Diphyllobothriosis was first recorded in humans in Argentina in 1892 and in introduced salmonids in 1952. The aim of this work is to assess factors influencing the values of prevalence and abundance of plerocercoids in fishes that could increase the risk of transmission of Dibothriocephalus spp. in Andean Patagonian lakes. We analysed two key issues potentially related to the occurrence of tapeworms in fish: the presence of cities on coastlines (as potential sources of eggs to nearby lakes) and the difference between native and exotic fishes in susceptibility to infection. We investigated the probability of finding parasites in fish, the variation in parasite abundance in different environments and the relationship between host length and occurrence of plerocercoids. A total of 3226 fishes (belonging to six autochthonous and four introduced species) were analysed between 2010 and 2019 in eight environments. Plerocercoids were counted, and a subset was determined molecularly to species level. Two species, Dibothriocephalus latus and Dibothriocephalus dendriticus, were identified from both salmonids and native fishes, this being the first molecular confirmation of these tapeworm species parasitizing native South American fishes. Salmonids had higher levels of infection than native fishes, and these levels were higher in aquatic environments with a city on their coastline. Transmission to humans seems to occur mainly through Oncorhynchus mykiss, which showed the highest infection values and is the species most captured by fishers. Based on previous data and the present results, eggs shed by humans, dogs and gulls in cities could be the principal factors in maintaining the life cycle of this parasite in surrounding aquatic environments.

The spectrum of immunomodulating molecules produced by tapeworms is not yet well understood. The aims of this study, on the tapeworm Diphyllobothrium dendriticum, were: 1) detection and quantification of prostaglandins (PGs) E2 and D2 by high performance liquid chromatography; 2) visualization of PGE2 and PGD2 in specific cells, using methods of immunocytochemistry and confocal laser scanning microscopy; and 3) investigation of the ultrastructure of the cells potentially producing PGE2 and PGD2. The PGE2 immunoreaction (IR) was found in the apical terminals of the frontal glands and sensory organs in the tegument and in small neurons belonging to the main cords and commissures. PGE2-IR partly coincided with α-tubulin-IR. PGD2-IR occurred in the muscle fibers of longitudinal and transverse body muscles and coincided with phalloidin TRITC staining. Both PGE2 and PGD2 were found in the flame cells of the excretory system. Ultrastructural study of the tegument revealed two types of structures that potentially produce PGE2: ciliated and unciliated free nerve endings and frontal gland terminals reinforced with neurotubules. In the main nerve cords, small neurons were identified as potentially exhibiting PGE2-immunoreactivity. In homogenates of the plerocercoids, the measured content of PGE2 and PGD2 was 33.15ngmg-1 and 1.94ngmg-1 of fresh tissue weight, respectively. We found evidence of PGE2 and PGD2 in D. dendriticum parasitizing Coregonus autumnalis (fish) and proved excretion of PGE2 and PGD2 in response to C. autumnalis blood serum. Prostaglandins produced by D. dendriticum probably play a dual role: 1) PGE2 and PGD2 potentially modulate the fish antiparasitic immune response; 2) PGE2 is presumably necessary for proper development and function of the nervous system, and PGD2 can act as an antagonist against mediators causing muscle contraction.

An excavation of the Vesakoyakha II-IV and Nyamboyto I burial grounds was conducted during the 2014 field season, and soil samples from intact burials dating from the 19th and 20th centuries, respectively, were analyzed to determine interactions between parasites and host/vectors. Considering the discovery of Diphyllobothrium sp. and Taenia sp. eggs in soil samples from the pelvic region, diphyllobothriasis was the most frequent helminthic infection among the Taz Nenets. The Nyamboyto Nenets mainly consumed uncooked fish, while the Vesakoyakha Nenets had a bigger variety in food choices, including reindeer meat. Nenets children were given raw fish from early childhood. The paleoparasitological results corroborate rare ethnographic records about the consumption of uncooked reindeer cerebrum which led to beef tapeworm helminthiases. This is the first parasitological report of helminthic diseases among the Taz Nenets, and, as such, it provides insight into their subsistence activities and food patterns and broadens our understanding of their health condition.

In the present study, the process of vitellogenesis of one of the most prolific organisms, the broad tapeworm, Diphyllobothrium latum, the causative agent of human diphyllobothriosis, was studied for the first time using transmission electron microscopy. Cytochemical staining with periodic acid-thiosemicarbazide-silver proteinate for detection of glycogen was applied. Starting from the periphery toward the center of the vitelline follicle four stages of vitellocytes are differentiated: immature vitellocytes, early maturing vitellocytes, advanced maturing and mature vitellocytes. Differentiation into mature vitellocytes involves the formation of shell globule clusters containing shell globules, large amount of saturated lipid droplets and glycogen. A peculiar ultrastructural feature of D. latum vitellogenesis is the presence of lamellar bodies in the cytoplasm of mature vitellocytes. This feature is similar to that present in the closely related caryophyllideans and spathebothriideans. Despite the great similarity observed in the embryonic development of diphylobothriideans, caryophyllideans and spathebothriideans, and the fact that their vitellocytes share a feature not reported from other cestode groups, there are substantial differences in the morphology of vitelline clusters, types, amount and localization of their nutritive reserves.

For the first time the agent of diphyllobothriosis Lake Baikal is the cestoda D. dendriticum establishted by T.P. Chizhova and P.G. Gofman-Kadoshnikov (1962). D. dendriticum reaches maturity in human intestine, but it is considered, that the relationships between the parasite and human are facultative property (Klebonovski 1985). The results of the investigation of the diet of sea-gull nestlings (control-uninfected and experimental-infected birds with cestoda groups) and stress influence (starvation) on the mass loss in experimentally and naturally infected ones with different duration conditions adaptation of experiments are discussed in this article.

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Experiments were made to infect young Ophiocephalus argus, the fish of prey delivered from eastern Asia in the Amu-Dar\'ya River basin, outside the area of the broad tapeworm Diphyllobothrium latum. The dalags were infected mainly by ingesting the local copepods Arctodiaptomus salinus, the experimentally invaded larvae of the broad tapeworm. The latter larvae were obtained from the development of eggs of the helminth isolated from strobilae from the patients treated in Perm Province. D. latum plerocercoids lived in the dalags nearly 3 weeks, then they died and lysed. Thus, the dalag cannot be a supplementary host of D. latum.