May 20, 2015
2 min read

New malaria test effective for large-scale screening

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A novel method for malaria testing could achieve large-scale screening and cost-effectiveness that is vital to successful disease control, according to research published in Clinical Chemistry.

“The rapidly shrinking malaria map takes us a step closer to worldwide eradication. However, substantial challenges still exist,” Zhi Zheng, professor, department of biochemistry and molecular biology, Peking Union Medical College, China, and colleagues wrote. “To achieve elimination and prevent resurgence, surveillance systems must be able to effectively interrupt transmission by detecting all possible malaria infections in the area in a timely manner.”

Zheng and colleagues wrote that methods often used in malaria elimination programs —microscopy and rapid diagnostic tests (RDTs) — fail in some instances to detect non-acute or asymptomatic cases that lead to an estimated 20% to 50% of malaria transmissions.

To enhance surveillance efforts, the researchers developed capture and ligation probe-PCR (CLIP-PCR), which they said at 60 cents per sample is as sensitive as reverse transcription PCR (RT-PCR) but does not require RNA purification or reserve transcription. Instead, CLIP-PCR quantifies 18S of ribosomal RNA (rRNA) of the genus Plasmodium released from blood based on how many ligated probes continuously bind to it.

The researchers collected 3,358 blood smears and dried blood spots (DBS) from study participants in three counties in the Yunnan and Anhui provinces from May 2013 to October 2013. Gengma, Tengchong and Feidong counties had malaria mortality rates of 0.85, 3 and 0.07 per 10,000 inhabitants, respectively, in 2012.

Nearly half of the Tengchong county population studied were migrant workers returning from malaria-endemic Myanmar, while nearly 10% of participants from Feidong County were migrant workers returning from malaria-endemic Africa, the researchers wrote.

“CLIP-PCR is highly efficient when screening large numbers of samples, since pooled samples are tested in 96-well plates in parallel,” Zheng and colleagues wrote.

CLIP-PCR and microscopy were both used, and each detected 10 malaria infections in Tengchong County and no infections among Feidong County residents. In Gengma County, where RDTs also were used, CLIP-PCR detected four asymptomatic infections not detected by microscopy or RDT. All four of these participants developed malaria-related symptoms within 2 months of testing, the researchers noted.

“With drastically improved throughput, sensitivity and affordability compared with current screening technology, CLIP-PCR can lead to a higher frequency of active surveys, a larger radius and coverage per survey, and a better detection rate for asymptomatic infections,” Zheng and colleagues wrote. “The major roadblock will shift from technical challenges of detecting all infections in an active survey to operational issues such as how to ensure full participation of a community.” – by David Jwanier

Disclosure: The researchers report no relevant financial disclosures.