Human T lymphotropic virus types 1 and 2: a point of view

Abstract

Reported at the beginning of the 1980s, Human T lymphotropic viruses type 1 and 2 (HTLV1, HTLV 2) were the first retroviruses to have been detected in human beings. HTLV 1 was isolated from adult T-cell leukemia (ATL) and first described by Takatsuki et al. in Japan in 1976, as a malignancy that only affects T cells and only in adults(1, 2). Albeit infrequent, HTLV-1 infection may lead to severe morbidity when it causes malignancy or degenerative conditions. The virus can also cause mild immune deficiency even in the absence of any malignancy. Fatal neurologic diseases, such as HTLV-associated myelopathy/tropical spastic paraparesis (HAM/TSP), uveitis, iritis, peripheral neuropathies, and arthritis can also be caused by HTLV-1. All these diseases can be autoimmune, but their exact mechanisms are not yet known(3). Human T lymphotropic virus type 2 (HTLV-2) was discovered in a patient with a T-cell variant of hairy cell leukemia. The virus has been associated with increased mortality and morbidity, risk for pneumonia and bronchitis, urinary tract infections, and rare neurologic manifestations. HTLV infection is life-long and disease symptoms can manifest some 20-40 years post-infection(4-6). Recently, an increased prevalence of psychiatric symptoms was described among HTLV-seropositive patients(7,8). Prevalence greatly varies in different regions of the world. HTLV-1 is endemic in southwestern Japan, in the Caribbean Islands, and in Central Africa. Carriers have been identified in South America, Papua New Guinea, the Solomon Islands, South China, and other isolated populations such as the Australia Aborigines. HTLV-2 can also be found in some Native American populations. HTLV-1 is transmitted by blood, through sexual contact, injectable drug use and from mother to offspring through breastfeeding(1-6). HTLV-2 is most often found in injectable drug users and in their sexual partners. As a consequence of the transmission routes, all blood donated at the Red Cross Blood Centers in Japan has been subjected to HTLV-1 antibody screening since November 1986 and carrier mothers have been instructed to refrain from breastfeeding to prevent HTLV-1 transmission(9-11). In the United States, screening began at the end of 1988 and in the entire world since 1990(12-15). At the beginning, blood donor screening was performed with enzyme immunoassays (EIAs) for antibodies against HTLV-1 and later against HTLV-1/2, which led to the unnecessary deferral of a great number of individuals. Confirmatory testing could be performed by Western blot but this was expensive and took a long time. Nowadays screening is performed by chemiluminescent immunoassay with a lower risk of false positives(16). Up to now there is no available licensed confirmatory test. The efficacy of this test reduces the number of indeterminate results and could be better than the lookback procedure for HTLV-1/2(17). Confirmatory testing by polymerase chain reaction (PCR), albeit expensive, is used in the great majority of blood banks around the world. The same serological difficulties are observed in Brazil as confirmatory testing is only performed by research groups in some blood banks. HTLV-1/2 infection is endemic in Brazil(18-22) and testing blood donors has been mandatory since 1993. Recently, Carneiro-Proentti et al.(22) analyzed all blood donations of three regional Brazilian Blood Banks located in São Paulo, Minas Gerais and Pernambuco during 2007-2009. Serological results were confirmed by Western blot. Results concerning donor age, gender, education status, and race confirmed the previously published results from other Brazilian blood banks(23,25). Prevalence increased with age, was higher among women and Blacks and was inversely correlated to the level of education. Prevalence variations in different blood banks were expected and probably reflect population origins (higher in Pernambuco than in Sao Paulo and Minas Gerais). The overall incidence rate was 3.59 per 100,000 person-years and the residual risk was 5.0/100,000 per repeat donor blood unit transfused, that is, lower than previously reported in southern Brazil(25). Seroprevalence rates were in the order of 1 to 2 per thousand first time donors which is higher than in the United States and Europe but lower than in the Brazilian general population(24). Besides HTLV screening difficulties, the public health system is also not prepared to confirm and counsel serum-positive donors thus creating a difficult situation as the virus can be transmitted through breastfeeding and the disease can appear almost 30 years after a serological positive result. Preventive measures, the follow up of donors and confirmatory testing procedures must be improved. In this issue of the Revista Brasileira de Hematologia e Hemoterapia, Lima et al. bring new data from the Caruaru Blood Center in Pernambuco(26).