Experimental elucidation of the life cycle of Drepanocephalus spathans (Digenea: Echinostomatidae) with notes on the morphological plasticity of D. spathans in the United States

Authors: ALBERSON, NEELY - Mississippi State University; ROSSER, THOMAS - Mississippi State University; WOODYARD, ETHAN - Mississippi State University; KHOO, LESTER - Mississippi State University; BAUMGARTNER, WES - Mississippi State University; POTE, LINDA - Mississippi State University; CUNNINGHAM, FRED - Animal And Plant Health Inspection Service (APHIS); GRIFFIN, MATT - Mississippi State University

Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/24/2022
Publication Date: 3/30/2022
Citation: Alberson, N.R., Rosser, T.G., Woodyard, E.T., Khoo, L.H., Baumgartner, W.A., Pote, L.M. 2022. Experimental elucidation of the life cycle of Drepanocephalus spathans (Digenea: Echinostomatidae) with notes on the morphological plasticity of D. spathans in the United States. Journal of Parasitology. 108(2)141-158. https://doi.org/10.1645/19-157.
DOI: https://doi.org/10.1645/19-157

Interpretive Summary: This study experimentally confirms the life cycle of Drepanocephalus spathans, a trematode parasite with a life cycle that sequentially involves double-crested cormorants, snail intermediate hosts and catfish. Findings from this research established key developmental timelines for trematode lifecycles, with temperature influencing these processes. Understanding these timelines is crucial for catfish health management, as it informs strategies to disrupt parasite transmission and mitigate infection risks in aquaculture systems.

Technical Abstract: The echinostomatid Drepanocephalus spathans (syn. Drepanocephalus auritus) parasitizes the double-crested cormorant Phalacrocorax auritus. In North America, the marsh rams-horn snail Planorbella trivolvis and ghost rams-horn snail Biomphalaria havanensis serve as snail intermediate hosts, both of which inhabit catfish aquaculture ponds in the southeastern United States. Studies have demonstrated D. spathans exposure can be lethal to juvenile channel catfish Ictalurus punctatus. Two studies were undertaken to elucidate the life cycle of D. spathans to establish a developmental time line. In both studies, D. spathans cercariae collected from naturally infected P. trivolvis individuals were used to infect channel catfish fingerlings, which were then fed to double-crested cormorants (DCCOs) that had been pharmaceutically dewormed. In study 1, laboratory-reared P. trivolvis and B. havanensis individuals were placed in aviary ponds with experimentally infected DCCO and examined bi-weekly for release of cercariae. Trematode eggs were observed in the feces of exposed birds 3 days post-infection. Birds were sacrificed 18 days post-exposure (dpe), and gravid adults morphologically and molecularly consistent with D. spathans were recovered. Snails from the aviary pond were observed shedding D. spathans cercariae 18–54 dpe. In study 2, trematode eggs were observed in the feces of exposed DCCOs beginning 8 dpe. Once eggs were observed, birds were allowed to defecate into clean tanks containing naïve laboratory-reared P. trivolvis individuals. Additionally, eggs from experimental DCCO feces were recovered by sedimentation and placed in an aquarium housing laboratory-reared P. trivolvis individuals. Birds in study 2 were sacrificed after 60 days, and gravid D. spathans specimens were recovered. Snails from the experimental DCCO tanks shed D. spathans cercariae 89–97 dpe. Lastly, trematode eggs were isolated and observed for the hatching of miracidia, which emerged on average after 16 days at ambient temperatures. No D. spathans adults were observed in control birds fed non-parasitized fish. This is the first experimental confirmation of the D. spathans life cycle, resolving previously unknown developmental time lines. In addition, the effects of fixation on adult trematode morphology were assessed, clarifying reports of pronounced morphological plasticity for D. spathans.