Methods of detection of Parasites

METHODS OF DETECTION

It is not always easy or possible to culture parasites, so the detection of these organisms in samples requires the use of methods such as microscopy and DNA amplification. The most commonly used method involves microscopy and this can be applied to clinical as well as environmental samples. For some organisms this approach remains the ‘gold standard’ for detection and identification. The advantages of microscopy are speed, cost and availability. In addition, fluorescent labelled antibodies raised to species-specific antigens can be utilized to help identify organisms to species or subspecies level, and other stains can be used to help determine the viability of cells. Examples of such stains include fluorescein diacetate which is cleaved by esterases in viable cells, releasing fluorescein (gives a green fluorescence) and propidium iodide which is excluded from viable cells but taken up by cells with damaged membranes (gives red fluorescence). However, there are a number of obvious limitations including the requirement for well-trained staff to perform the microscopy, limits of sensitivity of the method and, for some parasites, difficulty in differentiating species based on morphology. In addition, the parasite may not be present in easily available samples. Thus a variety of other approaches are used to help in detection.