Warmer temperatures in the United States are leading to the earlier presence of mosquitoes and the potential for mosquito-borne illnesses.
There are a number of arboviral diseases that occur in the United States, including St. Louis and La Cross encephalitis. Since its emergence in 1999, clinicians in the United States have been familiar with West Nile virus. Dengue is one you may not know as much about, and it has the potential to reestablish itself in the United States. Here’s a quick review.
By Dr. Bonnie M. Word
An emerging infection, dengue is transmitted by the mosquitoes Aedes aegypti and A. albopictus, which are found worldwide. The dengue virus complex consists of four related, but distinct, serotypes. Infection with one confers lifelong immunity, but there is no cross-protection against the other serotypes. Dengue fever (DF) is endemic in at least 100 countries in Asia, the Pacific, the Americas, Africa, and the Caribbean. It often peaks during seasons when rainfall is optimal for mosquito breeding. The Aedes mosquito is common in the southern United States, and dengue is endemic in northern Mexico. Most cases in the United States are seen in returning travelers or immigrants (MMWR 2005;54;556-8), including children (Am. J. Trop. Med. Hyg. 2012;86:474-6).
Since 1980 there have been seven outbreaks along the Texas-Mexico border. However, dengue can be acquired locally. In 2010, 28 cases were reported from Key West, Fla. They were the first cases of locally acquired dengue outside the Texas-Mexico border since 1995. The initial case was diagnosed by an astute physician in a patient from New York who had visited Key West (MMWR 2010;59:577-81).
Why is this virus reemerging in the United States? One thought is that the mosquito vector has optimal breeding conditions. It prefers to breed close to or inside a home, and it can lay eggs in natural or man-made water containers. It also is a daytime feeder with a preference for humans. Often, the mosquito has multiple feeds before a breeding cycle, thus exposing several persons in the same household.
Dengue should be considered in the differential diagnosis of all febrile patients who reside in the tropics or subtropics, including areas with subtropical climates in the United States, or in febrile patients who have a history of travel to such places in the 2 weeks before symptom onset. It is now the leading cause of a febrile illness in U.S. travelers returning from the Caribbean, South America, and Asia (N. Eng. J. Med. 2006;354:119-30). Because of the increasing number of cases in returning travelers, many of whom may still be viremic and capable of introducing the virus into the community, combined with the presence of an efficient mosquito vector, dengue became a nationally notifiable disease in 2009.
Symptoms typically begin 4-7 days after the mosquito bite and last about 3-10 days. Individuals, especially children, infected with dengue for the first time may be asymptomatic or have a nonspecific febrile illness, but subsequent infections are usually more severe. Classic DF is primarily a disease of older children and adults.
The World Health Organization defines DF as an acute febrile illness with two or more of the following: headache, retro-orbital pain, muscle aches, joint pain, rash, hemorrhagic manifestation, or leukopenia. The rash is either macular or maculopapular and generalized, is often confluent with small patches of normal skin, and may become scaly and pruritic. It usually appears as the fever subsides and lasts 2-4 days. Other signs and symptoms include flushed skin (usually during the first 24-48 hours), nausea, and vomiting. DF is usually a self-limited illness and is rarely fatal. Approximately 1% of patients with DF develop dengue hemorrhagic fever about 3-8 days after the onset of fever. There is evidence of vascular leakage, hemoconcentration, and thrombocytopenia.
Courtesy Jim Gathany/CDC
Warmer temperatures are leading to the earlier and added potential of mosquito-borne illnesses.
The primary serologic test for dengue virus (DENV) in patients with acute illness is IgM anti-DENV, which becomes positive more than 5 days after symptom onset. This, in combination with a compatible travel history and symptom profile, suggests a probable recent DENV infection. There are several commercially available diagnostic tests for dengue, although none have been approved by the Food and Drug Administration. Testing is available at some state laboratories, and through the Centers for Disease Control and Prevention (see "Requesting Dengue Laboratory Testing and Reporting" at www.cdc.gov/Dengue/clinicalLab/index.html). For additional information, contact the CDC Dengue Branch (787-706-2399) or visit http://www.cdc.gov/dengue/.
There is no specific treatment for DENV infections. Management involves bed rest and fluid maintenance during the fever, which can be controlled with acetaminophen. Headache, eye pain, joint pain, and muscle ache may require narcotics, but aspirin and nonsteroidal anti-inflammatory agents should be avoided. Patients should be instructed that, as the fever subsides, they should go to the hospital if they develop abrupt change to hypothermia, severe abdominal pain, persistent vomiting, bleeding, difficulties breathing, or altered mental status such as irritability, confusion, and lethargy. These may be signs of dengue hemorrhagic fever, which can prove fatal.