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    Scientists Use Computers to Predict Spread of Tropical Diseases

    By By Ines Perez, E&E reporter
    January 20, 2013, 7:21:55 AM EST

    From kudzu-eating bugs to flax lilies, everywhere we look we are bombarded with news of newly introduced species thriving in U.S. soil, often at the expense of the locals. But as climate change and other factors continue to favor invaders, the country also grows more vulnerable to diseases that might be carried by them. So researchers are using computer models to predict the potential spread.


    In a study published in the journal PLOS Neglected Tropical Diseases, scholar Diego Ruiz Moreno, of the Arturo Jauretche National University in Argentina, developed a computer model to see what would happen in the face of tropical virus Chikungunya reaching U.S. shores.

    Using quantified information based on mosquito surveillance programs, as well as population and temperature data for the three major U.S. ports of entry -- New York, Miami and Atlanta -- the researchers ran a model to determine the potential risk of a Chikungunya outbreak brought on by an unaware infected traveler.

    "In the event of an introduction and establishment of Chikungunya in the U.S., endemic and epidemic regions would emerge initially, primarily defined by the environmental factors controlling annual mosquito population cycles," the model showed.

    Anthology of a disease

    Like malaria and dengue, Chikungunya is a mosquito-borne disease, piggybacking on the yellow fever mosquito -- also vehicle of choice of the dengue virus. More recently, it has been riding on the Asian tiger mosquito. Chikungunya causes denguelike symptoms such as fever and severe joint pains that could last months or, in rare cases, years.

    What's peculiar about this virus, however, is the way it has expanded its range in recent years.

    Everything points to Chikungunya originating in central and east Africa. But since 2004, cases of Chikungunya have been reported in Kenya, the Indian Ocean's La Reunion Island, India, Southeast Asia and finally Italy.

    "It is clear this disease is moving -- and moving very fast -- and it's not a question of if but when it's going to arrive to the New World," Ruiz Moreno said.

    Mosquitoes, and the viruses that grow in them, are susceptible to climate conditions. In general, the higher the temperature, the faster they grow. According to Ruiz Moreno, one of the main threats is that climate change is affecting the seasons, not only the seasonal variation of temperature and rainfall but also the cyclic oscillations of vectors, hosts and other parts of the ecosystem.

    How these changes will affect the dynamic of infectious diseases, however, is hard to predict.

    Risky business

    As with the kudzu bug and the flax lily, the Asian tiger mosquito has also found its way into the United States. Since its introduction in the mid-1980s, it has established itself in more than 26 states. Its broad presence, added to the constant influx of travelers from around the world, makes the threat of a Chikungunya outbreak in the United States all the more real.

    "The movement of pathogens is a documented risk, and it's something we take very seriously," said Roger Nasci, chief of the Arboviral Diseases Branch at the Centers for Disease Control and Prevention.

    A couple of years ago, there was a small dengue outbreak in Key West, Fla., that persisted for almost two years. Back then, fingers also pointed at travelers.

    "The example is there, it's not something that is a hypothetical," Nasci said. And because people can't be prevented from traveling, it comes down to being prepared and making sure that people have the proper information and tools to detect quickly and respond effectively, he added.

    In the latest Atlas of Health and Climate -- a collaboration between the World Health Organization and the World Meteorological Organization -- officials state that one of the main challenges when dealing with infectious diseases and climate change is to understand and try to project their geographical distribution in time to prepare.

    According to Nasci, that's where some of these models come into play.

    "Though [models] are not experiments and are based on assumptions about complex interactions that will occur, they provide some potential scenarios," he said.

    Reprinted from ClimateWire with permission from Environment & Energy Publishing, LLC. 202-628-6500. E&E Publishing is the leading source for comprehensive, daily coverage of environmental and energy issues. Click here to start a free trial to E&E's information services.

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