Epidemiology

Worldwide, most people with HTLV infection are infected with type 1, which is divided into subgroups: A (Cosmopolitan), B (Central and West African), C (Australasian/Melanesian), D (Central African) and F (3). In Australia, HTLV-1C has been described in Central Australian Aboriginal people (5) but other subtypes may be observed in people originating from other parts of the world. A systematic review of published data on HTLV-1 origin and prevalence showed that it is an ancient virus and that its prevalence is complex with high endemicity and disease burden in specific geographical regions (6, 7). Currently available surveillance data are not comprehensive, and in many regions, accounting for six billion persons, the HTLV prevalence remains unknown. In Australia, a high prevalence of HTLV-1 among Aboriginal people was described for the first time in 1988 (8). However, recent hospital and community-based cohort studies in Central Australia reported the highest prevalence rates of HTLV-1 world-wide in certain Central Australian communities. A total of 33.6 %  out of 1889 people were HTLV-1 antibody positive and a sharp increase in age-specific prevalence rates was observed with age, reaching 41.7 % in the 50-64 years age group and up to 48.5 % in men older than 50 years of age (9). Another HTLV-1 high prevalence country is Japan, where an estimated 0.8 million people live with HTLV-1 infection; especially in Southern regions where 30–40% of adults older than 50 years of age and up to 5.8% of pregnant women have HTLV-1 infection.  HTLV-1 infection is also common in some other regions of the world, where surveillance studies are available, such as West Africa, Caribbean Islands, Brazil, Argentina, Iran and Romania (6).