{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,5]],"date-time":"2026-10-05T13:52:25Z","timestamp":1791208345536,"version":"4.1.0"},"reference-count":70,"publisher":"American Society for Microbiology","license":[{"start":{"date-parts":[[2026,10,5]],"date-time":"2026-10-05T00:00:00Z","timestamp":1791158400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"},{"start":{"date-parts":[[2026,10,5]],"date-time":"2026-10-05T00:00:00Z","timestamp":1791158400000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/journals.asm.org\/non-commercial-tdm-license"}],"funder":[{"name":"EU NextGenerationEU","award":["09I03-03-V04-00162"],"award-info":[{"award-number":["09I03-03-V04-00162"]}]}],"content-domain":{"domain":["journals.asm.org"],"crossmark-restriction":true},"short-container-title":["mBio"],"abstract":"<jats:title>ABSTRACT<\/jats:title>\n                  <jats:sec>\n                    <jats:title\/>\n                    <jats:p>\n                      Apicomplexan parasites have coevolved with animal hosts for hundreds of millions of years, yet only a handful of their lineages have made the transition to infecting vertebrates. Among the least understood vertebrate-infecting apicomplexans is\n                      <jats:italic toggle=\"yes\">Nematopsis temporariae<\/jats:italic>\n                      , recently rediscovered after nearly a century of neglect. Here, we isolated this parasite from tadpole tissues and examined its host relationship, ultrastructure, and phylogenetic placement. We show that\n                      <jats:italic toggle=\"yes\">N. temporariae<\/jats:italic>\n                      \u2019s monozoic oocysts are persistently associated with hepatic Kupffer cells in tadpoles of several frog species and undergo maturation within them, while being absent from adult hosts. Sporozoites possess a folded multimembrane pellicle, numerous paraglycogen granules, and an apical complex with polar rings and rhoptries. Exceptionally abundant micronemes are distributed throughout the cell rather than restricted to the apical region. Although several traits superficially resemble\n                      <jats:italic toggle=\"yes\">Nematopsis<\/jats:italic>\n                      eugregarines from marine bivalves, single- and multi-gene phylogenies demonstrate that\n                      <jats:italic toggle=\"yes\">N. temporariae<\/jats:italic>\n                      belongs to a distinct, distantly related lineage of freshwater actinocephaloid eugregarines. This evidence warrants the establishment of the new genus\n                      <jats:italic toggle=\"yes\">Cryptonaiada<\/jats:italic>\n                      gen. n. in the new family Cryptonaiadidae fam. n.\u2014the first known gregarine apicomplexan to have evolved vertebrate parasitism. We propose that\n                      <jats:italic toggle=\"yes\">Cryptonaiada<\/jats:italic>\n                      develops within macrophages upon engulfment, evading digestion, and actively modulating them through sporozoite-mediated secretion. The persistent intracellular interaction between\n                      <jats:italic toggle=\"yes\">Cryptonaiada<\/jats:italic>\n                      and tadpole macrophages may represent an early stage in parasite coevolution with vertebrate adaptive immunity, coinciding with a window of host immunological immaturity. Our findings highlight the value of studying neglected symbionts of amphibians, a group facing a significant global population decline.\n                    <\/jats:p>\n                    <jats:sec>\n                      <jats:title>IMPORTANCE<\/jats:title>\n                      <jats:p>\n                        How parasites evolve to infect vertebrate hosts with adaptive immunity remains a major question in parasitology. Apicomplexans provide a unique perspective on this transition, as vertebrate parasitism has arisen in only a handful of ancient lineages. Here, we characterize\n                        <jats:italic toggle=\"yes\">Cryptonaiada temporaria<\/jats:italic>\n                        , an early-branching freshwater apicomplexan infecting tadpoles. The evidence indicates that\n                        <jats:italic toggle=\"yes\">Cryptonaiada<\/jats:italic>\n                        represents a new gregarine genus and family that have evolved to infect tadpoles intracellularly, via oocysts engulfed by and developing within liver macrophages. The ultrastructure of the oocyst containing a single sporozoite reveals a semi-open state combining features consistent with environmental defense and secretion into the host cell.