ЭкспериментаΛьное изучение вΛияния метацеркарий Echinostoma caproni на выживаемость моΛΛюсков Biomphalaria pfeifferi Author Ataev, Gennady L. text Amurian Zoological Journal 2023 2023-12-28 XV 4 712 723 http://dx.doi.org/10.33910/2686-9519-2023-15-4-712-723 journal article 298642 10.33910/2686-9519-2023-15-4-712-723 8d14e039-7ef9-4095-9397-e40671140cf4 add_ISSN_here 11362243 7EDFB492-33F5-4F6F-BB32-FEC4BB86098F Mortality of B. pfeifferi due to metacercariae autoinfection The first deaths of B. pfeifferi snails from Group 1 were registered 3 weeks PI . This is when the release of cercariae first began. More than half of the snails died a month PI ( Fig. 2 ). The last snail from Group 1 died 38 days PI . By contrast, only 3 uninfected snails (6%) from the control group (Group 5) died during the experiment. As we mentioned earlier, the density of cercariae in the aquaria of Groups 2 and 4 was lowered artificially by either frequent filtration of water (Group 2) or by using uninfected snails (Group 4) as a biological cercarial filter in the aquarium with infected snails (Group 3). Fig. 1. Stages of development of an Echinostoma caproni trematode ( A–D ): A — SEM microphotograph of a mother redia; B — histological section of a cercaria embryo in a daughter redia; C — SEM micrograph of a cercaria with a discarded tail; D — SEM micrograph of a metacercaria. Legend: bp — birth pore, h — hemocytes, m — mouth, os — oral sucker, t — tail, vs — ventral sucker Рис. 1. СтаΔии развития трематоΔ Echinostoma caproni ( A–D ): A — SEM-микрофотография материнской реΔии; B — гистоΛогический срез эмбриона церкарии в Δочерней реΔии; C — SEM-микрофотография церкарии с отброшенным хвостом; D — SEM-микрофотография метацеркарии. УсΛовные обозначения: bp — роΔиΛьная пора; h — гемоциты; m — ротовое отверстие; os — ротовая присоска; t — хвост; vs — брюшная присоска This artificial decrease of cercarial density led to the extension of the lifespan of infected snails (Group 2 — up to 56 days, Group 3 — up to 60 days). The experiment also confirmed the pathogenicity of metacercariae since snails from Group 4 died within 58 days. Therefore, the results of the experiments on Groups 2, 3, and 4 indicate that the mortality of snails is attributed to metacercarial infection. The analysis of the survivorship curves of different experimental groups confirms this assumption ( Fig. 2 ). The graph shows that snails from Group 1 started dying sooner and faster than snails from the other groups. At the same time, survivorship curves for Groups 2–4 look very similar. These findings are also confirmed by statistical analysis. According to the Friedman test, the conditions of the experiment significantly affect the mortality dynamics of B. pfeifferi snails. A pairwise comparison of death times between Groups 1–4 (Wilcoxon test, including the Bonferroni correction) shows that the findings on Group 1 are different from the findings on Groups 2, 3, and 4 (p <0.001). At the same time, survivorship curves for Groups 2, 3 and 4 are statistically indistinguishable (p> 0.05). Thus, the analysis of survivorship curves of B. pfeifferi snails from different groups confirmed our assumption that E. caproni metacercariae are pathogenic to snails regardless of whether they were initially exposed to rediae or not.