Dengue: Will there be another mosquito-borne virus establishing itself in the continental United States?

Dengue (pronounced “den-gee” – with a hard “g”) virus was first identified in the 1950’s in Africa and Asia. It is now being seen in almost all regions of the world. The virus causes a disease that is characterized by a high fever accompanied by two or more of the following: a severe headache; severe eye pain; join pain; muscle and/or bone pain; rash; and/or mild bleeding. The person with this illness enters into a dangerous phase just as the fever begins to decline. Blood can begin to leak out of the small blood vessels, causing a failure of the circulatory system, shock, and raising the risk of death. Treatment by a physician is very important at this time. Dengue is actually caused by four different but related viruses. All result in a similar clinical picture. However, immunity against one strain does not protect against the others.

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Dengue was not common in the Caribbean or in North America until recently, as mosquito control programs have seen decreases in funding. The disease is spread via bites of two species of mosquitoes that are present and abundant in the United States: Aedes aegypti and Aedes albopictus. Cases of disease have been rapidly spreading in recent years. However, almost all cases of dengue in the continental United States have been among people who became infected while traveling elsewhere. There was a small outbreak in southern Texas in 2005 and another in Key West, FL in 2009, but those have been the exception. It is thought that the reason for no sustained transmission within the United States is that people have relatively little contact with the two vector species. However, there is no guarantee that this will always be the case. Public health officials are concerned about the risk of an unintended consequence of the World Cup in Brazil, where dengue transmission is sustained, in the summer of 2014. Hundreds of thousands of soccer fans, many from the United States, are expected to travel to Brazil for the World Cup. There could be many opportunities for introductions of the virus via infected fans returning from the games.

The Florida Department of Health in Monroe County (DOH-Monroe) provided insights into their efforts to contain dengue in Key West in 2009. Christopher Tittel, Public Information Officer and Marketing Director at DOH-Monroe explained, “DOH-Monroe took the lead on developing ‘Keys Action to Break the Cycle of Dengue,’ a partnership where leaders in various sectors of our community (government, business, schools, etc.) are encouraged to promote mosquito-prevention activities and messaging among colleagues and in the community.” DOH-Monroe also has ongoing mosquito control measures in place that, according to Mr. Tittel, are focused on “community-wide education, outreach, inspection, and spraying programs that help ensure that populations of all 40-plus species of mosquito that we see in the Florida Keys, including those species that can carry dengue, are kept to a minimum.” Further, residents are reminded about the importance of taking measures to protect their own health. Mr. Tittel said, “Specifically, we encourage them to drain standing water in and around their properties; cover any containers that can collect water; wear mosquito repellents with DEET, long pants and sleeves; close windows and doors and use air conditioning; and ensure there are no holes in screens where mosquitoes can gain access to homes.” The efforts of DOH-Monroe were successful in containing Dengue and no new cases were reported after November 2010.

Climate change has the potential to increase the transmission and geographic expansion of vector-borne diseases. Precipitation and temperature changes are known to affect the reproduction, development, behavior, and population dynamics of mosquitoes, the viruses they transmit, and the transmission cycles. Evidence has shown that the transmission of dengue is highly sensitive to climatic conditions; specifically, temperature, rainfall, and relative humidity. Overall, it has been established that climate change is happening, and research has indicated increased climatic suitability for dengue transmission and geographic expansion into traditionally temperate zones during the 21st century.

Local health departments are on the front lines to prevent and control the possible spread of dengue viruses and disease. Now is the time for assuring that we as a profession and as a nation are prepared for dengue. Treatments might only diminish the symptoms; there are no cures. There are also no vaccines to prevent infection. Local health departments will need to rely on traditional public health measures of surveillance, prevention, response, and education, and should consider the following actions to protect their communities from dengue:

  1. Local health departments are urged to review their mosquito surveillance capacities and assure they will be able to monitor the mosquito populations, measure for the presence and extent of the virus, and identify human cases.
  2. Local health departments are urged to review and update their community’s mosquito control plans and to assure that all participants in that plan are capable of responding to findings that would be a trigger for use of control measures.
  3. Local health departments are urged to review their vector control education plans for the public, medical providers, and laboratories serving their community. Awareness of the virus and disease, recognition of symptoms, personal measures for preventing mosquito bites, and community measures for eliminating Aedes mosquitoes and their breeding sites are all parts of a comprehensive vector disease prevention and control educational campaign.

About Paul Etkind
Paul Etkind, DrPH, MPH, is recently retired from NACCHO where he served as the Senior Director for Infectious Diseases. His work includes oversight of the Epidemiology, HIV/STI, Immunization and Infectious Disease projects, as well as coordinating those with Emergency Preparedness, Environmental Health, Food Safety, and Disability initiatives. NACCHO is extremely grateful to Paul for his years of public health service.

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