Schmallenberg virus outbreak in the Netherlands: routine diagnostics and test results

Area of Science:

• Veterinary Virology
• Epidemiology
• Animal Health

Background:

• Schmallenberg virus (SBV), an Orthobunyavirus, emerged in Germany in late 2011.
• Notifiable malformations in newborn ruminants were reported in the Netherlands from December 2011.
• Diagnostic investigations were initiated following these notifications.

Purpose of the Study:

• To summarize and evaluate diagnostic data related to SBV.
• To assess potential regional differences in SBV prevalence and impact.
• To gain insights into the epidemiology of SBV in affected livestock.

Main Methods:

• Necropsy of malformed newborns and brain tissue sampling for reverse transcription-polymerase chain reaction (RT-PCR).
• Serological testing of maternal blood samples using virus neutralization test (VNT) for antibodies.
• Analysis of 2166 brain samples and 1394 blood samples from lambs, calves, and goat kids/ewes, cows, and goats.

Main Results:

• RT-PCR positive rates were 29% for lambs, 14% for calves, and 9% for goat kids.
• Temporal trends showed decreasing RT-PCR positive malformed lambs and increasing calves.
• VNT positive rates were 92% for ewes, 96% for cows, and 43% for goats; 18% of farms tested positive by both methods.

Conclusions:

• Diagnostic data indicate widespread SBV exposure in Dutch livestock.
• RT-PCR sensitivity was 19% and specificity 97%; VNT sensitivity was 99% and specificity 6%.
• Regional analysis suggests SBV introduction into the central/eastern part of the Netherlands.