Testing and Indications for testing

The algorithms for HLTV testing are similar to HIV testing. In Australia most public and private laboratories can test serum for HTLV-1 and HTLV-2 antibodies by enzyme-linked immunosorbent assay (ELISA). If the screening test is found to be reactive, a confirmatory antibody test is performed by Western Blot (WB) assay through the National Reference Laboratory. The WB assay can result in three outcomes:

  • If positive, then the patient carriers the HTLV virus. The confirmation test also identifies the virus as type 1 or type 2.
  • If the WB is negative, then the patient needs to be informed that they do not carry HTLV-1 or -2, even if the screening test was reactive.
  • If the WB is indeterminate, which is defined as an incomplete banding pattern of antibodies to the HTLV proteins gag (p19 or p24) or env (GD21 or rgp46) (34, 35), this may indicate a history of exposure to HTLV-1 without full antibody seroconversion. A WB indeterminate sample needs to be followed up with an assay for HTLV-1 pro-viral DNA in blood leucocytes. If pro-viral DNA is detectable, then the patient carries the virus. If pro-viral DNA is negative, then (in the absence of national guidelines and based on personal expertise) the HTLV-1 pro-viral DNA assay should be repeated six months later. If HTLV-1 pro-viral DNA is still undetectable at six months, then the patient does not carry a significant risk of becoming ill with HTLV-1 diseases or transmitting the virus.

In order to assess people with HTLV-1 infection for risk of transmission and/or their risk of developing HTLV-1 disease, the HTLV-1 pro-viral DNA load should be determined (36). Pro-viral DNA load testing measures the proportion of T-lymphocytes that are infected with HTLV-1 (%). Unlike HIV, the HTLV-1 pro-viral DNA load generally does not change over time and is set at a patient-specific level.

 There are no international guidelines about who should be offered testing for HTLV-1 infection. In some countries, blood transfusion and organ transplantation services offer routine HTLV-1/2 screening and decline donations from a positive donor. HTLV-1/2 infection should be considered either to exclude infection as part of a diagnostic work-up of symptomatic patients, (i.e. neurological symptoms, blood malignancies, uveitis, unexplained skin lesions, bronchiolitis/bronchitis and Strongyloides stercoralis infection (37-40)) or to screen at-risk patients, i.e. people who inject drugs, babies of mothers living with HTLV infection, sexual contacts of people living with HTLV infection and people who are from HTLV high endemic areas.