The role of type-2 turkey astrovirus in poult enteritis syndrome

An experimental study was conducted to determine the comparative pathogenicity of type-2 turkey astrovirus (TAstV-2) obtained from turkey flocks afflicted with poult enteritis syndrome (PES) and from turkey flocks displaying no apparent signs of infection. In total, ninety 7-d-old poults, which tested negative for the presence of astrovirus, rotavirus, coronavirus, and reovirus by reverse transcriptase (RT) PCR, were divided evenly into 3 groups: A, B, and C. Birds in group A were inoculated orally with turkey astrovirus-positive intestinal contents from birds affected with PES. Group B received turkey astrovirus-containing intestinal contents from apparently healthy flocks. Group C served as a negative control and was given PBS. Clinical signs of diarrhea, depression, and dullness were observed in group A. Birds in group B also showed clinical signs similar to those in group A, although the signs were milder in nature. Birds in group C did not show any clinical signs. At 16 d postinoculation, the BW of birds in group A was significantly lower than that of birds in groups B or C. In addition, the bursa size was reduced in group A, but not in groups B or C. Birds in groups A and B, but not in group C, were found to shed turkey astrovirus in their feces, as detected by RT-PCR. These results provide a preliminary indication that TAstV-2 from PES birds may be more pathogenic than TAstV-2 from apparently healthy poults. Further studies are needed to determine if pathogenic and nonpathogenic strains of TAstV-2 exist in the environment. These results also reinforce our previous observations that astrovirus is involved in PES, causing significant retardation in growth and weight gain.

Comparison of capsid gene sequences of turkey astrovirus-2 from poult-enteritis-syndrome-affected and apparently healthy turkeys

This study was conducted to determine genetic variations in the capsid gene of turkey astrovirus-2 (TAstV-2) detected in apparently healthy and poult enteritis syndrome (PES)-affected turkeys. Capsid genes of astroviruses obtained from 30 PES-affected and 45 apparently healthy turkey flocks had sequence homologies of 73.4-100% and 72.4-100% at the nucleotide levels, respectively. The analysis of deduced amino acid sequences revealed one amino acid deletion at position 552 in 28 (93.3%) of 30 PES-affected cases. However, there were two deletions (at positions 551 and 552) in 31 (68.9%) of 45 TAstV-2 from apparently healthy flocks. The TAstV-2 (6.7%) from two PES-affected cases had two amino acid insertions each between positions 552 and 553, while TAstV-2 from 14 (31.1%) of 45 healthy flocks had two insertions at the same position. Phylogenetic analysis based on nucleotide sequences revealed that the astroviruses in this study were closely related to most of the previously published TAstV-2 isolates. The sequence homology of TAstV-2 in this study ranged from 70.4% to 99.4% at the nucleotide level with those of previously published TAstV-2 isolates. The variations at the amino acid level in the capsid gene suggest the possibility of the existence of different serotypes of turkey astrovirus. The close relationship of turkey astroviruses from apparently healthy flocks to those from PES-affected cases in capsid gene phylogeny necessitates further studies to compare complete capsid gene sequences from both types of flocks from different geographic areas for better understanding of TAstV circulating in turkeys.

Detection and molecular characterization of enteric viruses from poult enteritis syndrome in turkeys

This study was conducted to detect and characterize enteric viruses [rotavirus, turkey astrovirus-2 (TAstV-2), reovirus, and turkey coronavirus] from cases of poult enteritis syndrome (PES) in Minnesota turkeys. Of the intestinal contents collected from 43 PES cases, 25 were positive for rotavirus and 13 for small round viruses by electron microscopy (EM). Of the enteric virus-positive cases by EM (n=27), 16 cases had rotavirus or small round viruses alone and the remaining 11 cases had both viruses. None of the cases were positive for reovirus or coronavirus by EM. However, with reverse transcription-PCR (RT-PCR), 40 cases (93%) were positive for rotavirus, 36 (84%) for TAstV-2, and 17 (40%) for reovirus. None of the cases were positive for turkey coronavirus by RT-PCR. The viruses from all cases were detected either alone or in combination of 2 or 3 by RT-PCR. Thus, 8 (19%) cases were positive for a single virus, whereas a combination of viruses was detected in the remaining 35 (81%) cases. The rota-TAstV-2 combination was the most predominant (n=18 cases). Fifteen cases were positive for all 3 viruses. The rotaviruses had sequence homology of 89.8 to 100% with previously published sequences of turkey rotaviruses at the nucleotide level. The TAstV-2 had sequence homology of 84.6 to 98.7% with previously published TAstV-2, whereas reoviruses had sequence homology of 91.6 to 99.3% with previously published sequences of turkey reoviruses. Phylogenetic analysis revealed that rota- and reoviruses clustered in a single group, whereas TAstV-2 clustered in 2 different groups. In conclusion, a larger number of PES cases was positive for rotavirus, TAstV-2, and reovirus by RT-PCR than with EM. The presence of more than one virus and changes at the genetic level in a virus may affect the severity of PES in turkey flocks.

