Abstract:

Objective To understand the endemic status of major human parasitic infections in Sichuan Province. Methods According to the National Survey Plan and Implementation Rules for the Status of Human Major Parasitic Infections, total 45 survey sites were selected from 15 counties (cities and districts) within 5 ecological zones of Sichuan Province using stratified cluster and randomly sampling method for investigation of major human parasitic infections from April to June in 2015. No less than 250 rural permanent villagers (above 0 year old) were enrolled from each site in the survey and the fecal samples were collected from each participant. The intestinal helminth eggs were examined under microscope using modified Kato-Katz thick smear method (duplicate for each sample). The intestinal protozoan cysts and trophozoites were examined using Lugol’s iodine staining method and saline smear method, respectively. The Enterobius vermicularis eggs were identified using transparent tape anal swab method for children with 3-6 years old. SPSS 23.0 software was used for statistical analysis. The infection difference among different population and areas was compared by χ² test. Unconditional logistic multivariate regression analysis was used to analyze the risk factors of common parasitic infections. Results Total 11 403 participants were involved in the survey with overall prevalence of 15.5% (1 762/11 403) for all intestinal parasite infections. Five intestinal nematodes were identified in infected people including Ascaris lumbricoides (4.7%, 540/11 403), hookworm (7.1%, 811/11 403), Trichuris trichiura (3.2%, 360/11 403), Enterobius vermicularis (0.1%, 10/11 403) and Strongyloides stercoralis (0.1%, 6/11 403). Three tapeworms were identified with 55 cases of Taenia infections, 3 cases infected with Hymenolepis and 1 case with Spirometra mansoni. Total 9 protozoan species were identified in infected people including Entamoeba histolytica, E. coli, Gardia lamblia, Blastocystis hominis, E. hartmani, Endolimax nana, Balantidium coli, Iodamoeba butschlii and Embadomonas intestinalis with overall prevalence of 2.0% (223/11 403). The highest prevalence of intestinal parasite infections of 24.9% (563/2 257) was determined in the Southwest Sichuan-North Yunnan mountainous ecological zone and lowest (8.2%, 186/2 273) in the Eastern Tibet-Western Sichuan ecological zone, with statistical significance for the different prevalence among different ecological zones (P < 0.01). In terms of the distribution of parasitic infections, Leibo County had the highest prevalence of 53.9% (407/755), and Ruoergai County had the lowest of 1.9% (10/522), with significant difference among different counties (cities and districts) (P < 0.01). The prevalence of intestinal parasites in females (16.2%, 994/6 156) was significant higher than that in males (14.6%, 768/5 247) (P < 0.05). Regarding the age, the highest prevalence was identified in people aged 70-79 and over 80 years (21.4%, 221/1 034, 46/215) and the lowest prevalence in people aged 20-29 (12.3%, 100/813) and 40-49 (12.3%, 273/2 217), with significant difference of prevalence among different age groups (P < 0.01). Regarding the education distribution, the highest prevalence of intestinal parasites was found in people with low education of primary school (17.4%, 931/538) and the lowest in people with high school and secondary school (5.5%, 19/346), with significant difference among people with different educational levels (P < 0.01). Regarding the occupation distribution, the highest prevalence of 16.5% (1 397/8 475) was found in farmers, followed by school students (12.7%, 190/1 491), with significant difference among different occupations (P < 0.01). Regarding the ethnic distribution, the highest prevalence was found in Yi people (65.0%, 253/389), followed by Han (16.0%, 1 255/7 857), with significant difference among different ethnic groups (P < 0.01). Unconditional logistic multivariate regression analysis demonstrated that female, elders, Yi nationality and people with low education level were susceptible populations of intestinal parasite infections. Conclusion The soil-transmitted nematodes A. lumbricoides, hookworm and T. trichiura are the main species infecting people in Sichuan Province. The prevention and control measures should be focused on female, elders, Yi nationality and people with low education level, and those living in Southwest Sichuan-North Yunnan mountainous and Sichuan basin ecological zones who have the highest prevalence of intestinal parasites.

Key words: Major human parasites, Endemic statue, Sichuan Province