Response patterns in adventitial layer of Echinococcus granulosus sensu stricto cysts from naturally infected cattle and sheep

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.

Keywords: Adventitial layer; Echinococcus granulosus; Fibrosis; Histopathology.

Figure 1

Response patterns of adventitial layer of CE cysts. A, D Pattern I, fibrosis is found between inflammatory reaction and organ tissue. B, F Pattern II, fibrosis is found between the laminated layer and organ tissue, and no obvious inflammatory reaction is present. C, G Pattern III, fibrosis is found between the laminated layer and inflammatory reaction. D, H Pattern IV, there is diffused fibrosis within the inflammatory reaction. LL = Laminated layer, IR = inflammatory reaction, OT = organ tissue, F = fibrosis. A, B, C, D = Van Gieson stain. E, F, G, H = Haematoxylin–eosin stain. Size bar: 200 µm. CE = Cystic echinococcosis.

Figure 2

Response patterns between cattle and sheep fertile CE cysts. A, E Cattle fertile liver CE cyst (Pattern III), B, F Sheep fertile liver CE cyst (Pattern II), C, G Cattle fertile lung CE cyst (Pattern I), D, H Sheep fertile lung CE cyst (Pattern II). LL = Laminated layer, IR = inflammatory reaction, OT = organ tissue, F = fibrosis. A, B, C, D = Van Gieson stain. E, F, G, H = Haematoxylin–eosin stain. Size bar: 200 µm. CE = Cystic echinococcosis.

Figure 3

Fibrosis patterns between cattle and sheep non-fertile CE cysts. A, E Cattle non-fertile liver CE cyst (Pattern I), B, F Sheep non-fertile liver CE cyst (Pattern III), C, G Cattle non-fertile lung CE cyst (Pattern I), D, H Sheep non-fertile lung CE cyst (Pattern III). LL = Laminated layer, IR = inflammatory reaction, OT = organ tissue, F = fibrosis. A, B, C, D = Van Gieson stain. E, F, G, H = Haematoxylin–eosin stain. Size bar: 200 µm. CE = Cystic echinococcosis.