The rate of illness from West Nile virus could double each week as the heart of the summer progresses, a top Centers for Disease Control And Prevention official told USA Today. Most illness typically emerges after Aug. 1, as mosquitoes begin their yearly reign of nuisance.
This year, because of hot and dry conditions, mosquito numbers are expected to be high, and that is already leading to more disease. While many who are infected develop no serious symptoms, West Nile fever afflicts as many as 30% with a prolonged flu-like illness that can last weeks. A smaller fraction develop encephalitis, a serious swelling of the brain that can cause lasting damage or death.
From an environmental perspective, West Nile virus exemplifies three growing trends in world environmental issues: Global warming, invasive species and wildlife diseases. If hot and dry conditions lead to increased outbreaks of West Nile virus, then we can expect more and more each year. Global warming, by some measures, has already led to a worsening of summer heat waves and droughts. And scientists say there is more to come.
West Nile virus first appeared in the Western Hemisphere in New York in 1999. No one is sure exactly how it got here, but global trade and travel are likely culprits. Since the invasive virus -- so-called because it is foreign and spreads virtually without check from natural forces that are present in its native environment -- was first detected, it spread across the country. Such outbreaks -- whether by viruses, plants, insects or animals -- are considered "biological pollution" and besides spreading disease they are considered a chief culprit in the worldwide loss of species.
As a wildlife disease, West Nile virus is spread primarily from bird to bird by mosquitoes. But those same mosquitoes can sometimes infect a human after feeding on an infected bird. Such diseases -- scientists call them zoonoses because they originate in animals -- may become more common as environmental conditions deteriorate. Avian influenza, hantavirus and West Nile are all examples of diseases that jump the species barrier, in part due to environmental conditions that make that deadly jump possible.
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