**5. Clinical conditions in cattle**

Infections by different BPV types are related to several clinical conditions in cattle. The occurrence of the benign skin tumors that characterize cutaneous papillomatosis might be found in several areas of the animals' bodies. Depending on the extent of lesions, the devel‐ opment of the animals might be affected, they might become predisposed to secondary infections and/or infestations, and their hidescan be damaged. These possibilities are a few of the potential consequences that might result in economic losses for the beef and, even more so, dairy industries. Papillomas affecting the udders and teats of lactating cows cause diffi‐ culties with feeding calves and manual and mechanical milking, whereas secondary bacterial infections predispose the animals to clinical and/or subclinical ascending mastitis [30].

The interaction between specific BPV types and prolonged bracken (*Pteridium aquilinum*) intake has been suggested as the cause of enzootic hematuria and upper gastrointestinal tract cancers in cattle. With regard to enzootic hematuria, it is believed that latent or subclinical infections with BPV1 or BPV2 occur first in the bladder mucosa. Because the bladder represents the main target of bracken toxins, once the virus is established, infection might be reactivated, which might induce neoplasia through the immunosuppressant and carcinogenic chemical compounds present in bracken, which results in progression to malignancy [31].

Although the incidence of such tumors varies among cattle raised on bracken-infested pastures, it might be higher than 90% among adult animals [31,32].

With regard to gastrointestinal tract tumors, the immunosuppression associated with bracken intake is defining for the persistence of BPV4-induced papillomas, which might progress into malignant carcinomas under the influence of the carcinogenic elements present in bracken [33,34,35].

Therefore, although infection by these BPVs plays a central role in the pathogenesis of these cattle neoplasias, the presence of environmental and biological cofactors is essential for the development of such lesions [22,36].
