Search

West Nile virus (WNV) and Usutu virus (USUV) are mosquito-borne flaviviruses that have been associated with neurological diseases in humans and wild birds. Wild bird rescue centers are potential significant hot spots for avian infection surveillance, as recognized in the Italian Integrate National Surveillance Plan for Arboviruses. Here we report the results of a post-mortem active monitoring study conducted from November 2017 to October 2020 on animals hosted in five wild bird rescue centers of Central Italy. Five hundred seventy-six (n = 576) wild birds were tested by real-time polymerase chain reaction (RT-PCR) for the presence of WNV or USUV RNA fragments. No birds tested positive for USUV RNA (n = 0; 0.00%). Evidence of WNV RNA (Ct value = 34.36) was found in one bird (n = 1; 0.17%), an adult little grebe (Tachybaptus ruficollis subsp. ruficollis), that tested WNV positive in December 2019. This study highlights the strategic role of wildlife rescue centers in monitoring both the introduction and circulation of avian emerging zoonotic diseases. In addition, the presence of WNV during the cold season evidences the possible role of birds in overwintering mechanisms in the Italian territory and requires further investigations.

Introduction: Usutu virus (USUV) is an emerging mosquito-borne flavivirus. USUV-related outbreaks of disease and mortality in wild birds, as well as neuroinvasive disease in humans have raised a health concern in Europe. Although a few pathologic studies describe the morphologic features of USUV-associated encephalitis in naturally infected wild birds, data regarding the immune response in situ are still lacking. This study aims to characterize the immune-cell populations in Usutu virus-associated encephalitis, comparing uninfected birds with birds infected with two circulating virus lineages. Materials and Methods: Immunohistochemistry was performed with specific antibodies for CD3 (T cells), PAX5 (early B cells) and MUM1 (late B cells and plasma cells) on brain tissue. Cell count was performed, and results were compared between uninfected birds (n = 4) and birds infected with Europe-3 (n = 4) and Africa-3 (n = 4) USUV-lineage. Results: The numbers of T cells and early and late B cells were higher in USUV-infected birds compared with uninfected birds, the majority being CD3+ cells. The PAX5+ cell count was higher, to a small degree, in Africa-3 compared with Europe-3-infected birds. Conclusions: This study reveals a major T cell and a minor B cell involvement in the immunopathology of Usutu virus-associated encephalitis. A slightly higher number of B cells in Africa-3-infected birds suggests a possible difference in the host response to these two lineages. Further and larger scale studies are needed to characterize the T cell population.