Introduction: Human and animal diseases caused by mosquito-borne viruses (moboviruses) are of growing importance in many countries of Europe including Germany. Continuing eco-climatic changes and globalization create suitable conditions for the emergence of moboviruses in Germany. Up to now, four different moboviruses have been found in Germany. In 1968, Tahyna virus (TAHV) was isolated from mosquitoes that were trapped around Baunach in Bavaria. TAHV is the causative agent of Valtice fever, an influenza-like illness occurring in summer and early autumn. Therefore, TAHV is the first human pathogenic mobovirus that was isolated from mosquitoes in Germany. Since these early discoveries in the late 60s of the last century, mobovirus surveillance in mosquitoes, humans and animals was not performed regularly and therefore, longitudinal data sets are missing, especially from Germany. Thus, we initiated a program that compiles and analyses mobovirus and vector data collected over a number of successive years. This provided a solid base to determine the underlying causes of the seasonal fluctuations in mobovirus activity and the relative abundance of the mosquito vector species. This information can be used as a basis for vector control programs and might provide an early warning of the presence of moboviruses in Germany.
Results: Since 2009, mobovirus surveillance was performed mostly in south-west Germany. So far, more than 150.000 mosquitoes were captured and assayed for the presence of moboviruses. In 2009, Sindbis virus (SINV) was isolated from Culex and Anopheles mosquitoes that were exclusively trapped in the city of Weinheim, south-west Germany. SINV is the causative agent of a febrile illness in humans associated with maculopapular rash and joint pain. Consequently, a study was initiated to investigate the medical importance of SINV in that area. Only four out of 3389 investigated blood donor samples were tested positive for SINV-specific-IgG antibodies and all samples from 355 patients with clinically suspected acute SINV infections were tested negative for SINV-specific antibodies or SINV RNA, thus demonstrating the low medical importance of SINV in south-west Germany. In 2009, Batai virus (BATV) was isolated from Anopheles maculipennis mosquitoes trapped around the village of Waghäusel. BATV may cause a mild illness among sheep and cattle. Thus, 195 serum samples from cattle’s around the village of Waghäusel were investigated for BATV-specific-IgG antibodies and two samples were tested positive, demonstrating past BATV infections. In 2010, Usutu virus (USUV) was isolated from Culex pipiens pipiens mosquitoes trapped in the city of Weinheim. Since June 2011, considerable mortality in wild and captive bird species was observed in south-west Germany. Consequently, 168 dead birds were tested for the presence of USUV and USUV RNA was detected in 80 individuals from 6 species. Therefore, the mortality of birds was shown to be associated with the emergence of USUV. In addition, in January 2012, 4,200 serum samples from healthy blood donors from south-west Germany were collected and analysed for USUV-specific antibodies. One IgG- and IgM-positive blood donor was confirmed to have been infected by USUV. The blood donor reported no history of vaccination and did not have a fever during a period of three months before the blood donation. In addition, he had not been abroad during this period. These findings, taken together with the serological results corroborate the hypothesis of a pauci- or asymptomatic and autochthonous USUV infection of the blood donor during late summer 2011.
Conclusion: The early discovery of USUV in mosquitoes followed by the recent epidemic proof the importance and predictive value of our mosquito based monitoring program for zoonotic moboviruses. Moreover, public health authorities, blood transfusion services and clinicians in Germany should be aware of the risk of USUV infection in humans, especially during late summer.
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