Research Article: Human-Mediated Marine Dispersal Influences the Population Structure of Aedes aegypti in the Philippine Archipelago

Date Published: June 3, 2015

Publisher: Public Library of Science

Author(s): Eugenio Fonzi, Yukiko Higa, Arlene G. Bertuso, Kyoko Futami, Noboru Minakawa, Roberto Barrera.

Abstract: BackgroundDengue virus (DENV) is an extraordinary health burden on global scale, but still lacks effective vaccine. The Philippines is endemic for dengue fever, but massive employment of insecticides favored the development of resistance mutations in its major vector, Aedes aegypti. Alternative vector control strategies consist in releasing artificially modified mosquitos in the wild, but knowledge on their dispersal ability is necessary for a successful implementation. Despite being documented that Ae. aegypti can be passively transported for long distances, no study to date has been aimed at understanding whether human marine transportation can substantially shape the migration patterns of this mosquito. With thousands of islands connected by a dense network of ships, the Philippines is an ideal environment to fill this knowledge gap.Methodology/principal findingsLarvae of Ae. aegypti from 15 seaports in seven major islands of central-western Philippines were collected and genotyped at seven microsatellite loci. Low genetic structure and considerable gene flow was found in the area. Univariate and multivariate regression analyses suggested that anthropic factors (specifically the amount of processed cargo and human population density) can explain the observed population structure, while geographical distance was not correlated. Interestingly, cargo shipments seem to be more efficient than passenger ships in transporting Ae. aegypti. Bayesian clustering confirmed that Ae. aegypti from busy ports are more genetically similar, while populations from idle ports are relatively structured, regardless of the geographical distance that separates them.Conclusions/significanceThe results confirmed the pivotal role of marine human-mediated long-range dispersal in determining the population structure of Ae. aegypti. Hopefully corroborated by further research, the present findings could assist the design of more effective vector control strategies.

Partial Text: Aedes aegypti is the major vector of dengue virus (DENV). An estimated 96 million dengue cases and 300 million asymptomatic infections were reported globally in 2010 [1]. Currently, there is no effective dengue vaccine available and the principal way to prevent the spread of the virus and the occurrence of outbreaks is to suppress the populations of vector mosquitos. Insecticide spraying has been the most common and effective method in the past decades, but massive and indiscriminate use generated a selective pressure that led to the development of insecticide-resistant strains of mosquitos. Alternative population control methods consist in the release of modified mosquitos which will interbreed with wild populations and suppress or replace it. Depending on the technique, the released individuals are sterilized, genetically engineered or carry symbiotic bacteria of the genus Wolbachia [2].

The results suggested low genetic structure and considerable gene flow. Pairwise Fst values were generally low (0.005~0.147), in accordance with other studies conducted in Florida (0.004~0.171), Pakistan (0.013~0.17) and Southeast Asia (0.02~0.185) [17,19,48]. In the study area the migration of mosquitos was not affected by geographical distance, but increased with the intensity of human marine transportation. In our understanding, this is the first study that qualitatively and quantitatively shows how human ship transportation affects the migration of Ae. aegypti.



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