Very high prevalence of infection with the human T cell leukaemia virus type 1c in remote Australian Aboriginal communities: Results of a large cross-sectional community survey

Abstract

Infection with the human T cell leukaemia virus type 1 (HTLV-1) subtype C is endemic among Aboriginal people in central Australia. To provide insights into the risk factors for transmission, we conducted the first large-scale, community-based prevalence study in seven remote Aboriginal communities. Residents >2 years old were invited to participate in the study between August 2014 and June 2018. HTLV-1 infection was defined as a positive western blot (WB) test or a positive HTLV-1 PCR. 720 community residents participated in the study (children <15 years, 142; adults, 578). Prevalences for children and adults were 3.5% (5/142) and 36.8% (213/578), respectively, reaching 49.3% (106/215) for those older than 45 years. A wide range of proviral loads were measured for both asymptomatic and symptomatic participants with no difference within groups according to age or gender; however, median PVL was 1.34 log10 higher for symptomatic participants. The adult prevalence of HTLV-1 infection in central Australia is the highest reported worldwide. Sexual contact is likely to be the predominant mode of transmission.

Fig 1

Map of Australia showing the study area of approximately 68,000 km² (green rectangle) within the Apatula Indigenous region (dark brown). The basemap layer was obtained from Natural Earth: https://www.naturalearthdata.com/downloads/50m-natural-earth-2/50m-natural-earth-ii-with-shaded-relief-and-water/.

Fig 2. HTLV-1c proviral loads for 91 (asymptomatic, 75; symptomatic, 16) female and 128 (asymptomatic, 109; symptomatic, 19) male participants.

Pearson correlation coefficients and p-values for PVL versus age are shown for symptomatic and asymptomatic subjects (symptomatic group, solid lines; asymptomatic group, dashed lines). The symptomatic group includes i) radiologically defined bronchiectasis/bronchiolitis (27)(orange circles), ii) uveitis (2), retinitis (1) or chronic bilateral corneal opacities (1) (red squares), iii) myositis (1) (green square), iv) infective dermatitis (black cross)(2) and v) neurological symptoms associated with HTLV-1 (5)(green squares). Three participants had more than one HTLV-1 associated condition: a 59 year old woman (PVL 4.65 log10 copies per 10⁵ peripheral blood leukocytes, PBL) had possible HAM and eye disease (green square); a 58 year old man (PVL 3.62 log10 copies per 10⁵ PBL) had possible HAM and bronchiectasis (orange circle); a 43 year old man (PVL 3.37 log10 copies per 10⁵ PBL) had bronchiectasis and infective dermatitis (orange circle with black cross). Median (IQR) HTLV-1 PVL log10 HTLV-1 copies per 10⁵ PBL amongst females were 2.31 (1.06–3.14) for asymptomatic females (n = 75) and 3.19 (1.73–3.89) for symptomatic females (n = 16) (p = 0.120). Median (IQR) HTLV-1 PVL log10 HTLV-1 copies per 10⁵ PBL amongst males were 2.02 (0.68–3.27) for asymptomatic males (n = 109) and 3.72 (3.37, 4.28) for symptomatic males (n = 19) (p<0.001). Abbreviations: BE; radiologically defined bronchiolitis/bronchiectasis; eyes, non-diabetic eye diseases; HTLV-1, human T cell leukaemia virus; IDH, infective dermatitis associated with HTLV-1; neurology, ‘myelopathy’ or neurological symptoms associated with HTLV-1; p, p value; PBL, peripheral blood leukocytes; r, Pearson correlation coefficient between PVL and age by gender.

Fig 3. HTLV-1 prevalence according to age for 386 female and 334 male community residents.

HTLV-1 infection was confirmed for 218 participants, using HTLV-1 western blots (WB) and/or HTLV-1 PCR (WB positive/PCR positive, 209; indeterminate WB/PCR positive, 8; tested by dried blood spot, PCR positive, 1).