Diagnostic accuracy of loop-mediated isothermal amplification (LAMP) for screening malaria in peripheral and placental blood samples from pregnant women in Colombia

Abstract

BackgroundPregnant women frequently show low-density Plasmodium infections that require more sensitive methods for accurate diagnosis and early treatment of malaria. This is particularly relevant in low-malaria transmission areas, where intermittent preventive treatment is not recommended. Molecular methods, such as polymerase chain reaction (PCR) are highly sensitive, but require sophisticated equipment and advanced training. Instead, loop mediated isothermal amplification (LAMP) provides an opportunity for molecular detection of malaria infections in remote endemic areas, outside a reference laboratory. The aim of the study is to evaluate the performance of LAMP for the screening of malaria in pregnant women in Colombia.MethodsThis is a nested prospective study that uses data and samples from a larger cross-sectional project conducted from May 2016 to January 2017 in three Colombian endemic areas (El Bagre, Quibdó, and Tumaco). A total of 531 peripheral and placental samples from pregnant women self-presenting at local hospitals for antenatal care visits, at delivery or seeking medical care for suspected malaria were collected. Samples were analysed for Plasmodium parasites by light microscopy (LM), rapid diagnostic test (RDT) and LAMP. Diagnostic accuracy endpoints (sensitivity, specificity, predictive values, and kappa scores) of LM, RDT and LAMP were compared with nested PCR (nPCR) as the reference standard.ResultsIn peripheral samples, LAMP showed an improved sensitivity (100.0%) when compared with LM 79.5% and RDT 76.9% (p < 0.01), particularly in afebrile women, for which LAMP sensitivity was two-times higher than LM and RDT. Overall agreement among LAMP and nPCR was high (kappa value = 1.0). Specificity was similar in all tests (100%). In placental blood, LAMP evidenced a four-fold improvement in sensitivity (88.9%) when compared with LM and RDT (22.2%), being the only method, together with nPCR, able to detect placental infections in peripheral blood.ConclusionsLAMP is a simple, rapid and accurate molecular tool for detecting gestational and placental malaria, being able to overcome the limited sensitivity of LM and RDT. These findings could guide maternal health programs in low-transmission settings to integrate LAMP in their surveillance systems for the active detection of low-density infections and asymptomatic malaria cases.

Evaluation of Visual LAMP detection of Plasmodium falciparum&nbsp;and non-Plasmodium falciparum

“…Accurate diagnosis of malaria infection is critical. Microscope examination of blood smears is still considered the gold standard for the diagnosis of malaria, which was labor-intensive, time-consuming [7,10,16] , with detection limit of 100 malaria parasites/µl [10,16] . It was usually unable to detect low-density and mixed infections, the sensitivity and specificity of which depends on the skill of the technician, quality and staining quality of blood smear, and so on [3,17] .…”

“…The RDT is insensitive to Plasmodium vivax and Plasmodium ovale. The patients with asymptomatic Plasmodium falciparum infection may be malaria-infected reservoir [7,8] . Therefore, a high sensitivity diagnostic methods able to detect low-density malaria parasite emias for the elimination of malaria is critical [6,9] .There is urgent need for extremely sensitive and field-based diagnostic system [10] .…”

“…Molecular diagnosis is a highly sensitive method for detecting malaria infection [7,9,11] . For example, PCR is one of the most sensitive and reliable methods for detecting DNA of malaria, but it requires expensive equipment [7] .…”

“…Molecular diagnosis is a highly sensitive method for detecting malaria infection [7,9,11] . For example, PCR is one of the most sensitive and reliable methods for detecting DNA of malaria, but it requires expensive equipment [7] . The sensitivity of the ring-mediated so-mediated temperature amplification (LAMP) method is close to or exceeds the NEST-PCR [6,7,12,13] .…”

“…For example, PCR is one of the most sensitive and reliable methods for detecting DNA of malaria, but it requires expensive equipment [7] . The sensitivity of the ring-mediated so-mediated temperature amplification (LAMP) method is close to or exceeds the NEST-PCR [6,7,12,13] . LAMP method does not require expensive equipment and results can be judged by visual observation.…”