Abstract
African swine fever (ASF) is a contagiously the most dangerous and an important disease of the swine industry worldwide with causing heavy economic losses to the swine industry in many countries. The first confirmed case of ASF in Vietnam was reported officially in early-February 2019. To date, ASF virus (ASFV) have been detected on 63/63 provinces in Vietnam. In this study, the different results obtained by OIE recommended- conventional PCR and real-time PCR were further analyzed by sequencing method and virus isolation in combination with haemadsorption (HAD) test using porcine alveolar macrophages (PAM) culture. The results showed that when primer sequence matched perfectly to field isolate- sequences, a mutation in probe binding region was found, indicating that a single mismatch in probe binding site may cause a false negative result by real-time PCR to detect ASFV in clinical samples in Vietnam. These findings suggested that real-time PCR is the most sensitive and specific method to detect ASFV in tissue samples but not perfect method for the field diagnosis of ASFV in Vietnam. A combination with other OIE recommended methods, including sequencing and/or virus isolation in combination with HAD test are required for a diagnosis of ASFV from epidemics in Vietnam, particularly for primary outbreaks or first case of ASFV.

Key words: African swine fever, Pigs, PCR, Real-time PCR, Vietnam