Evaluation of histopathological changes, viral load and immune function of domestic geese infected with Newcastle disease virus.

Outbreaks of Newcastle disease in flocks of geese with high morbidity and mortality in southern and eastern China have been reported frequently since the late 1990s, which broke the traditional view that geese are considered to be the natural reservoir of Newcastle disease virus (NDV) but show few or no clinical signs after infection. In this present study, geese were infected intranasally with a local strain of NDV. Clinical disease and gross pathology were observed. Serum and immune organs were collected from geese sequentially euthanized or after disease-associated death. We studied the histopathology of immune organs by haematoxylin and eosin staining and NDV fusion protein was detected in tissues by immunohistochemistry. At the same time, the SYBR Green I real-time polymerase chain reaction assay was used to detect the viral load from the collected samples. Serum samples were tested for NDV-specific antibodies and avian influenza virus (AIV)-specific antibodies by haemagglutination inhibition (HI) test. The results showed that severe lesions and numerous positive reactions of NDV antigen were detected in the immune organs. High viral loads developed in immune organs of infected geese, correlating with the severity of clinical signs and lesions in the tissues. Furthermore, the infected geese developed low HI antibody titres to both AIV and NDV. The present study showed that the replication and dissemination of the NDV isolate was widespread in immune organs of geese. The study revealed that waterfowl may not only be a natural reservoir of NDV but also become susceptible to disease and may play a major role in the epidemiology of Newcastle disease.