Pathogenicity of turkey astroviruses Type 2 in poults

Authors: Pantin Jackwood, Mary; Spackman, Erica; Day, James

Submitted to: Western Poultry Disease Conference
Publication Type: Proceedings
Publication Acceptance Date: 11/13/2006
Publication Date: 3/26/2007
Citation: Pantin Jackwood, M.J., Spackman, E., Day, J.M. 2007. Pathogenicity of turkey astroviruses Type 2 in poults. In: Proceedings of the 56th Western Poultry Disease Conference, March 26-29, 2007, Las Vegas, Nevada. p. 5.

Interpretive Summary: Poult enteritis complex (PEC) is an economically important disease of young turkeys characterized by diarrhea, poor weight gain and in some cases high mortality. Turkey astrovirus type 2 (TAstV-2) has been identified as one of the possible causes of PEC. The pathogenicity of five different TAstV-2s was studied in SPF turkeys. These viruses belong to three different genotypes based on sequence analysis of the capsid gene. Poults were inoculated at one day of age and examined for clinical signs and virus shedding during the 14-day experiment. All isolates caused enteritis and growth depression; however there were differences in disease severity among the isolates studied. Virus shed was monitored by quantitative real time RT-PCR on cloacal and oral swabs and intestinal contents, at 3, 7 and 14 days post-inoculation (dpi), with the highest titers at 7 dpi. Virus was also detected in blood demonstrating systemic spread. Common macroscopic lesions observed at necropsy were distended intestines, with translucent walls, filled with watery contents and undigested feed, dilated ceca with foamy contents, and pale pancreas. Microscopic lesions present in the intestines consisted of villous atrophy and lymphocytic infiltration in the intestinal submucosa. Mild lesions were also observed in other organs including bursa, pancreas, spleen, liver, and kidneys, the extent of these lesions varying depending on the virus isolate genotype. In conclusion, genotypically different TAstV-2 viruses produce similar enteric diseases in turkeys; however the severity of the disease varies depending on the virus.

Technical Abstract: The pathogenicity of five different type 2 turkey astroviruses (TAstV-2) was studied in SPF turkeys. These viruses belong to three different genotypes based on sequence analysis of the capsid gene. Poults were inoculated at one day of age and examined for clinical signs and virus shedding during the 14-day experiment. All isolates caused enteritis and growth depression; however there were differences in disease severity among the isolates studied. Virus shed was monitored by quantitative real time RT-PCR on cloacal and oral swabs and intestinal contents, at 3, 7 and 14 days post-inoculation (dpi), with the highest titers at 7 dpi. Virus was also detected in blood demonstrating systemic spread. Common macroscopic lesions observed at necropsy were distended intestines, with translucent walls, filled with watery contents and undigested feed, dilated ceca with foamy contents, and pale pancreas. Microscopic lesions present in the intestines consisted of villous atrophy and lymphocytic infiltration in the intestinal submucosa. Presence of viral antigens was demonstrated by immunohistochemistry in both villi and crypt enterocytes in the jejunum and, less frequently, the duodenum. Mild lesions were also observed in other organs including bursa, pancreas, spleen, liver, and kidneys, the extent of these lesions varying depending on the virus isolate genotype. In conclusion, genotypically different TAstV-2 viruses produce similar enteric diseases in turkeys; however the severity of the disease varies depending on the virus. The role of the capsid gene in pathogenesis needs to be established.