Complete Coding Sequence of Usutu Virus Strain Gracula religiosa/U1609393/Belgium/2016 Obtained from the Brain Tissue of an Infected Captive Common Hill Myna (Gracula religiosa)

Usutu Virus Epizootic in Belgium in 2017 and 2018: Evidence of Virus Endemization and Ongoing Introduction Events

Wildlife surveillance allowed the monitoring of the zoonotic mosquito-borne Usutu virus (USUV) in birds and bats (Pipistrellus pipistrellus) in southern Belgium in 2017 and 2018. USUV-RNA was detected in 69 birds (of 253) from 15 species, among which 7 species had not previously been reported to be susceptible to the infection. Similarly, 2 bats (of 10) were detected positive by reverse transcriptase quantitative polymerase chain reaction (RT-qPCR). USUV-associated lesions were mainly found in Eurasian Blackbirds (Turdus merula), in which USUV antigens were demonstrated by immunohistochemistry in the brain, heart, liver, kidney, intestine, and lung. Partial nonstructural protein 5 gene-based phylogenetic analysis showed several identical or closely related strains from 2016, 2017, and 2018 clustering together within Europe 3 or Africa 3 lineages. Further, one USUV strain detected in a common chaffinch (Fringilla coelebs) manifested a close genetic relationship with the European 1 strains circulating in Hungary and Austria. Our data provide evidence of USUV endemization in southern Belgium in local birds and bats, extension of the host range of the virus and ongoing virus introduction from abroad, likely by migratory birds. Our results highlight the need for vigilance in the forthcoming years toward new virus-associated outbreaks in birds and possible human infections in Belgium.

Usutu Virus Epizootic and Plasmodium Coinfection in Eurasian Blackbirds ( Turdus merula) in Flanders, Belgium

At the end of the summer of 2016, unusually high levels of mortality were detected in Passeriformes and Strigiformes in Flanders, Belgium, mainly in Eurasian Blackbirds ( Turdus merula). A passive surveillance program demonstrated a widespread Usutu virus outbreak and revealed a coinfection with Plasmodium in 99% of the dead passerine birds that were necropsied.

Complete coding sequence of a novel picorna-like virus in a blackbird infected with Usutu virus

Using random high-throughput RNA sequencing, the complete coding sequence of a novel picorna-like virus (a 9,228-nt contig containing 212,202 reads) was determined from a blackbird (Turdus merula) infected with Usutu virus. This sequence shares only 36% amino acid sequence identity with its closest homolog, arivirus 1, (an unclassified member of the order Picornavirales), and shares its dicistronic genome arrangement. The new virus was therefore tentatively named "blackbird arilivirus" (ari-like virus). The nearly complete genome sequence consists of at least 9,228 nt and contains two open reading frames (ORFs) encoding the nonstructural polyprotein (2235 amino acids) and structural polyprotein (769 amino acids). Two TaqMan RT-qPCR assays specific for ORF1 confirmed the presence of high levels of this novel virus in the original sample. Nucleotide composition analysis suggests that blackbird arilivirus is of dietary (plant) origin.

West Nile Virus and Usutu Virus Monitoring of Wild Birds in Germany

By systematically setting up a unique nation-wide wild bird surveillance network, we monitored migratory and resident birds for zoonotic arthropod-borne virus infections, such as the flaviviruses West Nile virus (WNV) and Usutu virus (USUV). More than 1900 wild bird blood samples, from 20 orders and 136 different bird species, were collected between 2014 and 2016. Samples were investigated by WNV and USUV-specific real-time polymerase chain reactions as well as by differentiating virus neutralization tests. Dead bird surveillance data, obtained from organ investigations in 2016, were also included. WNV-specific RNA was not detected, whereas four wild bird blood samples tested positive for USUV-specific RNA. Additionally, 73 USUV-positive birds were detected in the 2016 dead bird surveillance. WNV neutralizing antibodies were predominantly found in long-distance, partial and short-distance migrants, while USUV neutralizing antibodies were mainly detected in resident wild bird species, preferentially with low seroprevalences. To date, WNV-specific RNA has neither been detected in wild birds, nor in mosquitoes, thus, we conclude that WNV is not yet present in Germany. Continued wild bird and mosquito monitoring studies are essential to detect the incursion of zoonotic viruses and to allow risk assessments for zoonotic pathogens.