Research from the Friedrich-Loeffler-Institute in Germany is pointing to additional biosecurity measures as a means of better controlling bovine viral diarrhea.
BVD, also a disease that affects U.S. cattle, leads to severe disease and significant economic losse. Caused by the Bovine Viral Diarrhea Virus, BVD suppresses the immune system and causes a variety of symptoms, including respiratory problems, infertility, and abortion.
Because of its economic impact, Germany has attempted to eradicate the disease. But in 2012 a highly virulent type of BVD virus was introduced into a cattle farm in Germany and transmitted to other farms.
"A dairy farmer first noticed a reduction in milk yield, respiratory symptoms, nasal discharge, fever, sporadic diarrhea and sudden deaths -- these symptoms were also noted on other farms as the infection spread, but did not immediately indicate BVD as the cause," said Dr. Jörn Gethmann, lead author of the study.
"We were surprised by the high morbidity and mortality an induced by a BVDV strain in this outbreak," he said.
The researchers supported the competent local authorities in tracing the spread of the virus. They visited eight farms and obtained data on a further 13 farms. They discovered that the virus was not transmitted directly by infected cattle, but mostly by people such as vets and traders who were moving between farms.
"We were surprised to see the effective transmission to other farms without persistently infected animals involved," Gethmann said.
Lab analyses revealed the source of the outbreak was a BVD type 2c virus that has a particular addition to its genome. The virus appears to be associated with more severe symptoms than BVD; the fatality rate was up to 60% and between 2.3% and 29.5% of the cattle on each farm died during the outbreak.
Once the cause was identified, swift measures were taken to control the outbreak. Veterinary authorities imposed trade restrictions on affected farms. People who had been in contact with infected cattle were generally advised to increase biosecurity measures, for example by wearing disposable clothing.
While effective at controlling the disease, researchers say it is important to revisit biosecurity programs regularly and adapt them to the changing situation as new virulent strains appear.
"The results of our study may help to revise existing BVD control regulations and increase biosecurity in cattle farms, in particular by reducing the risk of disease transmission through person contacts and trade," Gethmann said.
"We also hope our study will inform farmers about the risks of the introduction of new BVD types into their farms."