[Cost-effectiveness evaluation and investigation of control measure changes in areas of schistosomiasis transmission control in hilly regions of mountain areas I epidemiological investigation and analysis of prevalence factors of schistosomiasis].

OBJECTIVE

To investigate and analyze the schistosomiasis endemic status and influencing factors in areas of schistosomiasis transmission control in hilly regions of mountain areas, so as to provide the reference for establishing the strategy and measures to achieve the target of schistosomiasis transmission-interrupted in the similar areas.

METHODS

Dongpo District of Meishan City, Sichuan Province, which was appropriate to the standards of schistosomiasis transmission controlled by national evaluation in 2008, was selected as a study area. The data of schistosomiasis control from 2008 to 2010 were collected. A survey for epidemiological factors was carried out from April to November in 2011. The survey of Oncomelania snails was performed with the systematic sampling combined with environmental method. The schistosome infection status of residents was investigated by the seroimmunological test and fecal hatching examination. The schistosome infection status of cattle was investigated by the plastic cup with top tube hatching method. The infested water contact of residents was investigated with questionnaire. At the same time, in 2011, a simple random sampling combined with rapid field assessment method was used to investigate the distribution of outdoor feces, outdoor feces containing schistosome eggs, snails and infected snails in two spots of Jingyang District, Deyang City and Renshou County, Meishan City which had been appropriate to the standards of schistosomiasis transmission controlled in 2006 and 2007 respectively.

RESULTS

From 2008 to 2010, 182.6 thousand-213.3 thousand local residents were examined in Dongpo District, the positive rate of sero-immunological tests of population was 6.30% - 6.81%, and the infection rate of population was 0.02% -0.07% by estimated calculation. Totally 2 835-7 260 heads of cattle were examined and no positive cases were found. The areas of snail habits were 190.00-232.00 hm2, the intensities of living snails were 0.02-0.19 snails/0.1 m2, and no infected snails were found. In 2011, totally 204.4 thousand residents were examined and the positive rate of sero-immunological tests of population was 4.98% but no positive cases were founded through the parasitological tests. A total of 1 735 heads of cattle were examined and no positive cases were found. The areas of snail habits were 99.00 hm2, the intensity of living snails was 0.18 snails/ 0.1 m2, and no infected snails were found. Questionnaire analyses of a total of 537 residents in 4 villages showed that ditch, channel, pond, and paddy field were the major environments of the infested water contact of the residents. In the ditches and paddy fields, the average annual median values of water contact of residents were 15 and 20 person-times respectively before the area was appropriate to the standards of schistosomiasis transmission controlled, and 20 and 30 person-times respectively after the area was appropriate to the standards of schistosomiasis transmission controlled, and there were no significant differences (chi(ditch2) = 1.61, chi(padd field2) = 0.03, both P > 0.05). Whereas, in the channels and ponds, the average annual median values of water contact were 15 and 30 person-times respectively before the area was appropriate to the standards of schistosomiasis transmission controlled, but they were significantly reduced after the area was appropriate to the standards of schistosomiasis transmission controlled (chi(channel2) =10.35, chi(pond2) =18.69, both P < 0.01). In 2011, the rapid field investigation and assessment showed that the average appearance rates of snails through screening were 60.15% and 12.12% respectively in the 2 villages. The average densities of living snails were 1.19 snails/0.1m2 and 0.20 snails/0.1m2 respectively in the 2 villages, and there were no infected snails. A total of 78 outdoor feces of cattle and sheep were collected and the fecal hatching examinations showed that there were no positives.

CONCLUSIONS

After the schistosomiasis endemic areas in hilly regions of mountain areas are appropriate to the standards of schistosomiasis transmission controll, the achievements have been consolidated. However, the potential schistosomiasis endemic factors still exist, such as the high positive rate of schistosome sero-immunological tests in population, frequently bovine flowing, and no obviously decrease of the snail area and density of living snails. Therefore, it is an urgent need to develop more suitable new technologies and measures to accelerate the process of schistosomiasis prevention and control.