Visualization of the dengue fever virus. Courtesy of 3dciencia
A fever run amok
Its name – dengue fever – vaguely suggests some sort of infectious tropical disease and, until relatively recently, that’s exactly what it was. Until 1970, the ailment characterized by symptoms like fever, headache, muscle and joint pains, and a skin rash resembling the measles was endemic to just nine tropical nations, according to the World Health Organization.
Now cases of dengue fever (also colloquially known as breakbone fever) have been reported in more than 110 countries and, according to a new paper in Nature, the annual infection rate may be as many as 400 million cases worldwide, four times higher than the WHO’s prevalence estimate.
“Not only are the number of cases increasing, the geographic range is increasing,” study co-author Thomas Scott, an entomologist at UC Davis, told NPR. “So (dengue) is spreading in to areas where it was not previously, but we are also seeing more and more cases.”
Climate change is one driving factor, according to some scientists. As more of the planet gets warmer, more of the planet becomes amenable to mosquitoes that carry and transmit the virus.
The latest study also blames the spread on the growth of overcrowded slums with poor sanitation.
“People living in substandard conditions where they’re storing water and they don’t have proper disposal of waste [are more at risk],” said Scott. “Rainwater accumulates in containers and the mosquito that transmits this virus, Aedes aegypti, then lays its eggs in those places.”
Often, dengue produces no or mild symptoms, which may be part of the reason it is under-reported. For a small percentage, however, the infection can develop into life-threatening dengue hemorrhagic fever characterized by bleeding, low levels of blood platelets and blood plasma leakage, or dengue shock syndrome, where dangerously low blood pressure occurs.