Experimental approaches to study the transmission and infection of cardiocephaloides longicollis (Rudolph, 1819) Dubois, 1982 (Trematoda, Strigeidae) in fish

• Autores: Gabrielle Shira van Beest
• Directores de la Tesis: Ana Isabel Born Torrijos (dir. tes.), Francisco Esteban Montero Royo (codir. tes.), Juan Antonio Raga (codir. tes.)
• Lectura: En la Universitat de València ( España ) en 2023
• Idioma: inglés
• Tribunal Calificador de la Tesis: Xavier De Montaudouin (presid.), Ana Pérez del Olmo (secret.), Gerardo Pérez Ponce de León (voc.)
• Programa de doctorado: Programa de Doctorado en Biodiversidad y Biología Evolutiva por la Universitat de València (Estudi General)
• Materias:
  • Ciencias de la vida
    • Biología animal (zoología)
      • Parasitología animal
      • Zoología marina
• Enlaces
  • Tesis en acceso abierto en: TESEO
• Resumen

  • Researchers have recently shown interest in digenean trematodes (Platyhelminthes), especially on their transmission and infection strategies. Digeneans are ubiquitous components of ecosystems and usually have a complex life cycle with three hosts, being the transmission events from one host to the next essential for the continuation of the life cycle. The main aim of this PhD thesis was to achieve a better understanding of the transmission strategies of parasites with complex life cycles, using the model organism Cardiocephaloides longicollis (Rudolphi, 1819) Dubois, 1982. Their miracidia (free-swimming larval stages) infect the first intermediate host, nasariid snails. After asexual reproduction, the free-swimming cercariae emerge from snails and infect the second fish intermediate host, encysting in its brain as metacercariae. These stages are trophically transmitted to the definitive host, fish-eating birds, in which C. longicollis develops into an adult and reproduces sexually. Part of the life cycle of C. longicollis was replicated in the laboratory, which allowed experimental assays to be conducted. The behaviour of cercariae after their emergence from snail until the infection of the fish brain was examined, and protocols to study possible behavioural alterations in infected fish were optimized. In vivo fluorescent dyes can be useful in the study of cercariae, but need to be tested in advance to ensure high quality results. Their use revealed the penetration pattern of C. longicollis cercariae into Sparus aurata fish under laboratory conditions. Cercariae showed a preference for areas near the head, dorsal fin and ventral side, likely associated with areas close to the brain or migration routes connected with it. Cercariae of C. longicollis showed versatile functionality of its body structures that allows them to adapt to different phases, i.e. crawling with both suckers as anchors whereas using the oral sucker to burrow and open the path into the tissue. After artificial infection of S. aurata with C. longicollis cercariae, histological analyses showed that cercariae migrate through connective tissue and muscle fibres toward the brain. To individually differentiate S. aurata in experimental assays, Visible Implant Elastomer tags (VIE) were tested and were found to be safe and reliable for long- and short-term tagging of S. aurata under laboratory conditions. No severe immune response was observed, however, this is the first report in fish in which silicone, the main component of VIE, was observed to migrate to tissues different from the injection site. VIE-tagged fish were used in behavioural experiments, showing preliminary results that brain-encysted C. longicollis did not affect the perception of the light gradient by S. aurata, but further studies need to be conducted as it may affect the acuity of other responses, likely affecting other behaviours.