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Poultry | December 2024

Duck circovirus detected in necropsies on ducks In 2024, GD detected duck circovirus (DuCV) several times in Dutch ducks that had been submitted for post-mortem diagnostics. It is possible that this virus is not new in the Netherlands but is now being detected because of extensions to diagnostic testing.

Abnormalities caused by DuCV Duck circovirus can negatively affect the bird’s defence mechanisms, resulting in poorer performance and elevated disease susceptibility. In the Netherlands, the virus is now being linked to flocks that do not grow well and in which uniformity keeps worsening as the birds get older. Upon necropsy, very extensive erosions of the gizzard are seen and in some cases the thymus (an organ involved in immune responses) is affected. The gizzard abnormalities may perhaps not be caused directly by the circovirus, instead being an indirect consequence of the reduced health status and secondary infections (of the gut) taking hold in ducks whose immune systems have been compromised by the virus.

Preventing infection with DuCV Circoviruses are well capable of surviving for long periods in the surroundings and they are resistant to many of the commonly used disinfectants. Extra attention is therefore required at farms where there is an infection to cleaning and disinfection in-between rounds, to prevent the next batch from becoming infected again. There are no vaccines available and there is no treatment.

Photo: Ducks with disappointing growth performance, poor uniformity and a general picture of retarded development. Severe gizzard erosion was observed in these animals and they tested positive for duck circovirus.

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Further tests on the ILT strains form the 2024 outbreak Earlier we reported on the ILT outbreak in the third quarter of 2024 in which fourteen poultry flocks became infected with wild-type infectious laryngotracheitis (ILT) virus, eight of which were in the Gelderse Vallei region, which has a dense poultry population. Some of the wild-type strains found were examined further by sequence analysis (DNA examination of the virus), which gives a clearer picture of the viruses involved in the outbreak, as well as the links between them.

Result of further tests on the recent ILT strains To analyse them, we sequenced twelve samples from the recent ILT outbreaks. Eleven of the samples came from commercial poultry farms and one from ‘backyard’ chickens. It proved possible to get a picture of the complete genome (the whole genetic makeup of the virus) for four samples. The genome was almost complete for two other samples, allowing limited analysis of these specimens too. Less of the genome was available from the other six samples, allowing us to draw only very limited conclusions. The four complete genomes were extremely similar to each other. One of the two genomes that were incomplete but analysable came from the backyard chickens. This genome could clearly be categorised as wild-type ILT, yet demonstrated clear differences with respect to the specimens taken from the recent outbreaks among commercial poultry. It is therefore unlikely that there was any link between the case involving backyard chickens and the outbreaks among commercial poultry.

Comparison against the ILT strains from 2018 Samples from ILT outbreaks were sequenced in 2018, which at the time led to the development of a differentiating PCR (PCR that can distinguish between strains found in the field and those used for vaccines). Those samples were included in the analysis. The samples from the current outbreaks among commercial poultry were clearly different to the wild-type ILT strains that were examined in 2018.

Provisional conclusion The analysis of the genetic material shows that at least five of the outbreaks among commercial poultry are epidemiologically linked. The strain from the backyard poultry is unrelated to the strains from the outbreaks among commercial poultry. The recent ILT strains are not related to the strains that were sequenced from the 2018 outbreaks. The difference between vaccine-like and wild-type strains remains clear, based on the whole genome and the ILT SNP typing PCR carried out by GD (the differentiating PCR).

Rise in Brachyspira hyodysenteriae infections in laying poultry In the Poultry Health Surveillance highlights report of September 2023, we reported a case of Brachyspira hyodysenteriae at a laying farm in the Netherlands. We also detected several infections in 2024. Over the course of three months (August, September and October), GD detected B. hyodysenteriae infections in laying hens submitted for necropsy. These came from eight laying flocks at seven different laying farms. These were six free-range flocks and one that was indoors. The ages ranged from 27 to 75 weeks (see Table 1). The bacterium was present in large numbers in one of the flocks. In all cases, one or both of the Brachyspira species commonly known in poultry farming (namely B. intermedia and/or B. pilosicoli) were also present. These Brachyspira species can also be present in clinically healthy flocks. Whether the infection leads to clinical problems depends on other factors (intestinal health, the presence of other pathogens or worms in the intestine). B. hyodysenteriae is known as an intestinal pathogen in pigs. A relationship with pig manure or the presence of pigs on the farm or in the surroundings was noted in five of the seven cases. However, carrier status for B. hyodysenteriae also occurs in wild ducks and it circulates abundantly in mouse populations. These factors also cannot be excluded as the source of introduction.

