Peculiarities of Host-Parasite Relationships between Calodium sp. (Nematoda: Capillariidae) and Common Shrew Sorex araneus
Authors:   Institute of General and Experimental Biology SB RAS, Batueva M. D-D , Moroldoev I. V. ,   Institute of Systematics and Ecology of Animals SB RAS, Naidanov T. I. ,   Buryat State University, Abasheev R. Yu. ,   Buryat State University
Published: January 2023

ematodes of the genus Calodium Dujardin, 1845 (syn. Capillaria, Hepaticola) are parasites and cause hepatic capillariasis in rodents and other mammals, including humans. The life cycle of Calodium spp. may be completed in a single host species. However, the eggs, which are laid in the liver, must mature outside of the host body (in the environment) prior to infecting a new host. The death of the host in which the adults reach sexual maturity, either by being eaten or dying and decomposing, is necessary for completion of the life cycle [Moravec, 1982]. For the first time, we described the feature of the host-parasite relationship – the nematode Calodium sp. – common shrew. During monitoring studies of the parasite fauna of rodents and insectivores on the Baikal territory, we found the parasite Calodium sp. In some individuals, we noted fibrous formations on the surface of the liver, which were noticeable with the naked eye. Histological examination revealed the presence of petrified helminth fragments in the fibrous focus and eggs surrounded by connective tissue fibers. No inflammatory response of host to Calodium sp. was noted. Eggs of Calodium sp. translucent, oval in shape, covered with villi and located under a thin shell. Their length is 69.66±1.86 (63.88–72.88); width with shell 38.3±0.89 (35.49–41.11); width without shell 31.92±0.72 (29.48– 34.93). Caps are located on the poles of the eggs. Developing larvae are clearly visible, which are brightly stained with hematoxylin-eosin and Ziehl-Neelsen. The eggs are located compactly, the liver parenchyma at the site of localization is replaced by connective tissue. Connective tissue strands surround each egg and delimit it from the surrounding tissue. Perl’s staining did not reveal the content of hemosiderin and macrophages in the liver. No liver edema was observed. The structures of the liver were destroyed, destruction of the hepatic lobules was revealed near the accumulation of parasite eggs, but without the destruction of hepatocytes. The areas occupied by the parasite accounted for almost a quarter of the volume of the liver: this is an extensive fibrous formation with a dead nematode inside and massive accumulations of eggs in a network of connective tissue fibers. No histopathological changes were found in the rest of the liver. Due to the lack of a mature specimen of the parasite, it was not possible to determine the nematode to the species level. Although C. soricidae is a specific parasite for the common shrew, the size of the eggs in this species is smaller than in the parasite we studied. With regard to the widespread nematode C. hepatica, the nature of the hostparasite relationship has been studied in some detail. In most studies, in rats Rattus rattus and Rattus norvegicus, parasite encapsulation and an inflammatory reaction around the nematode and eggs are expressed, the extent of liver fibrosis is not as significant as in the shrews we observed [De Andrade and Andrade, 2004; Millán et al., 2014; Fuehrer, 2014].