Monthly Surveillance Report Published October 2004 Highlights Blackhead causing losses in free-range layers Fowl pox diagnosed in layer pullets Salmonella virchow causing losses in turkeys

Salmonellosis

Salmonella Virchow was isolated from eight, four-week-old turkey poults in a flock where deaths had been encountered over the previous 7 days. In all 519 deaths occurred in two sheds, 137 out of 1200 birds in one, and 382 out of 1700 in another. Just under 10,000 turkeys were kept on this farm in eight sheds. Other sheds contained birds that were much older and kept for farmgate sales, and stags for the catering trade.

Birds were being found dead with little premonitory signs. Necropsy revealed spleen enlargement, airsacculitis, peritonitis and perihepatitis. White plaques were seen adhered to the mesentery. The Health Protection Agency (HPA) was informed and an advisory visit was carried out to advise on the risk of zoonotic infection and the biosecurity precautions associated with the farm gate sale of older birds.

Blackhead

Histomoniasis (Blackhead) was diagnosed by Luddington on two separate turkey units following necropsy of affected birds. The units were rearing freerange birds for the Christmas market with one flock of 500 and the other of 2000 poults (in 4 groups of 500). Clinical signs including malaise, ill-thrift, yellow diarrhoea and deaths were reported with birds affected at 20 and 14 weeks of age in respective flocks.

Losses of birds at 38 weeks of lay in a free range flock of chickens led to the submission of several birds to Winchester for post-mortem examination. Two of the birds submitted showed the presence of white focal lesions in the liver. In one bird these were 1-3cm in diameter with irregular edges. In this bird a small area of caecal necrosis was present. In the second bird the liver showed the presence of white miliary focal lesions and the presence of necrotic cores in the caecae. Parasitological examination carried out on intestinal contents from the group of birds submitted showed the presence of Heterakis, Ascarid and Capillaria worms. Histopathological examination of tissues showed lesions consistent with histomoniasis.

Interstitial pneumonitis

Post mortem examination of a 9-week-old female duck by Luddington resulted in the diagnosis of an unusual interstitial pneumonitis. The duck was the seventh to be lost in five days from one brood. Clinically, malaise was reported. The other backyard domestic poultry on the premises were unaffected. Necropsy findings included the duck to be in average condition with splenomegaly and yellow fibrin deposits over the thoracic air sacs with caudal pulmonary consolidation seen. No significant microbiology findings were made to support the suspected differential diagnoses of septicaemia (Riemeralla, Erysipelothrix or Listeria species infections). Histopathology identified a subacute, severe interstitial pneumonitis, subacute multifocal myocarditis and mild periacinar hepatocyte degeneration.

The lesions were consistent with those described by Randall (1987) as an unusual intracellular infection in ducks. It is suspected that these cases may relate to a severe protozoal infestation but the organism has never been characterised (Randall C.J., Lees S., Pepin G.A. and Ross H.M. 1987, Avian Pathology, 16: 479 – 491.)

Erysipelas

Two turkeys from a unit raising birds for the Christmas market were submitted to RVC for examination following a number of deaths on the unit. The lesions seen were typical of infection with Erysipelas and the diagnosis was confirmed on bacteriological culture of the organism from the viscera. Although the farm had previously had a vaccination policy, the current crop of birds had not been vaccinated.

Vaccine associated lameness

Between 10 and 15% of 6000 laying pullets aged 17 weeks were showing a unilateral lameness, mainly involving the same limb on each bird. This occurred 2 weeks after a vaccine was administered into what was assumed to be the same limb when loaded for transportation. Post mortem examination showed a marked swelling of one limb, with clearly delineated lines of skin discolouration readily visible (Fig. 1). There was an underlying sub-cutaneous oedema, and superficial necrosis of muscle. No other abnormalities were identified. The VMD were informed.

Fowl pox

The loss of 7 of 14 mixed fancy breed, 15-week-old layer pullets over a 2- week period was investigated. A further 27 free-range layers which mixed by day with the pullets, but were housed separately overnight, were reportedly unaffected. Necropsies on three fresh, casualty pullets revealed all to be in very poor bodily condition (average weight 493g) with multiple, raised, crusted brown/yellow cutaneous lesions irregularly distributed over the skin of the head of each pullet. Additionally, irregularly distributed across the oropharyngeal and rostral oesophageal mucosa of each pullet were multiple, discrete, pale yellow/cream-coloured, raised necrotic lesions, 2-6 mm in diameter (see figure 3).

Mucoid “rhinitis and tracheitis” were also seen. The morphological diagnosis of fowlpox (cutaneous “dry pox” and oropharyngeal fibrinonecrotic “wet pox” forms) was endorsed by histopathological examinations which revealed severe, ulcerative dermatitis with granulomatous inflammation and intracytoplasmic inclusions suggestive of pox virus. Recommendations included culling severely affected birds, close monitoring of the remaining pullets for the presence of typical pox lesions, attention to hygiene and flock anthelmintic treatment.

Fig 3: Raised necrotic lesions in the oropharynx of birds affected by Fowl Pox