Infection with a pathogenic turkey coronavirus isolate negatively affects growth performance and intestinal morphology of young turkey poults in Canada.

Turkey coronavirus (TCoV) is an important viral pathogen causing diarrhoea of young turkey poults that is associated with sizeable economic losses for the turkey industry. Using a field isolate that was found to be free from turkey astrovirus and avian reovirus we were able to reproduce the clinical disease associated with TCoV. Clinical signs and weight gain of poults during experimental infections were compared with age-matched, uninfected controls. Poults infected at 2 days of age had 100% morbidity and 10% mortality, and birds infected at 28 days of age showed 75% morbidity and no mortality. Diarrhoea was consistently seen in infected poults at 2 to 3 days post infection (d.p.i.) with a duration of about 3 to 5 days. Mean body weights of birds infected at 2 or 28 days of age were significantly reduced compared with uninfected birds by 7 d.p.i. and remained significantly lower for the duration of the study. At 44 days of age, poults infected at 2 or 28 days of age weighed only 68.1% or 77.7%, respectively, compared with uninfected turkeys of the same age on the same diet, a mean difference in body weights of 683 or 477g, respectively. Infected birds had profound villus atrophy with some compensatory crypt hyperplasia at 5 to 7 d.p.i. Villus heights in the duodenum were significantly reduced at 7 d.p.i. We were able to reproduce enteric disease using only a pathogenic field isolate (MG10) of TCoV that negatively affected growth performance and intestinal morphology of young turkey poults.

Virus shedding and serum antibody responses during experimental turkey coronavirus infections in young turkey poults.

The course of turkey coronavirus (TCoV) infection in young turkey poults was examined using a field isolate (TCoV-MG10) from a diarrhoeal disease outbreak on a commercial turkey farm in Ontario, Canada. Two-day-old and 28-day-old poults were inoculated orally with TCoV-MG10 to examine the effect of age on viral shedding and serum antibody responses to the virus. The presence of coronavirus particles measuring 105.8+/-21.8 nm in the cloacal contents was confirmed using transmission electron microscopy. The pattern of cloacal TCoV shedding was examined by reverse-transcription polymerase chain reaction amplification of the nucleocapsid gene fragment. TCoV serum antibody responses were assessed with two recently developed TCoV enzyme-linked immunosorbent assays that used TCoV nucleocapsid and S1 polypeptides as coating antigens. Poults were found equally susceptible to TCoV infection at 2 days of age and at 4 weeks of age, and turkeys of either age shed virus in their faeces starting as early as 1 day post-inoculation and up to 17 days post-inoculation. Poults infected at 2 days of age were immunologically protected against subsequent challenge at 20 days post-inoculation. The protection was associated with measurable serum antibody responses to both the nucleocapsid and S1 structural proteins of TCoV that were detectable as early as 1 week post-infection.

Complete genomic sequence of turkey coronavirus.

Turkey coronavirus (TCoV), one of the least characterized of all known coronaviruses, was isolated from an outbreak of acute enteritis in young turkeys in Ontario, Canada, and the full-length genomic sequence was determined. The full-length genome was 27,632 nucleotides plus the 3' poly(A) tail. Two open reading frames, ORFs 1a and 1b, resided in the first two thirds of the genome, and nine additional downstream ORFs were identified. A gene for hemagglutinin-esterase was absent in TCoV. The region between the membrane (M) and nucleocapsid (N) protein genes contained three potential small ORFs: ORF-X, a previously uncharacterized ORF with an associated putative TRS within the M gene (apparently shared among all group III coronaviruses), and previously described ORFs 5a and 5b. The TCoV genome is organized as follows: 5' UTR--replicase (ORFs 1a, 1b)--spike (S) protein--ORF3 (ORFs 3a, 3b)--small envelop (E or 3c) protein--membrane (M) protein--ORF5 (ORFs X, 5a, 5b)--nucleocapsid (N) protein--3' UTR--poly(A). TCoV genome structure and sequence was most similar, but distinct from, avian infectious bronchitis virus (IBV). This is the first complete genome sequence for a TCoV and confirms that TCoV belongs to group III coronaviruses.