Improved duplex RT-PCR assay for differential diagnosis of mixed infection of duck hepatitis A virus type 1 and type 3 in ducklings.

Infection with duck hepatitis A virus (DHAV) causes an acute, rapidly spreading, and fatal disease of young ducklings. DHAV type 1 (DHAV-1) and type 3 (DHAV-3) have been identified in China. In this study, a duplex RT-PCR assay was developed to identify DHAV-1 and DHAV-3 with mixed infection. The method was shown to be high specificity and sensitivity. The minimum detection limit of the method has been determined to be 10pg total RNA templates extracted from duck liver samples or 10² copies viral RNA of DHAV-1 and DHAV-3 respectively. Using the method, from 60 clinical liver samples of 26 duckling flocks in Shandong, Guangdong, Sichuan and Henan provinces of China, 15 (57.7%) flocks were identified as mixed infection of DHAV-1 and DHAV-3, and 9 (34.6%) flocks were DHAV-1 or DHAV-3 single infection. Among them, 38.3% (23/60) of duckling samples were detected as mixed infection of DHAV-1 and DHAV-3, and 48.3% (29/60) of samples were DHAV-1 or DHAV-3 single infection. These results indicated that the improved duplex RT-PCR method provides a rapid and cost-effective laboratory differential diagnosis for mixed infection of DHAV-1 and DHAV-3 in ducklings.