\n                        <jats:italic toggle=\"yes\">Cryptonaiada<\/jats:italic>\n                        is absent from metamorphosed adults, suggesting that it exploits a developmental window of reduced host immune competence. These findings reveal an unusual form of intracellular vertebrate parasitism in gregarines, providing new insight into the evolutionary transition of apicomplexans from invertebrate to vertebrate hosts.\n                      <\/jats:p>\n                    <\/jats:sec>\n                  <\/jats:sec>","DOI":"10.1128\/mbio.01957-26","type":"journal-article","created":{"date-parts":[[2026,10,5]],"date-time":"2026-10-05T13:01:11Z","timestamp":1791205271000},"update-policy":"https:\/\/doi.org\/10.1128\/asmj-crossmark-policy-page","source":"Crossref","is-referenced-by-count":0,"title":["Cellular organization and phylogeny of\n                    <i>Cryptonaiada<\/i>\n                    gen. n. (Cryptonaiadidae fam. n.) shed light on the evolution of intracellular vertebrate parasitism in Apicomplexa"],"prefix":"10.1128","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-8313-1580","authenticated-orcid":true,"given":"Andrea","family":"Valigurov\u00e1","sequence":"first","affiliation":[{"id":[{"id":"https:\/\/ror.org\/02j46qs45","id-type":"ROR","asserted-by":"publisher"}],"name":"Department of Botany and Zoology, Faculty of Science, Masaryk University","place":["Brno, Czech Republic"]},{"name":"Department of Zoology, Faculty of Natural Sciences, Comenius University in Bratislava","place":["Bratislava, Slovak Republic"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kirill V.","family":"Mikhailov","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/010pmpe69","id-type":"ROR","asserted-by":"publisher"}],"name":"Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University","place":["Moscow, Russia"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Vladimir V.","family":"Aleoshin","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/010pmpe69","id-type":"ROR","asserted-by":"publisher"}],"name":"Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University","place":["Moscow, Russia"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Nat\u00e1lie","family":"Gl\u00fcckov\u00e1","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/02j46qs45","id-type":"ROR","asserted-by":"publisher"}],"name":"Department of Botany and Zoology, Faculty of Science, Masaryk University","place":["Brno, Czech Republic"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Aurelie","family":"Chambouvet","sequence":"additional","affiliation":[{"name":"Sorbonne Universit\u00e9, CNRS, UMR7144 AD2M, ECOMAP, Station Biologique de Roscoff","place":["Roscoff, France"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Petr","family":"Pape\u017e\u00edk","sequence":"additional","affiliation":[{"name":"Department of Zoology, Faculty of Natural Sciences, Comenius University in Bratislava","place":["Bratislava, Slovak Republic"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Miloslav","family":"Jirk\u016f","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/01c7rrt10","id-type":"ROR","asserted-by":"publisher"}],"name":"Institute of Parasitology, Biology Centre of the Czech Academy of Sciences","place":["\u010cesk\u00e9 Bud\u011bjovice, Czech Republic"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6547-749X","authenticated-orcid":false,"given":"Jan","family":"Janou\u0161kovec","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/02p1jz666","id-type":"ROR","asserted-by":"publisher"}],"name":"Centre Algatech, Institute of Microbiology of the Czech Academy of Sciences","place":["T\u0159ebo\u0148, Czech Republic"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"235","published-online":{"date-parts":[[2026,10,5]]},"reference":[{"key":"e_1_3_5_2_2","doi-asserted-by":"publisher","DOI":"10.1111\/jeu.12691"},{"key":"e_1_3_5_3_2","doi-asserted-by":"publisher","DOI":"10.3390\/microorganisms9071430"},{"key":"e_1_3_5_4_2","first-page":"205","volume-title":"Illustrated guide to the Protozoa","author":"Clopton RE","year":"2002","unstructured":"Clopton RE. 2002. 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