Evaluation of loop-mediated isothermal amplification as a surveillance tool for malaria in reactive case detection moving towards elimination

Abstract

BackgroundAs malaria transmission decreases, the proportion of infections that are asymptomatic at any given time increases. This poses a challenge for diagnosis as routinely used rapid diagnostic tests (RDTs) miss asymptomatic malaria cases with low parasite densities due to poor sensitivity. Yet, asymptomatic infections can contribute to onward transmission of malaria and therefore act as infectious reservoirs and perpetuate malaria transmission. This study compared the performance of RDTs to loop-mediated isothermal amplification (LAMP) in the diagnosis of malaria during reactive active case detection surveillance.MethodsAll reported malaria cases in the Engela Health District of Namibia were traced back to their place of residence and persons living within the four closest neighbouring houses to the index case (neighbourhood) were tested for malaria infection with RDTs and dried blood spots (DBS) were collected. LAMP and nested PCR (nPCR) were carried out on all RDTs and DBS. The same procedure was followed in randomly selected control neighbourhoods.ResultsSome 3151 individuals were tested by RDT, LAMP and nPCR. Sensitivity of RDTs and LAMP were 9.30 and 95.50%, respectively, and specificities were 99.27 and 99.92%, respectively, compared to nPCR. LAMP carried out on collected RDTs showed a sensitivity and specificity of 95.35 and 99.85% compared to nPCR carried out on DBS. There were 2 RDT samples that were negative by LAMP but the corresponding DBS samples were positive by PCR.ConclusionThe study showed that LAMP had the equivalent performance as nPCR for the identification of Plasmodium falciparum infection. Given its relative simplicity to implement over more complex and time-consuming methods, such as PCR, LAMP is particularly useful in elimination settings where high sensitivity and ease of operation are important.

Use of real-time multiplex PCR, malaria rapid diagnostic test and microscopy to investigate the prevalence of Plasmodium species among febrile hospital patients in Sierra Leone

“…LAMP, a recently developed isothermal DNA amplification technology, holds promise of exceeding sensitivity of PCRbased malaria assays without the need for expensive and time consuming thermal cycling [42]. At least two different CE-marked commercial pan-malaria LAMP kits are available that are capable of detecting multiple Plasmodium species in ~ 60 min and require minimal handson manipulations for sample prep [43][44][45]. However, these pan-malaria LAMP kits-at their current stage of development-lack multiplexing capability (for species identification), have relatively high false positive rates compared to PCR, are still expensive on a per-sample basis, and have cold chain requirements [46,47].…”

Evaluation of Visual LAMP detection of Plasmodium falciparum and non-Plasmodium falciparum

“…Meantime it shows limited sensitivity when detecting low-density infection [16,22] , and less sensitivity to non-P.f P.v as 66.0-88.0%, P.o as 5.5-86.7%, P.m as 21.4-45.2% [19] . PCR is one of the most sensitive and reliable methods for detecting DNA of malaria, with a high sensitivity and specificity limit to 1-10 malaria parasites/μl [10,11] . However, it requires technical expertise and infrastructure which limit its wide range of applications.…”

“…At the same time, due to increasing travel and population movements to malaria-endemic areas, imported malaria is still widespread [21] . Particularly, asymptomatic malaria infection and lowdensity malaria parasite emias are hard to be detected by microscope examination and RDT due to below the detection threshold [11,24] , causing misdiagnosis or delayed diagnosis [3,21] . But they could maintaining transmission of malaria as infected intermediate host [24,26] .…”

“…But they could maintaining transmission of malaria as infected intermediate host [24,26] . It has been reported that subclinical malaria accounts for 70-80% of all malaria infections [11] . Therefore, it is a challenge to detect the asymptomatic malaria parasite infection and low density malaria parasite emias in malaria prevention and control [8,24] .…”

“…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] .…”