The burden of dengue and chikungunya worldwide: implications for the southern United States and California

Abstract

Background: Dengue virus (DENV) spreads to humans through the bite of an infected Aedes aegypti or Aedes albopictus mosquito and is a growing public health threat to both industrialized and developing nations worldwide. Outbreaks of autochthonous dengue in the United States occurred extensively in the past but over the past 3 decades have again taken place in Florida, Hawaii, and Texas as well as in American Samoa, Guam, Northern Mariana Islands, Puerto Rico, and the US Virgin Islands. As the Aedes vectors spread worldwide it is anticipated that DENV as well as other viruses also transmitted by these vectors, such as Chikungunya virus (CHKV), will invade new areas of the world, including the United States.

Objectives: In this review, we describe the current burden of dengue disease worldwide and the potential introduction of DENV and CHKV into different areas of the United States. Of these areas, the state of California saw the arrival and spread of the Aedes aegypti vector beginning in 2013. This invasion presents a developing situation when considering the state's number of imported dengue cases and proximity to northern Mexico as well as the rising specter of chikungunya in the Western hemisphere.

Findings: In light of the recent arrival of Aedes aegypti mosquito vectors to California, there is now a small but appreciable risk for endemic transmission of dengue and chikungunya within the State. It is likely, however, that if DENV or CHKV were to become endemic that the public health situation would be similar to that currently found along the Texas-Mexico border. The distribution of Aedes vectors in California as well as a discussion of several factors contributing to the risk for dengue importation are discussed and evaluated.

Conclusions: Dengue and chikungunya viruses present real risks to states where the Aedes vector is now established. Scientists, physicians, and public health authorities should familiarize themselves with these risks and prepare appropriately.

Keywords: California; antiviral; arbovirus; chikungunya; dengue; flavivirus; vaccine.

Figure 1. The global distribution, burden, and risk of dengue, 2010–2014

Distribution of dengue virus and disease is cosmotropical across the planet however it is also found in some temperate regions. Dark-shaded nations are considered to be widely endemic to dengue while light-shaded counties show a widespread transmission risk in only certain regions or counties. Hatched lines represent isotherms delineating an approximate 10°C winter minimum, the hypothetical l ower limit for Aedes to survive and overwinter.

Figure 2. The distribution, burden, and risk of dengue in the United States, 2010–2014

Light-shaded states represent those where an imported case of dengue disease has been reported to and confirmed by CDC, while dark-shaded states are those where a confirmed case of autochthonous dengue virus transmission has occurred. Values represent the number of imported cases over the four year period while numbers in parentheses represent cases of locally-acquired dengue. The hatched area bordered by the dotted line represents geographic regions at risk for dengue outbreaks based on approximate vector distribution as of 2013.

Figure 3. The distribution, burden, and risk of dengue in California, 2010–2014

Light-shaded counties are those where an Aedes aegypti infestation has been reported while a dark-shaded county has reported both Aedes aegypti and Aedes albopictus infestations; only Los Angeles county, as of early 2015, reports a continued Aedes albopictus presence. Values represent the number of dengue imported cases to that county over the four year period. All cases must be laboratory confirmed prior to incorporation into the USGS/CDC-ArboNET database.