Like its relatives Dengue and Zika, Chikungunya virus (CHIKV) is transmitted by Aedes mosquitoes, and both mosquitoes and viruses are extending their range. The name "chikungunya" means "to become contorted" in the African Kimakonde language and describes the stooped appearance of patients with severe joint pain. In most infected individuals, disease symptoms (which also include fever, nausea, and muscle pain) pass after a few days, but in some patients the joint pain lasts for months, with debilitating consequences.

CHIKV infection causes symptoms that are similar to Dengue and Zika as well as other viral diseases, including influenza. Accurate diagnosis of CHIKV is important for effective outbreak responses, including patient management and mosquito control. A study published in PLOS Neglected Tropical Diseases reports a rapid accurate test for CHIKV that is performed in a small portable laboratory and can be used anywhere.

Matthias Niedrig, from the Robert-Koch-Institute in Berlin, Germany, and colleagues work on rapid, cheap, and easy diagnostic assays for CHIKV and related viruses. In this study, they developed a reverse transcriptase (RT) recombinase polymerase amplification (RPA) assay for rapid detection of CHIKV in clinical samples. RPA-based detection of small amounts of DNA is an alternative to PCR and based on reactions that can run at constant temperatures rather than needing a thermal cycler. By adding RT, the assay can detect small amounts of RNA, including sequences unique to specific RNA viruses.

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Suitcase laboratory used for CHIKV diagnosis in the field
Image Credit: Ahmed Abd El Wahed

The researchers designed a set of CHIKV-specific reagents and showed that the assay was able to detect very small amounts of CHIKV RNA. The RT-RPA assay, the researchers report, is slightly less sensitive than RT-PCR, but both assays yielded identical results on clinical samples of 20 patients with known CHIKV infection and 58 samples from suspected cases.

Testing the RT-RPA assay on different CHIKV strains and a panel of related alpha - and arboviruses, the researchers found, that the assay reliably detected all 18 different CHIKV strains tested. In addition, there was no cross-reactivity of the assay with any of the other tested viruses except for the very closely related O'nyong'nyong virus (ONNV). Using a modified set of assay reagents, the researchers were able to eliminate the problem of false-positive results caused by ONNV.

Discussing the findings, the researchers highlight that RPA reagents are stable at ambient temperature (25-38°C), meaning they do not need to be refrigerated. In its current form, however, the assay still requires multiple pipetting steps, and the researchers say further simplification and miniaturization is needed to bring the cost down from the current 5 USD per sample 1 USD, which would maximize use in affected countries.

Overall, the researchers conclude, "the CHIKV RPA assay presented here is a promising tool for CHIKV diagnostics at the point of need. Integration into a multimer or multiplex assay for simultaneous and detection of CHIKV, Dengue virus and Zika virus as well as an internal control would improve outbreak investigations, since the three viruses induce same clinical picture upon infection and increasingly co-circulate in many parts of world".

The authors received no specific funding for this work.

All authors have no financial interests except MK is employed by GenExpress Gesellschaft für Proteindesign and has commercial interest in the molecular RNA standard. This does not alter the authors´ adherence to all PLOS policies on sharing data and materials.

Article: A Field-Deployable Reverse Transcription Recombinase Polymerase Amplification Assay for Rapid Detection of the Chikungunya Virus, Pranav Patel, Ahmed Abd El Wahed, Oumar Faye, Pauline Prüger, Marco Kaiser, Sasikanya Thaloengsok, Sukathida Ubol, Anavaj Sakuntabhai, Isabelle Leparc-Goffart, Frank T. Hufert, Amadou A. Sall, Manfred Weidmann, Matthias Niedrig, PLOS Neglected Tropical Diseases, doi:10.1371/journal.pntd.0004953, published 29 September 2016.