A 1994 study that drew up the phylogenetic tree and mapped the distribution of the human T-lymphotropic virus type I (HTLV-I) has shown the close relationship between the Ainu people, and the the native inhabitants in India and South America (Colombia and Chile).
The Human T-lymphotropic virus type I (HTLV-I) (1, 2), the retrovirus causing adult T-cell leukemia (ATL) (3) and HTLV-I-associated myelopathy or tropical spastic paraparesis (HAM/TSP) (4), was considered to be mainly endemic in Japanese in East Asia and Blacks in Africa and the Caribbean basin. But recently, researchers found HTLV-I carriers in other various regions in the world.
HTLV-I is known to be transmitted only by cell-associated infection and mainly by vertical infection from mother to child; consequently, the distribution of the virus is considered to be related to the anthropological background and past human movement. Hence, the present distribution of the cosmopolitan type of the HLTV-I virus can be explained by human movements in the past.
Three major types of HTLV-I are known and the tree clearly shows the existence of three lineages (subtypes A, B, and C) of HTLV-I in the cosmopolitan type. Subtype A consists of Caribbean, South American (Chilean and Colombian) and Japanese isolates, including that from the Ainu together with one Indian isolate, whereas subtype B consists of other Japanese isolates and another Indian isolate. The analysis found that there are two (or more) lineages of Japanese HTLV-I and that both Japanese lineages (subtypes A and B) are related to the Indian isolates, but only one of them-that is, subtype A-is closely related to Caribbean and South American isolate.
Fig 2 above shows the geographical distribution of HTLV-I in the world and a possible movement of the cosmopolitan type in the past based on the topology of the phylogenetic tree and movements in the past.
Miura’s 1994 study concluded:
Two (or more than two) Mongoloid lineages of HTLV-I carrying people moved to Japan in the Paleolithic period, resulting in the present existence at least two lineages of HTLV-I in Japan (subtypes A and B). However, only one of the two lineages in Japan, subtype A, is thought to have crossed Beringia and to have reached the Caribbean and South America; the other lineage, subtype B, probably reached Japan after Beringia was disconnected. Subtype A implies a close connection of the Caribbean and South American natives with the Japanese and thereby a possible migration of the lineage to the American continent via Beringia in the Paleolithic era.
From the paleoanthropological viewpoint, it is suggested that the first immigrants to the North American continent, arrived about 12,000 years ago from North Asia, passing through Beringia and then gradually spreading from the North American continent to the South American continent. (Phylogenetic analysis of mitochondrial DNA and HLA type analysis also confirm the relationship between Japanese and Paleo-Indians in South America.)
In Japan, HTLV-I is mainly endemic in the southwest and in remote populations of frontier areas such as “Ryukyuans” on Okinawa and Ainu people on Hokkaido Island. Ishida and Hinuma proposed that “Jomon” people, ancient inhabitants of Japan who carried HTLV-I, were shoved away by the HTLV-I-free Yayoi people who entered the Asian continent more than 2300 years ago. The first immigration to the Japanese archipelago is considered to have occurred more than 10,000 years ago, and the mixed HTLV-I population of subtypes A and B in Japan revealed by the tree may indicate plural immigrations of HLTV-I carrying people before or during the “Jomon” period.
The West African lineage subtype C Caribbean HTLV-I has generally been considered to have been brought from West Africa during the period of slave trade to the Caribbean basin by the slave trade several hundred years ago, forming the subtype C. The 1994 study also supported the existence of subtype C according to its analysis. but it indicated the existence of another lineage, subtype A, related to Asian HTLV-I, in the Caribbean basin. This suggests a possibility of mixed blood between Asian and African populations in the Caribbean.
Source and references:
Proc Natl Acad Sci U S A. 1994 Feb 1;91(3):1124-7.
Phylogenetic subtypes of human T-lymphotropic virus type I and their relations to the anthropological background. (Full pdf doc. here) Miura T et al.
Institute for Virus Research, Kyoto University, Japan.