Surveillance on schistosomiasis in ve provinces of the People’s Republic of China in the post-elimination era

Background: The People’s Republic of China (P. R. China) has made signicant progress on schistosomiasis control. Among the 12 provinces (municipality, autonomous region) with schistosomiasis endemic in P.R. China, Guangdong, Shanghai, Fujian, Guangxi and Zhejiang provinces (following called as ve provinces) had successively eliminated schistosomiasis during 1985-1995. However, given the increasing mobilization of the population and goods, wetland protection, climate changes etc., consolidation of the schistosomiasis elimination in these ve provinces remains challenging. In the current study, we sought to understand the epidemic situation in these post-elimination areas and their surveillance capabilities on schistosomiasis. Methods: ( (cid:0) ) Through the national schistosomiasis reporting system, annual data reecting the interventions and surveillance on human beings, cattle and snails based on county level from 2005 to 2016 were collected and analyzed to understand the epidemic status of schistosomiasis in ve provinces. ( (cid:0) ) A standardized score sheet was designed to assess the surveillance capacity for schistosomiasis of selected disease control agencies in ve provinces and ten counties. Assessment on surveillance capacity consisted of two parts: the rst part focused on the capacity of testing skills including schistosomiasis diagnostic skills, identication of snails’ living and infection status; the second part was to assess the knowledge level about schistosomiasis and its control. Results: The comprehensive assessments showed that no local cases in humans and cattle or infected snail were found in these ve provinces from 2005, and the surveillance abilities on schistosomiasis of the prevention and control institutions in ve provinces were appropriate. However, from 2005 to 2016, a total of 221 imported cases were detected in Zhejiang, Shanghai and Fujian provinces, and 11.98 hm 2 of new snail habitats were found in Zhejiang, Shanghai and Guangxi provinces. In addition, snail infestation reoccurred in 247.55 hm 2 of former snail habitats since 2011.


Background
Schistosomiasis, caused by parasitic trematode blood-dwelling ukes called Schistosoma, is one of the most important neglected tropical diseases in the world in terms of public health impacts [1,2]. According to the report of World Health Organization (WHO), schistosomiasis is transmitted in 78 countries around the world. In 2017, at least 220.8 million people needed prophylactic treatment for schistosomiasis [3]. In the past decade, with the increased quantity of donation of praziquantel by international organizations and companies and increased willingness to give priority for schistosomiasis control or elimination by governments of endemic countries, great progress had been obtained in many countries. Meanwhile, elimination of schistosomiasis is regarded as an achievable goal in endemic regions or countries if continuous interventions and adequate resources are provided.
Schistosomiasis japonica is the only disease caused by schistosomes for human beings and livestock in P. R. China, distributed in twelve provinces along and south of Yangtze River with a long history. Investigations conducted in the 1950's proved that there were 380 endemic counties within 12 provinces, with about 12 million people and 1.2 million cattle infected with schistosomes, and over 100 million people at risk of infection. In addition, the total habitat area of Oncomelania hupensis, the only intermediate host of S. japonicum, was approximately 14.5 billion m 2 [4][5][6][7]. Following three decades of unremitting efforts with control strategies shifted from snails control to morbidity control, Guangdong (1985), Shanghai (1985), Fujian (1987), Guangxi (1989) and Zhejiang (1995) provinces eliminated schistosomiasis successively.
Being a zoonotic parasitic disease, the transmission of schistosomiasis japonica is in uenced by biological, natural and social factors. Multiple studies proved that schistosomiasis easily rebounded or spread to new areas due to weakened interventions, ecological changes caused by ooding, construction of water conservancy projects, increased migration of goods or human resources etc., without a sensitive surveillance and response system [8][9][10][11]. As Shanghai, Guangdong, Fujian, Guangxi and Zhejiang had eliminated schistosomiasis at least twenty years before, we evaluated the epidemic situation and the surveillance capabilities on schistosomiasis among the ve provinces, to facilitate the consolidation of elimination achievements in post elimination era and provide reference for other regions where schistosomiasis had been eliminated or will be eliminated.

Study sites and research design
Among the ve provinces, Shanghai and Zhejiang provinces are located in the Yangtze River Delta, in the east of China, Fujian, Guangdong and Guangxi provinces are located in the south of China. According to the epidemiological characteristics, the endemic areas in Shanghai belong to waterway-network regions, while the endemic areas in Zhejiang, Guangdong, Guangxi and Fujian provinces are mainly hilly and mountainous regions (Fig. 1).
The study consisted of two parts: ( ) Data re ecting the schistosomiasis intervention and surveillance conducted in Shanghai, Guangdong, Fujian, Guangxi and Zhejiang provinces based on county level were collected and analyzed to understand the epidemic status of schistosomiasis. ( ) A standardized score sheet was designed to assess the surveillance capacity for schistosomiasis of selected disease control agencies.
The sample counties were selected according to their endemic situation before elimination. Counties with more schistosomiasis patients or higher density of snails were selected to assess their surveillance capacity.

