Avaliação diagnóstica da infecção por Strongyloides stercoralis em indivíduos asmáticos, utilizando antígenos recombinantes

Abstract

Strongyloides stercoralis is the main etiological agent of human strongyloidiasis, a neglected disease with a wide distribution worldwide. The infection is usually chronic and asymptomatic. However, in immunocompromised individuals using systemic glucocorticoids, such as individuals with severe asthma, infection by S. stercoralis can progress to severe forms, hyperinfection and/or dissemination, with low therapeutic response and a high mortality rate. Currently, the definitive diagnosis of infection by S. stercoralis is made by examining the larvae in the feces. However, this parasite releases few larvae and intermittently, which makes it necessary to examine several fecal samples on alternate days. Objective: To evaluate the presence of S. stercoralis infection in asthmatic individuals treated at the Asthma and Allergic Rhinitis Control Program (ProAR), Bahia, Brazil, through parasitological and immunological diagnosis, using crude and recombinant antigens (NIE and SsIR). A total of 500 serum samples from asthmatic individuals treated at ProAR were included in the study. Materials and methods: The diagnosis of strongyloidiasis was made through three parasitological methods: spontaneous sedimentation (SE), Baermann-Moraes (BM) and Agar Plate Culture (CPA); and serological diagnosis, through determination of IgG4 and IgE levels against S. stercoralis through ELISA, using membrane antigen of S. venezuelensis. Samples from individuals with positive diagnosis by parasitological and immunological methods (n=66) were reevaluated through ELISA using recombinant antigens (NIE and SsIR). Results: Of the individuals studied, 21.2 (106/500) and 78.8% (394/500) were male and female, respectively. Approximately 42 (210/500) and 58% (290/500) of the individuals had mild/moderate or severe asthma, respectively. A frequency of enteroparasite infection of 8.6% (43/500) was demonstrated. The most prevalent pathogenic parasite was S. stercoralis, 2.2% (11/500). The sensitivities of ELISA(s) for the detection of IgG4 and IgE antibodies to S. stercoralis, using membrane antigen, were 91.7% and 91.2%, respectively, and the specificities were 95.7% and 95.4%, respectively. The detection of IgG4 antibodies to S. stercoralis in asthmatic individuals was 8.2% (41/500) and for IgE anti-S. stercoralis 9.8% (49/500). The sera of individuals positive for detection of larvae and specific antibodies (n=66) reevaluated by NIE-ELISA and SsIR ELISA were 22.7% (15/66) and 43.9% (29/66), respectively. Immunoblotting confirmed a positivity of 39.4% (26/66) of the positive samples with revelation of immunoreactive bands of 20, 38, 48, 68 100 and 140 KDa. Regarding the use of corticosteroids, 36.2% (181/500) reported having received one or more cycles of oral corticosteroids for 3 or more days in 1 year and 8.4% (42/500) one or more cycles of injectable corticosteroids in 6 months. Among the 66 individuals who tested positive (detection of larvae in feces and anti-S. stercoralis antibodies), 63.6% (42/66) used corticosteroids, 60.6% (40/66) by inhaled route, 30.3% (20/66) by oral route and 9.1% (6/66) by injection, with no statistically significant association observed in any of the three routes of corticosteroid therapy and infection by S. stercoralis (p = 0.798, 0.351 and 1.0, respectively). Conclusion: This study demonstrates that the agreement between the methods used was weak, therefore, there is a need for studies to develop an effective and reproducible test for the diagnosis of strongyloidiasis. Furthermore, the study did not demonstrate a correlation between S. stercoralis infection and the use of glucocorticoids.