The main findings of the current study were; the prevalence of placental malaria infections was 0.9%, 30.8% and 31.8% by microscopy, histology and PCR, respectively, the sensitivity and specificity of the PCR was 45.5% and 74.3%, respectively compared with placental histology. Recently, two studies in the Eastern Sudan have shown that, the prevalence of placental P. falciparum was 1.7% (5/293) and 3% (7/237) by microscopy examinations and the prevalence was 32.0% and 19.5% by the histology [5, 23]. Interestingly, 40 (32%) of the 125 smear-negative pregnant women in the Eastern Sudan had submicroscopic P. falciparum (PCR) infections . The low sensitivity and specificity of PCR in this study goes with the recent previous observation from Colombia where the sensitivity and specificity of PCR (histology was the gold standard) was 47% and 77%, respectively . However, our findings should be compared with the results of later study cautiously, because the vast majority of the infections in our study were past infection while one third (33%) of the infections in the later one were acute and the rest were chronic (7%) and past (60%) infections.
Histological examination of the placenta biopsy is considered the gold standard for diagnosis of placental malaria. Furthermore, the placental histology indicates the presence of malaria parasites and pigment in the placental tissue. Therefore malaria infection can be classified in active (parasites in the placenta), chronic (parasites and pigment in placenta), past (only pigment in placenta) and no infection (no parasites or pigment in placenta). However, due to limited resources, technical expertise, such placental histology is rarely available in endemic areas with low recourses [12–14]. PCR is the most sensitive tool for detection parasites (for both peripheral and placental malaria), however, requires a trained staff and specialized equipment, which might not available in the field in settings with low resources [13, 16]. Furthermore PCR-based methods have no standard in method for DNA extraction, choice of primer sets, and amplification protocol . On the other hand PCR is very sensitive in detecting Plasmodium nucleic acids, yet it is not obvious if this is derived from a non-viable sequestered parasite, or a viable one or even gametocyte. In the current study the different rates of PCR-positivity reported between women with past infections and normal placentae is a significant finding. PCR in the women with past infections may detect non-viable parasites in treated women, viable sub microscopic persisting infections or re-infections in women at increased risk for infection. It is worth to be mentioned that, although placental histology can provide a quantitative result based on the number of parasites, conventional PCR (not the real time PCR) gives a qualitative result but allow species discrimination .