West Nile Virus Lineage 2 in Free-Living Corvus cornix Birds in Poland

Abstract

The summer temperatures recorded in Poland in 2022 were among the highest in over 30 years and, combined with higher-than-expected rainfall, gave the impression of an almost tropical climate. Such climatic conditions were ideal for the transmission of vector-borne zoonotic diseases such as West Nile fever. In northeastern Poland, in the Mazowieckie region, the Polish event-based surveillance network reported increased fatalities of free-living hooded crows (Corvus corone cornix). West Nile virus (WNV) lineage 2 was identified for the first time as the etiological agent responsible for the death of the birds. WNV was detected in 17 out of the 99 (17.17%) free-living birds tested in this study. All the WNV-infected dead birds were collected in the same area and were diagnosed in September by the NVRI and confirmed by the EURL for equine diseases, ANSES, in October 2022. Unnaturally high temperatures recorded in Poland in 2022 likely favored the infection and spread of the virus in the avian population. A nationwide alert and awareness raising of blood transfusion centers and hospitals was carried out to prevent human infections by WNV.

Keywords: (q) RT-PCR; RT-PCR; crow; detection; wild birds; zoonoses.

Figure 1

Infected free-living bird area in 2022, Warsaw, Poland. Holding with WNV-positive cases is marked with black dot. Defined nature reserve in the Central Mazowieckie Lowlands.

Figure 2

Phylogenetic analysis of a WNV strain sequence from avian species (Corvus cornix) studied in Poland and compared with obtained WNV sequences from other countries/continents representing different WNV lineages (Lin 1–9) deposited in the GenBank NCBI database.The frame shows the sequences of strains classified as lineage 2 of WNV circulating in Central Europe, which are arranged in one characteristic group, showing close similarity. In addition, the black dot indicates the sequence of the WNV strain that was marked in Poland for the first time.