Monday, February 18, 2008
Experts warn of potential dengue fever outbreak in the United States
David Morens, MD, and Anthony Fauci, MD, caution that dengue fever could pose a significant threat to the continental United States.
by Kirsten H. EllisIDN Staff Writer
Dengue fever and its severe forms, dengue hemorrhagic fever and dengue shock syndrome, are potential threats to residents of the continental United States, according to a recent commentary by leading health experts.
Public health officials need to be aware of the threat because no treatments or vaccines for dengue are currently available. Dengue fever is already present along the U.S.-Mexico border and in Puerto Rico.
“Clinicians should know how to identify and diagnose dengue fever. They need to be aware of dengue fever and where it can occur, which is theoretically anywhere in the United States for imported cases,” David Morens, MD, National Institute of Allergy and Infectious Diseases senior advisor, told Infectious Disease News. “Dengue fever was a common occurrence in the past and could be again where mosquito vectors are present, particularly in urban areas.”
Morens and Anthony Fauci, MD, director of National Institute of Allergy and Infectious Diseases, wrote about the threat of dengue fever in the United States in a recent edition of the Journal of the American Medical Association.
Reemergence of dengue fever
“In recent decades, dengue disease has followed vector expansion and dengue hemorrhagic fever, a deadly but poorly understood complication, has tended to follow,” Morens and Fauci wrote in their commentary. “The combined effects of global urbanization and increasing air travel are expected to make dengue fever a growing international health problem for the foreseeable future.”
Dengue fever is considered among the most important reemerging infectious diseases with an estimated 50 million to 100 million cases annually. WHO case estimates include 500,000 hospitalizations and 22,000 deaths each year, most of which occur in children.
In their commentary, Morens and Fauci outlined the background of dengue fever and the adaption and movement of its vector, Aedes aegypti, which already is established in much of the tropical and subtropical world. An alternative vector, Aedes albopictus, is spreading geographically into temperate climates, which could exacerbate the global dengue spread. Both mosquito species have been found in the United States.
“In 2001, the first dengue fever outbreak in Hawaii since World War II caused a lot of alarm, people got sick and there was great public concern,” Morens said. “We talk about ‘mild’ dengue, but people with classic dengue fever would probably dispute the word ‘mild.’”
The National Institute of Allergy and Infectious Diseases allocated $33.2 million in 2007 for nearly 60 dengue research projects, including vaccine, diagnostic and therapeutic development and clinical vaccine trials.
Dengue questions abound
Dengue fever is complex and multiple factors confound scientific answers, including risks and the lack of understanding about pathogenesis of dengue hemorrhagic fever and dengue shock syndrome.
Classic dengue fever symptoms are similar to those of influenza, but can confound diagnosis because symptoms are not predictive markers for disease severity, progression or hypotension. These variables make this virus complex and difficult to understand.
Risk for dengue hemorrhagic fever and dengue shock syndrome most often are associated with second dengue infections. However, dengue hemorrhagic fever in infants aged 5 to 8 months does not follow this pattern because the first, rather than the second infection, is more likely to progress beyond classic dengue. Risks for these more severe forms typically decrease with each subsequent infection, but this decrease also may depend on the virus serotype.
Other questions arise regarding vaccination development strategies because antibodies could decrease efficacy over time and vectors may develop resistance.
The National Institute of Allergy and Infectious Diseases’ dengue research program includes the development of animal models to gain understanding of the basic mechanisms of infection. Researchers also are working to understand how dengue viruses elicit antibodies, which is key to unlocking the mode through which viruses infect host cells. Research is underway on biological markers to gain insight into predictors of whether dengue fever will develop into dengue hemorrhagic fever or dengue shock syndrome.
Researchers also are trying to determine what causes capillaries to leak plasma in people infected with dengue hemorrhagic fever and dengue shock syndrome and investigating a possible genetic susceptibility to infection. Promising dengue vaccines have already reached phase 2 safety and efficacy testing including inactivated, live attenuated, chimeric, subunit and DNA vaccines, Morens and Fauci wrote.
For more information:
Morens DM, Fauci AS. Dengue and hemorrhagic fever: a potential threat to public health in the United States. JAMA. 2008;299:214-216.
Infectious Disease News