山丘型流行区血吸虫感染者人数低估原因探讨

Study on reasons of underestimation of the number of Schistosoma japonicum infected persons in mountainous endemic regions

目的探讨山丘型流行区血吸虫感染者人数低估的原因。方法在山丘型流行区随机选择A、B、C、D4个调查点,湖沼型流行区选择一个参照点。用ELISA方法筛查4个点的居民,对阳性感染者及参照点人群同时采用尼龙绢集卵孵化法和改良加藤法进行病原学检查。以两种方法的合并阳性数为标准,估算病原学方法的相对漏检和病人低估数;就参照点敏感性较高的粪孵法漏检,分析山丘型流行区血吸虫病人数严重低估的原因。结果调查点ELISA检查5563人,阳性1536例,阳性率27.61%;A、B点病原学检查阳性数分别为38、28例,其感染率分别为3.12%和2.96%,结果均远低于相应流行分类的感染率。4个调查点粪孵的检出率均高于加藤法,粪孵相对漏检8例,加藤法相对漏检72例;参照点粪孵检出率低于加藤法,粪孵相对漏检59例,加藤法相对漏检19例。结论病原学方法的敏感性造成病人数一定程度的低估,反复使用吡喹酮使人群虫荷和感染度降低以及化疗药物的抑制导致病人数漏检,是山丘型流行区血吸虫感染者人数严重低估的原因。

Objective To study the reasons of underestimation of the number of Schistosoma japonicum infected persons in mountainous endemic regions. Methods Four study pilots （A,B,C, D） were selected at random in mountainous regions and one site （E） was selected in a lake region for reference. The target population of four study pilots were screened by ELISA, and those positive in ELISA in mountainous regions and the reference population in the lake region were checked by hatching test after egg concentration with a nylon-tissue bag and modified Kato technique for etiological examination. With the standard of total positive population of parasitologieal examination of the above two techniques, the number of comparatively missing examination and underestimation of persons infected with S. japonicum was calculated. In accordance with the sensitivity of missing examination of hatching test in the control site, the reasons of underestimation of the number of S. japonicum infected persons in the mountainous regions were analyzed. Results Among a total of 5 563 people in study areas examined by ELISA, 1 536 were positive. The positive rate was 27.61%. The positive numbers of etiological examination of A and B sites were 38 and 28, and the infection rates were 3.12% and 2.96%, respectively. The infection rates of A and B sites were lower than that of the endemicity classification. The detection rates of the hatching test were higher than those of the modified Kato method in the 4 study sites. The missing numbers were 8 by the hatching test, and 72 by the modified Kato method. The detection rate with the hatching test is lower than that of the modified Kato method in the reference area, with 59 cases of missing examination by the hatching test, and 19 cases of missing examination by the modified Kato method. Conclusions The sensitivity of etiological examination was the reason of underestimation of infected persons, while the low egg burden after repeated chemotherapy and the restrained effect of medicine may be the reasons for missing examination in mountainous endemic regions.