Echinococcosis is caused by adult or larval stages of cestodes belonging to the genus Echinococcus (Taeniidae). Larval infection (hydatid disease; hydatidosis) is characterized by long-term growth of metacestode (hydatid) cysts in the intermediate host.
Echinococcus granulosus and E. multilocularis--the two major species of medical and public health importance--cause cystic echinococcosis (CE) and alveolar echinococcosis (AE), respectively. While both CE and AE are serious diseases, AE has a high fatality rate and poor prognosis if managed inappropriately.
China is endemic for both CE and AE, with a greater prevalence in the north and north-west. (1) Human cases of CE reported from 33 provinces/autonomous regions in China account for more than 98% of echinococcosis cases with Gansu, Ningxia Hui Autonomous Region (NHAR), Qinghai, Sichuan, and Xingjiang being co-endemic for CE and AE. (1,2) Red foxes and small mammals are the main definitive and intermediate hosts, respectively, for E. multilocularis in the NHAR. (3) E. granulosus is primarily transmitted between domestic dogs and sheep. CE is present throughout the NHAR, whereas AE occurs in three confluent mountainous counties (Guyuan, Haiyuan, Xiji) in southern NHAR.
We undertook a community survey in 2002 and 2003, using ultrasound and serology, to detect asymptomatic cases for assessing the true prevalence of human CE and AE among rural communities in Guyuan, Longde and Xiji, We also sought to identify risk factors for both these diseases.
Study area and population Guyuan, Longde and Xiji counties are situated on the Liupan mountains (average altitude 2200 m above sea level). The socioeconomic structure, land-use and population density of these counties are representative of rural mountainous regions of NHAR. People in this region are poor; subsistence agriculture and livestock herding (sheep, goats, cattle) are the main income sources. During the course of the community surveys and searches of local government records, it became evident that the dog population had decreased dramatically by 1997 due to poisoning as the secondary effect of a poison-bait rodent control programme.
Half the population of Guyuan and Xiji is Han while the other half is Hui Chinese (a minority ethnic group, with their distinct religion (Islamic), lifestyle and customs). Though the majority (91%) living in Longde county are Han, their lifestyle is comparable to those from Guyuan and Xiji. Village populations ranged from 200 to 1900 people (average, 400). We also surveyed three local primary and middle schools in Xiji.
We used hospital records and "AE-risk" landscape profiles (4) to select village communities in Guyuan, Longde and Xiji counties predicted at risk of human CE and/or AE. We received approval for the surveys from the Ethics Committee of Ningxia Medical College, and obtained written consent from all adult participants and parents of minors five years or older who agreed to participate. We conducted participant interviews using a questionnaire to collect demographic, epidemiological and risk factor data. We took a small blood sample from the ear lobe of each participant for specific antibody testing by enzyme linked immunosorbent assay (ELISA) using E. granulosus cyst fluid antigen B (AgB) and E. multilocularis crude protoscolex extract (EmP). (5,6) We performed an abdominal ultrasound (US) scan on each participant, using a portable ultrasonograph (Aloka, Japan, model 3.5 MG67N35F2.4) to differentiate advanced AE from CE in the liver. (7) We used serum (prepared from 5 ml venous blood samples) from individuals with a surgical history of CE or AE, an abnormal US image and those with no cystic lesions detected by US during the surveys, as negative controls. We transported serum samples at 4[degrees]C and later stored them at -20[degrees]C before processing for ELISA. …