Scientists at Rice University are making headway in the development of a novel HIV test aimed at increasing the accessibility of HIV testing in areas with little access to healthcare. The highly sensitive test can both diagnose HIV infection and monitor viral load in a highly accurate manner without relying on laboratory facilities that are often scarce in developing countries. The study has been published in Analytical Chemistry.
Antibody tests are the most common technique employed to detect HIV because of their accuracy, portability and low cost. These first-line indirect tests (as opposed to direct tests which look for viral constituents such as viral proteins) can also give results very quickly and some do not rely on laboratory equipment, meaning they can be carried out in a wide variety of settings. However, these tests are not applicable to infants and young children because they cannot distinguish between antibodies from the infected mother that have crossed the placenta.
Infant testing therefore relies on direct tests which pick up viral genetic material. The same tests are also used to monitor viral loads (the amount of virus in the blood) of infected patients which help to assess disease progression. While this technique, called polymerase chain reaction (PCR), is also very sensitive it has limitations in poorer nations because it relies on laboratory equipment and trained individuals to carry out the test.
In order to solve this issue, Rice University bioengineers developed a test which follows on from their novel diagnostic technique which was designed earlier this year to detect the causative agent of the diarrheal disease cryptosporidiosis. The test is called recombinase polymerase amplification (RPA) and can be carried out in a single tube.
RPA is similar in principle to PCR in that it amplifies (multiplies) and then detects viral nucleic acids (genetic material), but the team are in the process of developing the technique so that the entire process can be carried out between room and body temperatures. PCR on the other hand requires stages to be carried out at various different temperatures using a thermal cycler. This therefore means that RPA is an ideal candidate for a point-of-care test in resource poor settings where PCR is unavailable.
RPA can also be extended to monitor the levels of virus present in a patient in a process called quantitative RPA (qRPA), which involves tagging specific sequences of HIV DNA with fluorescent probes that can be detected and quantified by portable equipment. Software that analyzes the data provided is able to give accurate details on the amount of virus present in the sample.
Although this technique was developed for use in infant HIV detection, the researchers say that it will be a highly useful resource in viral load monitoring in infected patients. “It’s important for clinicians to be able to quantitatively monitor patients’ viral loads in order to ensure the disease is responding to therapy,” said co-lead author Zachary Crannell in a news-release.
According to the researchers, in order for the new test to be viable in a clinical setting it needs to be able to quantify viral loads over four orders of magnitude; they report that the technique easily attains this requirement.
Although the test is not ready to be used in the field yet, these preliminary results suggest that in the future it could be a powerful point-of-care tool for HIV detection and viral load monitoring in developing nations with poor access to medical resources.
