The potential use of corticosteroid hormones in rodent biocontrol

Abstract

The feasibility of immunosuppression by corticosteroid hormones for the biocontrol of vertebrate pests was studied using water-soluble derivatives of prednisolone and dexamethasone administered by intubation to the levant vole (Microtus guentheri). Effect of treatment was determined through changes in body weight, histological changes in the spleen and bone marrow, and total and differential counts of white blood cells. Dexamethasone had a more drastic effect than prednisolone. In a group treated daily with 100 mg dexamethasone/kg body weight, signs of illness appeared in about 40% of the voles and death occurred in 18% of them 6–7 days after the start of the treatment. There was a loss of up to 22% in body weight, marked atrophy of the germinal center, corona and perifollicular zone of the splenic lymph nodules, but no effect on the bone marrow constitution. A similar treatment with prednisolone produced no external signs of illness or change in body weight, yet 17% of the voles died 8–10 days after the start of the treatment, and partial atrophy in the splenic lymph nodules occurred in 50% of the animals. In a group treated with 100 mg dexamethasone/kg once every 3 days, from which blood samples were taken repeatedly from the same eye, mortality was 100%, with death occurring 3–12 days after start of the treatment. Differential white blood cell counts indicated depletion of lymphocytes and monocytes, and increase in the number of granulocytes in the peripheral blood. Results of preference tests showed that prebaited voles do not reject wheat grain baits treated with a dexamethasone solution in water.