Abstract
Cystic echinococcosis is a zoonotic disease caused by the metacestode of Echinococcus granulosus sensu lato. The disease is characterized by the development of cystic structures inside viscera of the intermediate host, mainly liver and lungs. These cysts are formed by three layers: germinal, laminated, and adventitial layer, the latter being the local host immune response. Metacestodes that develop protoscoleces, the infective stage to the definitive host, are termed fertile, whereas cysts that do not produce protoscoleces are termed non-fertile. Sheep usually harbor fertile cysts while cattle usually harbor non-fertile cysts. Adventitial layers with fibrotic resolution are associated to fertile cysts, whereas a granulomatous reaction is associated with non-fertile cysts. The aim of this study was to analyze cellular distribution in the adventitial layer of fertile and non-fertile E. granulosus sensu stricto cysts found in liver and lungs of cattle and sheep. A total of 418 cysts were analyzed, 203 from cattle (8 fertile and 195 non-fertile) and 215 from sheep (64 fertile and 151 non-fertile). Fertile cysts from cattle showed mixed patterns of response, with fibrotic resolution and presence of granulomatous response in direct contact with the laminated layer, while sheep fertile cysts always displayed fibrotic resolution next to the laminated layer. Cattle non-fertile cysts display a granulomatous reaction in direct contact with the laminated layer, whereas sheep non-fertile cysts display a granulomatous reaction, but in direct contact with the fibrotic resolution. This shows that cattle and sheep cystic echinococcosis cysts have distinct local immune response patterns, which are associated to metacestode fertility.
Highlights
Cystic Echinococcosis (CE) is a zoonotic parasitical infection caused by the metacestode of Echinococcus granulosus sensu lato
For many years, the adventitial layer of CE cysts has been described as a host-derived fibrous capsule surrounding the parasite [22], and while this remains true for many fertile CE cysts, currently the adventitial layer is considered to be the result of the local immune response against fertile and non-fertile CE cysts, with granulation tissue, plasma cells, lymphocytes, eosinophils, and other innate immune cells [5, 16, 23]
It was reported that cattle CE cyst fertility was associated with the local inflammatory response, with fertile CE cysts with low PSC viability showing higher levels of granulomatous reaction near the laminated layer than high PSC viability cysts [5]
Summary
Cystic Echinococcosis (CE) is a zoonotic parasitical infection caused by the metacestode of Echinococcus granulosus sensu lato. CE has worldwide distribution, with higher prevalence in human and animal hosts in south Europe, middle Asia, north and south Africa and south America [1, 2]. It is recognized by the World Health. Echinococcus granulosus sensu lato has an indirect life cycle, with herbivores as intermediate hosts and canids as definitive hosts. In the domestic life cycle, ruminants, such as sheep and cattle, are the primary intermediate hosts, and dogs are the definitive hosts. CE cysts are composed by an inner germinal layer (GL) and an outer laminated layer (LL), that are of parasite
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