Human T-Lymphotropic Virus Type II Among Guaymi Indians -- Panama

Human T-lymphotropic virus type 2 (HTLV-II) is one of four retroviruses (i.e., HTLV-I, human immunodeficiency virus type 1 (HIV-1), and HIV-2) that are known to infect humans. During 1988, investigators from the Gorgas Memorial Laboratory (GML) and the National Institutes of Health (NIH) tested serum specimens collected during 1978-1987 throughout Panama to determine the prevalence of HTLV-I infection (1), which is endemic in southern Japan and the Caribbean basin (2). HTLV seropositivity rates were low in all areas of Panama except among the Guaymi Indians in Changuinola (9%),* a city in western Panama (Figure 1). During 1989-1991, additional testing of 36 seropositive specimens from Guaymi Indians detected that the infections were due to HTLV-II (3,4). This report summarizes risk factor data for HTLV-II infection among Guaymi Indians.

During December 1989-March 1990, Guaymi households were randomly selected and contacted for a cross-sectional study to determine risk factors for HTLV-II infection. Serum was collected from 254 persons aged greater than or equal to 1 year for whom consent was obtained, and risk data (i.e., sexual behavior and history of injection) were collected from participants aged greater than or equal to 7 years.

The median age of participants was 16 years (range: 1-72 years); 140 (55%) were male. Although none of 59 participants aged less than 7 years tested HTLV-antibody-positive, 17 (9%) of 195 persons aged greater than or equal to 7 years tested HTLV-I/II-antibody-positive; all were confirmed by additional testing to be infected with HTLV-II.

Seropositivity rates increased with age and were highest (15%) for those aged greater than 30 years. Although no other association reached statistical significance, infected persons were more likely to report a history of one or more marriages (odds ratio (OR)=3.2; p=0.1), cohabitation with one or more partners (OR=2.1; p=0.3), one or more lifetime sex partners (OR=2.0; p=0.4), and to be seropositive for herpes simplex virus type 2 (OR=2.1; p=0.2). HTLV-II infection was not associated with histories of blood transfusion, vaccination, injection, or tattoo.

Reported by: F Gracia, MD, L Castillo, MD, B Armien, MD, Gorgas Memorial Laboratory, Panama. RM Giusti, MD, PH Levine, MD, WA Blattner, MD, National Cancer Institute, Bethesda, Maryland. Retrovirus Diseases Br, Div of Viral and Rickettsial Diseases, National Center for Infectious Deseases, CDC.

Editorial Note

Editorial Note: HTLV-II has primarily been associated with injecting-drug users (IDUs) and their sex partners (5). In the United States, the initiation of volunteer blood-donor screening for HTLV infection in November 1988 resulted in the identification of approximately 2000 seropositive units of blood donated each year. Of these, at least half were infected with HTLV-II (6).

The Guaymi in Changuinola, who have migrated from traditional living areas in the mountains of western Panama, are the first nondrug-injecting population known to have high rates of HTLV-II infection. Associations of HTLV-II infection with other Native American Indian groups have been reported but not confirmed by population-based studies (7).

HTLV-I and HTLV-II are closely related (60% genomic homology) and, like the immunodeficiency viruses, have a tropism predominantly for CD4 lymphocytes and infect the human host for life. Serologic tests for HTLV-I, including enzyme immunoassay, Western blot, and radioimmunoprecipitation assay, also detect HTLV-II through cross-reactivity. Therefore, seropositive results are properly referred to as HTLV-positive or HTLV-I/II-positive, and not as HTLV-I-positive as is sometimes reported. Further discrimination between HTLV-I and HTLV-II requires additional testing with techniques such as polymerase chain reaction or newly developed HTLV type-specific peptide serologic assays. HTLV serologic tests do not cross-react with HIV.

Notification and counseling of infected persons has been difficult because of the lack of information concerning disease risk and transmission. HTLV-II has not been linked with disease. However, because as many as 5% of persons infected with HTLV-I have developed adult T-cell leukemia/lymphoma or HTLV-I-associated myelopathy/tropical spastic paraparesis (8), there is concern about possible disease associations with HTLV-II infection.

Similarly, the modes of transmission of HTLV-II are not well documented. Both HTLV-I and HTLV-II are highly cell associated, and transmission of either virus is thought to require passage of infected lymphocytes, rather than cell-free body fluids. Within areas endemic for HTLV-I, breastfeeding, sex, and transfusion of infected cellular blood products have transmitted HTLV-I (8).

Preliminary findings among the Guaymi suggest that there may be important differences between HTLV-I and HTLV-II transmission; for example, despite the universal practice of breastfeeding among the Guaymi, lack of seropositivity among young Guaymi children suggests that HTLV-II may not be efficiently passed by this route. In contrast, preliminary data suggest that sexual contact may be the most important route of transmission in this population.

To resolve these issues and to obtain data that may be difficult to acquire from other populations, investigators from the GML, the NIH, and CDC began pilot studies during November 1991 in preparation for a three-part study of HTLV-II infection among Guaymi Indians. Phase I, in which approximately 5000 persons are expected to be enrolled, is a cross-sectional serosurvey of all Guaymi in Changuinola aged greater than or equal to 1 year. In phase II, persons identified as infected with HTLV-II in phase I will be compared with seronegative controls to assess differences in risk behaviors, diseases, and laboratory-measured immunologic parameters possibly associated with HTLV-II. Phase III will be a hospital-based study to identify possible disease associations; HTLV-II infection rates among Guaymi patients will be compared with rates in the general Guaymi population.

References

1. Reeves WC, Levine PH, Cuevas M, Quiroz E, Maloney E, Saxinger WC. Seroepidemiology of human T cell lymphotropic virus in the Republic of Panama. Am J Trop Med Hyg 1990;42:374-9.

2. Blattner WA. Retroviruses. In: Evans AS, ed. Viral infections of humans: epidemiology and control. 3rd ed. New York: Plenum, 1989.

3. Lairmore MD, Jacobson S, Gracia F, et al. Isolation of human T-cell lymphotropic virus type 2 from Guaymi Indians of Panama. Proc Natl Acad Sci USA 1990;87:8840-4.

4. Heneine W, Kaplan JE, Gracia F, Lal R, Roberts B, Reeves W. HTLV-II endemicity among Guaymi Indians in Panama. N Engl J Med 1991;324:565.

5. Kwok S, Gallo D, Hanson C, McKinney N, Poiesz B, Sninsky JJ. High prevalence of HTLV-II among intravenous drug abusers: PCR confirmation and typing. AIDS Res Hum Retroviruses 1990;6:561-5.

6. CDC. Human T-lymphotropic virus type I screening in volunteer blood donors -- United States, 1989. MMWR 1990;39:915,921-24.

7. Hjelle B, Mills R, Swenson S, Mertz G, Key C, Allen S. Incidence of hairy cell leukemia, mycosis fungoides, and chronic lymphocytic leukemia in first known HTLV-II-endemic population. J Infect Dis 1991;163:435-40.

8. Kaplan JE, Khabbaz RF. HTLV-I: newest addition to blood donor screening. Am Fam Physician 1989;40:189-95.

• Among other populations in Changuinola, HTLV I/II infection was low or nonexistent (i.e., Teribe Indians (5/180, 3%), Mestizos (0/152), and blacks (0/46)).

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