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Published Date: 2012-05-11 09:39:14
Subject: PRO/AH/EDR> Schmallenberg virus - Europe (39): Belgium, epidemiology
Archive Number: 20120511.1129973

SCHMALLENBERG VIRUS - EUROPE (39): BELGIUM, EPIDEMIOLOGY
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Date: Thu 10 May 2012
From: Thierry van den Berg <thierry.vandenberg@coda-cerva.be> [edited]

Schmallenberg virus - Belgium: newborn calves rRT-PCR positive without clinical signs
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Since 7 Mar 2012, the Animal Health Center of Flanders (DGZ Vlaanderen) received 48 newborn calves (Holstein-Friesian and Belgian Blue) for postmortem examination. The calves were born at term between 1 Mar 2012 and 1 May 2012 without any external anatomical malformation and died within the 7 days after birth. No clinical manifestation indicative of an infection with Schmallenberg virus (SBV) or any pathognomonic clinical signs (diarrhea, pneumonia, …) were observed before death. While some of the calves showed general malaise, the others died without any clinical sign.

Among these 48 calves, 3 calves showed hydranencephaly at necropsy, while in 7 other calves, histopathological lesions in the central nervous system strongly suggestive for an infection with a teratogenic agent were observed. Brain tissues from the 48 calves were sent to the Belgian reference laboratory for animal disease (CODA-CERVA) for SBV diagnosis. SBV was detected in the brain tissues by rRT-PCR (FLI protocol, Germany) in 10 calves (= 20.41 percent). One out of the 3 calves with hydranencephaly and 3 out of the 7 calves with histopathological brain lesions were rRT-PCR positive for SBV. The 6 other rRT-PCR SBV positive calves showed neither macroscopic nor histopathological lesions indicative of SBV infection. Spleen tissues from all calves were also analysed for BVDv [bovine viral diarrhea virus] by antigen ELISA, and all samples were BVDv-negative.

It seems most probable that these rRT-PCR SBV positive calves that were viable at birth were infected by SBV in utero, but that this infection did not lead to any congenital malformations that have been described till now. However, at the moment, it cannot be excluded that these rRT-PCR SBV positive calves were infected after birth. This seems however unlikely considering the low vector activity between February and May 2012 in Belgium and the fact that no horizontal SBV transmission has been described so far.

The postmortem necropsies were funded by "Veepeiler Rund".

Animal Health Center of Flanders (DGZ Vlaanderen): Hans Van Loo, Jo Maris, Marieke Strubbe, and Koen De Bleecker
CODA-CERVA: Nick De Regge, Brigitte Cay, and Thierry van den Berg

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Dr Thievery van den Berg
Operational Director Viral Diseases
Veterinary and Agrochemical Research Centre (VAR)
B-1180 Brussels
Belgium
<thvan@var.fgov.be>

[The information above is a welcome additional contribution of the Belgian team to the scientific community studying the emerging SBV.

The report addresses 48 investigated neonate calves of 2 breeds born in Belgium during March-April 2012, which died during their 1st week without external anatomical malformations or distinct, clinically observable symptoms of disease except, in some cases, general weakness.

In 10 of the calves, CNS changes which may be attributed to a teratogenic pathogen, were demonstrated either by gross-pathology or by histopathology means (hence group A). No such or other changes were detected following similar examinations in the remaining 38 calves (hence group B). When the brains of all 48 calves were tested for the presence of SBV by rRT-PCR (the test currently applied in all 8 SBV-affected EU countries), 4 out of the 10 in group A and 6 out of the 38 calves in group B were found positive. While negative results in 6 apparently affected calves can be explained (such as, period of time since infection), explanation for the positive results in 6/38 (15.8 percent) of apparently unaffected calves is in need of explanation(s).

It will be interesting to note if positive tests in apparently unaffected calves have been observed in other SBV countries. A validated serological test, to be applied in offspring and in their mothers, and particularly enhanced studies into SBV epidemiology including the vector issue and its annual activity are anticipated to help in clarifying such findings.

A recent update on the epidemiology of SBV, presented during the 8 May 2012 meeting of SCFCAH (Standing Committee on the Food Chain and Animal Health) in Brussels, including graphical presentation of SBV temporal spread in the various susceptible species between the 51st week of 2011 and the 15th week of 2012 (19 Dec 2011-15 Apr 2012), is available at http://tinyurl.com/csx675c. - Mod.AS

A HealthMap/ProMED-mail map can be accessed at: http://healthmap.org/r/1zJs.]

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