Hot Zone—A Warming Planet's Rising Tide of Disaster

It was a hot, sticky day when patient zero arrived at a local hospital in Brownsville, Texas, in June 2005. Her body was racked with chills, she couldn’t stop vomiting, her blood pressure was perilously low, and she was passing blood in her urine. Clueless as to the cause, doctors pumped her up with fluids to treat dehydration, dosed her with antibiotics, and sent her home. But when blood tests and clinical evaluation were done with the help of the regional Texas Border Infectious Disease Surveillance project, a surprising culprit was unmasked: dengue hemorrhagic fever, a deadly viral disease usually regarded as a risk only in the tropics.

Long thought eradicated in the United States, dengue is roaring back. There had been prior cases of the disease’s milder cousin, classic dengue fever, in Brownsville, a bustling metropolis of about 140,000 people at the southernmost tip of Texas on the Gulf coast. But this was the first well-documented case of the more serious form of dengue infection, hemorrhagic fever, in a Texas resident infected in the continental United States. It is unlikely to be the last. From 1995 to 2005, some 10,000 cases were reported in the United States and the Texas-Mexico border region. The Centers for Disease Control and Prevention (CDC) believes that many cases are never counted, so these figures may be a vast underestimate.

A range of factors influence the spread of the dengue virus, but rising global temperatures may be the most important of all. Like many tropical diseases, dengue is spread by mosquito bites, and mosquitoes are exquisitely sensitive to climate. Frost kills both adults and larvae, which is why the disease hadn’t previously been able to get a foothold in the United States. With the advent of warmer winters, there is nothing holding the insects back. As a result, the two species of mosquito capable of transmitting dengue fever—Aedes aegypti and Aedes albopictus, also called the Asian tiger mosquito—have substantially expanded their habitat range since the middle of the 20th century