virus was first isolated from an adult woman in the West Nile District of Uganda in 1937. The ecology was characterized in Egypt in the 1950 s. The virus became recognized as a cause of severe human meningoencephalitis (inflammation of the spinal cord and brain) in elderly patients during an outbreak in Israel in 1957. Equine disease was first noted in Egypt and France in the early 1960 s. The first appearance of WN virus in North America in 1999, with encephalitis reported in humans and horses, and the subsequent spread in the United States may be an important milestone in the evolving history of this virus.
West Nile Virus” is a flavivirus commonly found in Africa, West Asia, and the Middle East.
It is closely related to St. Louis encephalitis virus found in the United States. The virus can infect humans, birds, mosquitoes, horses and some other mammals.
While all residents of areas where virus activity has been identified are at risk of getting West Nile encephalitis; persons over 50 years of age have the highest risk of severe disease. It is unknown whether people suffering from autoimmune disorders are at increased risk for West Nile Virus.
West Nile Virus is an “arbovirus” that causes encephalitis (inflammation to the brain). Blood-feeding insects such as mosquitoes transmit these viruses. Mosquitoes draw the virus from infected birds and transmit it to animals and humans through bites. During the incubation period the West Nile Virus multiplies in the persons’ blood system and crosses the blood brain barrier to reach the brain. The virus interferes with normal central nervous system functioning and causes inflammation of brain tissue. A person contracting WNV is assumed to develop an immunity that will be lifelong, but it may wane in later years.
Most infections with WNV have been identified in wild birds, but the virus can also infect horses, dogs, cats, domestic rabbits, domestic birds as well as humans.
West Nile virus may be transmitted when an infected mosquito bites a human to take in blood. Mosquitoes become infected when they feed on infected birds, which may circulate the virus in their blood for a few days. The virus is located in the mosquito’s salivary glands. During blood feeding, the virus may be injected into humans, where it can multiply and possibly cause illness.
In addition, a recent investigation has confirmed West Nile Virus transmission through transplanted organs.
Investigations of other patients who developed WNV infection within several weeks of receiving blood products or organs are ongoing to determine whether WNV was transmitted by transfusion or transplantation in any of these cases.
The incubation period in humans (from time of infection to onset of disease symptoms) is usually 3 to 14 days. If you are determined to be at high risk and have symptoms of West Nile encephalitis, your provider will draw a blood sample and send it to a commercial or public health laboratory for confirmation.
Contact your health care provider if you have concerns about your health.
If you or your family members develop symptoms such as high fever, confusion, muscle weakness, and severe headaches, you should see your doctor immediately.
There is no specific treatment for West Nile virus infection. In more severe cases, intensive supportive therapy is indicated, often involving hospitalization, intravenous fluids, airway management, respiratory support (ventilator), prevention of secondary infections (pneumonia, urinary tract, etc. ), and good nursing care.
Because West Nile Virus is a virus and not a bacterial infection, there is no magic pill that will cure the patient. Viruses are totally immune to the effects of antibiotics.
At the present time, there is no vaccine but several companies are working towards developing one.
There are no side effects associated with the treatment methods used. However there are known side effects associated with one of the methods used in prevention. Many insect repellents are made with Permethrin (or DEET), which has received great attention not only for its excellent repellent qualities, but its possible adverse effects related to developmental defects, as a cause of cancer, and its general effect on the environment.
Apply insect repellent sparingly to exposed skin. The more DEET a repellent contains the longer time it can protect you from mosquito bites. A higher percentage of DEET in a repellent does not mean that your protection is better-just that it will last longer. DEET concentrations higher than 50% do not increase the length of protection. Choose a repellent that provides protection for the amount of time that you will be outdoors… Spray clothing with repellents containing permethrin or DEET since mosquitoes may bite through thin clothing.
Do not apply repellents containing permethrin directly to exposed skin. If you spray your clothing, there is no need to spray repellent containing DEET on the skin under your clothing… When possible, wear long-sleeved shirts and long pants whenever you are outdoors… Place mosquito netting over infant carriers when you are outdoors with infants… Consider staying indoors at dawn, dusk, and in the early evening, which are peak mosquito biting times. Install or repair window and door screens so that mosquitoes cannot get indoors.
Help reduce the number of mosquitoes in areas outdoors where you work or play, by draining sources of standing water. In this way, you reduce the number of places mosquitoes can lay their eggs and breed… At least once or twice a week, empty water from flower pots, pet food and water dishes, birdbaths, swimming pool covers, buckets, barrels, and cans… Check for clogged rain gutters and clean them out… Remove discarded tires, and other items that could collect water…
Be sure to check for containers or trash in places that may be hard to see, such as under bushes or under your home.
The public can play an important role in monitoring West Nile virus through reporting dead birds to state and local health departments. However, in some areas, birds are no longer being collected. In addition, state and local agencies have different policies for collecting and testing birds.
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West Nile Story
by Dickson Despommier Ph. D.
, Robert J. Demarest (Illustrator)
Malaria, West Nile, and Other Mosquito-Borne Diseases (Diseases and People)
by Nancy Day.