Intravenous drug abusers in New York City and Vietnam have onething in common with at least a dozen Amerindian tribes of Northand South America. All of their veins harbor a surreptitious retroviruscalled human T cell lymphotrophic virus type II (HTLV-II).
These disparate populations now share this rare viral distinction witha 59-year-old African pygmy woman of the Bakola tribe, in a remoteequatorial forest of Cameroon.
Virologist Robert Gallo, at the National Cancer Institute, describedthe hitherto unknown human retrovirus, HTLV-II, in 1982, two yearsafter he discovered its predecessor, HTLV-I.
Gallo went on to co-discover HIV, the human immune deficiencyvirus, in 1985, with Luc Montagnier of the Pasteur Institute inFrance. At first HIV bore the misnomer "HTLV-III," but asRockefeller University virologist William Hall told BioWorld Today,"HIV is genetically, phylogenetically and historically unrelated to theHTLVs." Hall's special field of research is HTLV-II and he headsRockefeller's laboratory of medical virology.
Unlike HTLV-I, he observed, "The role of HTLV-II in humandiseases is very poorly defined." Hall added that "there are about 10reported cases of a neurological disease similar to the one caused byHTLV-I." That affliction is tropical spastic paraparesis (TSP), alower-limb weakness similar to multiple sclerosis. HTLV-I is alsoguilty, as its name implies, of causing T cell leukemias andlymphomas. Hall said the two types, I and II, are 65 percent identicalon physical maps.
HTLV-II Long Deemed `Confined To The Americas'
Virologist Guy De The heads the Unit on Epidemiology ofOncogenic Viruses at the Pasteur Institute in Paris. "The first HTLVtype," he told BioWorld, HTLV-I, is found everywhere in the world,mostly in Africa, southern Japan, Central and South America. HTLV-II, on the other hand, up to last year was confined to the Amerindiantribes of North and South America."
After that," De The explained, "HTLV-II was found to havedeveloped as an epidemic in IV drug abusers in North America _but again confined to the Americas."
Hall, however, said, "We have a very interesting population ofintravenous drug abusers in South Vietnam, and we think the HTLV-II virus was actually introduced by American troops. Over 60 percentof those drug abusers in Ho Chi Minh City are now infected withHTLV-II. It's an enormous problem."
A problem of a different order suddenly confronts the viral historicalepidemiologists. In the April 25 Proceedings of the NationalAcademy of Sciences, Guy De The reports having cornered anapparently familial strain of HTLV-II in an African pygmy tribe.
"What we described," he said, "is the isolation and molecularcharacterization of HTLV-II in a genuine isolate in Africa. This isvery important because it raises the basic question of the origin ofthis virus, and probably of all these HTLVs. They are perhaps theoldest human retroviruses in human populations, with their probableorigin in Africa."
For Biotechnology: `The Core Of The Matter'
De The suggested that "the core of the matter _ that HTLV-II mightbe more widely distributed around the world than originally thought_ is important for biotechnology." He explained: "I think theyshould now develop a reagent for HTLV-II detection andcharacterization."
Here is how De The described his virus-hunting expedition last yearin Africa:
"We were looking for HTLV-II, based on some previousobservations in health workers in Cameroon, whom we found, fromserological tests, to be infected with that viral type. We felt it waseither an imported disease or a genuine indigenous virus. Andtherefore we were looking for it."
They looked first among some family contacts in the Bakola villagesof the interior. The Bakola Pygmies are hunter-gatherers. The virus-hunters found individuals who had tested positive for HTLV-IIantibodies a decade earlier. The daughter of one of them was a 59-year-old healthy woman, likewise HTLV-II seropositive. She hadnever been transfused, nor had any intimate contact with Europeansor Americans.
In her sampled peripheral blood they searched for HTLV-IIantibodies by ELISA, immunofluorescence and other tests. AWestern blot of her serum looked strangely unlike that of the better-known HTLV-I. PCR analysis of DNA from cells confirmed that herinfection was indeed HTLV-II, not HTLV-I.
De The observed that William Hall had described the scanty casehistories of diseases associated with HTLV-II. Hall reported thatHTLV-I is associated with CD4 T cell leukemias andlymphoproliferations; CD8 with malignant diseases.
"But there are very few case reports yet of diseases associated withHTLV-II," De The said, "because this virus until recently had beenfound only in very remote ethnic groups, with no medical coverage."
Hall agreed that HTLV-II hasn't yet been associated withlymphoproliferative or leukemic disorders, although, he added, "onemight anticipate that that's going to happen."
He finds "the major problem right now is the difficulty ofdifferentiating the two types, I and II. When you go to the blood bankand screen it, you can't tell which is which."
Both HTLVs May Accelerate AIDS
"This creates a lot of problems," Hall pointed out. "Because ifsomeone has HTLV-I infection, that can have a significant impact ontheir life, in terms of the neurologic or leukemic disorder. WithHTLV-II, probably nothing will happen to them."
But something clinically significant already is happening to theintravenous drug users in New York and other urban American areas,Hall went on. That is, besides HTLV-II, a lot of them are alsoinfected with HIV-1.
"So I think," he warned, "there is a potential for interaction betweenthese two viruses. Both infect mature lymphocytes. Both in vitro cantransactivate each other. And, as is known for example in theCaribbean, where you have dual infection with HIV and HTLV-I,there is much more rapid progression of AIDS."
Reverting to the debate on the origin of human retroviruses, Hallsaid, "What's interesting about De The's finding is that because ofHTLV-II's relative restriction to American Indians, it's considered bymany to be a New World virus. This in contrast to HTLV-I, which isalmost certainly of African origin."
Hall said its more likely that HTLV-II "was brought to the NewWorld from the Old, probably during the migrations of the AmericanIndians," 10,000 to 40,000 years ago. n
-- David N. Leff Science Editor
(c) 1997 American Health Consultants. All rights reserved.