Culicoides fauna and bluetongue virus serotype 8 infection in South American camelid herds in Germany
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Bluetongue (BT) is a Culicoides-born infectious disease caused by bluetongue virus (BTV). From 2006 to 2010, BTV serotype 8 (BTV-8) spread throughout Europe, causing severe disease in domestic and some wild ruminant species and in an alpaca. Compulsory vaccination of susceptible animals was the most effective strategy to control and eradicate the BTV-8 epizootic in Europe. However, South American camelids (SAC) were not included in the BTV-8 vaccination programmes in Europe. The presented work elucidates the potential role of SAC in the epidemiology of BTV as reservoirs and risk for the ruminant population as well as the outcome of BTV-8 vaccination in SAC. The investigation of BTV-8 vectors, pathogenesis, epizootiology, diagnosis and immunoprophylaxis in SAC herds comprised four approaches: The entomological monitoring on SAC farms in Germany from 2008 to 2009 revealed a significantly high abundance of Culicoides belonging to the C. obsoletus and C. pulicaris complexes potential vectors of BTV. At the same time, a high seroprevalence was found in BTV-8 exposed SAC herds in Germany. However, no BTV RNA was detected in the analysed Culicoides midges and SAC blood although the BTV-8 epizootic was still going on. The unexpected virological results of these two studies prompted the investigation of BTV pathogenesis in SAC. Experimental infection of SAC with BTV-8 revealed considerable differences in their pathogenesis compared to ruminants. SAC displayed only very mild, unspecific clinical signs. BTV genome load was significantly lower than in bovine blood, was only transiently detected in SAC blood and rapidly declined after seroconversion. This matched the results of the blood-cell binding experiment, which demonstrated that significantly lower amounts of BTV-8 adsorbed to SAC blood cells compared to bovine blood cells. Therefore, whole blood, serum or plasma should be used for BTV diagnosis in SAC, but not blood cell pellets. Within the scope of this work, available serological and virological test systems were validated for BTV diagnosis in SAC. The crucial outcome of these three studies was the virological results indicating that SAC obviously play a negligible role in the epidemiology of this virus infection. Furthermore, BT is apparently not an important disease of SAC although fatalities may sporadically occur. The vaccination study demonstrated for the first time that SAC vaccinated twice with any one of the three inactivated BLUEVAC®-8, BTVPUR® AlSap 8 and Zulvac® 8 Bovis vaccines remain BTV-seropositive for over one year. However, seroconversion was only found in 79% of SAC vaccinated with a single dose. Furthermore, this is the first study demonstrating that colostral BTV-8 antibodies occur in crias from vaccinated dams for 2 to 7 months after birth. Good tolerance of the studied vaccines was reported retrospectively by SAC owners. This work provides vaccination recommendations to initiate an appropriate BTV-8 antibody response in SAC. The new insights obtained by the presented work provide an important basis for further research on particularities of BTV infection in SAC and on their protective immunity after BTV-vaccination. Additionally, these results will facilitate risk assessment and the design of policies for the control of BT in SAC herds in case of a BTV outbreak in the future.Verknüpfung zu Publikationen oder weiteren Datensätzen
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