Padronização do cultivo de ovos e larvas de Strongyloides venezuelensis Brumpt, 1934 para avaliação do efeito da dexametasona sobre o desenvolvimento larvário

Abstract

Human strongyloidiasis, caused by the Strongyloides stercoralis nematode, is an important parasitic disease that, despite the high prevalence and severity associated with parasite hyperinfection and dissemination, has been admittedly neglected. The study of S. venezuelensis biology has enabled advances in varied aspects of the knowledge of strongiloidiasis. In the present study, a priori, the standardization of the in vitro culture conditions of S. venezuelensis (Experiment I) was evaluated. Posteriorly, the effect of dexamethasone on larval development was evaluated (Experiment II). Initially, saturated solutions of NaCl or sucrose were used for centrifugal-flotation recovery of S. venezuelensis eggs from fecal material of Meriones unguiculatus experimentally infected by the parasite. The maintenance and development of hatched larvae of eggs in deionized water, aqueous glucose media (5%) and M. unguiculatus feces (1%) in two types of containers were also evaluated: cell culture plates or Khan’s tubes at 27 °C. Then, the ideal volume of culture medium (1, 2 or 4 ml) was tested. Through Experiment I, it was found that saturated saline solution made it possible to recover eggs with up to 89% efficiency, without interference in the subsequent larval development until the third stage (L3i). The cultivated eggs in Khan’s tubes haven’t developed. In cell culture plates, egg development up to L3i was significantly higher in the 1% fecal medium when incubated in 1 or 2 ml. In addition to the characteristics of the culture medium, the differences observed as a function of the container used indicate the influence of the air contact surface and/or the height of the water column/medium on larval development and survival. Although there are culture processes for obtaining L3i from Strongyloides spp., the standardization of a methodology that allows monitoring of egg development to L3i in real time is desirable and may be useful for future tests drugs. With the results of Experiment I, S. venezuelensis eggs, recovered by centrifugeflotation in saturated saline solution, were cultured in cell culture plates containing 1 ml of fecal medium 1%. In the medium, dexamethasone was added at three concentrations: 0.5, 0.05 or 0.005 mg/ml. The plates were incubated at 27 ºC for 48 hours and larval development evaluated every eight hours. The cultivated eggs in dexamethasone 0.5 mg/ml haven’t developed in larvae. However, at lower concentrations, a significant effect of the drug in relation to the control was observed, promoting acceleration of the development of the larval stadium. The obtained results support the hypothesis of the direct effect of corticosteroids on larval development of Strongyloides species.