Surveys on Japanese Encephalitis Vectors in Taiwan Area during 2004-2008

Cheo Lin, Shu-Wan Jian, Hwa-Jen Teng

2010 Vol.26 NO.11

Correspondence Author： Hwa-Jen Teng

Abstract：

Abstract

The first Japanese encephalitis (JE) case in Taiwan in 2009 was detected in Pingtung County with the onset of the disease symptom in a patient on March 30, which was more than a month earlier than the first case in previous years, usually in May. Thus, it is necessary to obtain updated information on the temporal change of vector status. The purposes of this study are to understand the current status of JE vectors and the activity of JE virus in field mosquito population, and to understand the change of species composition of JE vectors over time in Taiwan. The surveys carried out by using light traps in different areas in Taiwan during 2004-2008, Cx. tritaeniorhynchus Giles was the dominant species in all areas, accounted for 64.1% to 100% of the total number of captured vectors. The species of Cx. fuscocephala Theobald accounted for 30.0% (the highest percentage among survey sites) of the mosquitoes caught in Kaohsiung County. Culex annulus Theobald was commonly captured in all the survey areas albeit in relatively small number. A single or double peak pattern in June, July, or September was seen in local population of Cx. tritaeniorhynchus in Pingtung County. The highest number of mosquitoes for single capture in each County/City ranged from 387 to 37,440 per trap-night, with the highest found in Puzi, Chiayi County. JE virus became active in field mosquito population mainly in May and June and 96.2% of total positive pools were from Cx. tritaeniorhynchus. In conclusion, Cx. tritaeniorhynchu is currently the major vector for JE transmission in Taiwan. In light of its relatively high population density and wide distribution as well as being the predominant species carrying JE virus every year, we suggest that in addition to continuing the current JE vaccination policy, an environmental management measure, as a part of integrated control, should be initiated to decrease the number of Cx. tritaeniorhynchus in JE high-risk counties and, thus, to prevent the occurrence of the related mosquito-borne diseases.