Sunday, October 12, 2014

Dang that Dengue!

News outlets across this world this week reported the story of six fatalities caused by dengue virus and thousands of other individuals infected in the Guangdong province of China.  According to an article from Chinese news agency Xinhua published October 6th, 21,527 cases of infection had been reported and that number was increasing by at least 1,000 with every passing day.  The majority of cases and fatalities are concentrated in Guangdong's capital city of Guangzhou, but the disease has been reported in nearly every city in the province.  The other southern provinces of Fujian, Hunan and Guangxi have reported cases of dengue virus infection as well.
Figure 1:  The location of Guangdong province within China and an enlarged map of the province indicating the location of capital city Guangzhou.

What is dengue virus and what does it do?  Dengue virus is a member of the Flaviviridae family of ssRNA viruses that has four serotypes (DENV-1, -2, -3, and -4).  Infection with dengue typically causes flu-like symptoms that resolve after a few days, but in some cases patients develop "severe dengue" including dengue hemorrhagic fever (DHF) or dengue shock syndrome (DSS), which can be fatal.  The full range of symptoms from mild to DHF or DSS can be produced by infection with any one of the four serotypes.  There is no effective vaccine or cure for the disease.  However, the likelihood of recovery among patients who develop DHF or DSS increases with supportive medical care including IV fluids and close monitoring. Other well-known members of the Flaviviridae family that cause severe disease are west nile virus, yellow fever virus and hepatitis C virus.

Figure 2:  Rendering of the dengue virus vision.

What happened to cause this outbreak?  According to the World Health Organization, dengue is a virus not transmitted human-to-human but instead by a mosquito vector.  As a result, it is unsurprising that the current outbreak in China can be linked to increased populations of the mosquitoes carrying the virus.  Populations of these mosquitoes are five times their normal size this year according to Xinhua.  More mosquitos, more virus, more infection.  But what caused the bump in mosquito population this year?  Chinese health officials are blaming climate effects, particularly the unusually hot temperatures and increased precipitation in Guangdong, which create an ideal environment for the mosquitos.

What are we doing about it?  Because dengue is mosquito-borne, most efforts to stop the current outbreak in China target reductions in the mosquito populations and elimination of potential breeding habitats:  spraying pesticides in the streets, disinfecting the sewers and distributing free mosquito repellant.  Beyond the efforts in China to stop the current outbreak, researchers across the globe are working steadily to produce vaccines against the virus and treatments for the disease, including right here at the Stanford School of Medicine!

Dengue remains a significant concern in many regions of the world, as is apparent in a map of global incidences of dengue produced by the CDC and HealthMap (Figure 3) using data from 2013.  Because it is mosquito-borne, dengue patterns follow the patterns of is arthropod vector and dengue is most prevalent in tropical regions.
Figure 3:  Global incidence of dengue virus, as of 2013.
            --Laurie Rumker
Fig. 1 from:
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