The most sensitive test for the detection of HIV in the body in the first stages of infection remains the blood test. However, it is not comfortable, and for many people, for religious reasons or for fear of blood it is impossible. Therefore, scientists are improving methods of virus detection from saliva samples. They argue that this technique can also work on the detection of other diseases.
The standard technique for detecting HIV infection is to do a blood sample. It is looking for anti-HIV antibodies, or proteins of the immune system, used to fight against the developing infection. Such a test is much more certain than searching for molecules of the virus itself, because the antibodies appear in the bloodstream at the very beginning of the infection in a larger quantity than copies of the virus. Sometimes, however, a blood test is uncomfortable or impossible, especially when a large group of people is planned to be tested (so-called "screening"). Then usually tests are performed on the basis of a saliva sample.
The detection of HIV infection from saliva is nothing new - current tests have a serious limitation in the early stages of infection. They are not sensitive enough to be able to detect the level of anti-HIV antibodies at the very beginning of the infection when there are still few. In turn, obtaining a false negative test result can result in the danger of infecting other people with this dangerous virus. In addition, antiretroviral treatment is most effective when it starts at the earliest possible stage of infection, and a person who is convinced of being infected can only visit the doctor when AIDS is known.
The situation is to change the new test, developed by researchers from Stanford University.
Increase sensitivity
Scientists, instead of looking for antibodies themselves, base their method of action on what antibodies do and what they look like, thanks to which they managed to achieve a much higher sensitivity of their method than methods available on the market. The antibodies have two arms, so they resemble the letter Y. These arms act as "snaps" recognizing and holding small aggressors such as HIV. This holding is made possible by the presence of DNA fragments on the arms of the antibody.
The test used small fragments of the HIV virus with complementary DNA fragments attached to them. When anti-HIV antibodies are present in the saliva sample, they attach the virus fragment to one of the arms, and the other arm connects to the complementary DNA fragment to form a double strand. And in turn such a double thread is much easier to detect (and at a much lower level) than the anti-HIV antibody itself.
It works?
The new test has been tested twice. The first study examined whether the method would be able to detect the HIV carrier in infected individuals, while not giving false positive results to healthy people. A small group of 22 HIV carriers and 22 uninfected persons participated in the study. In all infected patients, the test detected the presence of anti-HIV antibodies and with high sensitivity. At the same time, no healthy person showed a false positive result.
After confirming the specificity of the new test, saliva was left to judge its sensitivity to current saliva tests and a blood sample test. For this purpose, saliva from 8 HIV carriers was tested, in which the level of anti-HIV antibodies was low enough that traditional tests with saliva gave inconclusive results. The new test coped with 6 samples. This indicates the high sensitivity of the new method - however, the saliva test is still less sensitive than the traditional blood sample test.
The authors of the invention claim that a new method of increasing the sensitivity of tests performed from saliva samples may be useful also in the case of other infections, including tuberculosis bacilli or typhoid bacilli, determining the occurrence of allergies or the development of postvaccinal immunity.
Based:
C.-t. Tsai, et al.,Antibody detection by agglutination-PCR (ADAP) provides early diagnosis of HIV infection by oral fluid analysis. PNAS 115 (6) (2018) 1250-1255