Diagnosis of parasitic diseases: old and new approaches

Abstract

Methods for the diagnosis of infectious diseases have stagnated in the last 20-30 years. Few major advances in clinical diagnostic testing have been made since the introduction of PCR, although new technologies are being investigated. Many tests that form the backbone of the "modern" microbiology laboratory are based on very old and labour-intensive technologies such as microscopy for malaria. Pressing needs include more rapid tests without sacrificing sensitivity, value-added tests, and point-of-care tests for both high- and low-resource settings. In recent years, research has been focused on alternative methods to improve the diagnosis of parasitic diseases. These include immunoassays, molecular-based approaches, and proteomics using mass spectrometry platforms technology. This review summarizes the progress in new approaches in parasite diagnosis and discusses some of the merits and disadvantages of these tests.

Figure 1

Microscopy. Comparison of Trypanosoma cruzi trypomastogote (a) with Plasmodium malariae schizont (b) and with microfilaria (c: Mansonella perstans) in squirrel monkey blood smear. Giemsa stain: 70x oil-immersion objective (a) and (b) and 27.2x objective (c), adapted with permission of Comparative Medicine from [9].

Figure 2

Serology-based assays: ELISA. Enzyme-linked immunosorbent assay (ELISA) absorbance values for antibodies to T. cruzi in monkey samples. Median values are indicated by horizontal lines within the boxes; the 25th and 75th percentiles are enclosed by the boxes; the 5th and 95th percentiles are enclosed by the bars outside the boxes. Adapted with permission of Comparative Medicine from [9].

Figure 3

Molecular-based assay: PCR. Example of PCR results obtained for seven monkey samples, using the TCRUZ primers. Blood samples were processed as described in Materials and Methods. The PCR products were electrophoresed in a 2% agarose gel and stained with ethidium bromide. The 168 bp band (arrow) is the expected T. cruzi-specific product. The 360 and 550 bp are also specific products resulting from amplification of two or three of the 195 bp repeats found in tandem arrays in the T. cruzi genome. Lanes 1 to 6 contain the amplification products of DNA from T. cruzi-infected monkeys; 7, blood from noninfected monkey; 8, negative control (distilled water); and M, 100 bp ladder, adapted, with permission of Comparative Medicine from [9].