06.01.2017

EID, Vol. 23, No. 4 - April 2017

In late May 2016, a group B clade 2.3.4.4 H5N8 virus was detected in dead and hunted wild birds at Lake Uvs-Nuur, at the Russia–Mongolia border. On November 7, 2016, many dead tufted ducks (Aythya fuligula) were found at Lake Plön in Schleswig-Holstein, northern Germany, and at Lake Constance in Baden-Württemberg, southern Germany; most were positive for H5N8. The epidemic among wild birds continued and spread toward the center of the country. As of December 2016, several backyard holdings, 4 zoos, and a few large commercial operations were also affected. Direct or indirect contact with wild birds was the most likely route of virus introduction into the backyard holdings and zoos. Despite the generally high standards of commercial operations, possible biosecurity gaps were identified.
Most affected birds were found dead or exhibited severe clinical signs such as apathy or sudden deaths (in some parts of the affected chicken breeder farms, up to 90% died before culling). Macroscopic changes commonly observed in tufted ducks and poultry included severe diffuse hepatic necrosis, multifocal petechiae, and variably hyperemic and edematous lungs.  Some chickens also displayed severe diffuse catarrhal enterocolitis. 
The high pathogenicity for gallinaceous poultry was confirmed; intravenous pathogenicity index (IVPI) for 1 isolate (A/tufted duck/Germany-SH/AR8444/2016) was 2.93, comparable to the 2.81 index for H5N8 circulating in 2014 (A/turkey/Germany-MV/AR2472/2014). However, deaths of wild birds of a variety of species, in particular diving ducks, and extended pathologic changes in dead wild birds suggested a marked shift of pathogenicity from the viruses in Germany in 2014.  
All genome segments of the novel H5N8 clade 2.3.4.4 group B strains from Germany in 2016 differed significantly from the H5N8 clade 2.3.4.4 group A strains detected in 2014–2015 in Germany and other European countries.
This finding is in accord with findings of studies suggesting that there was no continued circulation of group A–like viruses among wild birds in the Netherlands from mid-November 2014 to January 2016. 
Clade 2.3.4.4 virus was closely related to viruses at the Russia–Mongolia border in 2016 but had new polymerase acidic and nucleoprotein segments. These new strains may be more efficiently transmitted to and shed by birds. 
There is yet no indication that mammals (including humans) are infected by these novel strains. Future studies in mammalian models (e.g., ferrets, mice) are needed to provide experimental data on the virulence for mammals.