In adults, infection with Asian-lineage Zika virus — an arbovirus transmitted via mosquitoes — has been associated with nonspecific symptoms such as fever and arthralgia, as well as Guillain-Barré syndrome. Mother-to-child transmission can cause microcephaly in infants. The Zika virus outbreak currently encompasses the American continents, and Africa may soon be affected.
The available diagnostic tests for Zika virus include virus isolation, serology after exposure to the virus, and viral RNA detection by reverse transcription polymerase chain reaction (RT-PCR). However, these modalities are often costly, and rapid and inexpensive tests for Zika virus are needed for surveillance and patient care purposes.
Loop-mediated isothermal amplification (LAMP) is quick and simple to perform and has been implemented successfully for the detection of other arboviruses in affected regions. Researchers, led by Joel Rovnak, PhD, and Nunya Chotiwan, MS, from Colorado State University, developed a rapid, sensitive, low-cost test for Zika using LAMP.
The LAMP assay for Zika virus differentiates between Asian- and African-lineage Zika viruses, although it cannot identify other viruses such as dengue or yellow fever. The assay can also be used for direct detection of Zika virus in mosquitoes and human plasma, serum, and semen. Unlike RT-PCR, the LAMP assay does not require reverse transcription or RNA isolation.
The limits of Zika virus RNA detection for the LAMP assay are similar to the limits for RT-PCR, and the sensitivity of LAMP is comparable to that of quantitative RT-PCR (qRT-PCR). A major drawback of LAMP and RT-PCR, according to Dr Rovnak, is that they can only detect Zika virus during active infection. “The virus and its RNA are quickly cleared after production of neutralizing antibodies after about 10 to 14 days,” he told Infectious Disease Advisor. Current research efforts are attempting to identify sites of low-level virus persistence, which is detectable by both assays.
“A main advantage of the LAMP assay is cost of implementation,” Dr Rovnak said. An RT-PCR machine costs approximately $20,000, not including the training of personnel. In contrast, the LAMP assay, if commercially developed, may cost only $500 for the equipment and less than $2 per assay. Thus, the LAMP assay may “provide a simple, in-office or in-clinic assay.”
“The assay was initially designed as a field assay for detection of Zika virus in mosquitoes,” said Dr Rovnak. “Just as with clinical samples, detection of Zika in mosquito populations requires well equipped, regional laboratories. We intend to deploy the assay, in comparison with qRT-PCR, to determine its effectiveness in monitoring virus in mosquitoes in support of focused and timely efforts in mosquito control.”
“I believe that the increased availability and speed of such a diagnostic [tool] will have a significant, positive impact on public health. Although there is no specific therapy for these virus infections beyond palliative care, the range of possible disease agents can be clearly defined and the data on the extent and timing of outbreaks will inform public health official's decisions regarding disease control efforts in the community,” he added.
Dr Rovnak pointed out that the LAMP assay is not yet available for clinical use. He and his colleagues plan to further develop the test for the clinical setting. “We will be doing direct comparisons between the current, approved standard diagnostic, qRT-PCR, and the LAMP assay on patient samples with our collaborators in Managua, Nicaragua, over the next year. The goal is to obtain more data on its utility at points of care,” he said.