Usutu Virus Infections Found among Austrian Blood Donors

Usutu virus (USUV) is an African mosquito-borne flavivirus belonging to the Japanese encephalitis virus serocomplex. USUV is closely related to Murray Valley encephalitis virus, Japanese encephalitis virus, and West Nile virus (WNV).

Besides wild birds, humans can also be infected with Usutu virus through mosquito bites. Usually human Usutu virus infections are asymptomatic though occasionally they may result in fever and rash. Neurologic symptoms and severe courses of the disease are rare in humans, although critical illness was reported in immunosuppressed patients.


European scientists led by those at the University of Veterinary Medicine (Vienna, Austria) collected samples of all blood donations collected from June 1, 2017 onwards by the Blood Service for Austrian Red Cross during the ongoing WNV transmission season 2017 and were sent to the German Red Cross, Blood Service for Baden-Württemberg-Hessen. In Germany they were screened in minipools of 19 samples using the automated nucleic acid (NAT) test on the cobas 8800 system.

The investigators reported that as of October 11, 2017, a total of seven of 12,047 blood donations collected between July 24 and August 25, 2017, reacted positive. WNV NAT-screening positive samples were retested by WNV- and Usutu virus (USUV)-specific reverse transcription (RT) - and quantitative reverse transcription polymerase chain (RT-qPCR) assays as well as by conventional RT-PCR tests amplifying a wide range of flaviviruses. While one blood donation was confirmed as containing WNV nucleic acid, the six others were negative by WNV-specific RT-qPCR, but positive by USUV-specific RT-qPCR.

The authors concluded that although USUV is a potential human pathogen, there are no specific regulations on screening blood donations for this virus. According to the general rules, only clinically healthy people are allowed to donate blood. However, the USUV-positive blood donors did not show any symptoms before and after donation. They propose that extension of flavivirus screening of blood donations might be taken into consideration by USUV-endemic European countries.

In order to raise awareness and allow timely actions, they intentionally wrote this paper at this point in time when the WNV and USUV transmission seasons are still ongoing, which, depending on weather conditions, may last in central Europe until the end of October. The study was published in the October 2017 edition of the journal Eurosurveillance.

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