Highlights

• Submission trends: Increase of 13 per cent in the total number of avian diagnostic submissions to AHVLA and SAC during Q4-2012 compared with Q4-2011. Decrease of four per cent in the total number of avian diagnostic submissions to AHVLA and SAC overall during 2012. Upward trend in the numbers of avian non-carcass diagnostic submissions to AHVLA discussed.
• New & Re-emerging diseases: Increased numbers of diagnoses of Blackhead (histomonosis) in turkeys and resultant supply chain impacts highlighted as a re-emerging threat. Summary of other threats seen during 2012.
• Unusual diagnoses: Pneumonia associated with intracellular yeast infection in ducks, scoliosis and Marek’s disease in turkeys, ORT in backyard chickens.
• Changes in disease patterns and risk factors: Confidence sustained in the poultry meat sectors with record day-old placings. Layer ration prices relatively stable since mid-year peak and stable egg prices. Over-supply concerns continue in the face of further rises in numbers of layer chicks placed.

New and Re-Emerging Diseases & Threats

October – December 2012

During Q4-2012 no new and re-emerging diseases were identified in GB for broilers, broiler breeders, layer breeders, layers, ducks and backyard flocks. However, a re-emerging threat was identified in the commercial turkey sector.

Blackhead in turkeys
An increase in the number of diagnoses of Blackhead (histomonosis) in turkeys was reported by poultry PVSs during the quarter. This was attributed to the wet summer conditions and associated problems in maintaining biosecurity standards. Blackhead is a well-characterised, non-notifiable disease of turkeys (and other poultry) caused by infection with the protozoan, Histomonas meleagridis. The disease is not recognised to present a threat to public health but is a disease of economic importance to the turkey industry in the UK, Europe and globally. Histomonosis can cause variable levels of mortality and morbidity in meat turkeys and turkey breeders. Callait-Cardinal and others (2007) described an average mortality of 19 per cent in 113 meat turkey flocks.

The veterinary medicines used for controlling Blackhead were withdrawn in EU Member States approximately 10 years ago. This was due to concerns regarding possible harmful effects to human health of residues of the previously authorised products when used in food producing animals. Control by vaccination has been proposed as an alternative approach to medication. European researchers have developed a Blackhead vaccine candidate, but this is not a licensed product. Therefore, prevention and control relies on good biosecurity and hygiene practices and routine flock worming. AHVLA, VMD, Defra and poultry PVSs have worked closely to identify the issues relating to this re-emerging threat, including those associated with the EU-wide absence of licensed medicines for treating Blackhead. The situation will continue to be monitored.

January – December 2012

AHVLA avian disease scanning surveillance activities, in partnership with SAC Consulting and working with private veterinary surgeons and industry continue to detect diseases and other threats in GB. This highlights hazards and risk pathways that may exist for the poultry industry and poultry populations. Seven new and re-emerging threats (NRT) were identified and investigated for the first time during 2012 (Table 1). These new and emerging threats and associated investigations have also been described in previous quarterly avian disease surveillance reports.

Maintaining good biosecurity standards, disease awareness and vigilance and prompt investigation of problems are essential to limit both the risk of introduction and spread of infection and the impact of disease outbreaks. Surveillance activities, PVS and industry contact continue to monitor for the presence of any potential new or re-emergent threats in the GB poultry population.

Table 1. New and emerging disease and threats identified and investigated in poultry by AHVLA and SAC Consulting during 2012

Ongoing New and Emerging Disease Investigations

Laboratory and field investigations continue into the reported cases of myocarditis associated with reovirus infection in fattening turkeys (two) and sinusitis in free-living red grouse (seven), conditions described in previous quarterly avian 'Emerging Threats Reports in GB'. Further information will be provided in due course. In addition, investigations into the previously described cases of so-called autumn cough syndrome in adult pheasants were concluded – see below.

Unusual Diagnoses

A number of unusual diagnoses were made in backyard and commercial poultry during Q4-2012 and the course of the year. A selection have been described in this and previous quarterly avian disease surveillance reports, as well as the monthly surveillance highlight reports published in the Veterinary Record by AHVLA and SAC (AHVLA, 2012; SAC, 2012). In 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.

Pneumonia associated with intracellular yeast infection in ducks
The loss of nine Muscovy ducklings over a period of several weeks on a pond with a collection of wild waterfowl was investigated. Clinical signs prior to death were non-specific (malaise and recumbency). Post-mortem examination of an affected ten-week-old Muscovy duckling revealed diffuse congestion of the upper respiratory tract. The thoracic air sacs were yellow and oedematous and the lungs were markedly congested and oedematous throughout. Yellow fluid also was present in the pericardial sac and the spleen was markedly congested. Histopathology identified an interstitial pneumonia with numerous intracytoplasmic organisms morphologically suggestive of yeasts of the Saccharomycetales family. This condition has been recognised previously in domestic and wild waterfowl based on characteristic histopathology and other findings, and may have a seasonal component in ducks (Randall and others, 1987; 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.

