Department of Land Resources & Environmental Sciences
Montana State University
Bozeman, MT 

       There seems to be no difference in distribution of WNV infection among age groups and between sexes (Nash et al. 2001, Tyler 2001), but, for unknown reasons, males appear to be at higher risk for WN neuroinvasive illness (Petersen and Marfin 2002, O’Leary et al. 2004). Children who are infected with WNV usually show no symptoms or only have a mild fever (Hayes and O’Leary 2004).

       The incidence of encephalitis and death increases with age (Tsai et al. 1998, Nash et al. 2001, Weinberger et al. 2001, O’Leary et al. 2004). Weiss et al. (2001) reported that persons ³ 50 years of age were more likely to present meningoencephalitis and had increased mortality rate, and other reports show that the incidence of neurologic symptoms and death may increase 10- (Sampathkumar 2003) to 20-fold (Nash et al. 2001, Tyler 2001) among persons ³ 50 years old. The risk for persons ³ 80 is 43 times higher (Sampathkumar 2003). Sixteen out of 18 fatal cases (89%) in 1999-2001 were > 60 years of age, with a median age of 75 (range 44 – 90) (Marfin et al. 2001). Pediatric cases of WNV infection seem to be relatively rare (Yim et al. 2004). In 2002, only 3.6% of cases were reported in people <19 years old (CDC 2003, Hayes and O’Leary 2004), and 1.3% of reported cases were in children <10 years old (Hayes and O’Leary 2004). No fatalities were reported in children or adolescents that year (Hayes and O’Leary 2004).
       Besides old age, the level of immunosuppression and diabetes mellitus are also considered risk factors (Granwehr et al. 2004, Jeha 2004). Other factors that have been postulated as important risk factors for severe disease include hypertension and cerebrovascular disease (Lillibridge et al. 2004). Diabetes and hypertension are independent risk factors for increased permeability of the blood-brain barrier (Lorenzi et al. 1986, Mooradian 1997, Kaya et al. 2003).

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Jeha, L.E. 2004. West Nile Virus in the Elderly: Transmission, Diagnosis and Treatment. Geriatric Times. Sept/Oct. 2004. 9-12.

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Lorenzi, M., D.P. Healy, R. Hawkins, J.M. Printz, and M.P. Printz. 1986. Studies on the permeability of the blood-brain barrier in experimental diabetes. Diabetologia. 29: 58-62.

Marfin, A.A., L.R. Petersen, M. Eidson, J. Miller, J. Hadler, C. Farello, B. Werner, G.L. Campbell, M. Layton, P. Smith, E. Bresnitz, M. Cartter, J. Scaletta, G. Obiri, M. Bunning, R.C. Craven, J.T. Roehrig, K.G. Julian, S.R. Hinten, D.J. Gubler, and the ArboNET Cooperative Surveillance Group. 2001. Widespread West Nile Virus Activity, Eastern United States, 2000. Emerg. Infect. Dis. 7(4): 730-735.

Mooradian, A.D. 1997. Central nervous system complications of diabetes mellitus: a perspective from the blood-brain barrier. Brain Res. Rev. 23: 210-218.

Nash, D., F. Mostashari, A. Fine, J. Miller, D. O’Leary, K. Murray, A. Huang, A. Rosenberg, A. Greenberg, M. Sherman, S. Wong, and M. Layton. 2001. The outbreak of West Nile virus infection in the New York City area in 1999. N. Engl. J. Med. 344(24): 1807-1814.

O’Leary, D. R., A.A. Marfin, S.P. Montgomery, A.M. Kipp, J.A. Lehman, B.J.Biggerstaff, V.l. Elko, P.D. Collins, J.E. Jones, and G. L. Campbell. 2004. The epidemic of West Nile virus in the United States, 2002. Vector Borne Zoonotic Dis. 4(1): 61-70.

Petersen, L.R. and A.A. Marfin. 2002. West Nile virus: a primer for the clinician. Ann. Inter. Med. 137: 173-179.

Sampathkumar, P. 2003. West Nile Virus: Epidemiology, Clinical Presentation, Diagnosis, and Prevention. Mayo Clin. Proc. 78: 1137-1144.

Tsai, T.F., F. Popovici, G.L. Campbell, and N.I. Nedelcu. 1998. West Nile encephalitis epidemic in southeastern Romania. Lancet Infec. Dis. 352: 1-5.

Tyler, K.L. 2001. West Nile Virus Encephalitis in America. N. Engl. J. Med. 344(24): 1858-1859.