**3. Epidemiology**

Lice spend their whole life on the same hosts: transmission from one host to another one is by contact. Transmission from herd to herd is usually through introduction of an infested animal, but flies or fomites may also occasionally transport lice. Up to 1–2% of the cattle in a herd can carry a high load of lice, even in the summer when high temperatures reduce the number of lice. These carrier animals are the source of reinfestation during the fall. Usually, they are a bull or a cow in poor body condition [8]. Winter housing provides the ideal conditions for the transfer of lice between cattle.
