A method for evaluating the viability of viruses with lymphotropism properties in patients after testing for lymphotropic virus infection, comprising: testing, by subjecting a biological material that has been collected from a patient suspected of infection by a lymphotropic virus, to polymerase chain reaction, PCR, wherein said testing indicates no infection by a lymphotropic virus, characterized by: obtaining a lymphocyte suspension from a blood sample of at least one healthy human subject; combining said lymphocyte suspension with an equal amount of said biological material to form an admixture; incubating the admixture; washing-out the lymphocytes from said admixture; removing lymphocyte membranes, separating the lymphocyte cytoplasm content suspected of infection by said lymphocyte virus by centrifugation; and detecting the presence or absence of virus RNA or DNA in the lymphocyte cytoplasm content by PCR, wherein the presence of the virus RNA or DNA in the lymphocyte cytoplasm content, with the earlier non-detection of infection, indicates the preserved viability of viruses in said biological material of said patient, and wherein the absence of the virus RNA or DNA in the lymphocyte cytoplasm content indicates the loss of virus viability in said biological material of said patient. testing, by subjecting a biological material that has been collected from a patient suspected of infection by a lymphotropic virus, to polymerase chain reaction, PCR, wherein said testing indicates no infection by a lymphotropic virus, characterized by: obtaining a lymphocyte suspension from a blood sample of at least one healthy human subject; combining said lymphocyte suspension with an equal amount of said biological material to form an admixture; incubating the admixture; washing-out the lymphocytes from said admixture; removing lymphocyte membranes, separating the lymphocyte cytoplasm content suspected of infection by said lymphocyte virus by centrifugation; and detecting the presence or absence of virus RNA or DNA in the lymphocyte cytoplasm content by PCR, wherein the presence of the virus RNA or DNA in the lymphocyte cytoplasm content, with the earlier non-detection of infection, indicates the preserved viability of viruses in said biological material of said patient, and wherein the absence of the virus RNA or DNA in the lymphocyte cytoplasm content indicates the loss of virus viability in said biological material of said patient. obtaining a lymphocyte suspension from a blood sample of at least one healthy human subject; combining said lymphocyte suspension with an equal amount of said biological material to form an admixture; incubating the admixture; washing-out the lymphocytes from said admixture; removing lymphocyte membranes, separating the lymphocyte cytoplasm content suspected of infection by said lymphocyte virus by centrifugation; and detecting the presence or absence of virus RNA or DNA in the lymphocyte cytoplasm content by PCR, wherein the presence of the virus RNA or DNA in the lymphocyte cytoplasm content, with the earlier non-detection of infection, indicates the preserved viability of viruses in said biological material of said patient, and wherein the absence of the virus RNA or DNA in the lymphocyte cytoplasm content indicates the loss of virus viability in said biological material of said patient.