool and other symptoms after 3dpi,at 5dpi, a small amount of ducks showing neurological symptoms, no death,; 55-week-old ducks showed similar symptoms, at 2dpi, showing loss of appetite, green loose stool, at 5-7dpi,some ducks showing neurological symptoms, at 7dpi 3 duck died and a decline in egg production. Necropsy lesions: the 10 days ducks were demonstrated epicardial and endocardial striped hemorrhage, splenomegaly with surface mottling, liver and kidney swelling with degeneration, meningeal congestion, and the lymph follicles of ileumcongestion and swelling; Part of 15-week-old ducks showed endocardial striped hemorrhage,splenomegaly with surface mottling, liver and kidney swelling with degeneration, meningeal congestion, and some ducks the lymph follicles of ileumcongestion and swelling But the lesions was significantly lighter than the 10-day-old ducks. The 55-week-old ducks displayed endocardial striped hemorrhage, splenomegaly with surface mottling, liver and kidney swelling with degeneration, meningeal congestion, and some ducks the lymph follicles ofileumcongestion and swelling, but 55-week-old ducks showed severer pathological changes in ovary: ovarian hyperemia, hemorrhage, deformation, and rupture, yolk peritonitis occurred in some ducks. The gross lesions of each group infected ducks were consistent: demonstrated epicardial and endocardial striped hemorrhage, splenomegaly, liver and kidney swelling with degeneration, meningeal congestion, and the lymph follicles of ileumcongestion and swelling.10 days, 15-week-old ducks’ lesions decreases with age gradually escalate. In addition to the above neuropathy 55-week-old ducks showed severer pathological changes in ovary: ovarian hyperemia, hemorrhage, deformation. Three inoculated groups showed seroposive at 3dpi. 10 days, 15-week-old ducks reached the peaks at 15 dpi, the two groups experienced some reduction in antibody titer over the remaining time period, but the anti-DTMUV antibody levels remained high until 21 dpi when the study was terminated,antibody levels were positively correlated with the ducks’ age, the 55-week-old ducks’ antibody levels reached the peaks at 17 dpi, subsequent declined. Three inoculated groups ducks’ IFN- and IL-2 levels significantly increased after 3dpi, 10 days ducklings reached the peak at 5dpi,however, 15-week-old and 55-week-old ducks reached the peak at 7dpi,subsequent declined, returned to normal levels after 11 dpi. For the 10 days, 15-week-old, the ducks’ age and serum IFN-γ and IL-2 levels was positively correlated. The 55-week-old ducks’ IFN-γ and IL-2 level is lower than the 15-week-old.Concerning the DTMUV viral titers, at 1dpi, DTMUV could be detected in all tissues in the 10 days ducks. DTMUV viral titers where highest in the spleen, the brain is also higher,the other groups DTMUV could be detected in all tissues expect brain. At 3dpi, the 10 days ducks’ brain, heart, liver, lung and kidney DTMUV viral titers reached the peak, the other groups’ liver, lung and kidney, reached the peak.What’s more, DTMUV could be detected in brain. At 5dpi, 15-week-old, 55-week-old ducks’ DTMUV viral titers in brain and heart reached the maximum.In addition, DTMUV viral titers could be detected in the 55-weeks-old ducks’ follicle theca at 1dpi and it is higher.At 5dpi, the 55-weeks-old ducks’ follicle theca DTMUV viral titers reached the maximum.TMUV show highly pathogenicty to different ducks.But the pathogenicty is obvious different.The 10-day-old ducklings is most susceptible; the 55-week-0ld laying ducks is susceptible;the 15-week-old ducks show strong resistance.