Generation and infectivity titration of an infectious stock of avian hepatitis E virus (HEV) in chickens and cross-species infection of turkeys with avian HEV

Abstract

Avian hepatitis E virus (HEV), a novel virus identified from chickens with hepatitis-splenomegaly syndrome in the United States, is genetically and antigenically related to human HEV. In order to further characterize avian HEV, an infectious viral stock with a known infectious titer must be generated, as HEV cannot be propagated in vitro. Bile and feces collected from specific-pathogen-free (SPF) chickens experimentally infected with avian HEV were used to prepare an avian HEV infectious stock as a 10% suspension of positive fecal and bile samples in phosphate-buffered saline. The infectivity titer of this infectious stock was determined by inoculating 1-week-old SPF chickens intravenously with 200 microl of each of serial 10-fold dilutions (10(-2) to 10(-6)) of the avian HEV stock (two chickens were inoculated with each dilution). All chickens inoculated with the 10(-2) to 10(-4) dilutions of the infectious stock and one of the two chickens inoculated with the 10(-5) dilution, but neither of the chickens inoculated with the 10(-6) dilution, became seropositive for anti-avian HEV antibody at 4 weeks postinoculation (wpi). Two serologically negative contact control chickens housed together with chickens inoculated with the 10(-2) dilution also seroconverted at 8 wpi. Viremia and shedding of virus in feces were variable in chickens inoculated with the 10(-2) to 10(-5) dilutions but were not detectable in those inoculated with the 10(-6) dilution. The infectivity titer of the infectious avian HEV stock was determined to be 5 x 10(5) 50% chicken infectious doses (CID(50)) per ml. Eight 1-week-old turkeys were intravenously inoculated with 10(5) CID(50) of avian HEV, and another group of nine turkeys were not inoculated and were used as controls. The inoculated turkeys seroconverted at 4 to 8 wpi. In the inoculated turkeys, viremia was detected at 2 to 6 wpi and shedding of virus in feces was detected at 4 to 7 wpi. A serologically negative contact control turkey housed together with the inoculated ones also became infected through direct contact. This is the first demonstration of cross-species infection by avian HEV.

FIG. 1.

Cross-species infection of 1-week-old turkeys with avian HEV from a chicken: anti-avian HEV antibody seroconversion in seven representative turkeys. All turkeys were seronegative at the beginning of the study. Three inoculated turkeys (turkeys 2792, 2872, and 2873) and one serologically negative contact control turkey (turkey 2786) housed together with the inoculated ones became positive for anti-avian HEV antibody at 4 to 8 weeks wpi. Three uninoculated control turkeys (turkeys 2793, 2798, and 2800) housed separately from the inoculated ones remained seronegative. Prior to the end of the study, one inoculated turkey (turkey 2872) was necropsied at 9 wpi and blood samples were collected from this turkey only for the first 8 weeks.