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UK Poultry Disease Quarterly Surveillance Report: April - June 2009

by 5m Editor
27 September 2009, at 12:00am

Highlights of the latest quarterly report from the Veterinary Laboratories Agency (VLA) include duck virus enteritis, <em>Salmonella pullorum</em> responsible for high mortality in chicks in a small backyard flock and a further outbreak of QX strain of infectious bronchitis in chickens.

Quarterly Surveillance Report Poultry: Volume 13. No. 2
April - June 2009
Published September 2009

Contents

OVERVIEW
- FACTORS INFLUENCING DISEASE AND SUBMISSION RATES
- NOTIFIABLE DISEASES
- FARM VISIT INVESTIGATIONS
- FOOD SAFETY INCIDENTS
- ZOONOSES

CROSS-SECTOR AVIAN DISEASES
ENDEMIC DISEASE SURVEILLANCE

Highlights

  • Duck virus enteritis causing deaths in ducks - It is likely that the disease seen in domestic ducks was the result of contact with wild waterfowl.

  • Salmonella pullorum responsible for high mortality in chicks in a small backyard flock - This case illustrates that backyard flocks are a potential reservoir for this organism.

  • Further outbreak of QX strain infectious bronchitis in chickens - This strain of IB virus is believed to have been imported into GB having originated in China. This outbreak provides further evidence that the backyard poultry population can act as a reservoir of infection.

  • Coccidiosis in game birds in Great Britain - A report of SAC and VLA findings from 2002 to 2008.

Notifiable Disease - Great Britain

Domestic poultry

No outbreaks of avian notifiable disease (AND) were confirmed during the quarter in Great Britain. Clinical material was however submitted to the National Reference Laboratory (NRL) for Avian Influenza (AI) and Newcastle Disease (ND), VLA Weybridge from three cases of suspected AND in domestic poultry. Two of these investigations were in game bird flocks (located in Cumbria and Oxfordshire), and one in a backyard layer flock (in Essex). A total of 105 samples were received, comprising sera (18), oropharyngeal swabs (18), cloacal swabs (18) and carcasses (51); all were tested with negative results. In addition, one commercial poultry premises was subject to follow-up investigations and sampling during the course of the annual 'National Survey for Avian Influenza Viruses of subtypes H5 and H7 in Domestic Poultry', details are described more fully below.

National survey for AI viruses of subtypes H5 and H7 in domestic poultry

The European Commission requires all Member States of the European Union (EU) to undertake surveys each year for avian influenza (H5 and H7) in domestic poultry [click here]. This routine annual survey has been running since 2003, typically during the autumn/winter months, and has been a success thanks to cooperation between individual poultry keepers, the poultry industry, Animal Health, VLA and Defra. This year, for the first time, the survey has included the requirement to sample game bird flocks (game ducks, pheasants and partridges). As a result, the start date of the survey was brought forward to early May 2009, and initial efforts have focussed on the successful recruitment and sampling of game bird and duck flocks. Other types of poultry flock will also be included in the survey from early August onwards. During the survey period to 30 June 2009, twenty-nine submissions were received from game bird and duck flocks at the NRL, VLA Weybridge, comprising 1,797 serum samples, with 3,674 haemagglutination inhibition (HI) tests screening for H5 and H7 antibodies performed. One commercial duck flock (located in Wiltshire) was identified to have HI test results that were not negative to H7. As part of follow-up investigations of this flock, 141 samples, comprising oropharyngeal swabs (47), cloacal swabs (47) and sera (47) were tested. No evidence of circulating H7 virus infection was detected.

The survey continues to provide valuable information across the EU for an early warning system of H5 and H7 subtypes in poultry. In Great Britain, a random list of poultry premises is selected, including chicken, turkey, duck, goose and game bird flocks. Blood samples are taken from a number of birds on each premises, which are then screened for the presence of antibodies to avian influenza viruses of subtypes H5 and H7 by HI test. If any H5 or H7 HI test results are not negative according to the methods prescribed in the EU Diagnostic Manual for AI (CEC, 2006), the premises is subject to a follow up investigation and sampling.

