Poultry | April 2026
Reovirus subtype 4.7 to be classified in a new genogroup from 2026 onwards
number of submissions with a diagnosis of viral tenosynovitis
High incidence and with slower-growing breeds over-represented Numbers of cases of tendon sheath inflammation caused by reoviruses remain high among broiler chickens. In 2025, 259 necropsies revealed reovirus tenosynovitis, making it the most common post-mortem diagnosis in broiler chickens at Royal GD. Regular broiler chickens were submitted less (16%) than broilers of slower-growing breeds (84%). The breakdown of broiler flocks in 2025 was 41 per cent regular and 59 per cent slower-growing, which thus means that reovirus was over-represented in the slower-growing flocks. By no means all animals affected by reovirus are sent to GD for post-mortem diagnostics, so this is merely the tip of the iceberg. GD necropsies: reovirus tenosynovitis 120 110 100 90 80 70 60 50 40 30 20 10 0
Other poultry Broilers (slower-growing) Broiler (regular)
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Figure 1. Number of submissions with a diagnosis of reovirus tenosynovitis among regular broilers, slow-growing broilers and other poultry (2021 to 2025) (source: GD)
Genotyping is being changed and there are indications of vertical transmission The genotypes (sets of hereditary characteristics) of the reoviruses found have been determined. The standard classification system used by GD is based on international agreements. It currently distinguishes between five genogroups, numbered 1 to 5. Because this grouping has recently been updated to reflect new findings, GD is also updating the classification shown in the results. This leads to some genogroup 3 viruses being reclassified as genogroup 7 and some of genogroup 4 as genogroup 6 (see Figure 2). Viruses belonging to subtype 4.7, which have caused numerous problems in recent years, have hereby been reclassified in genogroup 6. The group has also been changed for some viruses that previously belonged to genogroup 3. Following further discussions, we will implement these changes in GD’s results over the course of 2026. Several clusters stand out within both subtype 4.7 and genogroup 1. Four of these clusters involve chicks of the same breed that were hatched within a short period, suggesting vertical transmission. The fifth cluster consists of submissions involving various types of birds and breeds, meaning that vertical transmission can be ruled out.
Animal health monitoring Royal GD has been responsible for animal health monitoring in the Netherlands since 2002, in close collaboration with the veterinary sectors, the business community, the Ministry of Agriculture, Fisheries, Food Security and Nature, veterinarians 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 – rapid identification of health issues on the one hand and monitoring trends and developments on the other. Together, we team up for animal health, in the interests of animals, their owners and society at large.