| dc.description.abstract | Malaria diagnosis is largely dependent on the demonstration of parasites in stained blood films by
conventional microscopy. Accurate identification of the infecting Plasmodium species relies on detailed examination
of parasite morphological characteristics, such as size, shape, pigment granules, besides the size and shape of the
parasitized red blood cells and presence of cell inclusions. This work explores misclassifications of four Plasmodium
species by conventional microscopy relative to the proficiency of microscopists and morphological characteristics of
the parasites on Giemsa-stained blood films.
Ten-day malaria microscopy remedial courses on parasite detection, species identification and
parasite counting were conducted for public health and research laboratory personnel. Proficiency in species
identification was assessed at the start (pre) and the end (post) of each course using known blood films of
Plasmodium falciparum, Plasmodium malariae, Plasmodium ovale and Plasmodium vivax infections with densities
ranging from 1,000 to 30,000 parasites/μL. Outcomes were categorized as false negative, positive without
speciation, P. falciparum, P. malariae, P. ovale, P. vivax and mixed infections.
Reported findings are based on 1,878 P. falciparum, 483 P. malariae, 581 P. ovale and 438
P. vivax cumulative results collated from 2008 to 2010 remedial courses. Pre-training false negative and positive
misclassifications without speciation were significantly lower on P. falciparum infections compared to non-falciparum
infections (p < 0.0001). Post-training misclassifications decreased significantly compared to pre- training
misclassifications which in turn led to significant improvements in the identification of the four species. However,
P. falciparum infections were highly misclassified as mixed infections, P. ovale misclassified as P. vivax and P. vivax
similarly misclassified as P. ovale (p < 0.05).
These findings suggest that the misclassification of malaria species could be a common occurrence
especially where non-falciparum infections are involved due to lack of requisite skills in microscopic diagnosis and
variations in morphological characteristics within and between Plasmodium species. Remedial training might improve
reliability of conventional light microscopy with respect to differentiation of Plasmodium infections. | en |
