Re-Emerging Schistosomiasis in Hilly and Mountainous Areas of Sichuan, China Song Liang,A Changhong Yang,B Bo Zhong,C & Dongchuan Qiu C
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Re-emerging schistosomiasis in hilly and mountainous areas of Sichuan, China Song Liang,a Changhong Yang,b Bo Zhong,c & Dongchuan Qiu c Abstract Despite great strides in schistosomiasis control over the past several decades in Sichuan Province, China the disease has re-emerged in areas where it was previously controlled. We reviewed historical records and found that schistosomiasis had re- emerged in eight counties by the end of 2004 — seven of 21 counties with transmission control and one of 25 with transmission interruption as reported in 2001 were confirmed to have local disease transmission. The average “return time” (from control to re-emergence) was about eight years. The onset of re-emergence was commonly signalled by the occurrence of acute infections. Our survey results suggest that environmental and sociopolitical factors play an important role in re-emergence. The main challenge would be to consolidate and maintain effective control in the longer term until “real” eradication is achieved. This would be possible only by the formulation of a sustainable surveillance and control system. Keywords Schistosomiasis/epidemiology/prevention and control; China (source: MeSH, NLM). Mots clés Schistosomiase/épidémiologie/prévention et contrôle; Chine (source: MeSH, INSERM). Palabras clave Esquistosomiasis/epidemiología/prevención y control; China (fuente: DeCS, BIREME). Arabic Bulletin of the World Health Organization 2006;84:139-144. Voir page 143 le résumé en français. En la página 144 figura un resumen en español. Introduction administrative and professional health controlled areas in the seven provinces. organizations were established at vary- Nearly 800 000 people are infected an- Schistosomiasis remains a major public ing levels of governance specifically for nually and 60 million people are at risk health problem in many developing schistosomiasis control, such as a schisto- of infection in China.4, 5 countries in tropical and subtropical somiasis control committee at the central In Sichuan, by 1985, 20 counties had regions, with the majority of the disease’s level and anti-schistosomiasis stations attained transmission control status and impact in Africa. WHO estimates that at the county level. Commonly imple- 16 had attained transmission interrup- globally, 600 million people are at risk mented control measures include snail tion. By 2001, 21 counties had attained of exposure to infection, more than 200 control, chemotherapy, health education, transmission control and 25 counties had 6 million people are infected with schisto- and provision of sanitary water. attained transmission interruption. somiasis and 120 million of these show We reviewed survey data to describe 1 In China, over the past five decades, clinical symptoms. Of the three main schistosomiasis has been eradicated in the epidemiology of re-emerging schis- disease-causing schistosome species, three provinces (Fujian, Guangdong and tosomiasis in the hilly and mountainous Schistosoma japonicum, also known as Zhejiang), the municipality of Shanghai, regions of Sichuan Province, the control Asian or oriental blood fluke, is respon- and the autonomous region of Guangxi strategies implemented by local public sible for human and animal infections (in Province. This reduced the number of health professionals and the possible fac- mammalian hosts such as cattle and wild endemic provinces to seven — five in tors contributing to re-emergence of the disease in this province. rodents) in China, the Philippines and to the lower Yangtze lake region (Anhui, a lesser extent, Indonesia. Hubei, Hunan, Jiangsu, Jiangxi), and two Schistosomiasis was first docu- (Sichuan and Yunnan) in the mountain- Methods mented in 1924 in Sichuan, China.2 Its ous regions of the upper reaches of the Setting epidemiological pattern became evident Yangtze river — where incidence and Located in south-western China (lati- only when a series of large-scale surveys morbidity are now much lower than tude 26.52° N to 34.32° N, longitude were conducted in the early 1950s. Since they were in the 1950s.3 Despite this 97.35° E to 108.52° E (Fig. 1)), Sichuan then, schistosomiasis control has been achievement, since the mid-1990s the Province is the fourth most populous a public health priority in China and disease has been resurging in previously (84 million in 2000) and the fifth largest a Department of Environmental Health, School of Public Health, University of California, 140 Warren Hall, Berkeley, CA 94720-7360, USA. Correspondence to this author (email: [email protected]). b Institute of Health Information, Sichuan Center for Disease Control and Prevention, Chengdu, China. c