Identification of trypanosomes in animals, humans and Glossina.

A number of biochemical methods are now available for the identification of African trypanosomes. The method of choice depends on the number of trypanosomes present in the sample and the taxonomic level required. DNA probes based on repetitive DNA elements allow identification to subgeneric (e.g. Trypanozoon), species (e.g. Trypanosoma congolense, T. simiae) or subspecific (e.g. T. congolense savannah) levels. These probes are particularly useful for identification of trypanosomes in the fly midgut, where sufficient numbers are present to allow simple dot blot hybridization to be used (> 100). Greater sensitivity has been achieved by amplification of these repetitive DNA sequences by PCR (polymerase chain reaction), so enabling the small numbers of trypanosomes found in the fly mouthparts to be identified (> 1). At the subspecific level, isoenzyme analysis and latterly RFLP (restriction fragment length polymorphism) analysis have been widely used to characterize isolates within the T. brucei species. Two other techniques, karyotype analysis and RAPD analysis, are also useful for fingerprinting isolates. Molecular karyotypes are produced by size fractionation of chromosomal DNAs by PFGE (pulsed field gel electrophoresis). RAPD (random amplified polymorphic DNA) is a PCR-based technique, using arbitrary primers to generate a fingerprint consisting of 20 or so bands.