Phylogeny And Epidemiology Of Htlv1 And Htlv2

Phylogenetic analyses of BLV, HTLV-1, HTLV-2 and simian T-cell lymphoma/leukemia virus strains from around the world indicate that the PTLV diverged from BLV approximately 60,000 to 100,000 years ago.12 The PTLV are endemic to many, but not all, species of Old World primates including humans. It is clear that many incidences of cross-species transmissions have occurred over many thousands of years and PTLV strains are grouped more by geographic origin than by host species. The PTLV can be taxonomically divided into three major subsets (Figure 12-5). The PTLV-1 have two major subgroups (African and Asian/Austronesian), which differ by about 15

Figure 12-5. The complete genomes of many PTLV and BLV strains as analyzed by the neighbor-joining method. The relative distance of all branches are as indicated and the boot-strap values (>70 percent is considered statistically significant) for several of the branches are shown. The tree was rooted to the two BLV strains. The asterisks indicate the location of the PTLV-1 and PTLV-2 strains utilized to make antigens for most clinical HTLV serological assays. The PTLV-1 strains are divided into Asian/Austronesian (MACA and MEL5) and African (all others) subgroups. The PTLV-2 are divided into African (Pan-P and PP1664) and Paleo-Amerindian (all others) subgroups. The PTLV-L, found in Eritrean baboons, forms a unique subgroup, PTLV-3, not yet detected in humans.

Figure 12-5. The complete genomes of many PTLV and BLV strains as analyzed by the neighbor-joining method. The relative distance of all branches are as indicated and the boot-strap values (>70 percent is considered statistically significant) for several of the branches are shown. The tree was rooted to the two BLV strains. The asterisks indicate the location of the PTLV-1 and PTLV-2 strains utilized to make antigens for most clinical HTLV serological assays. The PTLV-1 strains are divided into Asian/Austronesian (MACA and MEL5) and African (all others) subgroups. The PTLV-2 are divided into African (Pan-P and PP1664) and Paleo-Amerindian (all others) subgroups. The PTLV-L, found in Eritrean baboons, forms a unique subgroup, PTLV-3, not yet detected in humans.

percent at the DNA level. Introduction into humans from other primates occurred at least twice in Africa and Austronesia. Hence, HTLV-1 is endemic in sub-Saharan Africa and throughout Australia and Melanesia. HTLV-1 has been disseminated throughout the world over the past 500 years via European exploration, the slave trade, blood product transfusion, intravenous drug use, and increased travel; it is now endemic in the Caribbean; Latin America; major cities throughout India, Europe, and the United States (particularly on the southern and eastern coasts and Hawaii); Iran; and Southern Japan.12

The PTLV-2 can be divided into two major groups, African and Paleo-Amerindian. The African subset has been found in pygmy chimps and isolated groups of human pygmies.13,14 Very little epidemiological investigation work has been done in these individuals and it is unclear as to whether they suffer from any clinical ailments. There is no evidence that these unique strains have disseminated out of very isolated parts of Africa. HTLV-2 is endemic to Paleo-Amerindians of the New World, being found in Indians of the American Southwest and Florida, Central America, and South America. By the same mechanisms described for HTLV-1, this virus has been disseminated worldwide.

The PTLV-3 consists of a few strains identified in Eritrean baboons whose ancient geographic range extended from the steppes of Central Asia to the Rift Valley in Africa.15 No other primate has been shown to harbor this strain nor are there any known disease associations, although, again, very little work has been done in this area.

Epidemiological data indicate that the PTLV is transmitted in utero to a very small degree, but at a rate of 10 to 30 percent via breastfeeding. The virus is also transmitted via sexual intercourse, with male to female infection occurring much more effectively than the opposite. The virus is also spread via intravenous drug abuse and the transfusion of cellular but not plasma products. There are no reported incidences of infection occurring via needle stick or other laboratory or clinical work-related injuries.12,16

Effective blood donor screening and public health policies (e.g., the use of condoms and bottle-feeding introduced in Japan over the past one to two decades) have had a significant impact on the dissemination of HTLV in certain endemic areas. In the United States all blood and organ donations are screened for HTLV-1 and HTLV-2. It is probably remiss that all pregnant women are not, in that preventing perinatal infection would probably have the most significant impact on preventing HTLV-associated diseases.

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