Scitech | Dengue on our doorstep

It starts with a sudden fever and a headache. Then comes nausea, skin rashes, and atrocious muscle and joint pain. There are no available vaccines or anti-viral drugs. Previously restricted to tropical regions, this dangerous disease is expanding into temperate regions and becoming more deadly.

If you haven’t heard of dengue fever before, you will soon, according to Dr. David Morens, the senior scientific advisor of the National Institute of Allergy and Infectious Diseases (NIAID). In a recent piece in the Journal of the American Medical Association, Morens and NIAID Director David Morens warned that dengue fever is on the rise around the globe.

“Worldwide, dengue is among the most important re-emerging infectious diseases, with an estimated 50 million to 100 million annual cases,” they wrote. “Globally, dengue and DHF case counts have been increasing steadily for more than 50 years…. [Dengue fever will be a] growing international heath problem for the foreseeable future.”

Global warming is among the possible culprits behind this expansion. As the average temperature in North America increases, mosquito distribution will expand. As the fever is transmitted through mosquito bites, it will spread with mosquito populations. The illness, which was previously restricted to tropical climates, now threatens continental regions like the Texas-Mexico border. If temperatures keep increasing, the disease will climb up North America with them.

Yet the range of the illness depends on more than temperature. In an interview with The Daily, Dr. Morens stressed the urban nature of the dengue fever.

“Rapid urbanization plays a much more important role in the expansion [than temperature],” he said. “The mosquitoes responsible for the disease only live in sites where human beings live. They deposit their eggs in anything that holds water: old tires, tin cans, and coconut shells.”

Efforts to control the disease have accordingly tried to rid cities of standing water, so that mosquitoes have nowhere to lay eggs. But the efficiency of these preventive measures in densely populated cities is questionable. Singapore, for example, still struggles with a soaring incidence of dengue fever, despite the implementation of a house-to-house inspection program that fines owners for lingering rubbish and pools of stagnant water.

Because attempts to control the disease through sanitation have largely failed, Dr. Morens says vaccines are humanity’s best hope for dengue control. Although clinical trials are currently underway, it will be a few years before any immunization campaign becomes a reality.

The main difficulty in creating a vaccine is in the pathology of the disease. Because there are four types of the virus, vaccines must guard against all four types. The challenge is made even more complex by the fact that vaccines that guard against less than all four types make people more susceptible to the neglected virus types.

So being inoculated with an undeveloped vaccine could actually increase one’s chances of getting the virus. These safety concerns have made it hard to test vaccines, and are slowing down their development. Dr. Brian Ward, associate director of the McGill University Health Centre’s Centre for Tropical Diseases, expresses the problem succinctly.

“We have to be sure it works. If you don’t do it right, [the vaccine] will make [the virus] worse.”

But until a vaccine is found, the fever will continue to spread northward, and kill an estimated 5 million people per year worldwide.


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