Dengue virus identified in Houston Potentially lethal disease carried by mosquitoes found in city

Mosquitoes carry the dengue fever virus, for which there is no vaccine or treatment. The hemorrhagic strain of the disease can cause death. Take a look at 13 things that attract the pests and how to avoid them. Mosquitoes carry the dengue fever virus, for which there is no vaccine or treatment. The hemorrhagic strain of the disease can cause death. Take a look at 13 things that attract the pests and how to avoid them. Photo: Dr. Bastiaan Dress Photo: Dr. Bastiaan Dress Image 1 of / 21 Caption Close Dengue virus identified in Houston 1 / 21 Back to Gallery

Dengue fever, a virulent tropical disease thought to be eradicated from the United States in the 1950s, has re-emerged in Houston, according to a new study.

Baylor College of Medicine scientists are reporting the mosquito-borne virus has recently been transmitted in Houston, the first evidence the disease so prevalent in the developing world has spread to a major U.S. city in large numbers. In the past decade, it has been identified in Hawaii, south Florida and along the Texas-Mexico border.

"Dengue virus can cause incredibly severe disease and death," said Dr. Kristy Murray, a professor of tropical medicine at Baylor College of Medicine and the study's principal investigator. "This study shows that Houston may be at risk of an outbreak, that people need to be on the lookout."

Murray's team investigated the possibility that dengue might be in Houston because the area has the type of mosquitoes known to carry the virus and a dense population full of frequent travelers south of the border, where the virus is endemic. But the study, published Wednesday in the journal Vector-Borne and Zoonotic Diseases, found that most of the infections were transmitted in Houston.

There is no vaccine or treatment for the virus.

A pandemic outside the United States - hot spots are in India and Bangladesh, Indonesia, Brazil and Mexico - dengue infects more than 100 million people a year, killing at least 25,000. Identified in nine tropical countries before 1970, it has spread to more than 100 today.

It can be fatal

Dengue symptoms resemble West Nile: fever, rash, severe headaches and joint pain, usually lasting no more than a week. But a more severe form of the disease, dengue hemorrhagic fever, can cause death, particularly among infected infants between 5 and 8 months of age and those previously exposed to a different strain of the virus.

Dr. Peter Hotez, dean of Baylor's National School of Tropical Medicine, said it is a significant concern that the dengue strain identified in Houston is different from the one confirmed in 2010 in Key West, Fla. He said if either strain spreads to the other side of the Gulf Coast, it could mean a fatal outbreak.

"This shows there's a need for aggressive dengue surveillance not only in Houston, but across the Gulf Coast," said Hotez.

Murray's team found evidence of dengue in blood and cerebrospinal fluid samples submitted for West Nile virus testing between 2003 and 2005, a period during which the Houston health department banked such specimens. They found 47 of 3,768 were positive for antibodies to acute dengue infection, which Murray characterized as "the tip of the iceberg" because the samples only involved people sick enough to seek treatment. She said the cases suggest there was a dengue outbreak in 2003.

Two of the 47 died from the infection, the study found.

There are no banked specimens after 2005 to conduct further retrospective dengue, but Murray and Hotez said the virus is likely still here. Murray has created a dengue working group to make testing for the virus more routine during the dengue season next summer and plans a prospective study. She noted that doctors hadn't checked for dengue in any of the identified 47 cases in the study.

Public health concern

Dr. Amesh Adalja, a researcher at the University of Pittsburgh Medical Center's Center for Biosecurity who has published an influential study of emerging U.S. infectious diseases, said the study "adds to the evidence dengue is a rising public health concern in the U.S."

"There are definitely areas that need to be attuned to the risk, areas where physicians and public health officials need to think about dengue for patients whose symptoms are compatible with the disease," said Adalja. "The study is a good model for how researchers in, say, Louisiana or other Gulf Coast areas can look at stored samples and likely find viruses of concern."

No longer using DDT

The Baylor study of dengue in Houston follows the 2004 identification of a number of cases in Brownsville and a major outbreak in Galveston in the 1920s. DDT ended the problem in the 1950s, but mosquitoes returned after the insecticide fell out of favor. Asian tiger mosquitoes, which are very aggressive and carriers of the dengue virus, are now rampant in Houston.

Hotez said the identification of dengue in Houston was a matter of "seek and ye shall find."

"People talk about emerging diseases, but my guess is that dengue has been here a long time, just not looked for," said Hotez. "We suspected it was here and all we needed to do was conduct a study to be proved right."