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Researchers map chikungunya spread in Panama
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Researchers have traced the spread of chikungunya virus across Panama through its primary vector, which may use the highways for its distribution.
Matthew J. Miller, PhD, of the Smithsonian Tropical Research Institute, and José R. Loaiza, PhD, of the Instituto de Investigaciones Científicas y Servicios de Alta Tecnología, Panama, analyzed extensive nationwide surveillance data on Aedes spp. mosquitoes from Panama’s Ministry of Health, including the geographic coordinates and dates for confirmed samples of A. albopictus — an efficient vector of three genotypes of chikungunya virus and all dengue serotypes — between 2002 and 2013.
José R. Loaiza
Some of the earliest cases of autochthonous transmission of chikungunya in Panama were reported in the summer of 2014 in the eastern outskirts of Panama City, where, coincidentally, the first specimen of A. albopictus was collected 12 years earlier. The disease has since spread across much of the country.
According to Miller and Loaiza, A. albopictus had been limited to the eastern areas of Panama City, but mosquito density increased and eventually expanded into western Panama from 2010 to 2013.
The researchers developed species distribution models using advanced software to identify factors associated with the mosquito’s expansion across the country, including climate, population density and road networks. They found that road networks alone best predicted the distribution of A. albopictus in western Panama. “The vector is not moving organically across the landscape,” Miller said in a press release.
Although other studies have accurately predicted the global expansion of Aedes mosquitoes through climate, Miller and Loaiza said their data may explain the Aedes invasion on a more local level.
“At global scales, all of Panama is within the climate threshold for [A. albopictus]; therefore, the immediate geographic spread across Panama is likely to be determined by factors other than ecology,” they wrote.
Based on the finding that A. albopictus relied on road networks for its distribution — either as larvae in open water, such as used tires, or as adults inside motor vehicles — the researchers recommend fumigation of vehicles at checkpoints, which already are in operation in Panama to prevent the carriage of Cochliomyia spp., or screwworms — fly larvae that plague cattle.
In addition, Miller and Loaiza caution against the strategy of introducing genetically modified A. aegypti mosquitoes, which began in May 2014. The aim of these programs was to render A. aegypti offspring unviable, but they may only have a short-term impact on the vector population and could potentially increase the likelihood for A. albopictus to fill the niche once occupied by A. aegypti.
“Dengue transmission in Panama is a two-vector species problem (Aedes aegypti and Aedes albopictus), and so a strategy that only focuses on one of the two species will fail to bring the number clinical cases down,” Loaiza told Infectious Disease News. “Our data demonstrate a remarkable population expansion velocity for A. albopictus, and local eradication plans for Aedes mosquitoes in Panama are likely going to require constant inputs to get population levels down, even at local scales.” — John Schoen
Disclosure: The researchers report no relevant financial disclosures.
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