Field evaluation of a real time loop-mediated isothermal amplification assay (RealAmp) for malaria diagnosis in Cruzeiro do Sul, Acre, Brazil

PLoS One. 2018 Jul 11;13(7):e0200492. doi: 10.1371/journal.pone.0200492. eCollection 2018.

Abstract

Conventional molecular methods, such as nested polymerase chain reaction (PCR), are very sensitive for detection of malaria parasites, but require advanced laboratory equipment and trained personnel. Real-time loop-mediated isothermal amplification (RealAmp), a loop-mediated isothermal amplification-based molecular tool (LAMP), facilitates rapid target amplification at a single temperature setting, reducing the need for sophisticated equipment. We evaluated the performance of a field-adapted RealAmp assay for malaria diagnosis in Cruzeiro do Sul, Acre State, Brazil, a remote area in Brazil with limited laboratory capabilities. We enrolled 1,000 patients with fever (axillary temperature ≥ 37.5 C) or history of fever in last 24 h presenting for malaria diagnosis from February through June 2015. DNA was extracted from dried blood spots using a boil and spin method (heat treatment) at the sample processing site, and also using commercial kits at a Brazilian national reference laboratory. RealAmp was performed for Plasmodium genus, P. falciparum, and P. vivax identification. In addition, Giemsa-stained blood smears were prepared and examined by two independent well-trained study microscopists. A combination of Real-time PCR and nested PCR was used as reference test. The sensitivity and specificity of RealAmp in the field site laboratory were 94.1% (95% confidence interval [CI]: 90.1-96.8) and 83.9% (95% CI: 81.1-86.4), respectively. The sensitivity and specificity of local microscopy were 87.7% (95% CI: 82.6-91.7) and 98.9% (95% CI: 97.8-99.4), respectively, while study microscopy showed sensitivity of 96.4% (95% CI: 93.0-98.4) and specificity of 98.2% (95% CI: 97.0-99.0). None of the three tests detected 20 P. falciparum and P. vivax mixed infections identified by the reference test. Our findings highlight that it is possible to implement simple molecular tests in facilities with limited resources such as Cruzeiro do Sul in Brazil. RealAmp sensitivity was similar to that of microscopy performed by skilled professionals; both RealAmp and study microscopy performed poorly in detection of mixed infection. Attempts to develop and evaluate simpler molecular tools should continue, especially for the detection of malaria infection in remote areas.

Publication types

  • Evaluation Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Brazil
  • Female
  • Humans
  • Malaria, Falciparum* / blood
  • Malaria, Falciparum* / diagnosis
  • Malaria, Falciparum* / genetics
  • Malaria, Vivax* / blood
  • Malaria, Vivax* / diagnosis
  • Malaria, Vivax* / genetics
  • Male
  • Nucleic Acid Amplification Techniques / methods*
  • Plasmodium falciparum / genetics*
  • Plasmodium vivax / genetics*
  • Sensitivity and Specificity

Grants and funding

This study was supported by the Amazon Malaria Initiative, which is funded by the United States Agency for International Development (USAID). The funding sources for this study had no role in study design, data collection, analysis, or interpretation. The opinions expressed herein are those of the authors and do not necessarily reflect the views of the USAID or the US Centers for Disease Control and Prevention (CDC).