If you live in the United States and don't travel abroad, chances are you'll never come down with dengue fever. That's not the case for people living in tropical and subtropical climates, like South America, Africa and the Caribbean.
Between 50 and 100 million of these people catch the mosquito-transmitted dengue virus every year. Most of them will bounce back after 2 weeks of rest and extra fluids. A small percentage, however, won't be so lucky. After contracting dengue a second time, some people may develop a potentially fatal dengue hemorrhagic fever.
Scientists suspected that the human immune system might be to blame for making the second infection more dangerous, but until recently they weren't sure how.
Using computer simulations, epidemiologists at the Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland, learned that the infected person's antibodies—proteins that should fight off dengue—actually help the virus copy itself. More copies make the virus a better predator, allowing it to spread faster and infect more people.
But the researchers—Derek Cummings and Donald Burke, who is now at the University of Pittsburgh in Pennsylvania—also learned that the virus actually causes its own demise. Like a hungry wolf pack that clears out the local deer population, the virus eventually starves itself. Infecting too many people reduces its "food" supply.
This work is just one example of how researchers can develop models to answer questions about outbreaks of dengue or other diseases. With a mathematically based model, ecologist Pejman Rohani at the University of Georgia in Atlanta examined 30 years of epidemiological data from Thailand, a hot spot for dengue. He learned that environmental factors, like warmer temperatures, can re-route mosquito flyways and in turn change dengue infection rates.