Fifth Type of Dengue Discovered
By Amesh A. Adalja, MD, FACP, FACEP, October 25, 2013
On first exposure, dengue fever, the Aedes mosquito-borne infection that causes sickness in an estimated 400 million people yearly,1 is usually a benign illness caused by one of 4 known strains of the virus. However, when a person is infected a second time with a different strain of the virus, the antibodies to the first can enhance the body’s reaction to the second strain and may cause severe dengue hemorrhagic fever (DHF), dengue shock syndrome (DSS), and possibly death.
Because of the heavy burden of dengue in much of the world and its ability to cause severe disease, a vaccine is a high priority. The promise of a vaccine against dengue fever is based on inducing balanced immunity to the 4 strains of dengue virus. If immunity is not balanced, the risk of DHF could be increased. However, such vaccines, currently in the late stage of development, may be in jeopardy given the recent discovery of a new fifth strain of the virus. This discovery was announced by Nikos Vasilakas, of the University of Texas, Galveston, at a Dengue conference in Bangkok this month.2
The new strain of the virus was discovered during research on a 2007 dengue outbreak in Malaysia. Nucleic acid sequencing uncovered a distinct fifth type of the virus that elicited a unique antibody response in a monkey model.2
Implication for Control
At this time, the implications of this discovery for vaccine development are not clear, as the newly discovered strain has only been found in one outbreak. However, this prompts several research questions:
- Is there any evidence of this strain in other outbreaks?
- How phylogenetically distinct is this strain from the other 4?
- When did it emerge?
- Does it circulate in other species (eg, primates)?
- What is the course of disease caused by this strain as compared with the others?
- Can it cause DHF or DSS?
- Are there any unique host characteristics among people infected with this strain?
- Does it have the same transmission potential in vector mosquitoes?
As evidenced by nearly 400 million cases globally, and by recent reports in the US of dengue outbreaks in Florida3 and local transmission in Houston,4 dengue is a clear and growing threat to human health. Discovery of this fifth strain may make control of this disease even more complex than it is now.
- Bhatt S, Gething PW, Brady OJ, et al. The global burden and distribution of dengue. Nature 2013;496:504-507.
- First new dengue type in 50 years. Science Insider. October 21, 2013. http://news.sciencemag.org/health/2013/10/first-new-dengue-virus-type-50-years.
- Dengue. Florida Health website. Florida Department of Health. http://www.floridahealth.gov/diseases-and-conditions/dengue/index.html. Accessed October 23, 2013.
- Murray KO, Rodriguez LF, Herrington E, et al. Identification of dengue fever cases in Houston, Texas, with evidence of autochthonous transmission between 2003 and 2005. Vector-Borne and Zoonotic Diseases 2013; http://online.liebertpub.com/doi/abs/10.1089%2Fvbz.2013.1413. Accessed October 23, 2013.