Table 1. Overview of laying flocks that were positive for Brachyspira hyodysenteriae in August, September and October 2024 (source: necropsies at GD) Farm Province

Breed

Age

Case history

Diagnosis

1 2

Layer flock Overijssel organic Gelderland organic

brown white

46 65

Production problems Production problems

white

4 5

Gelderland barn + free-range Gelderland organic Gelderland organic

white brown

75 + 46 57 34

Production problems and emaciation Production problems Production problems

6 7

Gelderland barn Overijssel free-range

white white

27 30

Digestion problems Reduced food intake, production problems, respiratory problems

Intestinal infection and threadworms Intestinal infection, roundworms and tapeworms Intestinal infection, roundworms, threadworms and tapeworms Intestinal infection and threadworms Intestinal infection, roundworms, threadworms and mycotoxosis Intestinal disorder and roundworms Avian pox virus, intestinal inflammation with necrosis, appendicitis

Bleeding in the caecum No No 1 bird house (1 of the 22 animals) No No No 1 of the 4 animals

Previous cases of Brachyspira hyodysenteriae The first report of an infection with B. hyodysenteriae received by GD was about a laying flock in Germany in 2008. After 2008, GD detected B. hyodysenteriae in necropsies of animals from Dutch poultry flocks on rare occasions. In 2023, the infection was detected in a Dutch laying flock with intestinal problems (intestinal inflammation and worm infections). The affected flock had too much water in proportion to their feed, wet manure and wet feathers around the cloaca. The proportion of eggs with dirty shells was also too high. Upon section, the content of the small intestine was too watery and there were striking petechiae in the caeca of several birds (Photo 1). This flock included animals that were infected only with B. hyodysenteriae. There were also animals with mixed infections that included B. intermedia and B. pilosicoli, as well as birds with mixed infections that did not involve B. hyodysenteriae.

Photo 1. Petechiae in the caecum in a flock affected by B. hyodysenteriae (source: GD)

Microscopic examination of the caecum of hens with bleeding that were affected by B. hyodysenteriae showed mild inflammations, with the typical bacteria present (Photo 2). In the birds that had B. hyodysenteriae infections, the bacteria seem to have a greater tendency to penetrate the tissue of the caecum.

Photo 2. View under the microscope of the caecum (silver stained): the blue rectangle shows the damaged area where the black helical bacteria get in. There are also large numbers of black helical bacteria attached to the mucous membrane (spirochetes/Brachyspira sp.) (source: GD)

Because Brachyspira infections also occur in poultry in healthy flocks, predisposing factors* are important (e.g. intestinal inflammation, worm infections, infections with other intestinal pathogens) if they are to cause disease symptoms in practice. Based on the microscopic findings known to date, B. hyodysenteriae seems to be more invasive** than the other Brachyspira species in the same flocks. * **

Predisposing factors are ones that make an animal more susceptible to developing a specific condition. Invasive = the property of being able to penetrate the underlying tissue.

VMP project proposal: investigate the occurrence of B. hyodysenteriae in laying hens VMP is the collaborative partnership between poultry veterinarians and GD. An important element of VMP is a database for mandatory recording of the use of antibiotics. Additional data are also recorded in it, on a voluntary basis. This then includes the vaccinations administered and the findings of farm inspections, including cases where no antibiotics have been prescribed. VMP projects are initiated in response to specific questions from the practice. The projects then gather targeted data, or samples are taken by the veterinarians concerned. Investigations have started within VMP into the occurrence of B. hyodysenteriae in laying hens. In this study, laying flocks aged over 40 weeks are examined to see if Brachyspira hyodysenteriae is present in the manure, making distinctions between flocks that do and do not have problems and between those that are and are not free-range.

