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Turkey Viruses Dominate Enteric Health Session at AVMA Meeting

24 September 2013

The session on Enteric Health of poultry at the American Veterinary Medical Association (AVMA) Convention in Chicago in July 2013 focused largely on viruses in turkeys - particularly coronaviruses - as well as an astrovirus in chickens.

Age-related Prevalence of Enteric Viruses in Healthy Commercial Turkey Flocks

Different enteric viruses have been involved in gastrointestinal disease mostly in young turkeys with lesser implication in older birds, reported Olusegun Awe of Ohio State University. Longitudinal prevalence study of enteric viruses in turkeys is limited and data after 12 weeks of age has not been reported.

Prevalence of enteric viruses in three turkey commercial operations in Ohio was monitored. Faecal samples were collected from two turkey flocks per operation starting from placement to slaughter (21 weeks of age) with four-week intervals. Samples were screened for avian astrovirus, avian rotaviruses (AvRVs) groups A and D, reovirus, and turkey coronavirus (TCoV) by RT-PCR and adenovirus and parvovirus by PCR.

Results showed that parvovirus, astrovirus and rotavirus were most prevalent enteric viruses (57.5 per cent, 54.1 per cent and 40 per cent, respectively). Parvovirus were not detected at first week of age, however, they were consistently detected after four weeks of age. In contrast, astrovirus were detected in poults early as one week old until slaughter with gradual decrease in prevalence.

Similarly, rotaviruses were detected with high prevalence from one to five weeks of age. Interestingly, AvRV group A prevailed at first weeks of age, however, by five weeks of age, AvRV group D were the predominant genotype. Moreover, decreasing trend of rotavirus detection was noticed between nine and 21 weeks of age.

Avian reoviruses and adenoviruses were sporadically detected and all flocks were negative for TCoV at all ages.

In summary, turkey astroviruses, rotaviruses, and parvoviruses are prevalent in normal turkeys of wide age range. Also, parvoviruses are widespread as astroviruses and rotaviruses, the most frequently identified viruses in turkey flocks. Prevalence of AvRV genotype A and D varied by age of birds and their age dependent presence should be further investigated.

The Ohio State University study provides prevalence of enteric viruses in healthy flocks and prevalence and strain difference should be further studied in diseased turkey flocks.

Turkey Coronavirus Outbreak Epidemiology and Diagnostics

An extensive outbreak of Turkey Coronavirus (TCV) occurred in Arkansas and Missouri in 2012. Epidemiology of the outbreak was reported by Kabel Robbins of Butterball, LLC in Arkansas.

Coinciding with this outbreak, the Indirect Fluorescent Antibody (IFA) test - long considered the standard for TCV diagnosis - ceased to be available. An update on diagnostics for TCV focused on the current serological and molecular testing options.

A Coronavirus Outbreak in Turkeys in Northwest Arkansas

Brian Wooming of Cargill Turkey Production Llc reported on a severe outbreak of coronavirus that was detected in turkey flocks in Northwest Arkansas in October 2012.

His case report described the geographic progression and clinical presentation of this outbreak as it spread through two complexes. He also outlined the technical challenges involved with the diagnosis of the disease, as well as the response to the outbreak.

Turkey Coronavirus Outbreak in North Carolina

Turkey coronavirus causes enteric disease and production losses in infected flocks, according to Becky Tilley. With her colleagues at Butterball LLC in North Carolina, she explained that no effective vaccines are licensed for this economically important disease. Control relies on testing and quarantine of infected flocks.

An outbreak of turkey coronavirus in North Carolina involved three production companies located in the same geographic area, she reported. The presentation examined the diagnostic challenges, epidemiology of the outbreak, cooperation among the companies involved and assistance by the North Carolina State Veterinarian’s Office in management of the outbreak.

