Soil-transmitted helminths in China

The prevalence of soil transmitted helminths and its influential factors in Shandong Province, China: an analysis of surveillance data from 2016 to 2020

BACKGROUND

Soil-transmitted helminths (STHs) were previously endemic in Shandong Province, China. This study aimed to analyze the STHs prevalence trend and the natural, social, and human cognitive and behavioural factors influencing the discrepancies between high and low infection levels from 2016 to 2020 in Shandong Province in eastern China.

METHODS

STHs surveillance data of Shandong Province from 2016 to 2020 were obtained from China Information Management System for Prevention and Control of Parasitic Diseases. STHs infections were detected by modified Kato-Katz method. Comprehensive information on the natural and social factors, STHs-related knowledge and behaviours were collected through questionnaire surveys. Retrospective spatial scan analysis was performed using SaTScan v10.1 to evaluate any identified spatial clusters of STHs infection for statistical significance and Bayes discriminant analysis was used to discriminate the high or low infection groups of the villages.

RESULTS

In total, 72,160 participants were involved in our survey from 2016 to 2020. The overall STHs prevalence rate was 1.13%, with the eastern region of Shandong Province having the highest rate (2.02%). The predominant species was T. trichiura, with the prevalence rate of 0.99% and the ≥ 70-year age group possessed the highest rate of 2.21%. The STHs prevalence rate showed an annual linear downward trend from 2016 to 2020 ([Formula: see text] = 127.600, P < 0.001). Respondents aged ≥ 60 years had the lowest awareness level of STHs-related prevention knowledge (all P < 0.05), and were the most likely to adopt the practice of fertilizing with fresh stool (χ² = 28.354, P < 0.001). Furthermore, the southern region demonstrated the highest temperature and rainfall level and the lowest GNP and annual net income per capita (all P < 0.05).

CONCLUSIONS

There is a remarkable declining in STHs prevalence in Shandong Province from 2016 to 2020. However, the prevalence rates of STHs especially T. trichiura in the southern and eastern regions were still high, and the elderly were more susceptible to be infected with STHs owning to their low awareness level of STHS-related prevention knowledge and high adoption rate of dangerous production and living behaviours. Integrated approaches of health education, environment improvement and behaviour change should be strengthened to obtain a further reduction of STHs prevalence in China.

The spatial-temporal distribution of soil-transmitted helminth infections in Guangdong Province, China: A geostatistical analysis of data derived from the three national parasitic surveys

Background

The results of the latest national survey on important human parasitic diseases in 2015–2016 showed Guangdong Province is still a moderately endemic area, with the weighted prevalence of soil-transmitted helminths (STHs) higher than the national average. High-resolution age- and gender-specific spatial-temporal risk maps can support the prevention and control of STHs, but not yet available in Guangdong.

Methodology

Georeferenced age- and gender-specific disease data of STH infections in Guangdong Province was derived from three national surveys on important human parasitic diseases, conducted in 1988–1992, 2002–2003, and 2015–2016, respectively. Potential influencing factors (e.g., environmental and socioeconomic factors) were collected from open-access databases. Bayesian geostatistical models were developed to analyze the above data, based on which, high-resolution maps depicting the STH infection risk were produced in the three survey years in Guangdong Province.

Principal findings

There were 120, 31, 71 survey locations in the first, second, and third national survey in Guangdong, respectively. The overall population-weighted prevalence of STH infections decreased significantly over time, from 68.66% (95% Bayesian credible interval, BCI: 64.51–73.06%) in 1988–1992 to 0.97% (95% BCI: 0.69–1.49%) in 2015–2016. In 2015–2016, only low to moderate infection risk were found across Guangdong, with hookworm becoming the dominant species. Areas with relatively higher risk (>5%) were mostly distributed in the western region. Females had higher infection risk of STHs than males. The infection risk of A. lumbricoides and T. trichiura were higher in children, while middle-aged and elderly people had higher infection risk of hookworm. Precipitation, elevation, land cover, and human influence index (HII) were significantly related with STH infection risk.

Conclusions/Significance

We produced the high-resolution, age- and gender-specific risk maps of STH infections in the three national survey periods across nearly 30 years in Guangdong Province, which can provide important information assisting the control and prevention strategies.

