Kenya Medical Research Institute/United States Army Medical Research Unit, Kenya, Malaria Diagnostics Centre, Box 54 - 40100, Kisumu, Kenya.
Malar J. 2013 Mar 27;12:113. doi: 10.1186/1475-2875-12-113.
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.
疟疾的诊断在很大程度上依赖于通过常规显微镜观察染色血片中的寄生虫。准确识别感染的疟原虫种类依赖于对寄生虫形态特征的详细检查，如大小、形状、色素颗粒，以及寄生红细胞的大小和形状以及细胞内含物的存在。本研究探讨了常规显微镜检查对四种疟原虫的分类错误，相对于显微镜专家的熟练程度和吉姆萨染色血片中寄生虫的形态特征。
为公共卫生和研究实验室人员举办了为期 10 天的疟疾显微镜检查补救课程，内容包括寄生虫检测、种类鉴定和寄生虫计数。在每门课程开始（预）和结束（后）时，使用疟原虫 falciparum、疟原虫 malariae、疟原虫 ovale 和疟原虫 vivax 感染的已知血片评估种类鉴定的熟练程度，密度范围为 1,000 至 30,000 个寄生虫/μL。结果分为假阴性、未鉴定的阳性、疟原虫 falciparum、疟原虫 malariae、疟原虫 ovale、疟原虫 vivax 和混合感染。
报告的发现基于 2008 年至 2010 年补救课程中累积的 1878 例疟原虫 falciparum、483 例疟原虫 malariae、581 例疟原虫 ovale 和 438 例疟原虫 vivax 的结果。与非疟原虫感染相比，培训前未鉴定的疟原虫 falciparum 感染的假阴性和未鉴定的阳性分类错误明显较低（p < 0.0001）。培训后，分类错误明显低于培训前，这反过来又显著提高了对四种疟原虫的识别。然而，疟原虫 falciparum 感染高度误诊为混合感染，疟原虫 ovale 误诊为疟原虫 vivax，疟原虫 vivax 误诊为疟原虫 ovale（p < 0.05）。
这些发现表明，疟原虫种类的分类错误可能很常见，特别是在涉及非疟原虫感染时，因为缺乏微观诊断所需的技能和疟原虫种类内和之间的形态特征变化。补救培训可能会提高常规光镜对疟原虫感染的区分的可靠性。
