Kolesnikov I.A.*, Biserova N.M., Mustafina A.R. 2026. Host-parasite structural interactions in the Pyramicocephalus phocarum (Cestoda) – White Sea cod system // Invert. Zool. Vol.23. No.2: 258–275 [in English].
Department of Invertebrate Zoology, Faculty of Biology, Moscow Lomonosov State University, Moscow 119234 Russia.
* Corresponding author
Ivan Kolesnikov: kolesivan96@gmail.com https://orcid.org/0000-0003-4524-1476
Natalia Biserova: nbiserova@yandex.ru https://orcid.org/0000-0002-5481-0207
Alfia Mustafina: alfia_xx@bk.ru
doi: 10.15298/invertzool.23.2.04
ABSTRACT: Pyramicocephalus phocarum (Fabricius) Monticelli (Diphyllobothriidea) plerocercoids infect numerous species of commercial fish inhabiting the cold seas of the Northern Hemisphere bearing an impact on fisheries and aquaculture. Previous studies reported some details of the structure of the tegument, glandular and nerve systems. However, the structure of host-parasite interactions between the P. phocarum plerocercoid and the cod — particularly the host’s cellular response to the infection — has not yet been examined. Cod harbouring P. phocarum plerocercoids were caught in the Velikaya Salma Strait near the MSU WSBS (66°33′25″ N, 33°06′02″ E) during 2018–2024 in early June. Specimens of the plerocercoids with surrounding host tissues were obtained from euthanized fish, and examined with SEM, TEM, and light microscopy. Histological and ultrastructural analyses revealed the host’s immune response to infection in the form of a granuloma. The granuloma was found to be composed of fibroblasts, mast cells, neutrophils, macrophages, and epithelioid cells. The parasite produced a protective layer, the cyst, as a structural response to the host immune reaction. Structures involved in the protection against the host also included microtriches, extracellular vesicles, secretory products of the tegument, neurons, and specialised eccrine glands. A unique structural adaptation of the tegument of the P. phocarum plerocercoid was identified, namely the secretory poral cavities connected with both apocrine and neuro-exocrine secretion. These findings highlighted specialised adaptations of P. phocarum plerocercoids that may balance isolation from host immunity with access to nutrients, providing new insights into cestode–teleost relationships and the functional diversity of tegumental and neuroexocrine secretions.
KEY WORDS: immune response, parasitic infection, plerocercoid, tapeworms, tegumental secretion.