. Using the method of shifting assay of standardized indirect agglutination (SSIA), the prevalence of Newcastle disease viruses (NDV) and infectious bursal disease viruses (IBDV) in chickens reared in several districts of Thua Thien Hue province in the Spring-Summer and Fall-Winter seasons was determined. In the Spring-Summer season of 2011, about 22.3% of the chickens were infected with NDV, in which A Luoi accounted for the highest percentage of 25% of the infected chickens and Huong Thuy the lowest of 18.2%. Meanwhile, 36% of the same chickens were infected with IBDV, with the highest percentage (46.66%) also in A Luoi and the lowest (30.3%) also in Huong Thuy. The intensity of NDV infection in the Spring-Summer season in A Luoi and Phu Vang was highest (GMT = 1.45), and in Huong Thuy lowest (GMT = 1.31). In addition, in the Fall-Winter season, about 46% of the chickens were infected with NDV and 46.3% with IBDV in Huong Thuy and Phu Vang – two neighbouring districts of Hue City, in which NDV was detected in 54.4% of the chickens in Huong Thuy and 33.9% in Phu Vang. In contrast, IBDV was detected in 41.9% and 52.7% of the chickens respectively in the two districts. The infection was not inter-dependent. Methodically, although the differences in the infection rates were insignificant with the accuracy of 95%, faecal samples showed higher sensitivity in SSIA analyses for both cases of NDV and IBDV infection in comparision with mouth exudates. By SSIA method, results could be read clearly with unaided eyes for a long time after the performance, and it was also proven applicable for cases of haemagglutinating viruses if proper treatments for depletion of animal RBCs’ surface agglutinins could be applied.
