HTLV in the Americas

Abstract

It has been 25 years since the discovery of the first human retrovirus,human T-cell leukemia virus type 1 (HTLV-1) (1). Soon after HTLV-1 was dis-covered, a second human retrovirus, HTLV-2, was described (2). In 2005, twonew human retroviruses, HTLV-3 and HTLV-4, were reported in central Africa(3, 4). HTLV-1 was the first retrovirus linked to human disease (5). It has beenconvincingly associated with adult T-cell leukemia/lymphoma (ATL), HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), uveitis, andinfective dermatitis (6-9). The viruses, especially HTLV-1, have a worldwide distribution (10).Although the exact number of individuals who are seropositive for HTLV-1 orHTLV-2 is not known, it is estimated that about 15 to 20 millions persons(mostly HTLV-1-seropositive) live with these infections worldwide (10). Theareas of the world with the highest prevalence rates for HTLV-1 include south-western Japan, several countries in sub-Saharan Africa, Central America, andlocalized areas of Iran and of Melanesia. Higher prevalence rates are alsofound in several countries in the Caribbean, and somewhat lower seropreva-lence rates are found in several nations in South America (10). Known modesof HTLV-1 transmission include mother to child, predominantly throughbreast-feeding; sexual intercourse; and parenteral transmission by transfusionof infected cellular blood products or sharing of needles and syringes. In the Caribbean, Jamaica and Trinidad and Tobago have relativelyhigh (up to 6%) HTLV-1 or HTLV-1/2 seroprevalence rates in the general pop-ulation or in specific groups of individuals such as pregnant women andprospective blood donors (11, 12). Although no studies with representativesamples of the general population have been conducted so far in SouthAmerica, lower seroprevalence rates are found in several countries, includingBrazil and Colombia (10). Data from Argentina, Brazil, Colombia, and Peru are for the most part restricted to specific groups such as blood donors (up to2% of seropositivity for HTLV-1/2), pregnant women, Amerindian tribes, andintravenous drug users. Several studies have reported that indicators of lowersocioeconomic status, such as having fewer years of schooling, are associatedwith HTLV-1/2 infection in both endemic and nonendemic areas (13, 14). Thissuggests that social and environmental factors associated with poverty mayinfluence HTLV transmission. Similarly, HTLV-1-endemic countries (exceptJapan) have low per capita incomes and fewer resources to deal with a higherburden of HTLV-1/2 infection and associated diseases. The impact of HTLV-1-associated diseases on individuals and their communities is often devastating.No preventive vaccine exists, and the prognosis for ATL and HAM/TSP ispoor, in terms of both survival and quality of life (15). HAM/TSP is a long-lasting, progressive disease, and the financial costs for the infected individuals,their families, and health systems are immense. Given these realities, publichealth interventions such as counseling and the education of high-risk indi-viduals and populations are of great importance.HTLV screening of donated blood has been routinely implemented inBrazil, Canada, the United States, and other countries in the Americas.Although no specific studies have evaluated this intervention, it has certainlydiminished the occurrence of new infections among blood recipients.However, for many other countries in the Americas, this intervention is notsystematic and/or permanent, or it is not done at all. The development of ade-quate, cost-effective strategies for HTLV screening of donated blood should be