Abstract
The effect of host age on the outcome of duck tembusu virus (DTMUV) infection was studied in ducks. Three groups of Cherry Valley ducks at 1, 3, and 7 weeks of age were intramuscularly infected with DTMUV to systematically observe the clinical symptoms, pathological changes, tissue viral loads, and immune responses. Severe clinical symptoms and neurological dysfunction were observed in 1-week-old ducks as early as 2 days post infection (dpi) and some died at 5–7 dpi. Three weeks-old ducks showed similar but milder symptoms and no deaths. However, 7-weeks-old ducks showed only transient loss of appetite. Gross lesions gradually reduced in severity as ducks matured. One-week-old ducks showed endocardial hemorrhage, splenomegaly, swelling in the lymph follicles of the ileum, liver, and kidney swelling with degeneration, and meningeal hyperemia. Three-weeks-old ducks showed only mild pathological lesions. No visible lesions were observed in 7-weeks-old ducks. However, pathological histology analysis demonstrated all infected ducks displayed viral encephalitis. DTMUV could be detected in the brains of 1-week-old ducks as early as 1 dpi and virus titers of most organs in 1-week-old ducks were significantly higher than that of 3- and 7-weeks-old ducks at 3–5 dpi. The patterns of IFN-γ, IL-2, and serum neutralizing antibodies were similar, and there were significant difference between the youngest ducks and the older ducks at early infection stage (P < 0.05). More important is that although the antibody titers of all infected ducks were similar from 9 to 17 dpi, reduced clearance of virus was observed in the youngest groups comparing with the other two groups, indicating that immune system maturity was more important than the presence of neutralizing antibody. In summary, this study demonstrates that viral pathogenesis is strongest in 1-week-old ducks and the age-related immune response plays an important role in the pathogenesis of DTMUV in ducks.
Highlights
Duck tembusu virus (DTMUV) can result in an acute, contagious infection characterized by decline in egg production of laying ducks (Su et al, 2011)
Age-related outcomes of infection in ducks have been observed with West Nile virus, Japanese encephalitis virus, Hepatitis A/B virus and highly pathogenic avian influenza virus (Jilbert et al, 1998; Pantin-Jackwood et al, 2007; Shirafuji et al, 2009; Cleton et al, 2014; Song et al, 2014)
This study revealed that 1-week-old ducks infected with duck tembusu virus (DTMUV) demonstrated overt clinical signs of disease and high mortality (18%)
Summary
Duck tembusu virus (DTMUV) can result in an acute, contagious infection characterized by decline in egg production of laying ducks (Su et al, 2011). Pathogenesis of DTMUV in ducks (Kuno et al, 1998; Tang et al, 2012). Almost all species of ducks are vulnerable to infection with DTMUV, especially Shelducks, which are most susceptible to this virus (Yan et al, 2011; Li et al, 2012; Tang et al, 2015). Infected commercial ducks demonstrated loss of appetite, retarded growth, and neurological symptoms, while laying ducks displayed a severe drop in egg production. Autopsies showed ovarian hemorrhage and necrosis, endocardium and epicardium hemorrhage, liver degeneration, and swelling, and spleen necrosis (Cao et al, 2011; Su et al, 2011; Yan et al, 2011)
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