Experimental reproduction of poult enteritis syndrome: clinical findings, growth response, and microbiology

Poult enteritis syndrome (PES) is an infectious disease of turkey poults characterized by diarrhea, dullness, and depression. Five experiments were conducted to reproduce the disease in turkey poults using intestinal contents of PES-affected birds. In all experiments, poults at 14 d of age were divided into 4 groups and were orally given 2 mL of unfiltered supernatant, filtered supernatant, sediment dissolved in PBS, or PBS alone. Inocula in experiments 1, 3, and 5 consisted of intestinal contents from PES-affected birds of less than 2 wk of age, whereas those in experiments 2 and 4 consisted of intestinal contents from PES-affected birds of 4 to 6 wk of age. Poults in all groups were observed daily for clinical signs. The BW and microbiological criteria in experiments 1, 3, and 5 were evaluated at 5, 10, and 15 d postinoculation, whereas in experiments 2 and 4, these observations were made at 10 and 20 d postinoculation. Rotavirus, astrovirus, and Salmonella were present in all 5 inocula. Diarrhea and depression were the major signs in poults given PES material. Significant retardation of growth was observed in poults given any of the 3 PES materials, but this effect was more pronounced in poults given the sediment inoculum. Rotavirus, astrovirus, and Salmonella were detected in poults given PES material. In some cases, enterovirus was also detected. No major difference was noticed in experimental reproduction of PES when intestinal contents from different age birds were used as the inoculum.

Detection of antibodies to U.S. isolates of avian pneumovirus by a recombinant nucleocapsid protein-based sandwich enzyme-linked immunosorbent assay

The nucleocapsid (N) protein of subgroup C (United States-specific) avian pneumovirus (APV/US) was expressed in Escherichia coli, and antibodies to the recombinant N protein were shown to specifically recognize the approximately 47-kDa N protein of APV/US by Western immunoblot analysis. The recombinant APV/US N protein was used in a sandwich-capture enzyme-linked immunosorbent assay (ELISA), and the resulting assay was found to be more sensitive and specific than the routine indirect ELISA for the detection of APV/US antibodies in turkey sera.

Protective efficacy of high-passage avian pneumovirus (APV/MN/turkey/1-a/97) in turkeys

A U.S. isolate of avian pneumovirus (APV), APV/MN/turkey/1-a/97, was attenuated by serial cell culture passages in chicken embryo fibroblasts (seven passages) and Vero cells (34 passages). This virus was designated as APV passage 41 (P41) and was evaluated for use as a live vaccine in commercial turkey flocks. The vaccine was inoculated by nasal and ocular routes in 2-to-4-wk-old turkeys in 10 turkey flocks, each with 20,000-50,000 birds. Only 2 birds per 1000 birds were inoculated in each flock with the expectation that bird-to-bird passage would help spread the infection from P41-exposed birds to their respective flock mates. The virus did spread from vaccinated birds to the entire flock within 10 days as detected by reverse transcription-polymerase chain reaction. Mild respiratory illness was observed in a few birds 12 days postvaccination in 2 of 10 flocks. Within 3 wk postvaccination, all flocks became seropositive for APV antibodies as measured by enzyme-linked immunosorbent assay. In an additional flock, the virus was administered to all turkeys simultaneously in drinking water and seroconversion occurred within 2 wk. All 11 flocks remained seropositive until 10 wk postvaccination. When compared with unvaccinated flocks on the same farm from the previous year, the medication cost, total condemnation, and mortality rates attributed to APV were lower in P41-vaccinated flocks. When birds from vaccinated flocks were challenged with virulent APV under experimental conditions, no clinical signs were observed at 2, 6, and 10 wk postvaccination, whereas in the control unvaccinated birds, respiratory illness and virus shedding occurred after challenge. These results indicate that P41 administered by the nasal and ocular routes, and by drinking water, causes seroconversion and induces protection from virulent APV challenge for at least 10 wk.

RNA profile and structural protein analysis of rotaviruses isolated from diarrhoeal calves in India

Two isolates of group A rotaviruses (CR129 and CR156) were isolated from faecal samples of diarrhoeal calves reared in two dairy farms at Hisar (Haryana, India) by using MA-104 cell lines. These isolates were compared with three standard reference bovine rotaviruses, UK, NCDV and B223, to reveal differences, if any, in their genome and protein migration profiles. The migration of RNA segment 4 of CR129 was slower than that of NCDV, but faster than that of UK. Segment 10 of CR156 moved faster than that of the reference viruses. The segments 2 and 3 co-migrated in CR129, but resolved separately in CR156. Five protein bands of size 116-120 KD (VP1), 95 KD (VP2), 90 KD (VP3/VP4), 44 KD (VP6) and 34 KD (VP7) were detected by protein analysis. No significant difference was observed in the protein profile of these two bovine rotavirus isolates by immunoblotting. However, VP1 was of approximately 116 KD size in the two isolates, compared to 120 KD in the reference strains. These findings indicate that these rotaviruses isolated from diarrhoeic Indian calves differed from the 3 reference strains.