Highlights

• Submission trends: Highest total number of Q4 and annual avian diagnostic submissions to AHVLA and SAC since 2007. During Q4-2011, the total number of avian diagnostic submissions increased by 50 per cent, non-carcase diagnostic submissions up by 78 per cent and carcase submissions increased by 23 per cent compared with Q4-2010, largely due to a rise in chicken flocks submissions.
  
  
• New & Emerging diseases: Gizzard erosion (ventriculitis) with suspected viral involvement investigated in free-range layer flocks. Ongoing investigation of an “autumn cough” syndrome in pheasants. Four other conditions investigated in poultry flocks and reported during 2011.
  
  
• Unusual diagnoses: Including Listeriosis, Aspergillosis, Salmonella Pullorum and Heterakis isolonche in pheasant, duck and backyard flocks.
  
  
• Changes in disease patterns and risk factors: Unusual Newcastle disease outbreak in Europe. Some changes to industry demographics and husbandry practices in-year, including effects of high and volatile input costs and layer hen welfare legislation. Expansion of small-scale/backyard poultry flocks.

New and Emerging Disease

October – December 2011

During Q4-2011 no new and emerging diseases were identified from analysis of available avian scanning surveillance information for broilers, broiler breeders, layer breeders, turkeys, ducks, geese, game birds and backyard flocks. However, one new and emerging disease investigation occurred in commercial layers. There were no other new and emerging disease investigations during the quarter.

Ventriculitis in commercial free-range layer flocks in the UK

Ventriculitis (gizzard erosion) with suspected adenoviral involvement was investigated in separate freerange layer flocks aged 25- and 33-weeks. Transient drops in egg production and slightly increased mortality were reported. Adenoviral ventriculitis is a well-recognised condition in commercial broiler chickens, but the appearance of a similar condition in layer hens is seemingly novel. Post-mortem findings included marked carcass pallor with blood-tinged upper digestive contents and focal areas of gizzard erosion and ulceration with the occasional perforation (Figures 5-7) and peritonitis. All birds submitted were fully in lay. Histological examination revealed focal ventriculitis with glandular epithelial necrosis and intranuclear inclusion bodies, the latter feature raising the suspicion of adenoviral involvement. Other similar cases in free-range flocks have also been recently reported to AHVLA from different locations in England and Northern Ireland, with no immediately apparent link. Adenoviruses cause a range of conditions in poultry, are considered ubiquitous, are often self-limiting and are not associated with public health or international trade implications. Investigations, including attempted virus isolation, are continuing and the situation will continue to be monitored through AHVLA scanning surveillance activities and contact with private veterinary surgeons (PVS). We would therefore also be interested to hear from colleagues who have experienced similar cases.

Figures 5-7: Affected gizzards from free-range layer hens. Abnormal contents of fresh and dark, altered blood with focal erosion and ulceration of the gizzard lining at the proventriculus/gizzard junction.

January – December 2011

AHVLA avian disease scanning surveillance activities, funded by Defra, and in partnership with private veterinary surgeons, continue to detect avian disease threats in GB (Irvine and others, 2010). In turn, these highlight hazards and risk pathways that may exist for the poultry industry and poultry populations in general. Several new and emerging disease threats were identified and investigated during 2011 (Table 1). These new and emerging disease investigations are also described in previous quarterly avian disease surveillance reports, and are available with other advisory material for vets and poultry producers on the VLA website. Surveillance activities continue to monitor for the presence of any potential new or re-emergent disease threats in the GB poultry population.

Ongoing New and Emerging Disease Investigations

Seasonal respiratory disease in adult pheasants

During Q4-2010 an “autumn cough” syndrome was described affecting pheasants on a small number of estates in a localised geographical area of southern England (VLA, 2010). The disease is associated with pneumonia and airsacculitis in affected birds. The disease differs from the upper respiratory tract diseases more commonly observed in pheasants. Pneumonia and airsacculitis were identified grossly in pheasants examined in October and November 2011 from two game bird estates located in an area 55- 60 km from the original sites. This suggests that the disease may be becoming more widespread. The disease appears to represent a respiratory complex involving various infectious agents including Mycoplasma gallisepticum (MG), viruses and secondary bacterial infection of the lungs and airsacs with organisms such as Ornithobacterium rhinotracheale (ORT) and Avibacterium gallinarum. As the “autumn cough” problem is seen in released pheasants in the autumn and winter, successful treatment is difficult to achieve. Some veterinary practices have adopted vaccination with commercial poultry MG, turkey rhinotracheitis (TRT) and other respiratory disease vaccines under the cascade system. However, their efficacy is unproven and outbreaks of lower respiratory tract disease may occur despite the use of vaccines. The problem currently remains seasonal, but AHVLA surveillance activities will continue to monitor for the presence of the disease and potential control methods.

