Human T-cell lymphotrophic virus in California's injection drug users.

Human T-cell lymphotrophic virus I (HTLV-I) and human T-cell lymphotrophic virus II (HTLV-II) are closely related retroviruses that are highly prevalent in injection drug users (IDUs). The bulk of infection in this group probably occurs with HTLV-II, with a lower prevalence of HTLV-I. HTLV-I is known to cause adult T-cell leukemia/lymphoma and tropical spastic paraparesis. HTLV-II has not been proven to cause any human pathology, but may be immunosuppressive and is almost indistinguishable serologically from HTLV-I. As with human immunodeficiency virus (HIV), infection with these viruses is likely to be lifelong and the disease may have a latent period of many years. Unlike HIV, HTLV-I and/or HTLV-II are not likely to be transmitted from mother to child prenatally, and usually require breast-feeding for vertical transmission. It is likely that HTLV-I and/or HTLV-II has been prevalent in IDUs for far longer than the HIV epidemic. HTLV-I and/or HTLV-II are relevant to the AIDS epidemic in that they may function as biologic markers of behavioral risk status for HIV infection in IDUs or their sexual partners, and they may accelerate the course of HIV infection in persons coinfected with HTLV-I and/or HTLV-II and HIV. Coinfection will be more likely as the HIV epidemic progresses. Pregnant addicts entering outpatient methadone maintenance treatment in San Francisco County or Contra Costa County during 1990 were found to have an HTLV-II prevalence of 21% (n = 24). Important issues in counseling infected methadone patients are described.