converting website visitors - news, features, articles and disease information for the poultry industry

Featured Articles

GB Emerging Threats Report: Avian Diseases: October-December (Q4) 2014

27 March 2015


Among the notable items in this report from the Animal and Plant Health Agency (APHA) were outbreaks of H5N8 Highly Pathogenic Avian Influenza in Europe and Great Britain, a continued increase in diagnoses of blackhead (histomonosis) in chickens, infectious coryza in a hobby flock and gizzard erosion in free-range layers.


  • Review of H5N8 Highly Pathogenic Avian Influenza outbreaks in Europe and GB: no further diagnoses of Low Pathogenicity AI in the quarter
  • New & Re-emerging diseases: Continued increase in diagnoses of blackhead (histomonosis) in chickens; other emerging diseases across different sectors

New and Re-emerging Diseases and Threats

Maintaining good biosecurity and hygiene 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 and PVS and industry contact continue to monitor for the presence of any potential new or re-emergent threats in the GB poultry and game bird population.

Ongoing New and Re-emerging Disease Investigations

H5N8 HPAI outbreaks in Europe

During the period October to November 2014 in Europe, outbreaks of H5N8 Highly Pathogenic Avian Influenza (HPAI) were officially reported in poultry flocks in Germany, the Netherlands, Italy and the UK, as well as H5N8 HPAI infection being detected from different species of wild birds in Europe (Defra, 2014a,b; OIE, 2014). Statutory sanitary disease control measures were implemented on all affected poultry holdings. In the UK, one H5N8 HPAI outbreak was officially confirmed on a duck breeder premises in East Yorkshire on 16 November 2014. Clinical signs of disease were observed over approximately two weeks prior to official confirmation of H5N8 HPAI infection. These comprised reductions in egg production and increased mortality with aspergillosis and bacterial septicaemia also diagnosed as intercurrent flock health problems.

The H5N8 HPAI outbreaks in each country represent different poultry species and production systems and the entry of H5N8 HPAI into Europe, and its subsequent spread are considered likely to be epidemiologically distinct pathways. Long-distance transmission could have resulted from crossover between wild birds congregating in North Eurasian breeding sites resulting in the introduction of infection into the affected EU Member States as there are no known direct bird migration routes from Asia to Western Europe (EFSA, 2014). Extensive epidemiological investigations in all four affected EU Member States failed to show any direct links between all the infected premises. Therefore, indirect contact with wild birds is considered the most likely route of introduction with fomite transmission of virus from environments contaminated with infective wild bird faeces into poultry holdings.

Other relevant risk pathways identified comprise indirect transmission via contact with humans or livestock or animal-derived products (EFSA, 2014; Defra, 2015). To date, there have been no reports of human cases of H5N8 HPAI.

Further information regarding the H5N8 HPAI outbreaks in Europe is also available on the European Commission web site.

Since January 2014, H5N8 HPAI viruses have been detected from multiple poultry outbreaks in the Republic of Korea as well as poultry in China and Japan. Infection has also been detected from wild birds (species of ducks, swans and geese) in these countries. Furthermore, there has been a considerable increase globally in the frequency of HPAI outbreaks in poultry and reports of infected wild birds over the winter period (2014/15) involving H5N8 HPAI and other HPAI viruses, including Eurasian lineage H5N1 HPAI and other H5N1, H5N2, H5N3 HPAI strains (Defra 2015).

The increase in HPAI outbreaks, including activity associated with reassortant H5 HPAI strains circulating widely in China and South East Asia and the recent outbreaks in Northwest America and Northern Europe, emphasises the need for vigilance and increased biosecurity. In the UK, Defra consider there to be a constant low risk of incursion of any notifiable avian disease into poultry throughout the year, and the current situation in Europe means the UK is at an increased risk at present (Defra, 2014c).

Therefore, all poultry keepers are advised to maintain robust biosecurity measures, vigilance for clinical signs of disease and to promptly report suspect cases of notifiable avian disease to a local APHA office. Further information regarding avian influenza in poultry and wild birds is available:

  • Members of the public are also asked to remain vigilant for any wild bird mass mortality incidents and report these to the Defra Helpline: 03459 33 55 77
  • APHA office contact details and further information about avian influenza, and when and how to register your poultry flock are available on the APHA web site.
  • APHA, in collaboration with Defra, also monitors the international situation and distribution of avian influenza detections and further information can be found online.

