Strongyloides stercoralis is the etiological agent of strongyloidiasis, which affects about 600 million people worldwide. Brazil is considered a hyperendemic region, with an estimated prevalence of around 5.5%, varying by region. In the general population, infection tends to be chronic and asymptomatic; however, in individuals infected with human T-lymphotropic virus type 1 or 2 (HTLV-1/2), strongyloidiasis may progress to severe forms, mainly due to negative modulation of the protective immune response against S. stercoralis in coinfected individuals. HTLV-1/2 transmission occurs predominantly through sexual contact, and vertical transmission most often occurs through breastfeeding. Prenatal screening for HTLV-1/2 and avoidance of breastfeeding have led to an approximately 80% reduction in vertical transmission in Japan. This study aimed to evaluate possible routes of transmission in a family of 21 individuals, 17 of whom were infected with HTLV-1/2, and to measure serum levels of cytokines (produced by Th1, Th2, and Th17 cells) and total IgE levels in individuals infected with HTLV-1/2 coinfected or not with S. stercoralis . Members of a family (n = 21) living in a rural area in the southern coastal region of Bahia, in a situation of social vulnerability, participated in the study. Epidemiological data, family relationships, and infection status for HTLV-1/2 and S. stercoralis were evaluated. Serum levels of cytokines IL-2, IL-4, IL-6, IL-10, TNF-α, IL-17, and total IgE were measured and compared between coinfected and non-coinfected individuals. Analysis of the results showed that transmission most likely occurred through breastfeeding, starting from the matriarch infected with HTLV-1, who had four partners. Among the cytokines measured (IL-2, IL-4, IL-6, IL-10, TNF-α, IL-17), only TNF-α and IL-17 showed differences between individuals coinfected and not coinfected with S. stercoralis (p < 0.05). These cytokines may have contributed to exacerbation of the autoinfection cycle, as evidenced by the high number of larvae in coinfected individuals. Low total IgE levels were also detected in coinfected individuals, which may have contributed to a reduced innate immune response against parasitic infection. Vertical transmission through breastfeeding occurs in approximately 30% of children born to infected mothers who breastfed for more than 6 months; therefore, follow-up of pregnant women with HTLV-1 is essential to control vertical transmission. The immunological profile observed suggests that TNF-α, IL-17, and low IgE levels may play a role in susceptibility to severe strongyloidiasis in HTLV-1/2–infected individuals.
Soares et al. (Sun,) studied this question.
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