| The biological cycle of Fasciola hepatica involves participation by mollusks of the genus Lymnaea, which is an intermediate host in which the parasite develops and produces cercariae, which encyst and form metacercariae. With the aim of observing spontaneous elimination of cercariae of F. hepatica from infected L. columella, 138 of these mollusks were experimentally infected. The mollusks were placed in 24-well culturing plates and were individually challenged with three miracidia of F. hepatica. Twenty-four hours later, they were transferred to plastic boxes, to which 500 ml of dechlorinated water and lettuce leaves were added. Once a week, the water and leaves were changed. Fifty days after the mollusks had been infected, daily viewing of the boxes using an optical microscope started. After the first elimination of cercaria, 54 days after infection, the surviving mollusks were removed from the boxes, placed individually in Petri dishes and exposed every day to incandescent light (60 W), at two-hour intervals. During each interval, the plates were viewed under an optical microscope to observe the cercariae that had been eliminated. The metacercariae obtained were removed and quantified. The mollusks that died were dissected to investigate and quantify the presence of rediae. There were 32 live mollusks, thus indicating a survival rate of 23.18%, 50 days after infection. Elimination of cercariae was observed from 15 individuals, thus giving a positivity rate of 10.86% in relation to the number of mollusks infected. The duration of the cercaria elimination period was 25 days and it finished when the last mollusk died. The greatest numbers of cercariae eliminated were observed between the 13th and 21st days. The pre-patency period was 59.42 ± 5.24 days. There were 2.281 metacercariae and 292 rediae. The elimination of cercariae in this experimental infection of L. columella demonstrated the susceptibility of these mollusks to the parasite F. hepatica. |
