Fluorescent antibody test (FAT)
The FAT is a very useful technique for demonstrating leptospires in tissues from animals (including foetuses) which have died of leptospirosis (Cook et al., 1972; Kirkbride and Halley, 1982). Studies of Smith et al. (1966) showed that the FAT was superior to culture and histopathological methods in demonstrating the presence of leptospires in autolysed materials. In another study, Smith et al. (1967) reported that in fresh material homogenates with live leptospires the supernatant fluid contained more organisms, whereas in autolysed materials with dead organisms, the sediment was more likely to be positive.
Fluorescent staining of antibody in urine or cultures is a fast and accurate diagnostic method for detecting the presence of leptospirae and for identifying serotypes (Hodges and Ekdahl, 1973). Antibodies also appear in urine and milk and their measurement may have some significance in special circumstances. This test may be used with fresh or frozen tissues and urine and aids in the discrimination of leptospires from artefacts (Bolin et al., 1989c).
The FA-positive, culture-negative cases are usually the result of the overgrowth of cultures by contaminating microorganisms (Ellis et al., 1982c). In a recent study conducted by Miller et al. (1991b), it was concluded that the FA test utilising multivalent conjugates could be used successfully as an additional method for the diagnosis of leptospirosis (Miller et al., 1989).