Examining landscape factors influencing relative distribution of mosquito genera and frequency of virus infection

Abstract

Mosquito-borne infections cause some of the most debilitating human diseases, including yellow fever and malaria, yet we lack an understanding of how disease risk scales with human-driven habitat changes. We present an approach to study variation in mosquito distribution and concomitant viral infections on the landscape level. In a pilot study we analyzed mosquito distribution along a 10-km transect of a West African rainforest area, which included primary forest, secondary forest, plantations, and human settlements. Variation was observed in the abundance of Anopheles, Aedes, Culex, and Uranotaenia mosquitoes between the different habitat types. Screening of trapped mosquitoes from the different habitats led to the isolation of five uncharacterized viruses of the families Bunyaviridae, Coronaviridae, Flaviviridae, and Rhabdoviridae, as well as an unclassified virus. Polymerase chain reaction screening for these five viruses in individual mosquitoes indicated a trend toward infection with specific viruses in specific mosquito genera that differed by habitat. Based on these initial analyses, we believe that further work is indicated to investigate the impact of anthropogenic landscape changes on mosquito distribution and accompanying arbovirus infection.

Figure 1

Habitats in which mosquitoes were sampled. a Satellite overview of the sampling region. b Detailed satellite picture with sampling locations (image was taken January 30, 2003, Sensor: Landsat ETM+, Source: Global Land Cover Facility, www.landcover.org). Dark green areas indicate rainforest, lighter areas are habitats with lower and not so dense vegetation; areas with almost no vegetation are marked in red. Red dots indicate sampling sites. The red dot camp I combine two camps that are next to each other. c Figure shows at which heights the traps were installed for each habitat type.

Figure 2

Relative frequency of mosquitoes of the genera Aedes, Anopheles, Culex, Uranotaenia, and others in each habitat per trapping night. Number of trapped mosquitoes divided by number of trapping nights (mosquito abundance per trap night). Habitat types: Village, Taï and Gouléako village; Plantation, coffee and cocoa plantation; Secondary Forest, sampling sites I–III; Primary Forest, Sampling sites I–V, Camp, research camps I–IV.

Figure 3

Relative frequency of CPE causing mosquito homogenates in different habitats by genus. Mosquito homogenates (432 pools) were inoculated into C6/36 cells and observed for CPE. The proportion of captured CPE inducing mosquitoes per pool and per trapping period was calculated (see statistics). Habitat types: Village, Taï and Gouléako village; Plantation, coffee and cocoa plantation; Secondary Forest, sampling sites I–III; Primary Forest, Sampling sites I–V, Camp, research camps I–IV.

Figure 4

Distribution of virus isolates. RNA was extracted from all pools that induced CPE and cDNA was synthesized using random hexamer priming. Pools were tested by specific real-time PCR assays for the presence of Nounané virus (NOUV), Moussa virus (MOUV), Cavally virus (CAVV), Gouléako virus (GOUV), and Herbert Virus (HERV). The proportion of mosquitoes infected with these viruses per pool and per trapping period was calculated (see statistics). Habitat types: Village, Taï and Gouléako village; Plantation, coffee and cocoa plantation; Secondary Forest, sampling sites I–III; Primary Forest, Sampling sites I–V, Camp, research camps I–IV