Neglected Urban Villages in Current Vector Surveillance System: Evidences in Guangzhou, China

Abstract

: Numerous urban villages (UVs) with substandard living conditions that cause people to live there with vulnerability to health impacts, including vector-borne diseases such as dengue fever (DF), are major environmental and public health concerns in highly urbanized regions, especially in developing countries. It is necessary to explore the relationship between UVs and vector for effectively dealing with these problems. In this study, land-use types, including UVs, normal construction land (NCL), unused land (UL), vegetation, and water, were retrieved from the high-resolution remotely sensed imagery in the central area of Guangzhou in 2017. The vector density from May to October in 2017, including Aedes.albopictus(Ae.albopictus)'s Breteau index (BI), standard space index (SSI), and adult density index (ADI) were obtained from the vector surveillance system implemented by the Guangzhou Center for Disease Control and Prevention (CDC). Furthermore, the spatial and temporal patterns of vector monitoring sites and vector density were analyzed on a fine scale, and then the Geodetector tool was further employed to explore the relationships between vector density and land-use types. The monitoring sites were mainly located in NCL (55.70%-56.44%) and UV (13.14%-13.92%). Among the total monitoring sites of BI (79), SSI (312), and ADI (326), the random sites accounted for about 88.61%, 97.12%, and 98.47%, respectively. The density of Ae.albopictus was temporally related to rainfall and temperature and was obviously differentiated among different land-use types. Meanwhile, the grids with higher density, which were mostly concentrated in the Pearl River fork zone that collects a large number of UVs, showed that the density of Ae.albopictus was spatially associated with the UVs. Next, the results of the Geodetector illustrated that UVs posed great impact on the density of Ae.albopictus across the central region of Guangzhou. We suggest that the number of monitoring sites in the UVs should be appropriately increased to strengthen the current vector surveillance system in Guangzhou. This study will provide targeted guidance for local authorities, making more effective control and prevention measures on the DF epidemics.

Keywords: Ae. albopictus density; Guangzhou; Neglected macroscopic incubator; urban villages; vector surveillance system.

Figure 1

Study areas and GF-2 satellite data (Red: band5, Green: band4, Blue: band3) coverage of the four districts of Liwan, YueXiu, Haizhu, and Tianhe in Guangzhou City. (The “red” pixels mean the areas covered by vegetation. The GF-2 is the abbreviation of Gaofen-2, which is the name of a satellite image data.)

Figure 2

Spatial distribution of land-use types (a) and the monitoring sites ((b): the monitoring sites of BI, (c): the monitoring sites of SSI, and (d): the monitoring sites of ADI) in 2017(Amount indicates the number of monitoring sites in various land-use types. Percent indicates the proportion of monitoring sites of different land-use types in the total sites.).

Figure 3

The dynamic changes in the proportion of random sites among different land-use types (a) The proportion of random sites in each land-use type; (b) The proportion of random sites in the whole region; (c) New random sites for each land-use type account for the sum of new random sites in the whole region.

Figure 4

The temporal relationship between three vector indices (BI, SSI, and ADI) and meteorological factors, including rainfall and temperature.

Figure 5

The spatial and temporal distribution of vector density (BI, SSI, and ADI) from May to October.

Figure 6

Monthly variation in three vector indices (BI, SSI, and ADI) in various land-use types.

Figure 7

The comparison of the mean values of the vector indices in different land-use types ((a) BI, (b) SSI, and (c) ADI).

Figure 8

The q values of the factor detector from May to October ((a) BI, (b) SSI, and (c) ADI). The solid point means that the value is significant at the level of 0.10.