Retrospective data collections
A comprehensive surveillance strategy focused on clearing the internal snail habitats and infection source and preventing imported snails and cases from other provinces with ongoing schistosomiasis transmission was conducted in the ve provinces. Annual data re ecting the interventions and surveillance on human beings, cattle and snails based on county level from 2005 to 2016 were collected through the national schistosomiasis reporting system. Variables could be split into three categories: variables re ecting serological tests and stool examination for schistosomiasis(people with serum positive would do stool examinations if available and some oating people with higher infection risk from other epidemic provinces may get stool examination directly) on humans; variables on serological tests and stool examinations for schistosomiasis on cattle, and variables re ecting the distribution of Oncomelania snails including total habitats, new infested areas etc.

Assessment on surveillance capacity
A standardized score sheet was developed to assess the surveillance capacity after consulting experienced experts in the eld of schistosomiasis control. The score sheet included two parts: the rst part focused on the capacity of testing skills including schistosomiasis diagnostic skills, identi cation of snails' living and infection status among the professionals; the second part was to assess the knowledge level about schistosomiasis and its control among the professionals. The assessment was implemented during December 2015-March 2016 in a blind manner.

Assessment on schistosomiasis testing skills
Laboratory testing skills of schistosomiasis were performed at provincial and county level among laboratory professionals. Two counties were selected in each province. The assessed testing skills included: (1) Diagnostic skills included the indirect hameagglutination assay (IHA) and the miracidia hatching technique (MHT), which are most widely used in low endemic areas with light infection intensity for population screening and con rmation of schistosome infection respectively. (2) Snails dissection and microscopic method to identify the snails' living and infection status.

Preparation of reference panels for assessment
To ensure the consistence and comparability of the assessed results among different provinces, reference panels for testing methods were prepared and coded by National Institute of Parasitic Diseases, Chinese Center for Disease Prevention and Control. Each panel for IHA contained ve serum samples (four from schistosomiasis cases and one from healthy persons), while panels for MHT included two samples containing mature eggs of schistosome obtained from the liver of infected rabbits and three negative samples with boiled-water treated eggs. Each snail panel consisted of three dead Oncomelania snails and seven living snails, while three of living snails were infected by schistosomes con rmed by shedding method. The test results were determined by technicians from NIPD, China CDC and were regarded as gold standard. The same patch of diagnostic kits were provided to technicians from provinces and counties.

Laboratory testing and score
The technicians in selected agencies were asked to perform the IHA and MHT tests according to the protocol of each method [12][13][14] and judge the results. The results were documented and reported to NIPD, China CDC within the given time. The total score of testing skills was 20, ve points for IHA and MHT respectively and 10 points for snail identi cation. The detailed evaluation rules are provided in Additional le 1: Table S1.

Assessment on basic knowledge on schistosomiasis control
A questionnaire was designed to assess the basic knowledge of medical staff responsible for schistosomiasis surveillance. Three professionals from CDC and two medical agencies at provincial level and county level attended the assessment respectively. The questionnaire was composed of three parts: knowledge of epidemiological and transmission characteristics of schistosomiasis japonica, diagnosis and treatment, case reporting and management. Each part consisted of ve questions (The full questionnaire is provided in Additional le 2). The total score for the questionnaire was 10. One point would be deducted per error answer until the score was decreased to zero (Additional le 1: Table S1).  For snail identi cation, all agencies preformed excellent capacity to identify the snails' living status with the accuracy rate of 100% (150/150) (Fig. 2). The average accuracy rate of identifying infection status of snails was 98.06% (103/105, 95%CI: 95.44-100.75%). And two wrong judgement results occurred in one CDC at county level.

Questionnaires survey on basic knowledge of schistosomiasis
Total of 108 medical staffs in fteen disease prevention and control agencies attended the questionnaire survey ( Table 4). The results showed that the average accuracy rate of all respondents was 97.96% (529/540, 95%CI: 96.77-99.16%). Among ve provinces, respondents from Guangdong and Guangxi provinces answered all questions correctly. The wrong-answered questions were mainly about knowledge on national comprehensive schistosomiasis control strategies and diagnosis of schistosomiasis.

The scores of the comprehensive assessment
Based on the results of testing skills and snail detection (3.2.1) and questionnaire surveys (3.2.2), except for Fujian scored 29 points, the scores of the other four provinces were all 30 points (Table 5 OR Fig. 3). In ten counties, the scores ranged from 26 to 30 points.

