COMMENTARY

From Aedes to Zika: Mosquito-borne Viruses a Growing Concern

Paul G. Auwaerter, MD

Disclosures

January 11, 2016

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Hello. This is Paul Auwaerter with Medscape Infectious Diseases and the Johns Hopkins Division of Infectious Diseases, talking about travel-related infections. This winter season, many people think of traveling to warmer climates. Mosquitoes are often in these environments and are thought of as nothing more than a pedestrian, nuisance problem.

However, in the past couple of years, three viruses have grabbed a lot of attention, posing problems not only for travelers but for people living in Central and South America and the Caribbean. Chikungunya first swept in about 2 years ago, causing hundreds of thousands of cases. In 2014, cases began to be identified among returning travelers.[1] Chikungunya is a virus that can cause rather severe musculoskeletal pain and, uncommonly, neurologic and longer-term arthritic sequelae. Local transmission has even been documented in Florida, Puerto Rico, and the Virgin Islands.

Beyond chikungunya is the more serious virus, dengue, which has been on the radar of many public health officials for years. Dengue also causes fever, headache, and muscle and joint pain, and it is often hard to distinguish between the two viruses. Retro-orbital pain, if present, might be a distinguishing feature of dengue. Bleeding is more common with dengue, which can cause a petechial rash or the most feared complication of dengue, hemorrhagic fever.

The dengue virus is known to be endemic in the Virgin Islands and Puerto Rico, but cases have been seen in Texas and South Florida. Of interest, Hawaii is currently experiencing a small outbreak on the Big Island (probably from an imported case), where more than 181 cases have been reported since September of 2015.[2]

For travelers, these viruses could be a cause for concern. However, Brazil is currently experiencing a dramatic outbreak of dengue, where more than 1.5 million cases have been reported to date. This large number prompted public health officials in Brazil to approve the Sanofi Pasteur dengue vaccine, which has undergone clinical trials.[3] The vaccine appears to protect against four serotypes of dengue, with about a 60% reduction of disease in children. It may be more protective against severe dengue and the need for hospitalization, although by the third year after immunization there was an uptick in younger children needing hospitalization that is not quite understood yet. However, the vaccine has impressed public health officials, not only in Brazil but in two other countries that have approved the vaccine—the Philippines and Mexico—as one of the few tools other than routine mosquito avoidance measures to help combat the dengue epidemic.

Now a third virus, the Zika virus, has been a cause for concern. This virus, first described in Africa and Southeast Asia, appears to now be epidemic in Brazil. The Zika virus has also been reported in Mexico and no doubt is probably elsewhere in the same distribution in both the Northern and Southern Hemispheres, or certainly will be in short order.[4] It's a flavivirus, much like dengue or yellow fever. It can cause fever, rash, joint pain, and conjunctivitis, but generally has not resulted in death or severe illness.

However, it can be confusing because Zika represents a third virus that must be considered and which can be hard to distinguish on a clinical basis from the other two viruses. There has also been concern about an increased rate of birth defects in Brazil, specifically microcephaly, which might be caused by the Zika virus. The link isn't clear, but the possibility has created a lot of concern among pregnant women in that country.

For US travelers, unfortunately, the dengue vaccine is not yet available. Therefore, mosquito avoidance is the only practical measure to prevent dengue. This nice handout from the Centers for Disease Control and Prevention (CDC)[5] describes recommended mosquito avoidance maneuvers that should be followed as carefully as possible by anyone who is planning to travel to areas where they could acquire a mosquito-borne illness.

The Zika virus is new diagnostically, with no easy tests.[6] You have to contact your local health authorities to ship a sample to the CDC for polymerase chain reaction or antibody testing. But keep in mind that if you are evaluating a patient who has recently returned from Central or South America with a febrile illness, rash, and joint pains, maintain a suspicion for Zika virus, along with chikungunya and dengue. Thanks very much for listening.

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