Usutu virus in blackbirds (Turdus merula) with clinical signs, a case study from northern Italy

Abstract

Usutu virus (USUV) is a mosquito-borne virus belonging to the family Flaviviridae, genus Flavivirus. Natural transmission cycle of USUV involves mosquitoes and birds, so humans and other mammals are considered incidental hosts. In this study, USUV infection was diagnosed in all wild blackbirds, collected from July to September 2018 in a wildlife recovery center in the province of Bologna, in the Emilia-Romagna region, northern Italy. All blackbirds showed neurological clinical signs, such as overturning, pedaling, and incoordination. Moreover, the subjects died shortly after arriving at the hospitalization center. Virological investigations were performed by real-time PCR on frozen samples of the spleen, kidney, myocardium, and brain for the detection of Usutu (USUV) and West Nile (WNV) viruses. The small and large intestine were used as a matrix for the detection of Newcastle disease virus (NDV). All 56 subjects with neurological clinical signs were positive for USUV, only one subject (1.8%) tested positive for WNV, and no subject was positive for NDV. The most represented age class was class 1 J (58.9%), followed by class 3 (25.0%), and lastly from class 4 (16.1%). Most of the blackbirds before dying were in good (51.8%) and fair (39.3%) nutritional status, while only five subjects (8.9%) were cachectic. The USUV genomes detected in the blackbirds of this study fall within the sub-clade already called EU2 that has been detected since 2009 in the Emilia-Romagna region. Neurological clinical signs in USUV-affected blackbirds are still widely discussed and there are few works in the literature. Although our results require further studies, we believe them to be useful for understanding the clinical signs of Usutu virus in blackbirds, helping to increase the knowledge of this zoonotic agent in wild species and to understand its effect on the ecosystem. The goal of this study was to report—in the context of the regional passive surveillance program—the detection of USUV RNA in its most important amplifying host, the common blackbird, when showing clinical signs before death.

Combining host and vector data informs emergence and potential impact of an Usutu virus outbreak in UK wild birds

“…Based on the experience of wild bird mortality caused by USUV in mainland Europe (e.g. 4 , 9 , 10 ), the syndromic surveillance categories generalised ill health and neurological disease were considered of particular interest as a potential signal of infection. However, USUV could not be excluded as a possible underlying cause for DIRs categorised as musculoskeletal disease, trauma, predation, drowning or tick parasitism, or where blackbirds were found dead with no observed clinical signs.…”

Detection of West Nile and Usutu Virus RNA in Autumn Season in Wild Avian Hosts in Northern Italy

“…Assessing the causes of death of wild birds has been shown to be a useful practice to detect virus circulation [ 9 ] and should be maintained and encouraged also in the autumn–winter period, due to the importance of the health surveillance of these potentially zoonotic viruses. Most of the subjects had collision trauma but we cannot establish whether this was a consequence of the Flavivirus infection or a coincidental finding.…”

“…Most of the subjects had collision trauma but we cannot establish whether this was a consequence of the Flavivirus infection or a coincidental finding. By undermining the functionality of the neural system, Flavivirus might increase the risk of bird collisions with the surrounding environment and anthropogenic elements (e.g., buildings and cars) [ 9 ]. Most of the positive subjects were in a good nutritional state (7/9-77.8%), which could suggest asymptomatic positivity or acute virosis.…”

Serological Survey of Mosquito-Borne Arboviruses in Wild Birds from Important Migratory Hotspots in Romania

“…Previous studies suggested a possible sentinel role of the common blackbird in outbreaks of USUV infections, as the virus introduction in Europe was associated with increased mortality in this bird species in all the countries where outbreaks were recorded [7,30,34,35]. A possible explanation could be the weaker immune system of this species [36].…”