Abstract
The suitability of incubated blood culture material for forensic molecular malaria diagnosis was assessed for non-endemic settings for cases in which the differential diagnosis malaria was initially overlooked. For the proof-of-principle assessment, residual blood culture materials from febrile patients from tropical Ghana were investigated by real-time PCR and compared with available historic microscopic results. In 2114 samples, for which microscopical results and real-time PCR results were available, microscopical results comprised 711 P. falciparum detections, 7 P. malariae detections, 1 microscopically not-further-discriminable Plasmodium spp. detection as well as 13 detections of mixed infections comprising 12 cases of P. falciparum/P. malariae co-infections and 1 case of a P. falciparum/P. ovale complex co-infection, while real-PCR indicated 558 P. falciparum detections, 95 P. malariae detections, 10 P. ovale complex detections, 1 P. vivax detection and 4 detected P. falciparum/P. malariae co-infections. Concordance of routine microscopy and real-time PCR was imperfect. Using routine microscopy as reference was associated with a seemingly low agreement of positive real-time PCR results of 90.9%. However, if positive samples, either by routine microscopy or real-time PCR or both, were applied as a combined reference, the agreement of positive results obtained with real-time PCR was increased from 74.0% to 77.9%, while the agreement of positive results obtained with routine microscopy was decreased from 100% to 85.3%. The predictive value of routine microscopy for negative results in the reference was slightly better with 90.9% compared to real-time PCR with 86.9%; the concordance between routine microscopy and real-time PCR was imperfect. In conclusion, even suboptimal sample materials such as incubated blood culture materials can be applied for forensic malaria diagnosis, if more suitable sample materials are not available, but the molecular detection rate of positive results in routine microscopy is much lower than previously reported for non-incubated blood.
Highlights
Training options to maintain skills in routine malaria microscopy in non-endemic settings are limited because of scarcely available sample material
Non-commercial duplex real-time PCR for the discrimination of P. ovale wallikeri and P. ovale curtisi in case of P. ovale complex detections by real-time PCR or by routine microscopy (n = 11)
In a total of 732 out of the 2114 included cases, malaria was microscopically diagnosed with 711 P. falciparum detections, 7 P. malariae detections, 1 microscopically not-furtherdiscriminable Plasmodium spp. detection and 13 detections of mixed infections comprising
Summary
Training options to maintain skills in routine malaria microscopy in non-endemic settings are limited because of scarcely available sample material Similar species such as Plasmodium vivax, P. ovale curtisi and P. ovale wallikeri tend to be misinterpreted under the microscope [1–3] with more than 10% misidentification of P. vivax and. Due to the molecular assays’ high sensitivity [4–6], nucleic acid amplification tests for malaria are useful if a correct identification of early infections with low parasitaemia is desired or mixed plasmodial infections need to be excluded [7,8]. Molecular approaches such as PCR are more sensitive than antigen testing, including the recently introduced “ultrasensitive rapid diagnostic tests” [9,10]. Apart from the diagnostic needs in resource-rich non-endemic settings, the suitability of highly sensitive real-time PCR assays has been suggested for malaria eradication programs [11–16]
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