Summary
A Purdue University team reports a loop-mediated isothermal amplification assay for detecting Balamuthia mandrillaris. In laboratory testing, the assay detected multiple isolates with higher sensitivity than conventional PCR and produced a visible colour-based result.
Researchers at Purdue University have developed and evaluated a loop-mediated isothermal amplification (LAMP) assay for detecting Balamuthia mandrillaris, a free-living amoeba that can cause skin lesions, systemic disease and a severe central-nervous-system infection called Balamuthia amoebic encephalitis (BAE).
The work appears as a bioRxiv preprint posted on September 19, 2026. The authors report that their assay targeted the 18S rRNA gene of B. mandrillaris and detected the organism in laboratory tests with approximately 10- to 100-fold higher sensitivity than conventional PCR.
How the assay works
LAMP is a DNA-amplification method designed to operate at a constant temperature rather than using the repeated heating and cooling cycles of conventional PCR. In this assay, amplification can be observed by eye using phenol red, a colour indicator. That readout could make the method simpler to interpret than tests requiring specialised detection equipment, although the preprint evaluates assay performance rather than a complete clinical workflow.
The researchers tested DNA from 10 different B. mandrillaris isolates. The assay showed no cross-reactivity with DNA from the other free-living amoebae, protozoa, fungi and bacteria included in the evaluation. Cross-reactivity occurs when a test incorrectly responds to material from a different organism, so this testing addressed whether the assay's target signal was specific to the amoeba panel examined.
Sensitivity results and potential importance
The reported limit of detection was 10 femtograms per microlitre of extracted DNA. For cell-based samples, the assay detected 10 trophozoites per 100 microlitres in untreated samples and one trophozoite per 100 microlitres after heat treatment. Trophozoites are the active, growing form of an amoeba.
The team also used newly developed quantitative PCR and digital PCR methods to assess the assay's detection limit, obtaining an approximate value of one DNA copy per microlitre. The LAMP method retained its reported performance in samples spiked with cerebrospinal fluid, urine and blood, which are relevant types of material for diagnostic testing.
Early detection is important in BAE because the infection can progress rapidly. The preprint describes existing diagnostic methods as limited by long detection times, low sensitivity and availability mainly through highly specialised centres. BAE is also reported in the abstract to have an approximate mortality rate of 92%.
The study's findings are a laboratory validation of the assay using amoeba isolates, DNA, treated and untreated cells, and spiked sample matrices. The supplied report does not describe testing in a patient cohort, so clinical sensitivity, specificity and performance in routine diagnostic settings remain to be established. The authors propose that the assay could support faster detection, particularly in non-specialised centres and resource-limited areas.