Pigeon Paramyxovirus type 1 (PPMV-1) investigations

In total, thirteen cases of suspected PPMV-1 infection in lofts of pigeons were investigated during the quarter in Great Britain (GB), resulting in the receipt of 78 samples. Nine of the cases were located in England (Cheshire, County Durham [2], Essex, Hampshire [2], Hertfordshire, Lancashire and Lincolnshire). Two of these nine cases resulted in the submission of serum samples only (five each), with positive HI test titres (range 24 – 28). Serology was completed on all blood samples according to the standard protocol (CEC, 1992). Investigation of the other seven suspected cases in England resulted in the submission of pigeon carcasses (5), tissues collected at post-mortem examination (8), oropharyngeal swabs (6), cloacal swabs (22) and sera (7). PPMV-1 was detected from five of the seven cases (located in Cheshire, County Durham [2], Essex and Hampshire) by virus isolation. Of the remaining four cases investigated in GB, three were located in Scotland (Aberdeenshire, Angus and Lanarkshire), resulting in the submission of tissues collected at post-mortem examination (5), oropharyngeal swabs (5), cloacal swabs (5) and sera (3). PPMV-1 was detected from two of these cases (Aberdeenshire and Angus). The final case investigated was located in Pembrokeshire, Wales, with no evidence of PPMV-1 infection detected by attempted virus isolation of two swab samples submitted.

PPMV-1, a virulent variant Newcastle disease (ND) virus, is the causative virus of the continuing panzootic that began in racing and feral pigeons almost 30 years ago. Although a pigeon variant virus, PPMV-1 still meets the internationally recognised virulence criteria, and under EU legislation when it is found in any poultry species the infection must be regarded as ND.

Great Britain AI Wild Bird Surveillance (AIWBS)

H5N1 highly pathogenic avian influenza (HPAI) was not detected from any of the 125 wild birds tested during the last quarter in Great Britain, with no other avian influenza (AI) virus infections detected (Table 3) from any of the birds sampled.

Table 3. Number of wild birds tested and results in GB – 2nd quarter
Surveillance activity Number of birds examined* Positive AI virus result and species of bird Comments
Legally trapped (ringing) 12 (Nil) Nil Seasonal targeted surveillance (Spring & Autumn).
Found dead* 113 (335) Nil Scanning surveillance, all year round
* Number of birds examined: figures for April to June 2008 are shown in brackets.

Zoonoses

Salmonella

In the tables and figures below, an incident is defined as ‘the first isolation and all subsequent isolations of the same serovar or serovar and phage/definitive type combination of a particular Salmonella from an animal, group of animals or their environment on a single premises, within a defined time period (usually 30 days).

No clinical cases of disease due to S. Enteritidis have been recorded on VIDA in chickens during the quarter, or since 2004 when the last case was recorded.

Sampling of chicken layer flocks according to the requirements of the Salmonella National Control Programme (NCP) for layers is ongoing. More details on the Salmonella NCP in layers can be found on the Defra web site.

Sampling of chicken broiler flocks according to the requirements of the Salmonella National Control Programme (NCP) for broilers has commenced in 2009. More details on the programme can be found on the Defra web site.

The annual number of incidents of S. Enteritidis and S. Typhimurium in turkeys is shown in Table 6 below, and of S. Binza and S. Orion in pheasants in Table 7. In both of these tables the figures for 2009 (2nd quarter) are provisional.

Table 6. The annual incidents of S. Enteritidis and S. Typhimurium in turkeys
2005 2006 2007 2008 2009
Enteritidis (total) 0 0 0 0 0
Typhimurium (total) 23 38 12 1 0

Note: The incidents of S. Enteriditis and S. Typhimurium exclude isolates arising from the 2006/07 EU survey of turkey flocks (see Avian Quarterly Report 10:(3), July-September 2006, Appendix 1).

