Determinants of Schistosoma japonicum and soil-transmitted helminth infections, and associated morbidity in Hunan province, China: an epidemiological assessment

Introduction Schistosomiasis is one of the most important and widespread diseases of rural poverty. Worldwide, approximately 779 million people are at risk of infection, with 207 million already infected. Infections with Ascaris lumbricoides, hookworms and Trichuris trichiura, collectively known as the soil-transmitted helminths (STHs), are also highly endemic throughout the tropics, particularly in resource-poor settings. An estimated 1 billion people worldwide are estimated to be infected with STHs. Schistosomes and STHs often co-exist in the same epidemiological settings and, given the high prevalence of concurrent multiple species infections (multiparasitism), a combined approach to prevention and control could lead to significant improvements, including reducing costs associated with single-species control programmes. In China, rigorous national schistosomiasis control efforts over the past 60 years have decreased the prevalence by over 90%; however, since 2000 the number of infected individuals has been rising, possibly indicative of a re-emergence. Fishermen, migrant communities and poor households in rural areas may be most at risk of single and multiple-species parasitic infections and the associated morbidity. Objectives This Ph.D. thesis is structured according to four main goals and a number of specific objectives: Firstly, to update estimates of S. japonicum prevalence, intensity and associated morbidity levels in Hunan province, China, according to the third national PES carried out in 2004; Secondly, to investigate existing barriers in access to preventive, diagnostic and treatment services for advanced schistosomiasis; Thirdly, to compare and evaluate direct and proxy methods of measuring household socio-economic position, according to data on income, savings and asset-based estimations of wealth; and Finally, to explore and identify behavioural, demographic, economic, environmental and social risk factors associated with the distribution of S. japonicum, STHs and multiple species infections, in two villages of the Dongting Lake region, Hunan province, China. Methods Firstly, we used data from the third national schistosomiasis periodic epidemiological survey (PES) of 2004. In Hunan province, the PES was carried out in 47 villages of the endemic Dongting lake area. A total of 47144 human serological, 7205 stool, and 3893 clinical examinations were performed. For the reservoir hosts, stools from 874 buffaloes and other domestic animals were examined for schistosomiasis by the miracidial hatching test. Secondly, we conducted an in-depth study involving interviews with 66 schistosomiasis control staff and 79 advanced schistosomiasis patient, and six focus group discussions (FGDs), in the Dongting lake region, between August 2002 and February 2003. Using the Health-Access Livelihood framework we examined availability, accessibility, affordability, adequacy and acceptability of schistosomiasis control in the Dongting lake area. Lastly, we carried out two village-wide parasitological, clinical and questionnaire-based investigations between October and December 2006. Parasitological examinations for the prevalence of S. japonicum and the STHs were performed by the Kato-Katz thick smear method, with repeated sampling of each individual. We took fingerprick blood samples to assess haemoglobin levels, using a B-haemoglobin HemoCue photometer. The household-based questionnaire focused on direct and proxy measurements of household wealth, while the individual-based questionnaire focused on demographic and behavioural factors, treatment history and self-perceived symptoms. Results Human sero-prevalence was 11.9% (range: 1.3-34.9% at village level), and the rate of egg-positive stools was 1.9% (0-10.9%) for the same population. The prevalence of infection among buffaloes was 9.5% (0-66.7%). Extrapolating to the entire population of the Dongting Lake region, an estimated 73225 people and 13973 buffaloes were infected. Most frequently reported symptoms were abdominal pain (6.2%) and bloody stools (2.7%). Accessibility and affordability were major barriers in access to schistosomiasis control. Many of staff interviewed indicated that a majority of patients who develop advanced schistosomiasis resided in mildly-endemic or non-endemic settings. None of the patients interviewed had any form of health insurance, and most of their health expenses were out-of-pocket payments. Exploratory factor analysis generated internally robust proxy wealth indices, however these were not complementary to direct measures of household wealth, as indicated by low correlation co-efficients. We found wide disparities in household ownership of durable assets, utility and sanitation, within both settings. Pooled data from the rural and peri-urban settings highlighted structural differences in socioeconomic position (SEP), more likely a result of localised urbanization and modernization. We found higher infection prevalences in rural settings, than in peri-urban settings, for schistosomiasis (6.3% and 6.7% respectively), ascariasis (8.3% and 2.2%, respectively) and trichuriasis (5.1% and 0.5%, respectively), but lower for hookworms (0.1% and 1.5% respectively). Multiple species infections (2.6% and 0.2%, respectively) were less prevalent than single species infections (14.5% and 10.4%). There were significant disparities in the prevalence of parasitic infections between poorest and least poor quintiles of the cohort population. Anaemia and other symptoms, especially headache, stomach ache and swollen stomach, were common in both rural and peri-urban village settings. Conclusion The studies conducted within the framework of this Ph.D. thesis document the current situation pertaining to schistosomiasis and the STHs in Hunan province, China. Our findings highlight the need for increased surveillance, monitoring and health education, with relation to schistosomiasis and STHs, in non-endemic or post-transmission control settings. Based upon these results, we call for improved diagnostic tools, particularly in the case of low intensity infections and for hookworm, and propose an extension of the use of available infrastructure, human resources, knowledge and technology by integrating prevention and control of schistosomiasis with that of other intestinal helminths, particularly STHs. In the future, our studies may form a base from which to further examine local needs and priorities for parasitic disease control in the area