A new report from the Centers for Disease Control and Prevention confirms that for the first time in more than 65 years, dengue fever has returned the continental United States, The New York Times is reporting this week:

The upsurge is not unexpected. Experts say more than half the world's population will be at risk by 2085 because of greater urbanization, global travel and climate change. Over the past 30 years, a global outcry against using the pesticide dichlorodiphenyltrichloroethane, or DDT, has led to the resurgence of the mosquito, a voracious consumer of human blood and carrier of infectious disease.

Epidemics have become routine in Latin America, a continent on the verge of becoming highly endemic. Outbreaks are today raging in Brazil, Guatemala and other nations. Thailand, within a week of its annual dengue season this year, has already reported 18,000 cases and 20 deaths, according to the Ministry of Public Health.

In our Fall 2009 cover story, OnEarth looked at how climate change will force the U.S. to revamp its health-care defenses against diseases like dengue. Reporting from a Mexican town across the border from Brownsville, Texas, author Kim Larsen wrote:

Dengue is endemic in Matamoros; in 2004 a blood-sampling survey found dengue antibodies in 78 percent of the city's residents, which means all who tested positive had been infected with the virus at some point in their lives, though it may have gone undiagnosed. According to José Luís Robles López, the medical services coordinator for the city, dengue's grip has only tightened in the years since. It used to surge from August through October, in the wake of the summer rains, with cases leveling off throughout the rest of the year. But more and more, Robles López says, dengue is diagnosed steadily all year round.

The reasons are many, and Matamoros is not alone. Around the world, the incidence of dengue fever has risen thirtyfold in the last 50 years, with increases across all key indicators: the number of cases, the frequency of epidemics, the severity of the disease, and the geographic range over which outbreaks occur. Each year the virus is responsible for 50 million to 100 million infections, a half-million hospitalizations, and 22,000 deaths in more than 100 countries. Many experts believe that dengue is now the most worrisome arthropod-borne virus, or arbovirus, in the world (arthropods, which include insects, spiders, and crustaceans, have segmented body parts and an exoskeleton). And now it's making its way into the United States.

Learning about dengue fever and finding ways to block its spread can help the U.S. prepare for other tropical diseases likely to spread northward due to climate change, Larsen writes. Experts tell her that the effort needs to include nontraditional partners, such as climate scientists and urban planners, park rangers and health departments, eco-database modelers and sewage engineers, to ensure that our health-care defenses aren't overwhelmed.

To find out more about emerging climate-related diseases and how to fight them, read more of Larsen's story, The New Diseases on Our Doorstep.