West Nile Virus (WNV) is a viral disease previously seen only in Africa, Asia, and southern Europe. This virus can cause encephalitis or meningitis, infection of the brain and the spinal cord or their protective covering. For the past six years, WNV has caused disease in the United States.
In 1999, at least 62 people became seriously ill, and seven of those died. Since then, WNV has rapidly spread throughout North America. During the year 2000, 21 human cases of WNV encephalitis were reported in the United States, with two deaths. In 2001 there were 56 cases with seven deaths.
In 2002, 4,156 human cases of WNV encephalitis or WNV fever were reported, with 284 fatalities. During 2003, almost 10,000 human cases of WNV encephalitis and fever were reported from 46 states, with 208 fatalities. In 2004, there were some 2,500 human cases with 87 deaths, with the cases occurring primarily in the western United States. In 2005, there were 2,800 cases with 105 deaths.
In Ohio in 2005, WNV was reported in birds, mosquitoes, humans, and horses. There were 61 human and 15 horse cases identified. It is expected that WNV will continue to be a disease threat in 2006.
West Nile Virus is spread to people by the bite of an infected mosquito. The principal transmitter of West Nile Virus is the Northern House Mosquito (Culex pipiens). Mosquitoes first become exposed to the virus when they feed on birds that are infected with WNV. Once the mosquito is infected, it may transmit the virus to people or other animals when it bites them. Many birds can be infected with WNV, but crows and blue jays are most likely to die from the infection. Horses, too, are prone to severe WNV infection. People cannot get WNV from another person or a horse that has the disease.
Continued spread of this disease among wild birds and mosquitoes is anticipated. State, federal, and local agencies are working together to address the health risks of WNV to Ohio families and their animals. Public health officials found WNV in many species of birds, mosquitoes, and horses in 44 Ohio counties during 2005. Once this was known, mosquito control efforts were increased in those areas to protect people from the disease.
No. Mosquitoes are generally considered a nuisance pest, but they occasionally can transmit disease. Sixty-four different species of mosquitoes are known to occur in Ohio. While most cannot transmit WNV, several mosquito species common to Ohio are known to be carriers of WNV. Only female mosquitoes bite. They do this to get a blood meal for developing their eggs.
The mosquito that carries WNV typically lays its eggs in stagnant water and water-holding containers. Weeds, tall grass, and shrubbery provide an outdoor harborage for adult mosquitoes.
Many mosquitoes are most active two to three hours before and after dusk and again at dawn when the air is calm. This is the time when the females are most likely to bite. However, some species will feed at any time of the day.
Most people have become infected in summer or early fall when mosquitoes are most numerous.
Yes. During the winter months of 2000, health workers in New York City found over-wintering mosquitoes that contained evidence of WNV.
No. During the last six years, the states reporting WNV activity found many different bird species infected with WNV. However, crows and blue jays appear to be the most susceptible. This observation is not completely understood.
Yes. Other animals have also been found to be infected and have died from WNV. During the year 2000, reports from the Eastern states found WNV infecting 58 horses, two bats, a domestic rabbit, a skunk, a cat, a gray squirrel, and a chipmunk.
No. The virus is not spread by person-to-person contact, and there is no evidence that people can get the disease by handling infected animals.
Most people who are bitten by an infected mosquito will demonstrate no signs or symptoms. However, some will experience a mild infection with a slight fever, headache, body aches, and sometimes a skin rash or swollen lymph glands. Symptoms usually occur five to 15 days after being bitten by an infected mosquito. A very small number of people will suffer from a severe infection that is marked by a rapid onset of a high fever, a severe headache, neck stiffness, nausea or vomiting, confusion, muscle weakness or paralysis, seizures, coma, and, rarely, death.
While everyone exposed to a mosquito that carries the WNV is susceptible, people at greatest risk are those older than 50. Those who are immune-compromised may also be at greater risk. During the outbreak in New York City in 1999, everyone who died from WNV infection was 75 years of age or older. However, in 2001, two people in their 40s died from WNV infection.
To diagnose a WNV infection, a doctor will need to test either blood or cerebrospinal fluid from a spinal tap for antibodies to the virus. A second blood test is required two to three weeks later to confirm the diagnosis.
No, there is no specific treatment for WNV infection. While many people will not know that they have been exposed, nearly all of those with symptoms will fully recover. However, in some severe cases, hospitalization may be needed. There is no vaccine for WNV. There are no antibiotics or antiviral medications that can be used in the treatment of WNV. All care is supportive.
Yes. There are several other viruses circulating among mosquitoes in Ohio that can cause encephalitis. St. Louis Encephalitis, which is closely related to WNV, caused a major epidemic in 1975, resulting in 416 human cases and 29 fatalities. Every year, about 14 Ohioans, primarily children, are affected with La Crosse Encephalitis. In 1991, an outbreak of Eastern Equine Encephalitis affected horses in the Killbuck Marsh area in Holmes and Wayne Counties. Of the 19 laboratory-confirmed cases, 17 horses died.
The Ohio Department of Health, in collaboration with local health departments, has an ongoing program to monitor for these diseases. Although each of these viruses is somewhat different, prevention is basically the same — reduce the mosquito population and protect yourself from mosquito bites, especially during the summer and early fall.
You can reduce the number of mosquitoes around your home and neighborhood by eliminating places where they lay their eggs. Young mosquitoes are aquatic, and they must have standing water to develop from egg to adult. Here are some simple steps you can take:
The best way is to avoid being bitten by mosquitoes. Use personal protection while outdoors when mosquitoes are present.
These actions will reduce your chances of being bitten by mosquitoes:
During the fall of 2000, the Ohio Department of Health, in conjunction with the Ohio Departments of Agriculture, Environmental Protection Agency, and Natural Resources; The Ohio State University; the United States Department of Agriculture; and our local partners and other colleagues, organized a working group to address this emerging problem. The goal of the work group is to protect people and domestic animals from West Nile and other arboviral diseases. An integrated pest management (IPM) approach to accomplish this goal includes the following:
WNV was confirmed in Ohio in 2005. Infected mosquitoes, birds, horses, and humans were found in 44 Ohio counties in 2005. Therefore, it is likely that the virus is present throughout the state. Contact your local health department or log on to the web sites listed here for the current status on WNV in Ohio and for more information:
Ohio State University:
prevmed.vet.ohio-state.edu/Extension/WestNile/WNV.htm
Ohio Department of Health:
www.odh.state.oh.us/ODHPrograms/ZOODIS/ZooMain1.htm
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Keith L. Smith, Associate Vice President for Agricultural Administration and Director, OSU Extension TDD No. 800-589-8292 (Ohio only) or 614-292-1868