Scoliosis and Marek's disease in turkeys
Losses in a flock of 200 turkeys had been increased for several weeks, with more than 50 per cent of the culled birds exhibiting signs of lameness and leg crossing. Many of the birds were also showing general ill-thrift and wasting. Postmortem examination of four lame turkeys aged 20-weeks showed scoliosis of the spinal column (Figure 1) in three birds, the significance and cause of which were unclear. In addition, lesions typical of blackhead were present. This was considered likely to have been responsible for the poor body condition and several of the deaths, but did not explain the lameness. Further histopathological examination revealed lymphomatous infiltration suggestive of Marek’s disease in multiple tissues in all of the examined turkeys. Outbreaks of Marek’s disease in turkeys during 2012 have been described by AHVLA (Deuchande and others 2012), but the possible role of the disease in lameness remains uncertain.

Figure 1. Scoliosis of the caudal thoracic vertebral column in a five-month-old turkey

Ornithobacterium rhinotracheale in backyard chickens
Ten hens were purchased to form a backyard flock. A week after they were delivered, two showed respiratory signs. One died four weeks later and the other was presented for postmortem examination at AHVLA after treatment with antibiotic. The bird was in very thin condition, with fibrinous and caseous airsacculitis, caseous rhinitis and infraorbital sinusitis and reddened lungs with yellow exudate. Ornithobacterium rhinotracheale (ORT) was isolated from lung tissue and is likely to have accounted for the lower respiratory tract pathology. Mycoplasma iners was also detected in the lung tissue, but was unlikely to have been of primary significance. ORT is a well-recognised cause of respiratory disease and also lameness in turkeys, but is uncommon in chickens. In addition, a seasonal respiratory disease in adult pheasants has been investigated as a NRT by AHVLA; so-called autumn cough syndrome. This condition is characterised grossly by pneumonia and airsacculitis in affected pheasants and involves various infectious agents, including ORT (Anon, 2010, 2011; Welchman and others, 2013).

Changes in Disease Patterns, Industry and Risk Factors

Broilers

The number of day-old broiler chicks placed from UK hatcheries during Q4-2012 was higher than the same time last year but reversed the upward trend in placings seen since Q4-2011 (Figure 2). The total annual placings of day-old broiler chicks from UK hatcheries were 2.5 per cent higher for 2012 than 2011, at 918 million birds. This reflects continued confidence and consumer demand for chicken meat and wholesale chicken prices have largely stabilised after a slight decline in recent months.

Figure 2. Quarterly broiler chick placings (average) from UK hatcheries, 2010-2012

Layers

The number of layer chick placings remained relatively stable since the last quarter (Figure 3). However, the total placings for the year were 7.8 per cent higher than in 2011. National layer flock placings reached 34.7 million birds during 2012, the highest figure for 10 years.

Figure 3. Quarterly layer chick placings (average) from UK hatcheries, 2010-2012

Egg packing station throughput increased slightly (Figure 4). Free-range and organic eggs accounted for 47 per cent of eggs packed during Q4-2012, compared with 48 per cent in Q4-2011. The average price for eggs paid to producers was substantially higher than Q4-2011, but the price of feed has also increased substantially since last year. Rising input costs affect profitability for producers. This is considered a risk factor for both prevention and control of disease and scanning surveillance coverage as diagnostic services may be less likely to be sought. These issues were also described in the ‘Diagnostic Submission Trends’ section above and in the previous quarterly avian disease Emerging Threats Reports. Issues relating to feed and egg prices and the size of the national flock (including the impact of the EU-wide conventional layer cage ban) have also been discussed previously (Anon, 2011; 2012a,e).

Figure 4. Total and free-range UK packing station egg throughput 2010-2012

Turkeys

The numbers of turkey poults placed during 2012 was 6.0 per cent higher than in 2011, at 18 million birds. This represented an increase of 1 million poults placed compared with last year and an annual total last seen in 2005. Hence, the continued trend of gradual expansion of the turkey sector reverses a period of previous decline. Turkey poult placings in Q4-2012 were similarly higher than Q4-2011 (Figure 5). This parallels trends in the broiler sector and reflects continued confidence in poultry meat production, which has been particularly marked in turkeys compared with previous years.

Figure 5. Quarterly turkey poult placings (average) from UK hatcheries, 2010-2012

Avian diagnostic submission rates and surveillance information will continue to be monitored to assess, where possible, the impact of financial and poultry demographic changes on scanning surveillance activities and endemic, exotic, new and emerging or re-emerging avian disease threats.

Further Reading You can view the full report by clicking here. Find out more information on the diseases mentioned in this article by clicking here.

April 2013