Infectious Diseases 2020

Infectious Diseases 2020

Avian Influenza (H3N1) virus involved in outbreak, Belgium, 2019

EID: Vol. 26 No. 8- Aug 2020 4 July, 2020

In January 2019, H3N1 virus was isolated from an outdoor laying hens farm in Belgium. The affected flock was culled, but 3 months later (April), H3N1 virus was again detected on this farm. Since then, 82 holdings in northwestern Belgium were infected with H3N1 virus in a 16-week period, involving different poultry species and types of farms (Layers, Broilers, Broiler breeders, Light layer breeders, Turkeys, Quails and Ostriches). In France, 3 farms were H3N1-positive; 2 showed a direct link with a company from the affected area of Belgium.
The clinical picture in the field started mostly with discolored eggs for laying hens and breeders, followed by an increased mortality rate of up to 60% in breeder hens and 40% in laying hens. In addition, a marked egg drop, up to 100%, was reported. For the virus strain isolated in April from poultry on the index farm (A/Gallus gallus/Belgium/3497_0001/2019), the IVPI was 0.13, indicating a low pathogenicity phenotype.
In vivo infection studies, in SPF chickens (11-wks old) did not show clinical signs.  In vivo studies in 24-week-old laying hens, found that the virus is a pathogenic and can cause mortality with pathological lesion and no clinical signs.