quarta-feira, 29 de junho de 2011
Dengue virus circulating between monkeys and mosquitoes could emerge to cause human outbreaks
More than a thousand years ago, somewhere in Southeast Asia, a fateful meeting occurred between a mosquito-borne virus that infected mainly monkeys and a large, susceptible group of humans. Today, dengue virus -- which can produce high fever, excruciating joint pain and even death -- has spread throughout tropical Asia, Africa and South America, and in 2008 it re-appeared in the Florida Keys. It could be even more widespread along the U.S. Gulf Coast but there is no surveillance in place to detect it. Annually dengue strikes about 100 million people and causes an estimated 50,000 deaths, thriving in the urban environments infested by Aedes aegypti, the mosquito species primarily responsible for human dengue transmission. Meanwhile, the virus' forest-dwelling counterpart -- known as "sylvatic dengue" -- continues to flourish in Southeast Asia and West Africa, cycling between non-human primates and the mosquitoes that feed on them. Since the 1970s, sylvatic dengue has received very little scientific attention -- a situation that badly needs to be remedied, according to the authors of "Fever from the forest: Prospects for the continued emergence of sylvatic dengue virus and its impact on public health," an article published online June 13 in Nature Reviews Microbiology.
"This virus continues to circulate in the forests, and now economic and ecological pressures are driving more and more people into the forests in Africa and Southeast Asia," said University of Texas Medical Branch at Galveston assistant professor Nikos Vasilakis, lead author of the paper. "In the last 10 years we've seen a number of outbreaks of disease with real public health impact caused by what we call zoonotic viruses, viruses that start out in wild animals but can also be transmitted to humans -- look at SARS, Nipah and Hendra, for example. Sylvatic dengue could be capable of a similar emergence -- or rather, re-emergence, since we know previous dengue spillovers into urban and near-urban settings have occurred." Dengue virus may also be capable of movement from the widespread urban cycles into primates and forest mosquitoes of Latin America, which would establish a new reservoir for human infections in the New World. In the paper, Vasilakis and his collaborators identify two factors that make a dengue re-emergence a "clear and present danger": rapid human population growth near and in tropical forests, and the fact that little or no genetic change would be needed for sylvatic dengue to adapt to human hosts and urban mosquitoes. "Experiments show that there is little or no adaptive barrier to the emergence of sylvatic dengue into human populations," Vasilakis said. "In other words, the virus can emerge from its current environment at any time, without further adaptation."