Ningxia Hui Autonomous Region (NHAR), situated in the Loess plateau of central north-west China, is well known as a hyper-endemic area for both cystic (CE) and alveolar (AE) echinococcosis, especially in the southern part of the region.
A retrospective study was conducted using surgery records from hospitals to identify hyper-endemic foci of CE and AE in the NHAR. Human AE cases were only located in a confluence area of Xiji, Haiyuan and Guyuan counties. The coexistence of remarkably high prevalences of human echinococcosis in Xiji (6/100,000), Guyuan (5/100,000), Haiyuan (11/100,000) and Tongxin (13/100,00) counties between 1994 and 2001 and low prevalences in Longde (0.5/100,000) and Jingyuan (0.15/100,000) counties indicated a highly heterogeneous distribution of human AE and CE within the southern NHAR.
An ultrasound and serological based mass screening study was performed in a highly endemic focus located in this area to determine the true prevalence of CE and AE in the NHAR. A total of 4778 individuals in 26 communities from 16 townships were screened in November 2001, October 2002 and September 2003. In total, 14.5% of the natural community population was screened, which provided a sample of 2271 females and 2507 males. The participants comprised predominantly 2440 Han and 2316 Hui. Occupational groups were mainly comprised of farmers and students in Xiji and Guyuan counties but predominantly farmers in Longde County. The registered patients of echinococcosis presented heterogeneous distributions, showing a range of prevalences for AE of between 0 and 8% (mean= 2%) and CE of between 0 and 7.4% (mean= 1.6%). Comparing hyperendemic foci of Xiji County, the average prevalence of both diseases combined was 4.5%. There was relatively lower prevalence in Guyuan and Longde counties (0.9% and 0.6%, respectively). The overall prevalence for hydatid disease in the three counties was 3.6% (17114778). The AE prevalence in females (62.5%) was significantly higher than in males (37.5%). The age of people with AE ranged from 18 to 73 years with an increased prevalence in persons older than 30 years and for CE ranged from 18 to 79 years with an increased prevalence in persons older than 20 years. The prevalence of human echinococcosis varied by occupations and was 37% for housewife, 18.8% for general worker, 12% for herdsman, 5.2% for farmers and 0.07% for students. A questionnaire revealed that dog ownership for more than 10 years was associated with human CE prevalence. The incidence was also higher for people drinking river and collected water and well than those drinking tap or spring water. The public knowledge of echinococcosis was generally poor. The majority of persons with an understanding of this endemic disease comprised those with a history of echinococcosis or their relatives with such a history.
The effect of the drug, albendazole, for the treatment of echinococcosis was examined in a longitudinal study. A basic chemo-therapeutic course consisted of oral albendazole taken twice daily for 30 days, with an interval of 10 days between courses. The adult dose was 15 ~ 20 mg/kg/day with a maximum of 1200 mg daily per person. The response to treatment was evaluated by regular ultrasound, serology and clinical examination. After mass screening, a special community with many aggregated AE and CE cases within households was assessed in a follow up study. Those sero-positive individuals were distributed in every age group except those younger than 10 years old indicated an equal chance of exposure to infection for outdoor activities. However, an increased prevalence by age (≥20 years for CE and ≥30 years for AE) indicated that acquiring echinococcosis requires prolonged exposure to egg-contaminated environments and also depends on the susceptibility of individual subjects. Human AE prevalence was greater in females but the sero-positivity among surveyed young people showing no gender differences, which may be attributed to specific physiological and/or societal factors. The follow-up showed that the average diagnosis history of patients (7.5 years) was longer than that of treatment (4.7 years) and most AE cases were at an advanced stage of P3 and P4 (72% and 14%). Absorbed lesions due to natural progression or resulting from albendazole treatment were observed although drug efficacy in most cases was poor. Long-term treatment and follow-up may be required to assess the true value of albendazole treatment.
The DNA from isolates of Echinococcus from various hosts and geographic origins in North West China were compared for phylogenetic similarity by analyses of the atp6 gene. The study demonstrated that the common sheep strain (Gl genotype) of E. granulosus and the Eurasian strain of E. multilocularis coexist in this area.
Aggregation patterns of human echinococcosis cases in families or households were also investigated. Although there was evidence of aggregation, it was unclear to what extent this was due to human genetic factors or environmental exposure differences.
Echinococcus transmission patterns, based on infection prevalence, seroprevalence among offspring (age range from 7 to 18 years old) and geopolitical, landscape and ecoenvironmental factors, suggested heterogeneity of transmission and/or susceptibility to infection was occurring between geographic locations and communities. The transmission patterns also appeared to be changing over time.