Human T cell lymphotropic virus type II (HTLV-II) infection is endemic in a number of indigenous populations in North, Central, and South America. In the present study we have employed serological and molecular methods to identify HTLV-II infection in Indian communities in the Amazon region of Brazil. Sera (1324) from 25 different Indian communities were analyzed by ELISA and Western blot. One hundred and four samples (7.8%) from a number of culturally distinct and geographically unrelated populations were found to have reactivities consistent with HTLV-II infection. Of these, 67 were from the Kayapo Indian communities, which had an overall seroprevalence rate of greater than 30%. In addition, high seroprevalence rates were observed in three other communities, the Munduruku, Arara do Laranjal and the Tyrio, suggesting that there are additional foci of endemic infection in the Amazon region. In the Kayapo, seroprevalence rates tended to increase with age, supporting the importance of sexual transmission of the virus, and family studies demonstrated that vertical transmission is also an important route of infection. Restriction fragment length polymorphism (RFLP) and nucleotide sequence analysis of a region of the env gene demonstrated that the Kayapo are infected with the HTLV-IIa subtype. Moreover, nucleotide sequence analysis of the LTR demonstrated that this belonged to a distinct HTLV-IIa phylogenetic group. The identification of HTLV-IIa in the Kayapo is, as far as we are aware, the first identified endemic focus of infection by this subtype of HTLV-II in the Americas.

Human T lymphotropic virus, type II (HTLV-II), infection has been shown to be endemic in a number of American Indian populations, and high rates of infection have also been documented in intravenous drug abusers in urban areas throughout the world. Although the role of HTLV-II in human disease has yet to be clearly defined, there is accumulating evidence that like HTLV-I, infection may also be associated with rare lymphoproliferative and neurological disorders. In this article we review and summarize the epidemiology, molecular properties and clinical features of HTLV-II infection.

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HTLV was initially described in association with a form of leukemia in Japan and a neurological disease in the Caribbean. It was soon shown that HTLV-II was endemic among Amerindians and particularly among Brazilian Indians. The Amazon Region of Brazil is presently the largest endemic area for this virus and has allowed several studies concerning virus biology, the search for overt disease, epidemiological data including detailed demographic data on infected individuals, clear-cut geographic distribution, definition of modes of transmission and maintenance within small, epidemiologically-closed groups, and advances in laboratory diagnosis of the infection. A new molecular subtype named HTLV-IIc was further described on the basis of genome sequencing and phylogenetic analysis. This subtype is present in other areas of Brazil, indicating that the virus is additionally both a valuable marker for tracing past human migration routes in the Americas and a probable marker for social habits of the present human population. HIV, the other human retrovirus, is still not prevalent among indigenous communities in the Brazilian Amazon, but these groups are also easy targets for the virus.

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