Southern Texas Primed for an Outbreak of Dengue Fever

The findings of a recent study coordinated by the Centers for Disease Control and Prevention (CDC) and local departments of health in southern Texas highlight the risk for localized outbreaks of Dengue fever in the region and other areas of the United States with similar climatic and environmental conditions. This is particularly alarming as Texas is already well-within range of an outbreak of another vector-borne illness: Zika virus.

The study, published May 11 in the journal Emerging Infectious Diseases, identified 53 laboratory-positive cases of Dengue in southern Texas during an outbreak across the border in northern Mexico. Perhaps most troublingly, 26 (49%) of the cases acquired the infection locally, and 29 (55%) were hospitalized.

“South Texas has established populations of the mosquito vectors of Dengue virus—Aedes aegypti—as well as travelers frequently returning to the state from Mexico and other parts of Central America,” study co-author Lieutenant Commander Tyler M. Sharp, PhD, epidemiologist, CDC Dengue Branch, San Juan, PR told Contagion. “Hence, as has been seen during prior Dengue outbreaks in the region, South Texas continues to be at risk for local Dengue virus transmission, most particularly when transmission is high in northern Mexico.”

Dr. Sharp and his colleagues, who included researchers from the CDC and state and county departments of health in Texas as well as epidemiologists from the Division of Global Migration and Quarantine in San Diego, collected 83 patient specimens that were initially IgM negative based on enzyme-linked immunosorbent assay (ELISA) tests performed at a commercial laboratory. Of these, 14 (17%) were Dengue virus positive based on real-time reverse transcription polymerase chain reaction (PCR) testing performed at the CDC Prevention.

Among the study population, the research team identified Dengue virus types 1 and 3. Molecular phylogenetic analysis confirmed “close identity with viruses that had recently circulated in Mexico and Central America.” In addition, of the 51 household members of 22 Dengue patients who participated in household investigations, six (12%) had been recently infected with Dengue and reported no recent travel. The authors concluded that this suggests “intra-household transmission.”

“Health departments in areas of the United States where the mosquito vectors of Dengue virus are present should have disease surveillance systems to detect both travel-associated and locally-acquired Dengue cases,” he added. “Should locally-acquired Dengue cases be detected, response plans should be in place to immediately investigate and reduce the risk of additional cases. There are still multiple knowledge gaps in the US regarding where Aedes aegypti and Aedes albopictus mosquito species are present and at what density, both of which are determinants of a given areas’ levels of risk for local transmission of Dengue virus. Hence, additional mosquito surveillance is needed to better define the areas of the United States that are at risk for Dengue virus transmission.”

Brian P. Dunleavy is a medical writer and editor based in New York. His work has appeared in numerous healthcare-related publications. He is the former editor of Infectious Disease Special Edition.