A virus found primarily in injection drug users and a small number of Native Americans may increase the incidence of infectious diseases, according to a multi-center, longitudinal study headed by the University of California, San Francisco.
New findings show that people infected with human T-lymphotropic virus type II (HTLV-II) have a greater risk of acquiring bronchitis, bladder and kidney infections, oral herpes, and pneumonia. The study appears in the July 12 issue of the Archives of Internal Medicine.
HTLV-II is a retrovirus that infects white blood cells. It is closely related to HTLV-I, a retrovirus responsible for causing leukemia and a progressive spinal cord disorder called myelopathy. Whereas HTLV-I is found primarily in Japan, Africa, and the Caribbean, HTLV-II occurs primarily in Amerindian tribes in South and Central America where incidence rates can reach 30 percent.
In the United States, approximately 200,000 people are infected with HTLV-II. Injection drug users account for the vast majority of cases; roughly 10 to 20 percent of users have the virus. Approximately one to two percent of Native Americans are also infected.
“HTLV-II has been epidemic among injection drug users in the United States for over twenty years,” said Edward Murphy, MD, MPH, UCSF associate professor of laboratory medicine, medicine, and epidemiology/biostatistics. “Our study is the first step towards understanding the consequences of its infection.” Murphy is the principal investigator of the study.
Study participants were recruited between November, 1990 and February, 1993 from five major blood donation centers across the United States and six smaller blood banks in San Francisco and Los Angeles. The study cohort was made up of 1,213 individuals, including 136 people with HTLV-I, 337 people with HTLV-II, and 740 people with neither infection who were used as controls. Interviews and physical exams were routinely conducted for two years to assess the participant’s physical health.
People infected with HTLV-II were statistically more likely than the control group to acquire bronchitis (16 percent versus 9 percent), bladder or kidney infections (15 percent versus 8 percent) and oral herpes (5 percent versus 0.7 percent). In addition, people with HTLV-II were somewhat more likely to get pneumonia.
“Although 95 percent of the people infected with HTLV-II won’t get a major disease, our study shows that it does interfere with their lifestyle,” said Murphy. “People have to live with the knowledge of having this lifelong virus.”
The study also showed that HTLV-I caused statistically higher rates of bladder and kidney infections compared to controls (18 percent versus 8 percent).
Both HTLV-I and HTLV-II can be transmitted through the sharing of contaminated needles, sexual activity, and breast milk, said Murphy. Because they can also be transmitted through the transfusion of infected blood products, blood banks have been screening for the virus since 1988. About 0.03 percent of volunteer blood donors are infected with either HTLV I or II, according to Murphy’s previous research. Infected individuals are disqualified from giving blood.
HTLV-I and HTLV-II were the first retroviruses identified in humans (1980 and 1982, respectively), preceding the identification of HIV in 1994. Although HTLV is most closely related to the virus that causes bovine leukemia, it affects the same lymphocytes as HIV. The researchers speculate that their present work on the biological mechanisms of HTLV could lead to a better understanding of the AIDS virus.
“Understanding how HTLV works will fill out the knowledge of human retroviruses,” said Murphy. “A vaccine for HTLV may be easier to develop than a vaccine for HIV.”
In addition to Murphy, co-authors include Simone Glynn, MD, MPH, MSc, senior study director, Westat Incorporated; Joy Fridey, MD, senior vice president of medical affairs, Blood Bank of San Bernardino County; James Smith, MD, PhD, associate medical director, Oklahoma Blood Institute; Ronald Sacher, MD, professor, department of laboratory medicine, Georgetown University Hospital; Catharie Nass, PhD, managing director of donor management and research, American Red Cross Blood Services - Chesapeake and Potomac Region; Helen Ownby, PhD, American Red Cross Blood Services - Southeastern Michigan; David Wright, PhD, statistician, Westat Incorporated; George Nemo, PhD, project officer, National Heart, Lung and Blood Institute.