Painful, mosquito-borne diseases are no longer limited to distant, exotic locales. As the climate warms, U.S.-based labs should expect more orders to test for the mosquito-borne viruses that cause chikungunya, dengue fever, and West Nile virus (WNV). Cases of the former two could skyrocket, due to warmer weather, air travel to areas where they are endemic—particularly the Caribbean and Central and South America—and Americans’ near-total lack of immunity, according to experts. Similarly, WNV, already the leading cause of domestically acquired arboviral disease in the U.S., is poised to propagate further, writes Deborah Levenson in the June issue of CLN.
Aedes aegypti and Aedes albopictus mosquitoes transmit both chikungunya and dengue, while many more species serve as vectors for WNV; in 2012, the U.S. Centers for Disease Control and Prevention (CDC) identified 54 as carriers. After a long history in Sub-Saharan Africa, chikungunya landed for the first time in the Western Hemisphere—on the Caribbean island of Saint Martin—in 2013. In 2015, it became a nationally notifiable disease in the U.S., and at CLN press time, 126 cases in 26 states had been reported to CDC.
Dengue is endemic worldwide but has not been a major problem in the continental U.S., with nearly all reported cases acquired elsewhere by travelers and immigrants. However, the Caribbean—including Puerto Rico—and Mexico are considered dengue high-risk areas. “In any place with either of the two types of mosquitoes that transmit dengue and chikungunya, there’s risk for local transmission,” said Hollis J. Batterman, MD, laboratory medical director at San Juan Capistrano, California-based Focus Diagnostics, a subsidiary of Quest Diagnostics.
Florida and states that border Mexico have had dengue outbreaks in the past and could have significant cases of chikungunya, she pointed out, urging laboratorians to prepare themselves for questions from clinicians practicing in these regions and from those with sick patients recently returned from affected locales.
When clinicians suspect any of these diseases, it’s important to know what tests can provide an accurate diagnosis. Patients with symptoms of chikungunya and dengue should be tested for both. Polymerase chain reaction (PCR) tests are useful for testing for both diseases in the first days of symptom onset, but less so after several days or a week because viral levels in the blood diminish. At that point, immunoglobulin M (IgM) is the better test for both diseases.
Chikungunya RNA is detectable in the blood at symptom onset but declines to undetectable levels within 7 days, while IgM isn’t uniformly detectable until 5 days after onset. If cost is an issue, test for dengue first because it can be more serious, and supportive treatment is more time-sensitive, said Scott Weaver, PhD, director of the Institute for Human Infections and Immunity and scientific director of the Galveston National Laboratory at the University of Texas Medical Branch in Galveston. When WNV is suspected, serology—IgM and immunoglobulin G—tests should be used because when patients present, the viral load usually is too low to detect with PCR.
Pick up the June issue of CLN to learn more about testing for mosquito-borne diseases.