Bulimulus tenuissimus (Mollusca) como um novo hospedeiro experimental para Angiostrongylus cantonensis (Nematoda), um estudo morfológico e fisiológico da interação parasito-hospedeiro

Abstract

Molluscs are an essential requirement for the completion of the life cycle by the metastarogillid nematode Angiostrongylus cantonensis, the causative agent of infections in domestic and wild animals, mainly rodents, as well as neural angiostrongyliasis or eosinophilic meningitis in humans. The terrestrial gastropod Bulimulus tenuissimus is widely distributed in Brazilian territory and there are other species of the same genus that occur in Brazil and other countries, overlapping regions where there are reports of A. cantonensis and angiostrongyliasis. Despite this, there is no record in the literature about this species as an intermediate host for A. cantonensis. The present study aimed to experimentally infect the B. tenuissimus mollusc, using A. cantonensis L1 larvae under laboratory conditions, and to monitor the physiological changes that occurred. For this, during the period of the study, the parameters of B. tenuissimus reproductive biology, carbohydrate metabolism, nitrogen products and calcium were analyzed. Morphological studies were also performed using histology and scanning electron microscopy. Three weeks after exposure to L1 larvae, it was possible to recover 17.2% of the L3 larvae used for exposure to molluscs (1,200 L1 larvae). The larvae were observed in the cephalopodal mass (foot), ovotestis and mantle tissues, within a granulomatous structure constituted by hemocytes infiltration, but there was no deposition of calcium or collagen in these structures in a significant amount. The infected snails showed reduction in the fibrous muscle tissue in the foot, loss of acinar organization in the digestive gland, with increase of amorphous material inside the acini and loss of the epithelial pattern and the nuclear organization in the acinar cells. However, the ovotestis, even presenting developing larvae, was not affected by the infection, since there was a large number of developing oocytes and spermatozoa at different stages of formation. In the reproductive parameters studied, infected molluscs showed a small increase (+ 7%) in the total number of eggs laid in the first week of infection and a decrease of 5.4% in the number of molluscs hatched in the second week of infection in relation to uninfected molluscs. The galactogen content showed a negative relation with the time of infection. The glucose content in hemolymph increased (+ 71.56%) in the first week post-exposure, decreasing in the second (-4.92%) and third (+ 13.74%) weeks. The activity of lactate dehydrogenase (LDH) increased in the first week (11.00 ± 4.62 U/L) and even more in the second week (14.00 ± 5.3 U/L) after exposure, but the variations were not statistically significant when compared to the control group (10.00 ± 0.56 U/L). The glycogen stores in the cephalopedl mass and the digestive gland were reduced in the three weeks post-exposure. The content of pyruvic acid in the hemolymph of infected molluscs was reduced in the first (41.52%) and second (45.66%) weeks post-exposure, and oxalic acid increased (33.53 mg/g) in relation to the control group (28.05 mg/g). However, the variations were not significant. The total protein concentration increased in the first week (19.56%), returning to values close to those observed for the control group, which appeared to be related to tissue lysis, since the same pattern of variation was observed for the activities of AST and ALT was observed. Associated to this, a reversal vii of the excretory pattern, passing to predominantly uricotelic was observed in the second week after exposure, returning to the ureotelic pattern at the end of the pre patent period. The infection caused hypercalcification in B. tenuissimus shell infected with A. cantonensis, with a 242% increase in CaCO3 concentration, at the end of the pre patent period, in infected mollusc shells and hypercalcemia, especially at the end of the third week of infection (+18.51%) in relation to the control group. The results show that B. tenuissimus is a potential experimental host, which presents a physiological response pattern to infection with A. cantonensis, being able to maintain its basic physiological processes, besides supplying the parasite in development.