Pathology and tissue distribution of turkey coronavirus in experimentally infected chicks and turkey poults

Abstract

Twenty 1-day-old specific pathogen free chicks and 20 1-day-old commercially derived turkey poults were inoculated with a Brazilian strain of turkey coronavirus (TCoV) to study the pathogenicity and virus distribution up to 14 days post-inoculation by histopathology, immunohistochemistry, reverse transcriptase polymerase chain reaction and sequencing. At 2-14 dpi, TCoV antigens were detected in the paranasal sinus and lachrymal accessory gland (Harderian gland) of infected chicks and in the ileum, ileocaecal junction and caecum of infected poults. Lymphocytic inflammation was present in these tissues. TCoV was re-isolated from pooled tissue suspensions of nasal concha, Harderian gland and paranasal sinus from chicks, as well as from the ileum, ileocaecal junction and caecum of poults, after three consecutive passages in 28-day-old embryonated turkey eggs. Viral RNA corresponding to the spike gene region (1178-2073 genome position) was amplified from the upper respiratory tract of chickens and from the intestinal tract of poults and phylogenetic analysis confirmed the identity as TCoV. This is the first description of TCoV antigens and mRNA in upper respiratory tissues in experimentally infected chickens.

Fig. 1

(A) Inflammation within the Harderian gland of an infected chick. HE. (B) TCoV antigens in the cytoplasm of epithelial cells and in the glandular portion of chick Harderian gland at 7 dpi (arrowheads). IHC.

Fig. 2

Mucosa of the ileocaecal junction from (A) an uninfected turkey poult and (B) an infected poult at 7 dpi. There is evidence of inflammatory infiltration of the lamina propria in (B).

Fig. 3

Phylogenetic analysis based on the amino acid sequence of the 809 bp fragment of the spike gene of TCoV used to orally infect chicks and poults in the present study. The tree was constructed by a neighbour-joining method using Kimura's two-parameter correction and bootstrap values calculated from 1,000 trees. The TCoV recovered from respiratory and intestinal tissue suspensions identified in the present study is shown (arrow).