Parasitology



Echinococcosis on the Tibetan Plateau: prevalence and risk factors for cystic and alveolar echinococcosis in Tibetan populations in Qinghai Province, China


P. M. SCHANTZ a1c1, H. WANG a2, J. QIU a3, F. J. LIU a4, E. SAITO a1, A. EMSHOFF a1, A. ITO a5, J. M. ROBERTS a1 and C. DELKER a6
a1 Division of Parasitic Diseases, National Center For Infectious Diseases, Centers For Disease Control and Prevention, Atlanta, GA 30341, USA
a2 Qinghai University Medical School, Xining, Qinghai Province, China
a3 Sichuan Center For Disease Control, Chengdu, China
a4 National Hydatid Disease Control Center, Urumqi, Xinjiang Province, China
a5 Department of Parasitology, Asahikawa Medical College, Asahikawa, Japan
a6 Boulder-Lhasa Sister City Project, Boulder, CO, USA

Article author query
schantz p   [PubMed][Google Scholar] 
wang h   [PubMed][Google Scholar] 
qiu j   [PubMed][Google Scholar] 
liu f   [PubMed][Google Scholar] 
saito e   [PubMed][Google Scholar] 
emshoff a   [PubMed][Google Scholar] 
ito a   [PubMed][Google Scholar] 
roberts j   [PubMed][Google Scholar] 
delker c   [PubMed][Google Scholar] 

Abstract

Infections by larval stages of tapeworms of the genus Echinococcus (echinococcosis or hydatid disease) are zoonotic infections of major public health importance throughout much of the world. Humans become infected through accidental ingestion of eggs passed in faeces of canid definitive hosts. Tibetan populations of China have some of the highest documented levels of infections by both Echinococcus granulosus and E. multilocularis, the causes of cystic and alveolar echinococcosis, respectively. In this study we measured the prevalence of cystic (CE) and alveolar (AE) echinococcosis disease in Tibetan communities in Qinghai, Province, China, and identified putative risk factors for both infections in these communities. 3703 volunteers in three predominately Tibetan counties of Qinghai were surveyed between June 1997 and June 1998. Parasitic lesions were diagnosed by imaging of characteristic space-occupying lesions in abdominal organs (ultrasound) or the lungs (radiographs). Specific serodiagnostic assays (Dot-ELISA and Em2-ELISA) were performed on sera of positively imaged subjects to further distinguish the disease agent. All participants completed a questionnaire documenting age, sex, education level, occupation, lifestyle (nomadic or settled), slaughter practices, drinking water source, hygienic practice and association with dogs. Data were analyzed using SAS version 8. 6·6% of the volunteers had image-confirmed infection with E. granulosus (CE) and 0·8% had E. multilocularis (AE) infection. The significant univariate factors for echinococcal infection (both CE and AE) included livestock ownership, Tibetan ethnicity, female gender, low income, herding occupation, limited education, water source, age greater than 25 years old, poor hygienic practices, offal disposal practices and dog care. Multivariate analysis revealed that livestock ownership was a significant risk factor for both forms of the disease, as well as age greater than 25 years, female gender, herding occupation, and being nomadic (vs semi-nomadic or settled). No additional significant risk factors were identified among the 344 nomadic participants. Being female and being older than 25 years of age were significant factors among the 1906 semi-nomadic participants. Among the 1445 settled participants, allowing dogs to sleep indoors was statistically significant. Issues such as inadequate assessment of animal ownership, selection bias, disease misclassification, and loss of information may have led to reduction in strength of some risk factor associations and need to be addressed in future epidemiologic analysis of echinococcosis in this population.


Key Words: Alveolar echinococcosis; cystic echinococcosis; hydatid disease; China; epidemiology; risk factors.

Correspondence:
c1 Division of Parasitic Diseases, NCID, Centers For Disease Control and Prevention, Mailstop F22, 4770 Buford Highway, Atlanta, GA 30341, USA. Tel: 770 488-7792. Fax: 770 488-7761. E-mail: PSchantz@cdc.gov


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