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Entomological studies to control Bluetongue disease (BTD), WG 1
Project
Project code: 2806HS046
Contract period: 15.03.2007
- 30.06.2008
Budget: 94,250 Euro
Purpose of research: Applied research
In August 2006 BTD was introduced from Belgium and / or the Netherlands to Western Germany from where it spread within 1 year to most other regions of Germany. The Friedrich-Löffler-Institute (FLI) recognized that the virus belonged to the serotype 8, one of other 20 occurring in South Africa. The permanent catching of midges during the year 2006 of the group of the Düsseldorf University and the PCR-analysis of these insects at the FLI on the island Riems resulted in the finding that the very tiny species Culicoides obsoletus (0.8 mm in length) is the vector of the imported Bluetongue virus (Conraths et al. 2007, Mehlhorn et al. 2007).
As reaction of the intense spreading of the virus all over Germany the BMLEV Bonn (Dr. Bätza) established a monitoring program asking a group of experts (organized by Prof. Dr. Mehlhorn, Düsseldorf) to catch midges by UV-light traps at 90 farms all over Germany.
Traps and weather stations were placed close to stables of selected farms each being situated in regions of 45 square km. This program started in March 2007 and ran until June 2008. The UV-traps were activated during the nights of the 1rst until 8th day of every month and resulted in the catch of large amounts of ethanol preserved insects. The catch was send monthly to the different institutes at Düsseldorf, Bochum, Oldenburg, Großburgwedel, Gießen, Regensburg and Berlin. There the multiheaded research groups selected the midges from the other insects and determined the species according to their wing characteristics. The diagnosed Culicoides species were sorted into groups of males and females. Furthermore the latter became differentiated according to their feeding status (fed, unfed) and were finally sent within in fresh ethanol to the FLI at Riems for PCR- increase of virus-RNA. This very intensive cooperation resulted in the following findings:
1. There was no climate change - based migration of African or South European known vectors of BTD (such as Culicoides imicola). In all cases the two endemic species Culicoides obsoletus (70-90% of the catches) and C. pulicaris (10-20% of the catches) were predominant, as had been shown already by Mehlhorn et al. (2007) for the year 2006.
2. The PCR-studies at the FLI showed that predominantly C. obsoletus pools (50 specimens were investigated together) turned out to be viruspositive. However, viruspositive pools were also found among the caught C. pulicaris specimens. Catches of C. dewulfi were very scarce and thus no positive pool was detected.
3. Viruspositive pools of midges occurred only in catches beginning in August 2007 and lasted until end of November with clear peaks in September and October. In 2008 no positive pool was detected in the catches of January until Mai.
4. Clinical symptoms in infected ruminants occurred mostly 1.5-2 months earlier than viruspositive midges in the test. Thus it was proven that the monitoring of insects is not a helpful means to predict outbreaks of BTD.
5. The catches of midges indicated that these bloodsuckers breed close by or even inside the stables or may stay for long inside the stable, respectively. Therefore there was no midge-free period recorded indicating that the adult females may become infected even during winter time at indoor-blood meals on infected ruminants. This finding is epidemiologically important, since it supports the scenario of the survival of the virus in an endemic region.
6. The recording of the occurrence and large amounts of midges in the period of August-October and the finding that the temperatures during January until Mai 2008 were up to 4°C colder than during the same months in 2007 showed that in cooler years BTD will start later and probably at a low level, when less vectors are available. Thus BTD will occur probably in yearly waves with different amplitudes.
7. The vaccination (having started in Mai 2008) and the use of insecticides will limit the propagation of BTV but will not lead to its extinction in Germany since wild ruminants turned out to be infected, too.
Conclusions:
This worldwide unique monitoring project, when considering length and intensity, reached all goals intended and was able to illuminate the background of the ongoing BTV-epidemic in Germany. Of course it could not be determined, how the virus came to Europe, but the whole scenario made it clear that in times of globalization similar outbreaks of diseases must be (daily) expected since all vectors needed are already present and must not be imported.
Section overview
Subjects
- Animal health
