In 2006 and 2007, sheep and cattle farms in the Netherlands were hit by an epidemic of bluetongue virus serotype 8 (BTV-8). To gain insight into the rate of virus spread within the animal herds, Wageningen Bioveterinary Research examined five affected dairy farms and five affected sheep farms. The researchers published their findings in the scientific journal PLOS ONE.
How is BTV transmitted?
Bluetongue virus is transmitted between farm animals by midges, small blood-sucking insects, which transfer the virus as a vector by taking a blood meal from these host animals.
Research on the farms
Each farm was visited several times between the beginning of 2007 and the end of 2008. Each time blood samples were taken from all animals present for testing for the presence of virus (DNA) and antibodies. The observed patterns in the number of positives indicate a rapid spread of the virus within the herds during the vector season. During vector-free periods, a complete decrease in virus positivity was found to occur within months.
In this study, an estimate of the baseline reproduction number (R0) during the vector season ranges from 2.9 - 6.9 in the cattle farms (one herd not analyzed) and from 1.3 - 3.2 in the sheep flocks. Such information is, among other things, important for assessing the impact of control measures such as vaccination and limiting animal movements via transport.