Table 7. The annual incidents of S. Binza and S. Orion in pheasants
2005 2006 2007 2008 2009
Binza (total) 10 21 7 6 0
Orion (total) 3 3 2 2 2

Cross-Sector Avian Diseases

Blackhead (histomonosis)

Three incidents of histomonosis were recorded on VIDA in chickens during the quarter. There have been sporadic incidents of this disease in chickens during the quarter in recent years, as shown in Figure 11 below.

Figure 11. VIDA incidents of histomonosis in chickens (as a percentage of diagnosable submissions) April-June, 1999-2009
(Vertical bars represent 95 per cent confidence limits)

Classical blackhead hepatic 'target' lesions and severe immune-suppression were diagnosed in a batch of 60-day-old free-range organic broilers from a multi-aged farm with a history of poor growth and unevenness. Post-mortem examination was unremarkable in most of the carcasses but one, which showed multiple random classic target lesions on the liver surface and throughout the cut surface. Caecal lesions were not present. Histological examination confirmed liver lesions consistent with histomonosis in this carcass and a severe immune-suppression in most of the remaining carcasses characterised by diffuse bursal atrophy with heavy cryptosporidium infection in one. A revision of vaccination protocol was recommended.

Fowl cholera (Pasteurella multocida)

One incident was recorded during the quarter, in chickens, where very high mortality was reported in a flock of 8,000 barn hens aged 64 weeks. The diagnosis was confirmed by the isolation of Pasteurella multocida from heart blood.

Marek’s Disease

Sixteen incidents of Marek’s disease were recorded in chickens during the quarter, an increase on the same quarter last year (Figure 12). Many of these were in small hobby or backyard flocks.

Figure 12. VIDA incidents of Marek’s disease in chickens (as a percentage of diagnosable submissions) April–June 1999-2009
(Vertical bars represent 95 per cent of confidence limits)

Endemic Disease Surveillance

Commercial layers and layer breeders

Septic arthritis

Septic arthritis associated with enterococcal infection causing lameness and stunting in birds of between two and four weeks of age was diagnosed in a number of unrelated flocks this quarter. The likely source of the infection was not discovered.

Cannibalism and pecking damage

Cannibalism and pecking damage was the commonest diagnosis in this category of bird this quarter, followed by the peritonitis/salpingitis complex. In some cases, both conditions occur in birds in the same submission, and it is likely that in some individuals pecking damage leads to peritonitis and septicaemia.

Erysipelas

Erysipelas, mentioned in the previous Quarterly Report, was seen in a further two flocks aged 50 and 54 to 55 weeks. Mortality can be significantly elevated for several weeks in affected flocks. Limited treatment options for commercial egg layers makes vaccination of subsequent flocks destined for affected premises highly desirable.

Broilers and broiler breeders

Broilers

Vitamin B2 (riboflavin) deficiency


Submissions this quarter showed few trends, with a large number of post-mortem cases being virtual 'one-offs'. However in both post-mortem submissions and referred histopathology, there were several cases of birds around 25 days of age going off their legs and 'walking on their hocks'. In some, but not all of these, there was a peripheral neuropathy of the sciatic nerves consistent with vitamin B2 (riboflavin) deficiency. Response to riboflavin supplementation was reported to be variable.

Encephalomalacia

Vitamin E deficiency (encephalomalacia), currently a rare condition in domestic poultry, was diagnosed in a flock of 1300, 25-day-old free-range organic broilers. A history of nervous signs developing two days prior death and clinical signs including ataxia, lateral recumbency and tremors were reported. At postmortem examination varying degrees of congestion and petechiation of the cerebellum were noted. Histological examination of brains revealed large areas of necrosis in the cerebellar folia with local haemorrhages and prominent hyaline fibrin microthrombi in blood vessels. No other part of the brain was affected.

