Hydatid cyst detection by liver ultrasonography in sheep: impact of cyst abundance, viability and location

Cystic echinococcosis (CE) is a major zoonosis in Morocco, common in most livestock including sheep. The objectives of this study, performed in sheep of different ages in the Middle Atlas in Morocco, were (1) to compare CE detection, CE count and cysts classification into viable and calcified by ante-mortem hepatic ultrasound (US) scanning and post-mortem macroscopic hepatic inspection and (2) to investigate post-mortem the hydatid cysts present in the liver and lungs to determine in as far hepatic US scanning would fail to detect sheep with exclusive location of CE in the lungs that are not detected on ultrasound. Among 126 examined sheep, 106 were considered as infected by CE by US scanning, whereas 108 were detected at necropsy. Whatever the diagnostic method used; the total number of cysts increased significantly in function of age (p <0.001). Differentiation capacity between viable and calcified cysts was similar for US scanning and necropsy. Sheep considered as negative by US scanning (n = 32) were confirmed negative by necropsy, leading to a specificity of US scanning of 100% (95% CI: 90-100%) and sensitivity of 98% (IC: 92-99%). Part 2 of the study evidenced that among 97 infected sheep, 78% (IC 95%: 72-83%) presented hepatics cysts, whereas 22% (IC 95%: 17-28%) presented exclusively pulmonary cysts. 56% (IC 95%: 54-59%) of total cysts were located in the liver. Animals showing exclusively pulmonary cysts were lightly infected in comparison to sheep with liver or with liver and pulmonary cysts. Under the conditions of the Middle Atlas sheep farm, the US scan was able to detect 98% of sheep with liver cysts. The US scan therefore allows easy monitoring of the progress of the control measures and provides data on the infestation of animals without the need for autopsy.