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West Nile Virus: A Clinical Commentary for the Camp Health Care Community — Outdoor Hazards and Preventive Measures
Ah, summertime . . . camp . . . outdoor activities . . . water sports . . . jokes about the mosquito being the “camp bird” . . . phone calls from parents concerned about West Nile Virus . . .
The appearance of West Nile Virus in recent years is perhaps the most well-documented introduction of a new, vector-borne human pathogen into the U.S. in this century. Because of the spread of the virus via mosquitoes, the virus is of particular concern for camps located in rural, wooded, or wilderness areas. While the virus causes encephalitis and meningitis in serious cases, most cases are mild and require only symptomatic care. Education and prevention measures can help to place concerns about the disease in proper perspective.
Incidence and Spread
West Nile Virus was first isolated from an infected person and identified in Uganda in 1937. Until 1999, the virus was found only in the Eastern Hemisphere. Infrequent human outbreaks, mostly associated with mild illnesses in which fever was the main symptom, had been reported mostly in groups of soldiers, children, and otherwise healthy adults in Israel and Africa. Since the mid-1990s, the frequency and severity of West Nile Virus outbreaks have increased (1). United States public health surveillance has tracked disease caused by West Nile Virus each year since 1999, when it first appeared in New York City. These cases have been identified over an expanding geographic area (one state in 1999, three in 2000, and ten in 2001) (1). From January 1 to October 10, 2002, there were 2946 cases of West Nile Virus identified in 35 states and the District of Columbia, including 160 deaths (2). Importantly, the increase in reported cases is due in part to heightened awareness, surveillance, and testing for the illness, and not simply out-of-control spread.
West Nile Virus is thought to be maintained in a cycle involving infected birds and mosquitoes, which in turn pass the virus on to humans. Many of the “bridge vectors” — mosquitoes that bite both birds and humans — likely become infected in late summer and then pose an infection threat to humans. West Nile Virus cannot be spread from human to human or from animal to humans. The peak of reported cases between 1999 and 2001 has occurred in August and September (1). In warm or tropical climates, year-round transmission is possible.
Clinical Features of West Nile Virus Illness
The incubation period of West Nile Virus is estimated to range from three to fourteen days. Most human infections are not clinically recognized, simply because those affected may never feel very sick. A survey of serology in residents of New York City during the 1999 outbreak indicated that only approximately 20 percent of persons infected with West Nile Virus had developed fever, and only half of these had visited a physician for this illness (3). Thus, the cases that are reported are those few that result in serious disease.
Mild disease is characterized as an illness of sudden onset consisting of mild to moderate fever with varied symptoms that may include headache, muscle aches, pains, weakness, nausea, vomiting, rash, and/or swollen lymph nodes. The symptoms generally last three to six days. It is not necessary for people with these general, mild, symptoms to be tested for West Nile Virus; in fact, it would be no more helpful in treating the person than knowing which specific virus is causing someone’s common cold. There is no specific antibiotic treatment for West Nile fever; comfort measures are usually all that is needed.
People with more serious West Nile Virus infections are likely to be very ill. In contrast to the above noted signs and symptoms, they are likely to have very high fever, neck stiffness, disorientation, lack of muscle coordination, tremors, and/or convulsions and paralysis. In these severe cases, physician evaluation and care should be sought immediately. Blood testing would be done in order to identify the virus and be certain of the diagnosis. Again, there is no specific antibiotic treatment. Hospital care would focus on supporting the body systems as needed.
In fatal cases, advanced age has been found to be the most important risk factor. Encephalitis (brain involvement), severe muscle weakness, and change in level of consciousness are also clinical factors associated with increased risk of death. Immunosuppressed people, such as those undergoing chemotherapy, those taking long-term steroids, and those taking anti-rejection transplant drugs, are likely to be at additional risk. West Nile Virus encephalitis has recently been added to the list of designated reportable illnesses. Local public health departments should be notified of any confirmed cases. Recommended clinical and laboratory case definitions for West Nile Virus are available at www.cdc.gov/ncidod/dvbid/westnile/resources/wnv-guidelines-apr-2001.pdf.
Currently, prevention of West Nile Virus infection rests on two strategies: (1) reducing the number of mosquitoes that could transmit the virus; and (2) preventing those “vector” mosquitoes from biting humans. Many mosquitoes breed in small pools of standing water and have a limited flight range, so reducing mosquito populations in the immediate vicinity of human habitat and activity is useful. Property owners and municipalities can drain water from potential breeding sites, and coordinate plans for use of insecticides. Biological products (which consist chiefly of larva-killing bacteria) as well as pesticide chemicals, may be used. More detailed information about pesticides and other mosquito control measures can be obtained from the US National Pesticide Information Center at www.ace.orst.edu/info/npic/wnv/.
DEET (N,N-diethyl-meta-toluamide) is the most effective mosquito repellent currently available. It is available in many formulations and has an excellent safety profile. Products containing 10-50 percent DEET are considered sufficient, with concentrations greater than 50 percent demonstrating little additional efficacy. Manufacturer’s recommendations should be followed for periodic re-application of the repellent. The American Academy of Pediatrics recommends that repellents containing no more than 30 percent DEET be used in children, and that DEET not be used on infants under the age of two months (4). DEET can be applied to skin, pets, clothing, tents, bedrolls, and screens. While other products such as Skin-so-Soft®, citronella, etc., have mild repellent properties, the use of DEET should be promoted in order to prevent infections such as West Nile Virus that spread via mosquitoes (see sidebar).
Implications and Recommendations for Camps
West Nile Virus is presumed to be spreading in a pattern that will distribute it across North America at some point. Camps frequently are located in lake or woodland areas where mosquito populations flourish, and camps generally place emphasis on doing activities outdoors. Yet, camps do have a responsibility to provide the safest possible environment and program guidelines for their staff and campers. These guidelines should focus both on prevention strategies that minimize the potential for West Nile Virus exposure and surveillance that identifies a potential outbreak. In addition, camps should be prepared to provide information and resources for concerned parents and participants. Because this challenge is newly emerging, staying linked with reliable information will be key.
Protect Staff and Campers
Minimize the Mosquito Population
Recognize Clinically Significant Cases
Partner with Parents
While West Nile Virus may cause serious illness in children and adults, the actual likelihood of infection is low. A combination of education and prevention strategies can have a significant impact on the perceived and actual risk of the virus to campers and staff.
Ellen Reynolds, M.S.N., C.P.N.P., is a pediatric nurse practitioner with Children’s Community Pediatrics in Pittsburgh, Pennsylvan