GB Emerging Threats Report: Avian Diseases: April-June (Q2) 201421 November 2014
Among the highlights included in this quarterly report from the Animal Health & Veterinary Laboratories Agency (AHVLA) are H4N6 low-pathogenic avian flu virus infections in chickens, enterococcal and streptococcal infections in broilers,ILT in broiler breeders and two incidents of Salmonella pullorum in hobby chickens.
- Submission trends: Decrease of one per cent in the total number of avian diagnostic submissions to AHVLA and SAC during Q2-2014 compared with Q2-2013. This includes a fall of four per cent in the total number of avian diagnostic submissions received by AHVLA and a rise of 13 per cent received by SAC.
- New & Re-emerging diseases: H4N6 low-pathogenic infections in chickens; Enterococcal and streptococcal infections in broilers; ILT in broiler breeders; Salmonella Infantis in broilers.
- Unusual diagnoses: Two incidents of Salmonella pullorum in hobby chickens
- Changes in the industry and disease patterns: The average weekly placings of broiler and layer chicks in June were the highest for four years.
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 population.
Ongoing New and Re-Emerging Disease Investigations
H4N6 LPAI virus infections detected from chicken flocks in England & Wales
Two separate cases of non-notifiable H4N6 low pathogenicity avian influenza (LPAI) virus infection were detected in chicken flocks during May and June 2014 in central England and mid-Wales respectively.
The first H4N6 LPAI virus detection (May 2014) arose as a result of testing samples from a broiler breeder flock that were submitted through the 12-month pilot scheme enabling private veterinary surgeons in Great Britain (GB) to request chargeable Notifiable Avian Disease (NAD) Exclusion testing (AHVLA, 2014; Gibbens and others, 2014).
The second case was detected during June 2014 affecting a free-range chicken layer flock in mid-Wales. Clinical suspicion of NAD was initially reported due to increasing daily mortality (to ~100 hens daily) and reduced egg production (~16 per cent) over a five-day period. Official veterinary and laboratory investigations (in accordance with international standards) at AHVLA Weybridge confirmed infection with a non-notifiable H4N6 LPAI virus that was highly similar, but not identical to, the H4N6 LPAI virus detected during May 2014.
Detailed viral genome analyses also suggested that the H4N6 virus from the second case in Wales showed characteristics of a strain that had not recently transferred from wild birds, suggesting spread within the poultry sector. In both cases clinical signs resolved within a two-week period. However, LPAI viruses can cause mild or subclinical infections in poultry making recognition and detection of disease more difficult, a potential contributory factor conducive to spread (Irvine, 2013a,b).
The risk also exists of more extensive secondary spread in areas of higher poultry population density. Whilst the exact source of the H4N6 LPAI virus detected from these two cases was not definitively confirmed no other cases were reported.
The last NAD outbreak in GB occurred during June/July 2008 (H7N7 HPAI in a free-range layer flock, Oxfordshire; Defra, 2008). However, detections of non-notifiable avian influenza (AI) and avian paramyxovirus type 1 (APMV-1) virus infection in domestic poultry are not uncommon in GB; from February 2009 to April 2013 there were eight such cases.
These cases all resulted in official veterinary and laboratory investigations by AHVLA and were initially reported either as a result of laboratory testing of routine endemic disease scanning surveillance submissions or as statutory Report cases. These events highlight the continuous threat presented to poultry health by AI and APMV-1 viruses.
In the majority of these cases the source of infection was putatively attributed to be wild birds, but other risk pathways were also identified. Therefore, it is important to maintain good flock biosecurity and hygiene practices at all times, with prompt reporting of suspected NAD to the veterinary authorities.
Enterococcal and streptococcal infections in broilers
A variety of enterococci can cause infections in broilers. These include Enterococcus hirae which was identified by scanning surveillance as the cause of vegetative endocarditis in 21- to 24-day-old broilers during the quarter. Septicaemia, femoral head necrosis and vegetative endocarditis due to Streptococcus pluranimalium was seen in a submission of 44-day-old broilers with a history of unexpected mortality since thinning.