Other diagnoses

Other unusual and uncommon diagnoses included histomonosis (blackhead) in free-range broilers, and aspergillosis affecting the trachea and syrinx and causing stunting and abnormal vocalisation in 29-day-old standard commercial broilers, and found to be caused by Aspergillus versicolor.

Broiler breeders

Rupture of the Achilles tendon complex


The commonest problem seen in broiler breeders this quarter was rupture or partial rupture of the Achilles tendon complex (most often the gastrocnemius tendon) in birds in the early part of lay (from around 25 to 32 weeks of age). This condition presents as severe lameness necessitating culling. In some cases, the rupture is acute while in others, it has clearly occurred a week or two previously and has healed with extensive scarring and formation of a fibrous 'lump' in the affected tendon. In most cases, there is no evidence of infection in the affected tendons and it is assumed that the rupture has occurred because of overloading of poorly conditioned tendons, perhaps when additional strain is placed on the legs during mating, jumping from slats or nest boxes, or when attempting to escape the unwanted attention of other birds.

In two submissions for post-mortem examination, cases of both 'mechanical' tendon rupture and septic arthritis/tenosynovitis due to staphylococcal infection were found, but in different birds. The two conditions rarely occur in the same individual.

Cannibalism

Cases of cannibalism were also seen in broiler breeders (see Layers, above).

This can be a persistent problem once it occurs, sometimes with only a few birds causing most of the trouble. Identifying and culling the culprits can be well nigh impossible. Dimming the lights or using red light bulbs sometimes helps in both broiler breeders and layers.

Turkeys

'Starve out'

Two cases of 'starve out' were described this quarter. The first resulted in mortality in a flock of 450 seven-day-old turkey poults. The second case was in a group of six-day-old turkey poults. Presenting signs were empty crops and gizzards and enlarged gall bladders and a higher than expected mortality rate was observed.

Histomonosis

Severe typhlitis due to histomonosis in a three-year-old turkey was diagnosed in a hobby flock that had a series of sporadic deaths in one pen of turkeys.

Ducks and geese

Water deprivation

Water deprivation was the cause of six per cent mortality in two-day-old ducklings. Dehydration with proventricular haemorrhage was seen at necropsy. The drinkers had been elevated onto a grid to reduce contamination of the water by litter but had resulted in inability of some birds to access the water adequately.

Tetrameres spp. infestation

Tetrameres sp. infestation was identified as the cause of several small red nodules noted in the proventriculus of an adult laying duck that had died of septicaemia due to Staphylococcus aureus infection.

Amyloidosis

Hepatic and splenic amyloidosis was associated with ascites, abdominal distension and dyspnoea in an adult duck. The bird had a history of purulent arthritis.

Ducks are particularly prone to amyloidosis, which can occur as a result of chronic infections. Ascites is also recognised as a further potential sequel.

Duck virus enteritis

Duck virus enteritis (DVE) was seen on a number of occasions this quarter. Cloacal and oesophageal necrosis with multifocal hepatic haemorrhages were described in a Muscovy duck, which was one out of three birds in a small collection. Intranuclear inclusion bodies were detected in the liver. A further case was in one out of two Muscovy ducks on a smallholding. The bird had an enlarged, friable and mottled liver with multifocal pinpoint intestinal haemorrhages at necropsy. Intranuclear inclusion bodies were seen in the liver and intestine. Deaths in Runner ducks from a mixed flock of ducks, geese and chickens were associated with hepatomegaly and extensive linear oesophageal necrosis. Histologically the lesions were suggestive of duck virus enteritis.

Duck virus enteritis is caused by a herpes virus and Muscovy ducks are particularly susceptible. The strong seasonality of DVE – most cases tend to occur in the spring (see figure 13) – is coincidental with the spring migratory season and bird arrivals in the northern hemisphere, and the onset of wild waterfowl breeding season. Contact with visiting mallards has been stated as an epidemiological feature of DVE outbreaks in domestic waterfowl in the UK. Mallard ducks appear to be less susceptible to clinical disease and potentially can act as carriers of the virus. Mallards that survived DVE in North America have been shown still to be excreting virus after a period of four years, indicating a persistent infection, carrier status and the potential for recrudescence of the latent, causative herpesvirus. Water is important in the transmission of DVE virus between waterfowl, with large quantities of virus shed via the cloaca of infected birds. Natural infections of waterfowl may occur via the cloacal or oral routes.

