Abstract
Usutu virus (USUV) is a mosquito-borne flavivirus, closely related to the West Nile virus (WNV). Similar to WNV, USUV may cause infections in humans, with occasional, but sometimes severe, neurological complications. Further, USUV can be highly pathogenic in wild and captive birds and its circulation in Europe has given rise to substantial avian death. Adequate study models of this virus are still lacking but are critically needed to understand its pathogenesis and virulence spectrum. The chicken embryo is a low-cost, easy-to-manipulate and ethically acceptable model that closely reflects mammalian fetal development and allows immune response investigations, drug screening, and high-throughput virus production for vaccine development. While former studies suggested that this model was refractory to USUV infection, we unexpectedly found that high doses of four phylogenetically distinct USUV strains caused embryonic lethality. By employing immunohistochemistry and quantitative reverse transcriptase-polymerase chain reaction, we demonstrated that USUV was widely distributed in embryonic tissues, including the brain, retina, and feather follicles. We then successfully developed a primary cell line from the chorioallantoic membrane that was permissive to the virus without the need for viral adaptation. We believe the future use of these models would foster a significant understanding of USUV-induced neuropathogenesis and immune response and allow the future development of drugs and vaccines against USUV.
Highlights
Usutu virus (USUV) is a zoonotic arbovirus related to Japanese encephalitis (JEV) and West Nile (WNV) viruses [1]
We showed that all four USUV strains injected at high doses in the Embryonated chicken eggs (ECE) via the allantoic route successfully replicated in the AF and caused deaths to chicken embryos
This report is the first to use ECE and chicken embryo-derived cells as artificial models to study the histopathological lesions and virus tropism involved in the pathogenesis of USUV
Summary
Usutu virus (USUV) is a zoonotic arbovirus related to Japanese encephalitis (JEV) and West Nile (WNV) viruses (genus Flavivirus, family Flaviviridae) [1]. Its rapid geographic spread across Europe led to a noteworthy recrudescence of infections in birds, recorded in over 96 species from 36 families [4,5,6], as well as substantial avian mortalities, especially in Eurasian blackbirds (Turdus merula) [7,8]. As for WNV, most human USUV infections are asymptomatic. More than 80 cases of subclinical infections were described in blood donors or persons with risk of exposure in Italy, Serbia, the Netherlands, and Germany during WNV surveillance surveys, until now [9,10,11,12,13].
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