Institute of Parasitic Disease, Sichuan Center for Disease Control and Prevention, Chengdu, China. Ref. No. 05-025031 (Submitted: 29 June 2005 – Final revised version received: 29 August 2005 – Accepted: 1 September 2005) Bulletin of the World Health Organization | February 2006, 84 (2) 139 Policy and Practice Re-emerging schistosomiasis in China Song Liang et al. (485 000 km²) of 22 provinces, five au- Fig. 1. Distribution of schistosomiasis in Sichuan Province tonomous regions, and four national mu- nicipalities in China. It has 181 counties and districts. Sichuan is one of the most important agricultural bases in China. Most of the province (90%) is moun- tainous or hilly, with plains and plateaus covering the rest of the land area. Definitions Chuanbei Progressive stages of disease control in hilly region the endemic areas have been described as morbidity control, transmission control This map is an approximation of actual country borders. and transmission interruption (the last two were formerly known as “basic eradi- cation” and “eradication”, respectively).7 See Box 1 for definitions. Yaan mountains Disease surveys Disease surveys are routinely carried Chengdu out in Sichuan Province. On receiving Plain reports of re-emergent human infections from the county, health workers at the anti-schistosomiasis stations and office Changqiu of endemic disease control conduct hilly region site-specific, sometimes geographically extended, human and snail surveys to verify the existence of local transmission and to assess the degree of impact. The surveys include examination of infection Daliang N status of inhabitants between the ages mountains Miles of 4 and 60 years, through enzyme- 0 25 50 100 linked immunosorbent assay (ELISA), or No transmission Kato–Katz test. Transmission interruption Veterinarians from the department Transmission control Distribution of re-emerging counties Endemic area Chuanbei hilly region: Jingyang, Luojiang, Guanghan, of animal husbandry simultaneously Zhongjiang, Fucheng, Gaoxin, Anxian Re-emergent area examine cattle for infection. Cattle infec- Daliang mountains: Xide tion status is determined via hatch test. Snail distribution and infection The boundaries and names shown and the designations and dotted lines used in this publication do not imply the expression of any opinion whatsoever on the part of the World Health Organization concerning the legal status of any country, territory, status are determined through system- city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. atic sampling. Such sampling was either WHO 05.163 exhaustive, with samples taken every ten metres, or stratified, with samples Data collection reported. Clinical records of acute cases taken at different environmental points, In late 2004, we visited all the eight af- were obtained, where available. Clinical such as irrigation ditches, grasslands, or fected counties in Sichuan Province and forms record basic epidemiological in- orchards. examined local records of surveys on hu- formation, such as time of appearance of symptoms indicative of schistosomiasis Control activities mans, snails, and cattle, reports of acute human infection, and control activities. infection, time of hospitalization, locality After local transmission is confirmed, in- and duration of water contact, serologi- terventions targeting humans and snails We collected the annual schistosomiasis report forms of the past 5–9 years at the cal and/or parasitological examinations, are initiated to contain the spread of the as well as other clinical parameters. The township level. At anti-schistosomiasis disease and reduce morbidity. Control disease and snail reporting forms record stations in each county, we interviewed measures usually include selective or mass the human population examined (either administration of chemotherapy to the the staff involved in human and snail through immunoassay or parasitological inhabitants of affected villages, as well surveys, as well as reviewed the inter- test) and treated, infection status (acute, as focal snail control using molluscicides ventions following the occurrence of sub-clinical, or chronic), numbers of and/or environmental modification. acute infections, and the planning and cattle surveyed and treated, snail distri- However, control measures are usually implementation of routine surveillance bution and infection status, habitat type confined to places where humans are and control. (irrigation ditch, paddy, or grassland, for surveyed and infections confirmed, even Report forms at the village level example), and control activities (such as while acute infections continue to occur were retrieved in areas where acute cases, niclosamide spraying or pasting or envi- at other locations. infected snails, or infected cattle were ronmental modification). 140 Bulletin of the