Could the Level in Parasitaemia of <i>Plasmodium</i> Determine Sensitivity to Various Diagnostic Tests?

Abstract

The discovery of Plasmodium parasites and its incrimination as the principal cause of malaria in humans has continued to excite researchers towards inventing possible easier methods of diagnosing and identifying these pathological agents in order to mitigate, control and eliminate its continuous scourge to humanity. Currently, three diagnostic methods have been proposed, but agreements as to whether the level of parasitaemia in an individual could connote likely confirmations in the three methods i.e. gold standard, RDTs’ and PCR/NESTED PCR, have continued to be a subject of debate. To lay to rest the debate as reported in many studies, we collected blood samples from 100 symptomatic patients who reported to the Jos-Nigeria hospital and using the gold standard methods, we were able to confirm that 30 (30%) samples out of the 100 blood samples collected were positive to P. falciparum, chiefly recorded among duffy-negative Africans. Excited with our findings, we prepared the thick blood films for each sample and used it to estimate the levels of parasitaemia (parasites density) per μl of blood (i.e. 1+; 2+; 3+ and 4+) per 100 high power fields (|HPF). We then subjected the individually confirmed parasite density samples to the other two methods i.e. Rapid Diagnostic Test (one-step RTD and optimal-IT® RDT) and to molecular assay (PCR and the nested PCR). Interestingly, of the 30 positive samples, 18 (60%) were confirmed positive to the one-step and optimal-IT® RDTS, while 3 (30%) out of the 10 (100%) samples of various parasite density subjected to molecular assay (PCR and the nested PCR) were positive to only P. falciparum. Statistical analysis of variance based on single factor computed using SPSS indicates a no significant difference (P > 0.05) in the parasitaemia levels of the four groups/categories of patients; i.e. variance ratio of 0.011976 calculated was less than F-critical (2.816466) at 5% (0.05). Whereas gold standard could be considered as the optimal method, for the PCR/NESTED PCR, the sensitivity is dependent on high level of parasitaemia.