Discussion
Although the de nition of schistosomiasis elimination was announced by WHO in recent years and the debate of how to prove elimination is still going on, Guangdong (1985), Shanghai (1985), Fujian (1987), Guangxi (1988) and Zhejiang (1995) provinces were announced that schistosomiasis was eliminated successively according to the criteria issued by Chinese government at that time. Then the ve provinces transferred to post-elimination surveillance with main tasks to nd and eliminate local residual infectious sources and remaining snail habitats, and prevent the import of infectious sources and snails from other endemic areas [15][16][17]. Before our study, except one foci with two new cases reemerged in a farm of Guangdong province in 1992 but rapidly was under controlled [17,18], no new infections occurred in other provinces [19].
In our study, no local infection in reservoir hosts and intermediate host was detected in the ve provinces during 2005-2016, proving the successful consolidation of schistosomiasis elimination. And to improve the surveillance effectiveness on schistosomiasis in China, the sensitivity and speci city of the diagnosis reagents were improved and validated [20]. The comprehensive assessment results showed that the staffs have mastered the basic knowledge of schistosomiasis prevention and presented good capacity for schistosomiasis detection. All of these are elementary components of a sensitive and rapid surveillance platform. However, we noticed that there were some samples misdiagnosed and wrong answers for questionnaire answered by staff at county level. Capacity building should be strengthened focusing on schistosomiasis control and diagnosis through continued training and practices to consolidate local achievements on schistosomiasis control.
However, risks of the re-emergence and resurgence of schistosomiasis still existed in the ve provinces through our study. Over the past 12 years, a total of 221 imported cases were found in the ve provinces, mainly in Zhejiang province, neighbored with Jiangxi and Anhui provinces where the transmission of schistosomiasis is still going on. Studies showed that most of the imported cases in Zhejiang Province are farmers, migrant workers and merchants from schistosomiasis endemic areas, primarily from Anhui, Jiangxi, Hubei [21][22][23]. In recent years, owing to urbanization and economic development, the number of the oating population from domestic epidemic areas has an increasing trend. At the same time, with the escalation of international trade and entry-exit personnels, the risk of importing cases from abroad infected with S. haematotium or S. mansoni is also increasing [24][25][26]. In view of this situation, on the one hand, supervision and treatment should be strengthened for imported de nite cases to eliminate the transmission potential; on the other hand, health education should be promoted for the oating population from schistosomiasis endemic areas to spread the knowledge of schistosomiasis prevention and control [27].
The surveillance data proved that the area of snail habitats kept a low level during 2005-2016, compared with 95 900.70 hm 2 reported by Wu [17]. The remaining snail habitats mainly distributed in the places that the ecological environments are complicated or water level is unstable, where molluscaciding approach doesn't work well. In addition, several articles published also presented the evidence that the rebound or spread of snails habitats were occurred in Shanghai, Fujian, Guangxi and Zhejiang Provinces [17,[28][29][30]. It is worth noting that the connection of water systems or the transplanting of seedlings and aquatic plants from the snail habitat areas may also lead to the possibility of snail importation and spread [31,32]. The development of new snail habitats and snails reappeared in former snail habitats in four provinces except Guangdong Province, providing evidence that eliminating oncomelanid snails completely was quite di cult. Although Guangdong Province kept the achievement with no oncomelanid snails detected, a new challenge for Guangdong Province is the invasion and spread of Biomphalaria Strami [33].
Considering the potential risks of schistosomiasis still existed in ve provinces, snail control through environmental modi cation and surveillance focused on eliminating remaining snails and preventing imported infection sources should be continued and strengthened, to prevent the re-emergence of schistosomiasis, and consolidate the achievements of schistosomiasis elimination. Risk assessment should be conducted timely if there were large water conservancy projects or importing plants or animals from endemic areas etc [34,35]. Speci cally, the monitoring of the environments where snails infested previously or connected with snail habitats should be strengthened through multi ways [10,36].
Meanwhile, the oating people and livestock from the areas where the transmission of schistosomiasis has not been interrupted or the epidemic situation of schistosomiasis is recovering should be inspected emphatically, and the patients should be treated in time if they are found [37][38][39].

Conclusion
Elimination of schistosomiasis was consolidated successfully in ve provinces of P.R. China due to effective and strong post-elimination surveillance. Being a zoonotic parasitic diseases, challenges still exist to maintain the achievements as imported cases and snail habitats were detected during 2005-2016. Continuous surveillance should be strengthened through capacity building for staff responsible for schistosomiasis surveillance, providing adequate funding and resources etc.