Clinical picture of the bird flu infections in Putten and Blija In the fourth quarter of 2024, two outbreaks of high-pathogenic avian influenza (HPAI) were detected among commercial poultry. They affected a laying flock in Putten aged about 54 weeks and a flock of slow-growing broiler chickens aged 53 days. In both cases, elevated losses were the reason for suspicions being raised. Water and feed intakes were not abnormal in either case and egg production was still normal in the laying flock. Almost no sick animals were present in the broiler flock but there were birds in the laying flock in one part of the stall that were quieter, lethargic and distended. Blue discoloration of the combs was seen in the dead laying hens, as well as swellings of the spleen and liver in some cases. In addition to the spleen and liver swellings, pneumonia and pericarditis were observed among the broiler chickens, and a small number of chickens had subcutaneous bleeding in the feet. These outbreaks, combined with others elsewhere in Europe and reports of mortality among wild birds (including migrating birds), suggest that caution is still warranted in the coming period and that there should be no barriers to contacting a veterinarian in the event of sudden increases in losses.

Update on Salmonella Enteritidis among laying poultry Since 2023, there has been a strong increase in the number of laying flock infections with Salmonella Enteritidis (SE). A large number of flocks were infected in 2024 as well. For reasons of food safety, eggs from infected flocks must be sent to the egg-processing industry. The flock itself will remain infected throughout its life and will excrete the bacterium in the manure and secrete it in the eggs. Monitoring only at relatively long intervals can mean that a flock has already started secreting the bacterium before the monitoring picks it up, which thus creates a risk of SE being spread to other farms. Good biosecurity is particularly important at the moment because of the elevated number of laying flocks in the Netherlands that are infected with SE. Advice to poultry farmers is that strict hygiene measures should be observed when people come onto the premises and that they should only enter the bird houses if that is clearly necessary. Additionally, other biosecurity measures such as vermin control and prevention of introduction through unclean materials remain as important as ever.

Animal health barometer for poultry Disease/disorder/ Brief description 4Q 1Q 2Q health characteristic (numbers at the farm level) 2023 2024 2024 Execution decree (EU) 2018/1882 of the Animal Health Law (AHL) (EU) 2016/429 (Category A disease) Avian influenza (AI) Highly pathogenic AI (H5/H7)*: Number of farms in the Netherlands (first detection in flock) 3 0 0 (H5/H7) (Source: GD, WBVR, national * In commercial poultry and in Backyard poultry (>50 birds) government) backyard situations with >50 birds. 2 0 0

ND in the Netherlands

3Q 2024

Trend (OVER 2 YEARS)

È 0

Serological monitoring by GD: (first detection in flock) (antibodies for H5/H7)

Number of farms 1

Commercial poultry:

(Source: GD, WOAH)

Execution decree (EU) 2018/1882 of the Animal Health Law (AHL) (EU) 2016/429 (Categories B through E) Avian influenza (AI) Low pathogenic AI (H5/H7): Number of farms in the Netherlands (first detection in flock) 2 1 0 (H5/H7) (Source: GD, WBVR, national government)

Campylobacteriosis No data available Avian mycoplasmosis (Source: GD) Mycoplasma Serological monitoring by GD: gallisepticumA Reproduction sector: Layer pullets: Layers: - not vaccinated and infected: - vaccinated and infected: Turkeys:

n/a

0 0

Number of farms 0 0

0 0

0 2 0

4 1 1

0 3 0

0 1 0

È Ç -

Cases in EWSC based on positive serology and/or voluntary PCR testing: Reproduction sector: Layers: Turkeys: Backyard poultry:

Number of EWS reports

1 1 0 5

0 3 0 2

0 0 0 0

0 1 0 2

n/a

0 0

0 2

n/a Number of farms/cases 0 0 Number of farms/cases 0 0

0 0

West Nile fever Not monitored n/a n/a n/a Article 2.1 Designation of animal diseases in the ‘Rules for Animal Health’ of the Dutch Animal Act Avian chlamydiosis Detected by GD: Number of farms/cases (Source: GD) Commercial poultry: 0 0 0 Backyard poultry: 0 1 0

n/a

0 0

M. meleagridis (Source: GD) Salmonellosis (non-zoonotic salmonella) (Source: GD) Salmonella arizonae Salmonella Gallinarum (SG) Commercial poultry: Backyard poultry: Salmonella Pullorum (SP) Commercial poultry: Backyard poultry:

Disease/disorder/ Brief description 4Q 1Q health characteristic (numbers at the farm level) 2023 2024 Article 2.2. Designation of zoonoses in the ‘Rules for Animal Health’ of the Dutch Animals Act Salmonellosis (zoonotic salmonella) (at the flock level) (Source: GD) Salmonella Enteritidis Reproduction: 2 1 0 0 Layer pullets: 25 27 Layers: Salmonella Typhimurium

