able to mosquitoes. A researcher draws a water sample to test for the presence of Aedes mosquito eggs
CDC
It seems that common sense :. Reduce insect populations, diseases and insects -Internet also decrease. But a new study of dengue fever, a viral disease transmitted by Aedes mosquitoes, suggests otherwise. Mosquito control can result in more cases of dengue hemorrhagic fever (DHF), a rare and sometimes fatal disease caused by the virus.
Researchers believe that tens of millions of people in tropical regions are infected with dengue virus each year. The pathogen can stimulate dengue fever, which is marked by painful muscle and joint pain, but is rarely fatal. Some patients, however, develop more severe DHF, which can cause bleeding and is fatal. There are still many questions about the epidemiology of both diseases -. Including the importance of mosquito abundance
An international team of data gleaned from a massive national survey of Aedes mosquitoes made between 02 and 04 in Thailand, where the Dengue . The researchers compared this information with data on the incidence DHF collected by the Thai Ministry of Health. Overall, 83 out of 100,000 Thai contracted dengue each year. As expected, the team found that the incidence DHF has increased the percentage of households by district containing larvae or pupae Aede (the index House). But the trend held up to a point. House when the index climbed beyond 30, DHF incidence gradually declined, the team reports this week PLoS Neglected Tropical Diseases .
Co-author Yoshiro Nagao Osaka University Graduate School of Medicine in Japan said the likely explanation - which was supported by computer models - is that DHF usually develops the second time a person is infected . When there are a lot of mosquitoes, the second infection is more likely to come shortly after the first, so there is a better chance that person still has a strong immune response. When mosquitoes are less abundant, the more time passes between infections, antibodies decline, and protection diminishes.
The data show that mosquito control can have unintended consequences, says Nagao. For example, lowering the index House for 30 through Thailand could lead to a 40% increase in DHF. In an unpublished study, Nagao and others plan to show that the only way out of the problem is a vaccine, many of which are now in clinical trials.
But dengue researcher Duane Gubler of the University of Hawaii, Honolulu, said the story is more complicated. On the one hand, the study models assume that all strains of dengue and mosquito populations are similar. In reality, there are "huge variations" between infectivity and potential spread of virus strains, he said, and some mosquito populations are much better than other vectors. In addition, the House index, which assesses mosquito breeding sites, may not be a good indicator of population exposure to a virus, says entomologist Paul Reiter of the Pasteur Institute in Paris. What is important is not the number sites, but the number of adult mosquitoes they produce, he said.
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