Even though the overall infection risk of soil-transmitted helminths (STHs) in Guangdong Province decreased over time, it is still higher than the national average. Risk maps can assist spatial-targeting control and intervention. We developed Bayesian geostatistical models based on the data derived from three national surveys on important human parasitic diseases in Guangdong, conducted in 1988–1992, 2002–2003, and 2015–2016, respectively. Based on these, high-resolution, age- and gender-specific infection risk maps were produced. We found that the overall STH infection risk sharply decreased over time, from 68.66% to 0.97%. We identified that moderately endemic risk (>5%) mostly distributed in small areas of western Guangdong, and prevalence in all other areas was below 5% in 2015–2016. The higher infection risk of STHs was found among females. Children were most likely to be infected with A. lumbricoides and T. trichiura, however, middle-aged and elderly people had higher infection risk of hookworm. Therefore, results of this study suggested that the government can pay more attention to people in western Guangdong, especially middle-aged and elderly people engaged in farming. As such, the government may continue to strengthen the monitoring net in the historical endemic areas to avoid the re-infection.

Soil-transmitted helminthiasis in China: A national survey in 2014-2015

Background

Based on two national surveys, the prevalence of soil-transmitted helminthiasis (STH) in China had decreased from 53.58% in 1988–1992 to 19.56% in 2001–2004. To update the epidemiology and characteristics of STH in China, a third national survey was implemented in 2014–2015.

Methodology/Principal findings

This survey covered rural areas in 31 provinces in mainland of China. Multiple-stage stratified cluster sampling was employed, which included three levels (provinces, ecozones and economical levels). Stool samples were collected and the Kato-Katz method was applied for helminth eggs detection. Samples with hookworm eggs were selected and hatched to differentiate the species based on larval morphology. Between June 2014 and May 2015, a total of 484,210 participants from 604 counties were enrolled. The weighted prevalence of STH overall was 4.49% (95% confidential interval (CI): 2.45%-6.53%), including 2.62% (95% CI: 0.86%-4.38%) hookworm infections, 1.36% (95% CI: 0.49%-2.23%) ascariasis, and 1.02% (95% CI: 0.15%-1.89%) trichuriasis. The estimated population infected was 29.12 million (95% CI: 15.88 million-42.32 million) for all STH; 16.97 million (95% CI: 5.57 million-28.39 million) for hookworm infections; 8.83 million (95% CI: 3.18 million-14.45 million) for ascariasis; and 6.60 million (95% CI: 0.97 million-12.25 million) for trichuriasis. Overall, the prevalence of ascariasis and trichuriasis was relatively high in children, while hookworm infections were more common in the older population, especially those over 60. STH was highly prevalent in western China, and moderately in central areas, but low in eastern and northern regions. Out of 3,579 hookworm cases with species differentiation, 479 cases (13.38%) were infected with only Ancylostoma spp., 2,808 cases (78.46%) with only Necator americanus, and another 292 cases (8.16%) with both species.

Conclusions/Significance

This survey demonstrated the continuous decrease of STH in rural China. However, endemicity still prevails in the western areas of the country. Hookworm, especially N. americanus, is becoming the predominant species. Older farmers in western China should be prioritized for control due to the high prevalence of hookworm.

Soil-transmitted helminthiasis (STH) had decreased significantly in China based on the two national surveys implemented in 1988–1992 and 2001–2004, respectively. In 2014–2015, an updated national survey on STH was implemented in rural China. This survey covered rural areas of 31 provinces in mainland of China and multiple-stage stratified cluster sampling was employed. Stool samples were collected and examined for helminth eggs. Totally, 484,210 villagers from 604 counties in 31 provinces participated in the survey. The adjusted prevalence of STH was 4.49%, and that of hookworm infections, ascariasis, trichuriasis was 2.62%, 1.36%, 1.02%, respectively. The estimated population with STH was 29.12 million, while that with hookworm infections, ascariasis, trichuriasis was 16.97 million, 8.83 million, 6.60 million, respectively. Children showed a high prevalence in ascariasis and trichuriasis, while the older population had a high prevalence of hookworm infections. STH was still highly prevalent in western parts, moderately in central areas, and low in eastern and northern regions. Further efforts are needed to control STH in China.

