Padronização e validação de técnicas sorológicas utilizando extrato antigênico total de verme adulto (SWAP carbonato) para o diagnóstico da esquistossomose mansoni em uma população com baixa carga parasitária

Abstract

Schistosomiasis is a chronic and debilitating disease of great impact on public health in Brazil, affecting about 2 million people, while another 25 million live in areas at risk of acquiring infection. The laboratory diagnosis of this parasitosis has been based on the identification of eggs in the feces, mainly through the Kato-Katz technique. However, recent data show that individuals with low parasitic load are not easily identified by examining feces, and it is necessary to search for more sensitive forms for the diagnosis of this parasitosis. In this context, molecular and serological alternatives have been studied in order to create complementary alternatives that improve the sensitivity of the diagnosis, allowing a more effective control of schistosomiasis. The purpose of the present study was to evaluate the efficacy of an immunoenzymatic test using the total antigenic extract of adult worm previously used in intradermal testing (SWAP-carbonate) and different IgG isotypes as an auxiliary tool in the diagnosis of schistosomiasis in patients with low parasitic load of endemic regions. For this purpose, serum samples were taken from residents of the rural community of Brejo do Amparo, municipality of Januária in the north of Minas Gerais, an endemic area for schistosomiasis, which had already been characterized parasitologically through the examination of 18 Kato-Katz slides, 2 Salt Gradient, Helmintex® and Spontaneous Sedimentation tests at the beginning of the study and 12 months after specific treatment. After optimizing the concentrations of the different reagents, the reactivity of the IgG subclasses (IgG1, IgG3 and IgG4) of the participants serum against the antigens present in the SWAP-carbonate was tested and the diagnostic accuracy was evaluated in relation to the active infection reference (presence eggs in any parasitological test). Identification of reactive proteins in SWAP-carbonate in serum from individuals with different parasitological status was verified using Western Blot. The data reveal that IgG1- and IgG4-anti SWAP-carbonate, but not IgG3, were significantly elevated in individuals with active infection by S. mansoni in relation to those not infected and had better agreement in relation to the reference test (kappa = 0.3). IgG1 reactivity was more sensitive (81.3%), being reactive in all individuals with a load above 100 OPG and in 75% of those infected with less than 12 OPG, but the test had low specificity and the reactivity did not significantly decrease in healed individuals. On the other hand, IgG4 reactivity was less sensitive (60%), but it had better specificity (72%) and this reactivity reduced significantly 1 year after treatment. In addition, Western Blot analysis made it possible to identify a set of high molecular weight proteins (150-200 kDa) that were specifically recognized by these antibody subclasses. The data indicate the possibility of obtaining a serological test based on the reactivity of IgG subclasses, which is more sensitive for diagnosing individuals with low parasitic load living in endemic areas.