Transmission

The virus can be transmitted in the uterus so that the calf is born congenitally infected. The virus can also be transmitted to young calves via milk.

Infection can be spread by contact, although the mechanism is not fully understood. Calves and sheep have been experimentally infected via the oral route.  Ear-tagging or immunising needles are another means of mechanical spread.

The virus can be spread mechanically by inoculation with shared needles during routine vaccination or treatment and not disinfecting dehorning equipment between animals. The virus has also been spread by the inoculation of infected blood products during vaccination against babesiosis. The possibility of mechanical transfer during pregnancy testing is still being debated.