A retrospective study analyzing blood samples in Houston, Texas reveals that the virus that causes dengue fever was locally acquired, according to researchers from the Baylor College of Medicine (BCM).

The study, Identification of Dengue Fever Cases in Houston, Texas, with Evidence of Autochthonous Transmission Between 2003 and 2005, was published in the journal, Vector-Borne and Zoonotic Diseases on Oct. 9.

During this three year study, the research team led by Dr. Kristy Murray, associate professor and associate vice chair of research in the department of pediatrics at BCM and director of the Laboratory of Viral and Zoonotic Diseases at Texas Children’s Hospital, analyzed blood and cerebrospinal fluid samples submitted for West Nile virus testing in the Houston area during 2003-2005.

What they found was 47 of the samples were positive for dengue virus.

“We looked at clinical specimens that were banked at the city laboratory to see if there were potentially any other viruses that we could detect that weren’t known to be circulating in Houston but have the high potential to do so,” said Dr. Murray.

“We started with dengue virus since it was highest on the list of possible transmission here in Houston because we have the right kind of mosquitoes and a very large, densely populated city full of frequent travel to endemic areas, including Mexico and Central and South America.”

Murray and colleagues first checked the clinical samples for immunoglobulin M (IgM) antibodies, the antibodies that represent acute dengue infection, and found that 47 of the 3,768 samples were positive for IgM antibodies specific to the dengue virus. Two of those samples were positive for the actual virus in their blood, which happened to be dengue 2. This particular strain of dengue virus can be associated with severe illness, including hemorrhagic fever.

The other key finding was most of the cases had no history of travel to a dengue endemic area based on medical record review and interviews with patients. In fact, a medical record review identified two fatal cases, one of whom had been bed-bound for two years, so clearly had no history of travel outside of Houston.

Murray says most of the cases occurred in the summer months of 2003 and suggests there may have been a dengue outbreak at that time.

“Dengue virus is one of those diseases for which we suspected some low level of ongoing virus activity, and certainly Houston is a prime spot for these types of viruses to circulate,” said Murray.

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