Schmallenberg virus confirmed in midges - Vector identified

[Gert van der Hoek]

Belgium: SBV identified in culicoides

Date: Sat 10 Mar 2012

From: Thierry van den Berg [edited]


Belgium: Pools of Culicoides spp. found positive for Schmallenberg virus by RT-qPCR
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Since it was first identified in Germany in Nov 2011, Schmallenberg virus (SBV) has been confirmed in the Netherlands, Belgium, United Kingdom, France, Luxembourg, and Italy. Knowing that related viruses belonging to the same Simbu serogroup of Orthobunyaviruses are generally spread by midges and mosquitoes, it was assumed that these vectors could also spread SBV.

In Belgium, _Culicoides spp._ have been monitored since 2007 through a surveillance program financed by the Belgian Federal Agency for the Safety of the Food Chain (FAVV-AFSCA).

In order to examine the potential role of midges in the spread of SBV, pools of midges were analyzed at CODA-CERVA by RT-qPCR. Midges had been captured outdoors in September and October 2011 with an UV light trap at Betekom (Province of Vlaams Brabant, Belgium) by scientists of the Institute of Tropical Medicine (ITM, Antwerp). The pools consisted of 10 heads of culicoides each identified morphologically at species level. Although only 23 pools have been examined so far, SBV has been detected in 2 of them (by RT-qPCRs detecting S and L segments of SBV according to protocols provided by FLI, Germany). One pool consisted of _C. obsoletus s.s._ caught on 7 Sep 2011 (Ct=34.9 and 37.0 for S and L segment resp.) and another pool consisted of _C. Dewulfi_ caught on 4 Oct 2011 (Ct=38.1 for S and negative and L segments). These results strongly confirm the role of biting midges in the transmission and spread of SBV. This indication is strengthened by the fact that the examined pools consisted exclusively of heads, suggesting that midges act as real amplification vectors and were not simply SBV positive after a blood meal on viraemic animals.

More pools collected by the monitoring project will be tested to identify other possible SBV vectors among _Culicoides_ species and to shed light on the time of introduction of SBV in this and other regions. Pools of mosquitoes will also be tested to assess their potential role in the spread of SBV.

Coda-Cerva via ProMEDmail

 

[Gert van der Hoek]

Vector of Schmallenberg virus identified

Vector of Schmallenberg virus identified

Midges are really small. There is a reason why they are popularly called no-see-ums.
Here one is compared to a common mosquito.

Vector of Schmallenberg virus identified

16 Mar. 2012

Belgian scientists have found out how the infamous Schmallenberg virus is transmitted from animal to animal. The culprits are biting midges, the same that transmit bluetongue in Europe. This was proven in a joint effort by researchers from the Antwerp institute of Tropical Medicine (ITG) and the Belgian Veterinary and Agrochemical Research Centre (VAR).

The Schmallenberg virus showed up for the first time in November last year, in the idyllic German ski resort Schmallenberg. It causes grave congenital malformations and stillbirths in cattle, sheep and goats. Shortly thereafter, the new disease emerged in the Netherlands. In the mean time it has reached Belgium, Luxemburg, France, the UK, Italy and recently Spain. In Germany more than eight hundred livestock farms are hit.

Nobody knew how the virus was transmitted. But it was known that a related virus, Shamonda, was transmitted by midges. It emerged in the sixties in Nigeria, disappeared for thirty years, reappeared in the nineties in Japan to disappear again. The bluetongue virus, also hitting ruminants, is transmitted by midges as well.

So midges, Culicoides in scientific Latin, were logical suspects. Midges are minuscule insects, living in damp areas, where they can be a real nuisance to humans, attacking and biting in large swarms. There are many species of midges, and it takes a trained specialist to discriminate them under a microscope. That?s why the ITG scientists, who monitor for the Belgian authorities the distribution of midges as vectors of bluetongue, have developed a ?microarray?, a molecular technology that can be used by non-specialists to simply and accurately recognize midge species.

To map the distribution of midges, the scientists trapped them at several locations. This collection they now revisited to find out if it also contained the Schmallenberg virus. But it is not sufficient to demonstrate that a midge contains the virus. The virus might be accidentally present in ingested blood, without the midge being able to transmit it at the next bite. To achieve transmission, the virus has to leave the gut, travel to the salivary glands and wriggle its way into them.

Therefore the ITG scientists determined the species of each midge, decapitated them and gave only the heads to their colleagues at VAR, who had the molecular analytic technology to detect the virus. If they detected something, it should have come from the salivary glands.

In a few midges they had caught in September and October (so even before the disease emerged in Schmallenberg) they indeed found the Schmallenberg virus. The virus was demonstrated in Culicoides obsoletus, C. dewulfi and C. pulicaris, three of the five species that have been shown to transmit bluetongue and that are common in Belgium.

The scientists now work through the rest of their midge archive, in order to publish a well-documented article in a scientific journal. Of course they want to examine the new catch, but their commission to monitor midges ends in April, because in the meantime Belgium is bluetongue-free. They hope for an extension.

ITG

 

[Pathfinder]

Re: Schmallenberg virus confirmed in midges - Vector identified

East Anglia: Midge control recommended in battle against SBV

Thursday, April 12, 2012
10:07 AM

Independent parasitologist and entomologist Dr Peter Bates said midge control during breeding times and pregnancy was highly recommended, and there was a strong case for the use of anti-fly compounds in pregnant animals earlier in the year in order to reduce midge populations.
...
?Anti-midge products, containing synthetic pyrethroids (SPs), kill as well as repel so it is a good idea to treat the whole herd as this will reduce the midge population,? he said.

?For pregnant stock, I would recommend dosing in April and throughout pregnancy; this will help protect the foetus from the effects of SBV as well as help kill the midges that have emerged from overwintering larvae, so stopping them breeding to produce larger populations in the summer,? he added.

Thomas Tiley, a vet with Novartis Animal Health, said the use of a product such as Flypor, which contains the active permethrin, has shown in-vitro activity against midges and can be repeated at four week intervals in cattle.

?Because of the geographic spread and virus type, midges are the main suspect as the disease vector for Schmallenberg virus,? he said.
...
Full text:
http://www.eadt.co.uk/business/farm...l_recommended_in_battle_against_sbv_1_1346738