Reproduction: Layer pullets: Layers: Reproduction:

1 0 1

0 0 0

Other types of 0 0 Salmonella (S. Hadar, S. Infantis, S. Java, S. Virchow) Other WOAH-list poultry diseases in the Netherlands subject to compulsory notification Duck viral hepatitis Detected by GD: -

2Q 2024

Continuation of table 3Q Trend 2024 (OVER 2 YEARS)

1 0 17

1 0 26

0 0 0

(Source: GD)

Gumboro (IBD) (Source: GD, EWS)

Infectious bronchitis (IB) (Source: GD)

Infectious laryngotracheïtis (ILT) (Source: GD, EWS)

Mycoplasma synoviaeB (Source: GD)

Turkey rhinotracheïtis (TRT) (Source: GD)

Reported in EWSC: Broiler breeder pullets: Broilers: Layer breeder pullets: Layer pullets: Backyard poultry: Types most commonly detected by GD: Broilers: Layers: Reported in EWSC: Layer pullets: Layers: Broiler breeders: Broilers: Backyard poultry: Serological monitoring and/or dPCR GD: Broiler pullets: Broiler breeding: Broiler breeder pullets: Broiler breeders: Layer pullets: Layer rearing: Layer breeder pullets Layer breeders: Layer pullets: Layers: Turkeys: Detected by GD: Broiler reproduction sector (incl. pullets): Layer reproduction sector (incl. pullets): Broilers: Layer pullets: Layers: Meat turkeys:

0 7 0 1 0

0 9 0 1 0

Number of EWS reports 1 5 0 0 0

0 4 0 0 0

D388 4/91

0 1 1 0 1

0 0 0 0 0

Number of EWS reports 0 1 0 0 0

2 6 1 4 1

0% 0% 67% 30% 0% 0% 0% 15% 16% 63% 0%

0% 0% 54% 27% 0% 0% 13% 8% 26% 71% 14%

% of farms positive versus farms tested 0% 0% 42% 32% 0% 0% 0% 6% 20% 63% 19%

0% 0% 42% 27% 0% 0% 0% 11% 16% 70% 9%

Number of farms 1

0 0 2 1

1 1 3 1

2 0 1 0

0 0 5 0

È -

Ç -

Ç È

Ç -

Ç È Ç

Royal GD P.O. Box 9, 7400 AA Deventer The Netherlands

Disease/disorder/ health characteristic Other poultry diseases Avibacterium paragallinarum (Source: GD, EWS)

Histomonosis (Source: GD)

Pasteurella multocida (Source: GD)

Erysipelas (Erysipelothrix rhusiopathiae)

T. +31 (0)88 20 25 575 info@gdanimalhealth.com www.gdanimalhealth.com

Brief description (numbers at the farm level) Reported in EWSC: Layers: Small commercial farms (<250) Backyard poultry: Detected by GD: Reproduction (meat sector): Reproduction (layer sector): Layer pullets: Layers: Meat turkeys: Backyard poultry: Aangetoond bij sectie: Broiler breeder pullets: Layers: Turkeys: Detected by GD: Layers:

4Q 2023

1Q 2024

2Q 2024

Continuation of table 3Q Trend 2024 (OVER 2 YEARS)

3 6

Number of EWS reportsd 1 2 1 0

2 1 1

2 1 0 3 0 0

Number of farms 1 0 0 0 0 0

1 0 0 1 0 0

1 0 0 0 0 0

0 2 0

0 3 0

Number of farmsd 0 5 0 Number of farmsd 2

È È

0 0 0

(Source: GD)

Ç Increase or strong increase Ç Limited increase - Situation unchanged

È Limited decrease È Decrease or strong decrease

A B C

Based on serological monitoring Based on serological monitoring and/or differentiating Ms-PCR Early Warning System

Animal health monitoring Since 2002, Royal GD has been responsible for animal health monitoring in the Netherlands, in close collaboration with the veterinary sectors, the business community, the Ministry of Agriculture, Fisheries, Food Security and Nature, vets and farmers. The information used for the surveillance programme is gathered in various ways, whereby the initiative comes in part from vets and farmers, and partly from Royal GD. This information is fully interpreted to achieve the objectives of the surveillance programme – the rapid identification of health problems on the one hand and the following of more general trends and developments on the other. Together, we team up for animal health, in the interests of animals, their owners and society at large. GD3265/02-25