Effectiveness of ultrasound in sheep as a monitoring tool for the long-term control of cystic echinococcosis

Abstract

This study aimed to evaluate the effectiveness of ultrasound (US) in sheep compared with the necropsy (gold standard) as an in-vivo monitoring tool used in a long-term control program of cystic echinococcosis (CE). The study involved 10-randomly-selected farms, divided into a Treated-Group (TG, n = 5, receiving a control protocol for CE) and a Control-Group (CG, n = 5, no protocol), enrolled over 6-years in an endemic area of southern Italy. All sheep of ten farms destined for slaughter underwent liver and lung US followed by necropsy, during the study period. From a total of 1'175 sheep, 50.0 % (593/1'175) belonged to the TG and 49.5 % (582/1'175) to the CG were enrolled. Overall, the US showed a Sensitivity (SE) of 87.9 %, a Specificity (SP) of 72.3 % as well as a positive- (PPV) and negative-predictive-value (NPV), and Accuracy of 74.4 %, 86.7 %, and 79.7 %, respectively. A moderate Cohen's Kappa-Coefficient (K=0.599) were also detected between the two techniques. The generalised linear mixed model showed that distribution (p < 0.001) and type of lesion (p < 0.001) significantly influence the US performance. The higher SP and PPV in CG likely result from a greater disease prevalence and presence of older lesions; the higher NPV in TG might reflect the beneficial effects of the control program and lower disease exposure. Although technical and logistical challenges have to be addressed for its use, a US conscious integration into continuous surveillance program might promote the early in vivo identification of infected farms, limiting necropsy dependence for CE monitoring.

Keywords: Echinococcus granulosus; Monitoring tool; Screening test; Ultrasonography; Zoonosis.