Bovine papillomavirus type-4 (BPV-4) is responsible for the development of papillomas in the upper digestive tract (UDT) of cattle. The necessary steps for the development, growth and regression of papillomas are intimately related with the immunological status of the animal. The consumption of bracken fern (Pteridium aquilinum) has been pointed out as the major factor involved in the persistence of BPV-4 infection of the UDT. The theory involving the relationship between alimentary papillomas and the formation of squamous cell carcinomas (SCCs) suggests the persistence of alimentary papillomatosis through a chronic immunosupressive lymphopenic state induced by bracken fern. The papillomas would serve then as a development site of SCCs through the interaction of BPV-4 oncoproteins and bracken carcinogens. The objective of this study was to evaluate the relationship between lymphopenia and alimentary papillomatosis in spontaneous cases of chronic bracken fern poisoning of cattle. The age, intensity of papillomatosis and the leukon were evaluated of 40 cattle with SCCs of the UDT. Three animals had leukopenia and one had neutrophilia. The mean lymphocyte count (and standart deviation) of mild, moderate and severe papillomatosis was 5,395(±1,696)/mm³, 4,560(±1,561)/mm³ and 5,007(±1,786)/mm³, respectively. There were no statistically significant differences between the intensity of alimentary papillomasis, age and the lymphocyte count. Immunosupression by lymphopenia was a sporadic finding (three cases) in the present study. The results demonstrate that the persistence of alimentary papilomatosis in spontaneous cases of bracken fern-related SCCs of the UDT is not related to lymphopenia and it may be related to other immunological factors.
Poisonous plant; Pteridium aquilinum; papillomatosis; bovine papillomavirus type 4; plant poisoning; diseases of cattle
