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 [11].

Prevention

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/ [12].

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 [10]).

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

• Encourage body cover (long pants, shirts, socks, hats) as appropriate for the weather and activity. Shirts should be tucked in at the waist; socks should be pulled over pant legs.
• Apply an insect repellent containing 10 percent to 30 percent (recommended for children) to50 percent DEET. Reapply per package directions throughout the duration of the activity. Recommend spraying the repellent on clothing rather than skin when feasible. It does not need to be applied under clothing. Avoid eye and mouth areas, as well as cuts, wounds, and irritated skin. Avoid using sprays in enclosed areas. Do not use DEET near food. Consider creating related policies to ensure safe and consistent use of repellents, such as supervision or application of repellents by counseling staff. Wash repellent off skin when returning indoors, especially if repeated applications are used.
• Educate staff — especially those who live with campers or who accompany groups of campers from activity to activity — to notice children who are getting bitten by mosquitoes. Assess those campers for appropriate use of their repellent. Be prepared to try a different repellent if the camper’s formulation is ineffective at repelling mosquitoes.
• Avoid mosquito-borne habitats (wooded areas and marshes) during the dusk and dawn periods — a mosquito’s peak biting time. Avoid campouts near marshes and other wet areas.
• Monitor activity areas — are campers or staff commenting that mosquitoes are typically bad in certain areas?

Minimize the Mosquito Population

• Alert maintenance staff to eliminate areas of standing water (gutters, old barrels, boats, buckets) and keep window screens in good repair.
• Reduce exposure to mosquitoes’ long grass habitat by mowing paths of hiking trails; consider widening trails to further limit exposure.
• Be aware of measures being taken or recommended by local municipalities to decrease the mosquito population, such as pesticide spraying.
• Review and adapt the camp schedule as necessary to avoid use of outdoor activity areas when mosquitoes are heaviest.

Recognize Clinically Significant Cases

• Be aware of local guidelines for West Nile Virus testing. Ensure that access to reliable, up-to-date information (see sidebar on page 13) is available to health-care providers. In addition, work with the camp’s nurse and supervising physician to determine a case profile under which potential for West Nile Virus infection should be considered, and educate camp administrative staff to this directive. Currently, only persons with signs and symptoms of neurological disease should be tested for West Nile Virus. Patients with milder illnesses (e.g., fever and rash, fever and headache, lymphadenopathy) DO NOT need to be tested for West Nile Virus (5). Bear in mind that West Nile is only one in the family of viruses that cause illness affecting the central nervous system, which also includes California, Eastern equine, Powassan, St Louis, Venezuelan equine, and Western equine encephalitis (4).
• Any camper or staff with persistent high fever, altered mental status, focal neurological signs, significant muscle weakness, or other signs/symptoms suggestive of meningitis or encephalitis should be referred for physician evaluation.
• Campers or staff with fever, general malaise, headache, body aches, and/or swollen lymph nodes should be monitored and treated symptomatically per the individual camp’s health-care guidelines.

Partner with Parents

• Include a few sentences in precamp mailings regarding the measures your camp is taking to minimize risks from West Nile Virus.
• Make sure your packing list recommends an insect repellent containing adequate amounts of DEET.
• Have staff model appropriate repellent use and dress on opening day.

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.

Deet Recommendations [10]

References
1. Petersen, L.R., & Marfin, A.A. (2002). West Nile virus: A primer for the clinician. Annals of Internal Medicine, 137(3), E173-E178.
2. Centers for Disease Control (2002). Web site, www.cdc.gov [13].
3. Mostashari F., Bunning M.L., Kitsutani P.T., Singer D.A., Nash D., Cooper M.J., et al. (1999). Epidemic West Nile encephalitis, New York, 1999: Results of a household-based seroepidemiological survey. Lancet. 2001;358:261-4.
4. Kennedy, K. (2002). Calming West Nile fears. AAP Web site, www.aap.org/family/wnv-sept02.htm [14]. American Academy of Pediatrics.
5. Zimmerman, R.S. (2002). PA Dept. of Health: Health Alert # 31.

Reviewers
Mary Marugg, R.N., Sonlight Christian Camp, Pagosa Springs, Colorado
Susan Van Cleve, M.S.N., R.N., C.P.N.P., P.N.P., program director, University of Pittsburgh, Pennsylvania
John J. LaBella, M.D., pediatrician, Children’sCommunity Pediatrics, Pittsburgh, Pennsylvania

Ellen Reynolds, M.S.N., C.P.N.P., is a pediatric nurse practitioner with Children’s Community Pediatrics in Pittsburgh, Pennsylvania. She is also a camp nurse, with many years of affiliation with Concordia Language Villages in Minnesota. Ellen is serving her second term with the Association of Camp Nurse’s (ACN) Board of Directors, currently in the role of clinical chair.

Holly Bauer, R.N., is the health-care supervisor at the Lions Camp in Rosholt, Wisconsin. She is a regional facilitator and board member-at-large for ACN.

Originally published in the 2003 March/April issue of Camping Magazine.