The post-mortem findings included focal granulomatous-necrotic lesions in the liver and spleen, crumbly femoral heads and vegetative lesions in the heart valves. Routine cultures of heart valve lesions and a femoral head yielded profuse growth of alpha-haemolytic Gram-positive cocci further identified by molecular methods (16S rRNA gene sequencing) as Streptococcus pluranimalium.
This organism is recognised as a potential pathogen of the reproductive tract in cattle, and has been reported in association with septicaemia and vegetative valvular lesions in adult broiler breeders (Hedegaard and others 2009), but there appear to be no previous descriptions of its occurrence in broiler chickens.
The origin of these organisms is unclear, but they may relate to hygiene issues in the hatchery (particularly in the case of enterococcal infections in young chicks) or on farm. It is important to maintain a high standard of hygiene practices, including in areas such as water supply lines, to prevent infections becoming endemic on farms, as well as maintaining good biosecurity. The use of techniques such as 16S rRNA sequencing is required to differentiate organisms such as S. pluranimalium from other, phenotypically similar streptococci. Infections with these groups of Gram positive bacteria will continue to be monitored by means of scanning surveillance.
Antimicrobial resistant Salmonella Infantis in broilers
Multidrug resistant clones of Salmonella Infantis have emerged over the last few years in the broiler industry in Europe (Nógrády and others 2012). The further dissemination of such clones in broilers and in broiler meat may represent a threat to public health. The ability to identify emerging Salmonella threats and prevent them becoming permanently established in UK poultry flocks via efficient scanning surveillance and expert-led intervention is a major asset in terms of protecting public health, and the good reputation of the UK poultry industry for efficient Salmonella control.
Infectious Laryngotracheitis (ILT) in broiler breeders
The veterinary advisor to the British Poultry Council (BPC) wrote to the British Veterinary Poultry Association on 2 July highlighting the BPC’s concern over broiler breeder sites becoming regularly infected with ILT. Investigations were reported to have revealed that in many cases these infections have been associated with ILT vaccination on a nearby layer pullet rearing site.
It is alleged that many of these pullet rearers are using ILT vaccine either by spray or drinking water, which is “off label”, as the datasheet for the vaccine stipulates it should be administered by eye drop. The use of a vaccine other than via the authorised route is a consideration under the Cascade (VMD, 2013). The BPC considered that using the vaccine off-label may result in reversion to virulence of the vaccine with higher loadings of vaccine being excreted by vaccinated birds. ILT has been diagnosed by AHVLA in the course of scanning surveillance activities this year, including in broiler breeders, and airborne transmission from nearby layer farms and a rearing farm which may be vaccinating was considered a possibility.
ILT has also been diagnosed separately by AHVLA this year in backyard flocks. ILT is an economically important disease and is controlled in commercial and parent flocks in several different countries including GB by the use of live attenuated vaccines. However a recent review (Menendez and others 2014) has emphasised the importance of reversion to virulence of attenuated strains in the epidemiology of ILT, and this is exacerbated by poor mass administration of the vaccine.
This reinforces the need for good vaccination practice to control ILT, as advocated by BPC. Infection can be spread directly from bird to bird and windborne transmission is also recognised. The situation will continue to be monitored through AHVLA scanning surveillance activities.
Endemic poultry diseases, including some unusual cases, continued to be diagnosed in backyard and commercial poultry during Q2-2014 in GB. A selection has also been described in the surveillance highlight reports published in the Veterinary Record (AHVLA, 2014a, SAC C VS, 2014). 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.
Salmonella Pullorum (Pullorum disease)
Salmonella Pullorum infection was confirmed in two small hobby breeding flocks this quarter. Each case was associated with hatching eggs being brought onto the premises resulting in deaths of six out of 44 and five out of 40 chicks on separate holdings. Pullorum disease can be spread through the egg from an infected carrier hen and also through contamination of the environment, such as through contaminated incubators.
As a result, infection can result in the possibility of long term persistence on premises. If hatching eggs or hens are sold from these premises there is the risk that infection can be spread to other backyard farms. Only two to four cases have been recorded on VIDA each year between 2005 and 2012. It is a well recognised disease that is not zoonotic but is now rare in chickens.