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Trematodes of the family Cyclocoelidae are parasites mainly of the respiratory system of birds and present a cosmopolitan distribution. Although infection with these flukes can result in pathological changes and even bird death, information on their life cycles is scarce and almost entirely based on experimental infection data. Thus, the generation of knowledge on the mollusks that act as natural intermediate hosts of cyclocoelids is necessary and can aid control measures against these air sac trematodes. In the present study, gastropod mollusks collected in an urban stream from Belo Horizonte, Minas Gerais, Brazil, were subjected to the compression technique for the detection of non-emerging larval trematodes. Tailless cercariae with confluent ceca were found in 8/30 (26.7%) specimens of Biomphalaria glabrata and 3/33 (9.1%) specimen of Physella acuta. Samples of the cercariae were subjected to morphological characterization and genetic study (28S, Cox-1, and Nad-1). For comparative purposes, adult trematodes previously collected in the air sac of a common gallinule (Gallinula galeata) found dead in another waterbody from the same region were also characterized. The molecular sequences obtained revealed a high degree of similarity (100% in 28S, 99.2% in Cox-1, and 99.5% in Nad-1) between larval stages found in mollusks and adult parasites found in G. galeata and morphologically identified as Cyclocoelum mutabile. The conspecificity with this widely distributed cyclocoelid was also corroborated by phylogenetic analysis and comparison with isolates of this species previously characterized in Peru and the Czech Republic (99.4–100% and 96.7–97.0% of similarity in Nad-1, respectively). Thus, the integrative analysis carried out in the present work enabled us to identify C. mutabile in mollusks in South America for the first time. The finding of B. glabrata and P. acuta as new intermediate hosts corroborates the importance of freshwater gastropods in the transmission of C. mutabile, as well as the low specificity to the mollusk group, as previously characterized through experimental studies.

Cyclocoelum mutabile, un digeneo de la familia Cyclocoelidae, fue hallado parasitando los sacos aéreos de una polla de agua común (Gallinula chloropus), proveniente de alrededores del Refugio de Vida Silvestre Pantanos de villa, localizada en el distrito de Chorrillos en Lima, Perú. Un total de 7 parásitos fueron colectados e identificados por métodos morfológicos como C. mutabile. El diagnóstico fue confirmado por análisis molecular, amplificando los genes mitocondriales citocromo c oxidasa subunidad 1 (cox1) y deshidrogenasa NADH subunidad 1 (nad1). Las secuencias de nucleótidos de los aislados se compararon con secuencias previas de GenBank, y mostraron una similitud entre ellas (> 96%). Este hallazgo constituye el primer registro de C. mutabile para el Perú. Además, el trabajo realiza una breve descripción del parásito, así como la discusión de sus hospederos y distribución geográfica en Sudamérica.

In this study, changes were examined in surface structures and tegumental morphology or newly excysted, migrating, and adult Cyclocoelum mutabile obtained from experimentally infected coots (Fulica americana). Newly excysted juveniles were spinous and had two large depressions situated at the anterior tip of the body and a large acetabulum.

Infectivity of Cyclocoelum mutabile miracidia to 9 species and up to 4 size classes of pulmonate snails at 14, 16, and 20 C was studied under laboratory conditions. Of the 9 species examined, 6 (Stagnicola elodes, Lymnaea stagnalis, Gyraulus parvus, Gyraulus circumstriatus, Promenetus exacuous, and Armiger crista) were highly susceptible (infection success ≥25%), 2 (Physa jennessi and Helisoma trivolvis) had low susceptibility (infection success <25%, >0), and 1 (Physa gyrina) was not susceptible to infection. Within highly susceptible species, snail size was negatively related to susceptibility and temperature had variable effects. Infection success was not affected by temperature or snail size in species with low susceptibility. Production of cercariae was negatively correlated with susceptibility among snails of different sizes and species, but was not influenced by snail size for a given species. Among species, metacercariae production was typically higher in lymnaeids than in either planorbids or physids. Results of experiments where miracidia were provided with a choice of 2 different snails suggest that they do not discriminate between species with high and low susceptibility.

The transmission of Cyclocoelum mutabile to snails was examined under natural conditions by sampling the snail communities of 4 natural ponds that had been exposed experimentally to infection by laboratory-infected coots (Fulica americana). Five of 6 snail species in the ponds, Physa jennessi, Promenetus exacuous, Armiger crista, Gyraulus parvus, and Stagnicola elodes, became infected. No natural infections were found in the few Helisoma trivolvis examined. The second most abundant species Promenetus exacuous was infected most often, whereas Physa jennessi, the most abundant species present, was rarely infected. The temporal pattern of infections in the snail community suggests the transmission window of this parasite in southern Manitoba is limited by both the 14 C hatching threshold of the fluke eggs and the seasonality of ovigerous infections in the coot host. No naturally overwintering infections were found in snails from these ponds, which were examined the following spring. None of the 1,120 laboratory-infected snails placed in cages and held overwinter in the ponds survived, whereas 14 of the 1,120 uninfected control snails kept in the same cages survived. These results are consistent with the hypothesis that C. mutabile must be reestablished in northern waterfowl breeding areas each spring.

Cyclocoelum mutabile, growth and development during course of migration through liver and after establishment in air sacs of coots