In a study published in The Lancet Infectious Diseases, investigators demonstrated a significant gap in research on human T-cell lymphotropic virus type 1 (HTLV-1) and the effect of comorbidities on mortality in patients with this infection.1
While there are a large number of people with HTLV-1 worldwide, researchers identified relatively few robust epidemiologic studies of HTLV-1 disease associations. The majority of studies done were conducted in Japan, United States, Brazil, and Jamaica. Through a systematic review and meta-analysis, researchers found 39 studies (16 cohort, 14 case-control, and 9 cross-sectional studies) that met inclusion criteria in the evaluation of health outcomes between people with HTLV-1 and people without HTLV-1. These studies examined associated between the presence of HTLV-1 and 42 clinical conditions, including mortality, cancer, various infections, and several inflammatory diseases.
Results showed strong, high-grade evidence that HTLV-1 infection was associated with an increased risk for overall mortality (relative risk [RR], 1.57; 95% CI, 1.37-1.80). The association was slightly stronger among men than among women and younger age groups (individuals aged 15-29 years had a RR of 3.80 compared with RR of 1.2 for those aged ≥60 years). Consistency between the results of individual studies was high across geographic areas. The quality of evidence for an association between HTLV-1 and all-cause mortality was assessed to be high.
Although investigators acknowledged low-grade evidence, HTLV-1 was associated with an increased risk for a range of morbidities, such as the following:
- Seborrheic dermatitis in adults (odds ratio [OR], 3.89 [95% CI, 2.07-7.29])
- Bronchiectasis, bronchitis, and bronchiolitis (analyzed together; OR, 2.90 [95% CI, 2.0-4.3])
- Sjogren syndrome (OR, 3.25 [95% CI, 1.85-5.70])
- Tuberculosis (pooled OR, 2.04 [95% CI, 1.36-3.06])
- Self-reported urinary tract infection RR, 2.32 (95% CI, 1.50-3.59)
- Lymphoma other than adult T-cell leukemia-lymphoma (OR, 2.76 [95% CI, 1.36-5.62])
Conversely, gastric cancer was less likely to develop in people with HTLV-1 than in those without HTLV-1 (OR, 0.45; 95% CI, 0.28-0.71).
The study authors highlighted several limitations. Most of the included studies were done in countries of relatively low HTLV-1 prevalence, with few data from sub-Saharan Africa. In addition, the health effects of HTLV-1 may be even greater than suspected, because the effects of HTLV-1 on cardiovascular, cerebrovascular, and metabolic diseases are not understood.
“The perception of HTLV-1 being an indolent infection” needs to change and information about the condition “should be included in all medical training curricula,” noted Drs Lucy Cook and Graham Taylor from Imperial College London in an editorial commentary.2 In addition, there needs to be “a change in perception of the public health importance of HTLV-1 including cost-benefit analyses, by region, of screening programs” and “better funding to address the huge gaps in pathogenesis and treatment,” they concluded.
1. Schierhout G, McGregor S, Gessain A, Einsiedel L, Martinello M, Kaldor J. Association between HTLV-1 infection and adverse health outcomes: a systematic review and meta-analysis of epidemiological studies [published online October 21, 2019]. Lancet Infect Dis. doi:10.1016/S1473-3099(19)30402-5
2. Cook LBM, Taylor GP. HTLV-1: the silent impact revealed [published online October 21, 2019]. Lancet Infect Dis. doi:10.1016/S1473-3099(19)30432-3