Surveillance of malaria vector Anopheles in Guizhou Province from 2005 to 2019

Abstract

To understand the density, populations and habitats of malaria vector Anopheles in Guizhou Province from 2005 to 2019, so as to provide the evidence for formulating the countermeasures to tackle the risk of local transmission of imported malaria in the province. The malaria vector Anopheles density and populations were monitored using human bait trapping and light trapping techniques in Guizhou Province from 2005 to 2019, and all captured Anopheles was morphologically identified and counted. In addition, the distribution of Anopheles habitats was investigated. During the period from 2005 through 2019, the malaria vector Anopheles density increased from early June in Guizhou Province, peaked on early July and then declined, which appeared a single peak. The greatest Anopheles density was seen on early August, 2018 [57.34 mosquitoes/(person-night)], and the lowest density was found on late October, 2009 [1.29 mosquitoes/(person-night)]. The annual mean Anopheles density slowly reduced from 17.91 mosquitoes/(person-night) in 2005 to 12.34 mosquitoes/(person-night) in 2012, with a 38.02% reduction (χ2trend = 115.04, P < 0.01), while the annual mean Anopheles density showed a tendency towards a rise from 2017 to 2019 (χ2trend = 420.00, P < 0.01). The malaria vector Anopheles was captured during the period between 19 : 00 and 7 : 00 of the next day in Guizhou Province from 2017 to 2019, with the overall density appearing a tendency towards a rise followed by a decline, and the Anopheles activity was highly frequent during the period between 19 : 00 and 21 : 00. The malaria vector Anopheles was monitored for 938 times using the light trapping method in Guizhou Province from 2005 to 2019, and a total of 52 781 Anopheles mosquitoes were captured, including 49 705 An. sinensis, 804 An. minimus, 238 An. anthropophagus, and 2 034 other Anopheles mosquitoes, with a significant difference seen in the Anopheles composition (χ2 = 165.68, P < 0.01). From 2017 to 2019, a total of 24 557 Anopheles mosquitoes were captured in human housings, outdoors and livestock housings in Guizhou Province, with 67.65% captured in livestock housings and 12.01% in human housings, and there was a significant difference in the number of Anopheles mosquitoes captured from the three types of habitats (χ2 = 55.04, P < 0.01). An. sinensis, An. minimus and An. anthropophagus were captured form all three types of habitats, in which 98.07% was An. sinensis, and 0.09% was An. anthropophagus. The population structure of malaria vector Anopheles has changed in historically malaria-endemic areas of Guizhou Province, and An. sinensis has replaced An. minimus and An. anthropophagus to become the predominant malaria vector. The malaria vector Anopheles density has shown a tendency towards a rise in Guizhou Province during the recent years, and there have been a rise in the type and number of Anopheles mosquitoes, leading to a potential risk of local transmission of imported malaria. Long-term, persistent and extensive surveillance of malaria vectors is recommended in Guizhou Province.