LPAI virus infections in reat Britain

There were no further incidents recorded in Q3 or Q4 of non-notifiable low pathogenicity avian influenza (LPAI), following the two incidents seen in Q2, as described in the Q2-2014 report (anon, 2014b). However the 12-month pilot scheme enabling private veterinary surgeons in Great Britain (GB) to request chargeable Notifiable Avian Disease (NAD) exclusion testing in chickens and turkeys has continued (AHVLA, 2014; Gibbens and others, 2014). No submissions were tested in Q3 or Q4.

Blackhead (histomonosis) in chickens and turkeys

Histomonosis (caused by the protozoan parasite, Histomonas meleagridis) has been diagnosed regularly by APHA (formerly AHVLA) and SAC C VS in turkeys, and to a lesser extent chickens, in recent years in GB. As reported in the Q3-2014 report (Anon, 2014c), there is both anecdotal and published evidence that the disease is becoming more prevalent.

The VIDA data show consistent numbers of diagnoses in turkeys in Q4 (Figure 1), as in Q3, but there was an increase in diagnoses in chickens both in Q4 (Figure 2) and on an annual basis (Figure 3).

Figure 1. Incidents of histomonosis (blackhead) in turkeys in Q4 from 2001 to 2014 (VIDA data
Figure 2. Incidence of histomonosis (blackhead) in chickens in Q4 from 2001 to 2014 (VIDA data)
Figure 3. Incidence of histomonosis (blackhead) in chickens (annual) from 2001-2014 (VIDA data)

As reported previously (Anon, 2014c), the reasons for the apparent changes in the prevalence of histomonosis in chickens and its appearance on indoor units are not understood, but could include changes in virulence of the parasite, emergence of different strains (genetic heterogeneity) and interaction with other disease agents. An example of the latter was the diagnosis during Q4 of concurrent histomonosis and colibacillosis in an indoor broiler breeder flock aged 25 weeks. The control of histomonosis can be problematical as there are currently no licensed treatments available in the EU. Cases of histomonosis will continue to be monitored by means of scanning surveillance.

Infectious coryza in chickens

An outbreak of respiratory disease was investigated in 21-week-old birds in a hobby breeding flock, which comprised predominantly imported but also some home-bred stock. The birds had reared well but a few days after being moved from rearing to breeding accommodation, initially two or three birds were affected with nasal and ocular discharge and periorbital swelling, and two days later another eight birds were affected.

Post mortem examination of affected birds confirmed mostly unilateral swelling of the periorbital region (Figure 4), with clear to mucoid exudate in the sinuses, accompanied by caseation in two birds. Bacterial culture undertaken on a sinus swab yielded suspect Avibacterium paragallinarum, the causative agent of infectious coryza, subsequently confirmed by molecular methods. No pathogenic Mycoplasma organisms were detected in pooled tracheal and conjunctival swabs. There was a good clinical response to antibiotic medication in the water.

Figure 4. Swollen infraorbital sinus (arrow) in a hobby bird with confirmed infectious coryza

Infectious coryza is a contagious respiratory disease first confirmed in Britain in 2010 (Welchman and others, 2010) and can be transmitted by asymptomatic carrier birds. This is an important disease for which the backyard and hobby poultry sector acts as a ‘sentinel’ population, and there is the potential for spread to the commercial sector. The disease will continue to be monitored by scanning surveillance activities.

Gizzard erosion in layers

Gizzard erosion (or gizzard erosion and ulceration syndrome) is well recognised in broilers and a variety of causes have been identified including fowl adenovirus (Gjevre and others, 2013).

An investigation was undertaken in a flock of 4,000 free-range layers aged 24 weeks where a few dead birds were being found daily. There was no effect on egg production in the flock. The combs of the birds were pale, and post-mortem examination confirmed pallor in the carcasses of the affected birds associated with haemorrhage into the gastro-intestinal tract and also dark gizzard contents.

Histopathological examination of the gizzards revealed focal inflammatory changes and occasional deep basophilic intranuclear inclusion bodies, features similar to those seen in broilers affected by gizzard erosion caused by adenovirus.

