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Italy - Clinical and virological findings in patients with Usutu virus infection, northern Italy, 2018 - Eurosurveillance

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  • Italy - Clinical and virological findings in patients with Usutu virus infection, northern Italy, 2018 - Eurosurveillance

    nov 21 2019

    Seroprevalence studies in Italy indicate that the prevalence of antibodies against USUV in humans is higher than anti-WNV antibodies in areas where both viruses co-circulate [5-8], supporting the speculation that most human USUV infections are asymptomatic.

    Several cases of asymptomatic USUV infection were accidently identified when blood donors were screened with WNV nucleic acid amplification tests (NAT) that cross-react with other flaviviruses [9-14].

    Symptomatic USUV infections in humans are uncommon; only 20 cases have been described in the literature so far including: (i) two cases with fever from Africa [15], (ii) one blood donor with a rash from Austria [14], (iii) 13 cases with neuroinvasive disease from Italy [6,16,17], (iv) three cases presenting as meningoencephalitis, encephalitis and polyneuritis from Croatia [18], and (v) one case with facial paralysis from France [19].

    In Italy, USUV infection is a notifiable disease and USUV surveillance has been included in the national plan since 2017 [20].

    To improve knowledge on USUV disease in humans, we describe clinical and virological findings and the results of follow-up investigation of eight symptomatic USUV infection cases identified in the Veneto Region of northern Italy during the 2018 transmission season.

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    Background Usutu virus (USUV) is a mosquito-borne flavivirus, which shares its transmission cycle with the phylogenetically related West Nile virus (WNV). USUV circulates in several European countries and its activity has increased over the last 5 years. Aim To describe human cases of USUV infection identified by surveillance for WNV and USUV infection in the Veneto Region of northern Italy in 2018. Methods From 1 June to 30 November 2018, all cases of suspected autochthonous arbovirus infection and blood donors who had a reactive WNV nucleic acid test were investigated for both WNV and USUV infection by in-house molecular methods. Anti-WNV and anti-USUV IgM and IgG antibodies were detected by ELISA and in-house immunofluorescence assay, respectively; positive serum samples were further tested by WNV and USUV neutralisation assays run in parallel. Results Eight cases of USUV infection (one with neuroinvasive disease, six with fever and one viraemic blood donor who developed arthralgia and myalgia) and 427 cases of WNV infection were identified. A remarkable finding of this study was the persistence of USUV RNA in the blood and urine of three patients during follow-up. USUV genome sequences from two patients shared over 99% nt identity with USUV sequences detected in mosquito pools from the same area and clustered within lineage Europe 2. Conclusions Clinical presentation and laboratory findings in patients with USUV infection were similar to those found in patients with WNV infection. Cross-reactivity of serology and molecular tests challenged the differential diagnosis.
    “Addressing chronic disease is an issue of human rights – that must be our call to arms"
    Richard Horton, Editor-in-Chief The Lancet

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