key: cord-0825130-noipk2r7
authors: He, Junyi; Zhu, Hongqing; Bao, Ziping; Zhang, Lijuan; Li, Yinlong; Feng, Ting; Guo, Suying; Deng, Wangping; Wang, Can; Dang, Hui; Jia, Tiewu; Lyu, Chao; Qin, Zhiqiang; Cao, Chunli; Xu, Jing; Li, Shizhu; Zhou, Xiaonong
title: Rapid Assessment on Potential Risks of Schistosomiasis Transmission — 7 PLADs, China, 2019 and 2021
date: 2021-12-17
journal: China CDC Wkly
DOI: 10.46234/ccdcw2021.263
sha: f8f193f7cb296b32b9ab99766b7cd04985af0ce7
doc_id: 825130
cord_uid: noipk2r7

WHAT IS ALREADY KNOWN ABOUT THIS TOPIC? Oncomelania hupensis(O. hupensis) and livestock are main infection sources of schistosomiasis. The schistosome infected O. hupensis and livestock’s feces are important risk factors in the transmission of schistosomiasis. WHAT IS ADDED BY THIS REPORT? The potential risks of schistosomiasis transmission remain prevalent, giving an early warning to local government with information on existing transmission risks. It is expected that the effectiveness and efficiency of schistosomiasis surveillance could be improved by conducting rapid risk assessment at the beginning of transmission season. WHAT ARE THE IMPLICATIONS FOR PUBLIC HEALTH PRACTICE? Rapid risk assessment is essential in early detection and the active monitoring of indicators of the transmission risks of schistosomiasis in endemic areas. This could work synergistically with surveillance system to minimize infections and prevent rebounds of endemic schistosomiasis outbreaks.

Schistosomiasis was endemic to 12 provincial-level administrative divisions (PLADs) in the middle and lower reaches of the Yangtze River and southern China. Oncomelania hupensis (O. hupensis) was the only intermediate snail host of Schistosoma japonicum (1) . Previous studies had illustrated that the contribution of cattle feces to the transmission of schistosomiasis had accounted for 75% (2) . In order to detect these potential risks of schistosomiasis transmission, indicators including distribution and infection rates of O. hupensis and livestock's feces around O. hupensis habitats were assessed at the beginning of transmission season in the 7 PLADs where schistosomiasis elimination had not achieved the national criteria (3) . The rapid assessments were conducted in the spring of 2019 and 2021. The O. hupensis survey was performed by means of environmental sampling, and livestock feces samples were collected in surveyed O. hupensis habitats. Loopmediated isothermal amplification (LAMP) assay and miracidial hatching were used to detect for O. hupensis infection and livestock's feces samples, respectively. In 2021, 2 surveyed environments detected nucleic acids of schistosomes among O. hupensis snails by LAMP assay. Schistosome eggs were found in cattle feces collected from snail habitats both in 2019 and 2021. These results indicated that the distribution and infections of O. hupensis and livestock's feces may cause concerns in endemic areas, which also gave an early warning that rapid response measures should be implemented in key environments to eliminate the potential risks of schistosomiasis transmission as soon as possible.

The assessments were conducted in the schistosomiasis endemic areas of Hunan, Hubei, Jiangxi, Anhui, Jiangsu, Sichuan, and Yunnan Provinces. Stratified random sampling was used to select surveyed environments. In each surveyed environment, over 50 square frames of 0. 

Even though the current prevalence of schistosomiasis was relatively low across China (3), rapid assessments in 2019 and 2021 have found that the density of O. hupensis distribution remained high in several O. hupensis habitats and surrounding environments where fecal contamination was also observed. In addition, the infections of O. hupensis and livestock's feces were both detected in the assessments. The potential risks of schistosomiasis transmission are likely remaining prevalent, which is an early warning of the transmission risks of schistosomiasis at the beginning of transmission season. This finding further indicated that low sensitivity existed in schistosomiasis surveillance system. By conducting rapid risk assessments before the beginning of transmission season, the effectiveness and efficiency of schistosomiasis surveillance may be improved. In the index system for rapid assessment of environments with high transmission risk of schistosomiasis, morbidity in livestock and O. hupensis were regarded as the primary indices, and the secondary indices included the infection rate of livestock, areas with infected O. hupensis, and density of infected O. hupensis (4). This index system showed the importance of assessing transmission risks related to O. hupensis and livestock in not only building a comprehensive risk assessment system but also in realizing earlier detection and response to further reduce the possible infection in O. hupensis and livestock. Thus, the distribution and infection of O. hupensis and livestock's feces were assessed as essential indicators in the rapid assessments and surveillance on schistosomiasis transmission.

The existence and reemergence of O. hupensis can greatly affect the transmission of schistosomiasis across endemic areas in 12 southern PLADs (1). The optimal temperature for living O. hupensis is 20-25 ℃, and their main multiplying stage is between April and June (5), during which people and livestock may be more susceptible to schistosomiasis infections. Especially in marshland and lake endemic areas, the distribution of O. hupensis and the transmission of schistosomiasis may be facilitated after encountering flood disasters (6) . In the risk assessment of 5 PLADs affected by (2), a few livestock, including cattle and sheep, were found grazing around O. hupensis habitats during the assessments. The reemergence of livestock activities may lead to a rebound of schistosomiasis infections in endemic areas (9) . In terms of positive feces detected, harmless disposal of feces was conducted to prevent the transmission. The management of livestock activities should be strengthened as well.

This study was subjected to some limitations. First, the assessment was not conducted in 2020 due to the coronavirus disease 2019 (COVID-19) pandemic, which affected the continuity of assessments. There was 1 case of acute schistosomiasis reported in 2020 (3); therefore, assessing environments with transmission risks of schistosomiasis annually is needed based on historical reports and data to avoid infections (10). Second, only environmental sampling was applied in investigating O. hupensis habitats, which was not as comprehensive as systematic sampling applied in regular risk surveillance. Although our findings can point out potential risks by reporting the distribution and infection of these indicators in endemic regions, further assessment and surveillance should be performed on a broader scale.

In conclusion, in order to achieve the goal of eliminating schistosomiasis in China before 2030 (2), environments with potential risks of schistosomiasis transmission need prompt and efficient detection and surveillance to minimize the possibility of schistosomiasis infection in both humans and livestock. Rapid risk assessment should also be applied to actively monitor indicators of the transmission risks of schistosomiasis and prevent the rebound of the endemic schistosomiasis outbreaks.

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Expert consensus on the strategy and measures to interrupt the transmission of schistosomiasis in China

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