Adenoviruses are considered ubiquitous and can cause a range of conditions in poultry including gizzard erosion in broilers but this condition is much less well recognised in layer chickens. It is planned to undertake further investigation and scanning surveillance activity, to ascertain more information on the disease in layer chickens and its potential impact.

Update on selected other new and re-emerging disease investigations reported during Q1-Q3 2014

Enterococcal and streptococcal infections in broilers – reported in the Q2-2014 report (anon, 2014b). Additional isolations were reported in Q4, including Enterococcus hirae from a heart valve lesion in a 20-day-old broiler, E. cecorum from endocarditis and septicaemia in a separate 20-day old broiler flock, and E. hirae from septicaemia in 10-day-old broilers. These organisms appear to be increasingly emerging as pathogens; their origin is unclear but may relate to hygiene issues in the hatchery (particularly in young chicks) or on farm. Monitoring of this group of organisms by means of scanning surveillance will continue.

‘Atypical blackhead’ (tetratrichomonosis) in red-legged partridges - reported in the Q3-2014 report (anon, 2014c); a further case was also reported in Q4 following scanning surveillance investigation in a flock of 1,000 partridges where 10 to 20 birds per being lost per day and 200 had died in total. This manifestation of Tetratrichomonas gallinarum infection appears to be associated with a single strain of the organism, which is otherwise generally regarded as an opportunist in enteric disorders in game birds. The reason for the emergence of a virulent strain in partridges has not been established.

Marek’s disease in turkeys – reported in the Q1-2014 report (anon, 2014a); a further case was confirmed in Q4 by PCR testing of tumour tissue from a 14-week-old turkey which had lost condition and gone off its legs in a small flock of 100 birds. Marek’s disease is principally a disease of chickens but is increasingly being identified in turkey flocks, often following a background of direct or indirect contact with chickens. The availability of a PCR test for virulent Marek’s disease virus (MDV-1) has aided confirmation of the disease in turkeys and thereby enhanced scanning surveillance for the disease in this species.

Respiratory cryptosporidiosis (Cryptosporidium baileyi) in red grouse – reported in the Q3-2014 report (anon, 2014c) which described the more widespread distribution of this disease on moors in northern England. Respiratory cryptosporidiosis was also diagnosed in a red grouse submitted from a moor in south east Scotland in December 2014. The grouse was submitted for a post-mortem investigation as it was suspected of having ‘bulgy’ eyes. This was the only grouse seen to be affected. The diagnosis was confirmed by histopathology where heavy cryptosporidial infection was found in the nasal passage. The confirmation of the disease in Scotland is not unexpected considering the disease is present just over the border and there have been anecdotal reports of suspicious cases in southern Scotland since the first report. The disease will continue to be monitored by scanning surveillance. There are no known public health implications.

Unusual Diagnoses

A variety of endemic poultry diseases continued to be diagnosed in backyard and commercial poultry during Q4-2014 in GB. 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.

Leucocytozoonosis in a pheasant

A presumptive diagnosis of leucocytozoonosis was made in a 10-week-old pheasant, based on the histopathological findings in the brain. The bird was in a group of recently purchased pheasants that were in poor body condition. A one per cent mortality rate over a two-day period was seen.

The birds submitted alive were tick-infested, weak and uneven in size. No evidence of spironucleosis (hexamitiasis) was found. Histological examination in one bird showed perivascular lymphocytic 'cuffing' randomly distributed in the brain, and one area with four parasitic-like cysts suggestive of possible Leucocytozoon species infection. However no obviously parasitised blood cells were found in the histological sections in this case.

Leucocytozoonosis is a parasitic disease of birds affecting blood and tissue cells of internal organs, and its lifecycle includes invertebrate intermediate hosts, usually biting flies or midges. Infections are most often subclinical but can occasionally cause clinical and even fatal disease as a result of anaemia. The disease is rarely diagnosed in game birds in GB, but this report indicates it should be considered in the differential diagnosis of loss of condition and anaemia in game birds.

Further Reading

You can view the full report by clicking here.
Find out more information on the diseases mentioned by clicking here.

March 2015

Our Sponsors


Seasonal Picks

Animal Welfare Science, Husbandry and Ethics: The Evolving Story of Our Relationship with Farm Animals