By Elizabeth Eddy
July 17, 2008 11:22 pm The buzz of mosquitoes is an ever-present background noise during Massachusetts summers, but these bugs can occasionally become more than just a nuisance and cause serious illness. West Nile virus (WNV) and Eastern equine encephalitis (EEE) are two mosquito-borne infections that can strike Bay State residents, and though West Nile can be found anywhere in the state and presents a uniform risk through the commonwealth, EEE is not generally found in Essex County. Eastern equine encephalitis is much more limited in where it occurs, says Dr. Bela Matyas of the Massachusetts Department of Public Health. EEE is primarily found in the red cedar swamps in southeastern Massachusetts, although there was one human case of EEE in Essex County decades ago. "There is a geographic element to the risk of EEE," Matyas explained. Although West Nile is much more common than EEE, the latter kills up to half of its victims, because those who contract EEE experience its primary symptom, life-threatening encephalitis. In contrast, most people who are exposed to West Nile virus, up to 80 percent, do not show any signs of illness, and the 20 percent who do mostly develop mild, flu-like symptoms. Less than 1 percent of West Nile sufferers have neurological symptoms such as encephalitis, inflammation of the brain, or meningitis, infection of the lining of the brain, although these are cases that may prove fatal or result in lingering health effects. Since 2000, West Nile fatalities have equaled those caused by EEE, although the latter represented far fewer cases. "EEE is a very dangerous disease," Matyas said, and can cause some severe damage. EEE is not confined to Massachusetts. Three years ago, the first human cases occurred in New Hampshire, although EEE has been present in Massachusetts since the 1930s. "This represents a new focus for human risk for EEE," Matyas said, "although it is much too early to tell what that means going forward. It's not clear if there is a new location for EEE cases, or if these occurrences are transitory, so we can't predict what will happen. It needs to be studied." It is also not known which birds and mosquitoes played a role in the New Hampshire EEE cases, since both birds and mosquitoes are part of the virus cycle in these two illnesses. West Nile and EEE find a reservoir in birds, which carry the viruses. Mosquitoes become infected when they bite the birds, and then humans become infected when they are bitten by these mosquitoes. "The bird is an important part of the life cycle," Matyas explained. Dr. Catherine Brown, public health veterinarian for the Massachusetts Department of Public Health, said West Nile and EEE pose problems for both people and animals. In the early years of West Nile, the presence of the virus could be tracked by following the trail of dead birds, mostly crows and blue jays. The birds did not have immunity to this new disease, so they often died from the infection. "During the first cases, there were lots of dead crows around. Simply their presence was a good indicator of where the virus was in the environment," Brown said. As the virus has become more common in the environment, bird deaths have lessened and don't serve as well to warn the human population of possible risk. Similarly, EEE also could be pinpointed years ago when horses became ill or died, since they are particularly sensitive to this illness. Ostriches and emus are also affected. "We would know where EEE was and could advise people," Brown said. However, there is now an effective equine vaccine for EEE, so horses are now unlikely to become ill. Birds have also developed some immunity to West Nile, so the Department of Public Health now relies on mosquito surveillance to monitor the populations of the insects that spread both West Nile and EEE. "Now we have a group of crows that are less sensitive to the virus, so we don't see bird die-offs. The mosquito surveillance program has just become a reality of how we need to deal with mosquitoes, since the animals and birds are no longer as useful a tool," Brown said. Matthew Osborne, field coordinator for the arbovirus program at the Department of Public Health, is actively monitoring insect populations, and has some good and bad news about the mosquitoes buzzing around the commonwealth this year. He reports seeing fewer mosquitoes that spread EEE, since there has been inadequate rainfall and "the habitat for them is not there. They are still out there, but are a little less in numbers this year," he said. However, he said the conditions that support the mosquitoes that cause West Nile have been quite favorable. Osborne said Massachusetts weather, particularly small, intense rainstorms, have quickly filled both natural and artificial basins where the mosquitoes breed. The rains have been followed by high temperatures, which are also conducive to the completion of the mosquitoes' life cycle. Osborne said "even a cup of water can breed 150 mosquitoes, so people need to make sure they have no standing water in their yards." The brackish water that mosquitoes love can be found in many places, on tarps, on top of swimming pool covers and outdoor furniture, in plant saucers and pet bowls, and in clogged gutters. All these sources should be kept dry to prevent the number of mosquitoes from increasing. Avoiding mosquito bites is also prudent, since it is not possible to avoid the bugs altogether. "The risk of both viruses is a good reason to take mosquito protection recommendations seriously," Matyas said. Fortunately, there are now four compounds that effectively repel mosquitoes, including a new natural remedy that was just approved by the Centers for Disease Control. The latest preparation's generic name is IR3535, and it is expected to be the active ingredient in new solutions. The other repellents include DEET and the chemical alternative picaridin, and the natural compound oil of lemon eucalyptus. All four repellents can be applied to both skin and clothing, although all have some restrictions and people should follow manufacturers' guidelines when using them, Matyas said. Another effective way to avoid mosquito-borne illnesses is to stay indoors from dusk to dawn, when mosquitoes are most active. For more information, call the Gloucester Health Department at 978-281-9771. ><p>
This article is part of a regular health education series provided by the Gloucester Health Department.
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