Contribution of NIPD-CTDR to the parasitic diseases control and elimination in China: Memory of the 70th anniversary for NIPD-CTDR

China has achieved a great success in control and elimination of key parasitic diseases. In 2007, the elimination of lymphatic filariasis was verified by WHO. The schistosomiasis incidence and snail-distributed areas have reduced to the lowest level in the history. The transmission and disease burden of echinococcosis have been contained largely, and the populations infected with soil-transmitted trematode and food-borne parasites have also shown a significantly declining trend. Because of rapid globalization and climate changes, however, many new challenges have arisen. In his paper, the 2020-2030 roadmaps towards the control and elimination of these key parasitic diseases are described. Moreover, China is actively implementing its global health strategy, and will be more and more engaged into global health affairs, in which a series of China-Africa health cooperation projects have been in planning with a wish of making a greater contribution to the SDGs.

Multi-disciplinary integration of networking through the RNAS+: Research on other target diseases

In 2005, the network decided to increase its number of target diseases to include other helminthic zoonoses such as fascioliasis, clonorchiasis, opisthorchiasis, paragonimiasis and cysticercosis and in the process expanding membership to include South Korea, Vietnam, Thailand and Japan. NTDs were eventually included as awareness is heightened on these diseases affecting poor and developing countries. Researches on clonorchiasis and opisthorchiasis unravel the mechanism by which these diseases eventually predispose to cholangiocarcinoma. The liver cancer associated with these liver fluke infections necessitate the need to clarify the global burden of disease of these infections. The magnitude of these liver fluke diseases in endemic countries like China, Vietnam, Laos, Cambodia and Thailand is described. Success in elimination of lymphatic filariasis in PR China and Cambodia is highlighted to show how intensified multisectoral collaboration and strong political become strong ingredients in elimination of parasitic diseases like LF. New advances are presented that clarify species and strain differences in Fasciola spp., Paragonimus spp., Taenia spp. and Echinococcocus spp. Conventional diagnostic techniques are compared with new serologic techniques that are being developed. New control strategies such as the Lawa model are presented.

From country control programmes to translational research

From the time it was conceptualized in 1998 to the present, RNAS⁺ has largely concentrated on research that will generate results to facilitate control, prevention and elimination of its target diseases. Diagnostics has remained an active field of research in order to develop tools that are appropriate for each stage from the first efforts until attempts to block transmission. For example, with regard to schistosomiasis, chemotherapy has excellent impact on morbidity, while better diagnostics and vaccine research have been promoted to complement the other components of the control programme. The need for surveillance in areas where the prevalence has been brought down to very low levels necessitated development of spatio-temporal tools and ecological models based on geographical information systems (GIS) to produce risk and distribution maps for monitoring and evaluation of programme success. New knowledge and experiences in management of the diseases contribute to the formulation of new schemes in management and treatment. Ways of drawing attention to the disease, such as determining disability weights for use in computation of burden of disease, updating epidemiological profile and unravelling new aspects of the disease provide bases for modifying the operation of control programmes as we move forward. Programme evaluation based on reports of actual implementation of activities brought to the fore problems related to the distribution of chemotherapy as well as social, cultural and behavioural aspects of endemic communities. Importantly, this highlighted the necessity of adapting control activities to specific situations of the endemic areas. New models evolving from reviews of this kind and success stories, such us the elimination of lymphatic filariasis (LF) in PR China and Cambodia are presented.

Intestinal Parasite Infections among Inhabitants in Yanbian Prefecture, Jilin Province, China

To investigate the prevalence of intestinal parasite infections in Yanbian Prefecture, Jilin Province, China, epidemiological surveys were conducted on a collaboration basis between the Korean Centers for Disease Control and Prevention and the Yanbian Center for Disease Control and Prevention. A total of 8,396 (males 3,737 and females 4,659) stool samples were collected from 8 localities and examined with the formalin-ether sedimentation technique, and additionally examined with the cellotape anal swab to detect Enterobius vermicularis eggs. The overall rate of intestinal parasites was 1.57%. The prevalence of Ascaris lumbricoides was the highest (0.80%), followed by Entamoeba spp. (0.23%), heterophyid flukes (0.15%), Clonorchis sinensis (0.08%), Enterobius vermicularis (0.07%), hookworms (0.06%), Trichostrongylus spp. (0.06%), Giardia lamblia (0.04%), Paragonimus spp. (0.02%), Diphyllobothrium spp. (0.02%), Trichuris trichiura (0.02%). The prevalence by sex was similar, 1.58% (n=59) in males and 1.57% (n=73) in females. By the present study, it is partly revealed that the prevalences of intestinal parasite infections are relatively low among the inhabitants of Yanbian Prefecture, Jilin Province, China.