Unusual Diagnoses

October – December 2011

Listeriosis: Septicaemic listeriosis was diagnosed in two backyard flocks during Q4-2011. In one case, eight out of 11 free-range fancy fowl aged 10-weeks died following ill-thrift and diarrhoea. Concurrent Infectious Bronchitis virus (IBV) infection was also detected. In the second case, three of four bantams aged 13 weeks died due to myocarditis and hepatitis associated with Listeria monocytogenes infection. AHVLA VIDA records indicate that listeriosis is infrequently diagnosed in poultry - two cases were recorded during 2010, and one case per year from 2007-2009 (VIDA, 2010). L. monocytogenes is a wellrecognised zoonotic agent, but transmission to man is predominantly food-borne and/or associated with food processing rather than from infected animals. The organism is ubiquitous and infection can occur following ingestion, inhalation or wound contamination. However, in poultry the disease is rare and young birds are more susceptible than older birds. Outbreaks are often associated with other risk factors or infections, as seen in one of these flocks where concurrent IBV infection was detected. Encephalitic listeriosis affecting red-legged partridges (Alectoris rufa) was also investigated and reported during Q3- 2011 (AHVLA, 2011a). In this incident infection was suggested to have been acquired at the hatchery or during transit and unknown risk factors enabled disease to develop. In each case appropriate advice regarding zoonosis was provided to the flock owner. The situation will continue to be monitored through scanning surveillance activities and PVS contact.

January – December 2011

Backyard flocks

Separate cases of rodenticide poisoning and an outbreak of Salmonella Pullorum were diagnosed this year in backyard poultry flocks. Rodenticide poisoning occurred on two separate premises and highlighted the care required in the laying of poisonous baits for rodents in a backyard situation. The food safety implications of both cases were assessed and the owners advised accordingly. S. Pullorum infection was diagnosed in a small hobby breeding flock and was thought to also result in secondary rickets due to nutritional deficiency. S. Pullorum is a well-recognised agent that can be transmitted both vertically (in ovo) and horizontally, is considered to be of little public health significance and is now rare in chickens in Great Britain (VIDA, 2010). Disease is most often seen in young chicks infected from a carrier parent hen, and may also be occasionally detected in pheasants. In GB, S. Pullorum infection has been eradicated from commercial chicken flocks through a test and slaughter policy. The putative source of this outbreak was hatching eggs introduced onto the farm from another backyard flock. Therefore, backyard/hobby chicken breeding flocks may act as a reservoir of infection and present a risk to commercial flocks. Good biosecurity is essential to avoid introduction and appropriate control measures were advised. Further comments regarding backyard/hobby flocks are also provided in the ‘Changes in Disease Patterns, Industry and Risk Factors’ section below.

Ducks

An unusual intracellular infection in ducks was investigated. Clinically the group of sixteen Muscovy ducklings aged 5-weeks progressively developed lethargy and died over a period of days. At necropsy, pulmonary oedema was seen. This condition has been recognised previously based on characteristic histopathology findings (Randall and others, 1987) and may have a seasonal component in ducks. More recent work has reported that the cause may be an intracellular yeast infection (Millins and others, 2010). Further work on elucidating the causal agent and epidemiology of this disease is underway in collaboration with the University of Glasgow. During 2011, there were also several reports of unusual presentations of Aspergillosis in game birds, ducklings and adult ducks, including lameness in pheasants (due to infection of the spinal cord), acute and high mortality (up to 50 per cent) in 10-day-old ducklings (Barnett and others, 2011; Parker, 2011; Walker, 2012) and feather folliculitis in 41-day-old commercial ducks resulting in a high number of carcase rejects at processing. The source of infection was attributed to mouldy bedding (variously wood chips or baled wheat straw) and favourable environmental conditions enabling the further proliferation of fungal spores. Control methods centre on the use of bedding that is not visibly contaminated by mould. The situation will continue to be monitored.

Heterakis isolonche in pheasants

Heterakis species worms are found in the caecum of poultry and game birds. H.gallinarum is very common in pheasants and is considered of little pathogenic significance. It can also be found in chickens and turkeys in which it is of significance as the vector of Histomonas, the causative organism of Blackhead. In contrast, H.isolonche is a specific pathogen of pheasants, in which it causes severe caecal lesions. H.isolonche has largely disappeared from commercially reared pheasants in recent years (Potts, 2009), probably because of factors such as management changes and increased use of anthelmintic products. However, two suspected cases of H. isolonche were recorded by AHVLA in two separate pheasant flocks during 2011. Damage to the caecum can be caused by both the adult and larval stages of the worm. The widespread use of anthelmintics means that H. isolonche is unlikely to emerge as a significant problem in captive reared pheasants, but the situation will continue to be monitored through scanning surveillance activities.

In each of these cases, no wider threats were recognised and no specific actions required other than for producers and veterinarians to maintain vigilance for disease problems and investigate as appropriate.

Further Reading

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Find out more information on the diseases mentioned in this report by clicking here.