Figure 13. Seasonality of duck virus enteritis in ducks, 1999-2009

Backyard flocks

Cases this quarter again highlight issues regarding biosecurity in the backyard flock sector. Introduction of new birds to small flocks poses a constant risk of new infections arriving but there are also risks associated with the movement and mixing of show birds.

Infectious laryngotracheitis

In one flock of birds, which is kept for showing, infectious laryngotracheitis was diagnosed in Ancona bantams that had been recently purchased at an auction. As the causative herpes virus can persist in a carrier state in apparently healthy birds, the possibility of onward spread at poultry shows should be considered.

Pullorum disease

Pullorum disease caused by Salmonella pullorum is another disease where a proportion of infected birds can become adult carriers and spread the infection via their eggs. Salmonella pullorum, phage type 17, was identified this quarter as a cause of high mortality among seven-day-old chicks on a small hobby farm of mixed breed chickens.

Chicks hatching from an infected parent can be a potent source of infection, producing widespread contamination of the chick-rearing environment, incubator and breeding areas. The disease is difficult to control as the organism can survive outside the body for many months and adult birds can become carriers to spread the infection vertically. As pullorum disease is spread mostly by vertical transmission, it can be introduced on to a premises through the purchase of infected adult hens.

QX strain of infectious bronchitis virus

The QX strain of infectious bronchitis virus was the cause of an outbreak of respiratory disease among approximately 1,200 rare breed chickens. An estimated 40 per cent of a group of 500 young birds were affected by respiratory disease manifested as sneezing. Post-mortem examination revealed inflammation of the tracheal mucosa with patchy congestion of the lungs. This strain of infectious bronchitis virus has been isolated previously from backyard chickens (Veterinary Record. 2008. 162: 99-100).

Game birds

This quarter marks the peak of the game bird breeding season, and disease problems were reported both in adult breeding birds and in the young birds.

Marble spleen disease

Marble spleen disease has rarely been recorded in recent years but one outbreak was described. The disease was diagnosed as the cause of sudden death of two eight-month-old pheasant hens submitted for post-mortem examination. The gross findings for both birds were very similar with very congested and oedematous lungs and an enlarged spleen with a ‘marbled’ appearance. Histological findings for the spleen of both birds were consistent with lesions seen in marble spleen disease caused by type II adenovirus infection.

Coronavirus infection

Four incidents of nephritis associated with suspected coronavirus infection were recorded in pheasants on VIDA. The disease is typically associated with the unexpected deaths of adult birds in good condition, within the breeding pens, for example in a case where nine birds had died out of a flock of 175.

Control of the disease can be problematic, with measures including robust hygiene and biosecurity measures and ensuring access to plentiful supplies of clean drinking water in the pens. Sometimes vaccination against infectious bronchitis virus (IBV) coronavirus is advocated but unless a specific strain of IBV is detected, protection against pheasant coronavirus strains may be incomplete.

Rotavirus

Outbreaks of rotavirus disease can result in heavy mortality in pheasant and partridge chicks. In one outbreak, 200 out of 800 pheasant chicks at four to seven days of age were affected with presenting signs of malaise, ill thrift, recumbency and death and rotavirus was demonstrated in the caecal contents. Outbreaks in young chicks can follow cross-contamination at hatching, or infection acquired from a contaminated environment, and careful attention to hygiene is an important aspect of controlling the disease.

Spironucleosis (hexamitosis)

Spironucleosis (hexamitosis) was recorded as the cause of mortality in pheasant poults from two-and-a-half weeks of age but it is anticipated that this disease will become more evident in the next quarter when poults are moved to release pens from July.

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.


September 2009