A diagnostic system that evaluates scanned images of standard Giemsa-stained slides and reports species and parasitaemia has been appraised.

The device uses digital microscopes or imaging scanners to acquire the images that are stored and subsequently serve as the input for the algorithm to locate, identify and count the parasites.

An international team from the USA, UK, and Germany collaborated in the evaluation led by those at Hydas World Health, Hershey, PA, USA). The device was challenged with two independent tests: a 55 slide, expert slide reading test the composition of which is available from the World Health Organization ("WHO55" test, Geneva Switzerland), and a second test in which slides were made from a sample of consenting subjects participating in a malaria incidence survey conducted in Equatorial Guinea (EGMIS).

To use the World Health Technology (WHT; New Albany, OH 43054, USA) system, a slide is placed in the scanner or with an automated scanner many slides can be placed at one time, and the scanner captures images at the selected magnification. Localization, recognition and enumeration of the salient constituents of the scans, parasites and leucocytes, are based on pattern, color and shape recognition of parasites in red blood cells (RBCs) of a thin film and/or parasites that remain in a thick film after lysis of RBCs.

Two scanners were used for this study, IScan Coreo Gold (Ventana Corp., Sunnyvale, CA, USA) and a custom portable device made to WHT specifications called Doctor's Choice (Intracellular, Cincinnati, OH, USA). On the WHO55 test, the sensitivity was 89% and specificity was 70%. Species were correctly identified in 61% of the slides and the quantification of parasites fell within acceptable range of the validated parasitaemia in 10% of the cases. On the EGMIS test, it scored 100% sensitivity and 94% specificity, with 64% of the species correct and 45% of the parasitaemia within an acceptable range. A pooled analysis of the 174 slides used for both tests resulted in an overall 92% sensitivity and 90% specificity with 61% species and 19% quantifications correct.

The authors concluded that the device performs at a level comparable to that of many human slide readers. Because its use requires minimal additional equipment and it uses standard stained slides as starting material, its widespread adoption may eliminate the current uncertainty about the quality of microscopic diagnoses. The study was published on May 6, 2012, in the Malaria Journal.

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Hydas World Health
World Health Organization
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