Molecular Characterisation of Turkey Enteric Coronaviruses Circulating in the United States in 2012

The use of molecular diagnostic assays has allowed ongoing periodic monitoring of United States turkey flocks for suspected viral enteric pathogens such as reovirus, rotavirus, parvovirus and astrovirus.

Michael Day of the USDA/ARS Southeast Poultry Research Laboratory in Athens, Georgia, said that beginning in early 2012, monitoring of commercial turkey flocks in the Southeastern United States via a real-time reverse-transcriptase polymerase chain reaction assay (RT-PCR) revealed a sharp increase in the number of turkey enteric coronavirus (TCoV) positive flocks.

Over the course of 2012, numerous observations of suspected turkey coronavirus enteritis were reported from multiple integrators; many of these flocks experiencing enteric disease were positive for TCoV via the RT-PCR assay.

The presentation focused on the subsequent sequence analysis of the TCoV spike glycoprotein gene and the direct phylogenetic comparisons of TCoV isolates from North Carolina and Arkansas, and correlated the molecular data with observations from the field and serological data.

Avian Coronavirus Associated with Fulminating Disease of Guinea Fowl

Fulminating disease - also referred to as 'X disease'- of guinea fowl is an acute enteritis characterised by intense prostration and a very high mortality, explained Jean-Luc Guerin of the French national Veterinary school in Toulouse. This disease has been reported for decades in French guinea fowl industry and although its viral origin was previously suspected, the virus remained unknown.

At the AVMA, he reported work to reproduce experimentally the disease and identify its agent using unbiaised high throughput sequencing.

Guinea poults were housed in isolators and inoculated by oral route with clarified and filtered intestinal content of diseased birds.

Inoculated birds showed an intense prostration two days post-infection and died or had to be sacrificed within six days.

At necropsy, the most significant lesion was severe enteritis and in some birds, enlarged and whitish pancreas.

An unbiased metagenomic approach performed on the intestinal contents resulted in a total of more than 400,000 sequences. 0.33 per cent of reads matched with known viral sequences, 64 per cent of these viral reads being similar to avian coronaviruses.

These results were confirmed by coronavirus-specific RT-PCR on samples from both experimentally infected birds and spontaneous field cases.

Phylogenetic analysis showed that this fulminating enteritis virus is indeed a coronavirus that clusters with gamma-coronaviruses such as Turkey coronavirus (TCoV) and Infectious Bronchitis Virus (IBV).

The French group showed that an avian coronavirus is the agent of so-called 'fulminating disease' of guinea fowl. Coronaviruses cause enteritis in different avian species, turkeys or quails. Both pathological and epidemiological patterns of this peracute infection are still to be clarified.

Isolation of Chicken Astrovirus in Specific Pathogen-Free Chicken Embryos

Chicken astroviruses (CAstV) have been related with enteric disorders in many animal species, including chickens.

At the Convention, Luis Nunez Naranjo of the University of São Paulo and Orlando Marques de Paiva described the isolation, propagation and pathological characteristics of chicken astrovirus (CAstV) in specific pathogen-free (SPF) chicken embryos from chickens with diarrhoea. The chicken embryonated eggs were inoculated by yolk sac route.

The viral confirmation was carried out using PCR technique and Transmission Electronic Microscopy (TEM) throughout negative staining with ammonium molybdate. The samples faeces were screened for CAstV and differential diagnosis with avian nephritis virus (ANV), rotavirus, reovírus, chicken parvovirus (ChPV), infectious bronchitis virus (IBV) and fowl adenovirus group I (FAdV-1) in order to avoid cross-contamination.

Chicken embryos presented haemorrhages, oedema, gelatinous aspect, deformities and dwarfism. The supporting membranes were not showed any alteration.

The Brazilian group summed up, saying that they described the successful isolation of CAstV and its pathological characteristics in SPF embryonated eggs.

Further Reading

Go to our previous article on the 2013 AVMA Convention by clicking here.
Find out more about the diseases mentioned by clicking here.

September 2013

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