Table 1 Risk factors for the introduction of IBR and EBL into Swiss cattle farms

Animal contacts ( AC )

All farms which send their cattle, or part of it, to summer pastures (inside the country or across the border) and/or let their bovines participate in cattle shows

Physical contacts with potentially infected bovines from other farms

Higher-than-average animal movements on farm ( AM )

All farms having more cattle entries on farm per year than the yearly median value for their herd size category

Farms which purchase many bovines from outside have a higher risk of getting an IBR-positive animal into their herd than farms which do not purchase any cattle

Farm close to the border with another country ( FcB )

All cattle farms situated up to 5 km from the Swiss border and 500 m at most from a larger road (in this zone)

Uncontrolled contacts between potentially infected animals; airborne transmission of pathogens; veterinarians from neighbouring countries treating cattle (having contact with potentially IBR-infected animals); facilitated illegal importation of bovines

High density of cattle farms in the vicinity ( hDH )

All farms that have many (in our case >21) neighbouring farms within a radius of 1 km around their farm

Uncontrolled contacts between animals (over fences), or between animals and persons (neighbouring families, visitors...)

Importation of cattle ( IC )

All farms having imported cattle in their herds

Even though cattle destined for importation must originate from IBR-free herds, or, in the case of non-IBR-free countries, have to be tested for IBR, an introduction of the disease through cattle importation can never be excluded

Higher-than-average animal movements on farm ( AM )

All farms that have more cattle entries on farm per year than the yearly median value for their herd size category

Farms which purchase many bovines from outside, have a higher risk of getting an EBL-positive animal in their herd than farms which do not purchase any cattle

Importation of cattle ( IC )

All farms having imported cattle in their herds

Even though cattle destined for importation must originate from EBL-free herds, or, in the case of non-EBL-free countries, have to be tested for EBL, an introduction of the disease through cattle importation can never be excluded

Summer pasture with animals from other herds ( SP )

All farms which send their cattle, or part of it, on summer pastures (inside the country or across the border)

This risk factor implicates lengthy physical contacts between animals from different herds and therefore makes a transmission of EBL from one bovine to another possible; cattle are exposed to biting and stinging insects in the summer season (→ transmission of infected lymphocytes)