Screening of captive lions (Panthera leo) for selected infectious diseases of significance in Zimbabwe

Abstract

Fifteen lions from three captive/semi-captive establishments around Harare were captured for blood sampling. Routine health checks for viral diseases and other diseases of economic, public health or biodiversity conservation importance had never been done at the time the study was carried out. The serum samples were screened against feline immunodeficiency virus, feline leukaemia virus and canine distemper virus. All samples tested negative. This screening exercise was important in order to reduce the confounding effect of these infections on tests that utilise cell-mediated immune responses, such as the interferon-gamma (IFN-γ) assay for bovine tuberculosis (BTB) diagnosis. Whole blood processing using two antigens and three mitogens was carried out on samples collected in heparin tubes. Plasma was harvested at 24 hour and 48 hour intervals. A capture enzyme linked immunosorbent assay (ELISA) was performed on the samples towards validation of the lion specific IFN-γ assay for the diagnosis of BTB. The limit of detection (109 pg/ml) and limit of quantification (850 pg/ml) of the assay were determined. A comparison was made on the difference between two incubation periods and no significant difference was found. The best mitogen for use as a positive control was determined to be phorbol 12- myristate 13-acetate (PMA)/calcium ionophore (CaI) (at 0.1 μg/ml and 2 μg/ml respectively). The diagnostic cut off for negative lions was determined preliminarily to be ODbov 0.03. These preliminary results show the potential of this assay in the diagnosis of BTB as it shortens the testing turn-around time compared to the currently used intradermal tuberculin test.