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



©2006 RKD Peterson

West Nile Virus

Morbidity



Introduction

      Few data exist regarding long-term morbidity after West Nile infection. Substantial morbidity may follow hospitalization for West Nile infection (Petersen et al. 2003), but is also observed in patients with West Nile fever (Watson et al. 2004). Encephalitis cases seem to have more variable outcomes than meningitis cases, which tend to recover well (Granwehr et al. 2004). Very limited recovery has been observed in acute flaccid paralysis cases (Sejvar et al. 2003 a, b).

      Although patients with West Nile fever tend to recover well, median recovery time was 60 days for patients in Illinois in 2002 (Watson et al. 2004). The disease also has great impact on the patients’ lifestyle. Of 98 respondents with West Nile fever, 57 (58%) missed work/school, 82 (84%) had household activities limited, 47 (49%) had difficulty walking, and 89 (91%) had outside-of-home activities limited (Watson et al. 2004), which illustrate the substantial morbidity observed even with West Nile fever.

      In 2000, only 7 out of 19 (37%) of hospitalized patients in New York and New Jersey presented full recovery, while 10 (53%) had improved, but did not achieve previous level of function, and 4 (21%) were discharged to a long-term care facility (Weiss et al. 2001). Pepperell et al. (2003) reported that only 13 (28%) of 47 surviving Canadian patients were discharged home without assistance, 18 (38%) were either discharged home with extra support or moved in with relatives, and 16 (34%) were transferred to a rehabilitation facility, nursing home or acute care facility. Most still had neurologic deficits 30 days after discharge (Pepperell et al. 2003).

 In a long-term follow-up study on 42 West Nile encephalitis survivors 1 year after illness onset, only 37% presented full physical, functional and cognitive recoveries, and there was a substantially higher prevalence of impairment compared to baseline (Nash et al. 2001). Similarly, only 2 out of 8 (25%) patients in a study in New York presented full recovery after 1 year, 3 (37.5%) had neurological sequelae, and 1 (12.5%) had minimal impairment after 18 months (Asnis et al. 2001).
      Acute flaccid paralysis is a common neurologic complication,and the prognosis is usually poor (Saad et al. 2005). Deaths seem to be associated to paralytic involvement of all four extremities (Saad et al. 2005). At discharge, all 3 patients with acute flaccid paralysis, hospitalized in St. Tammany Parish, LA, showed no improvement in limb weakness (Sejvar et al. 2003a). These patients, as well as 2 (25%) of 8 patients with West Nile encephalitis, were discharged to a long-term rehabilitation facility and required walkers or wheelchairs for ambulation (Sejvar et al. 2003a). These studies suggest that most patients do not recover completely, and patients from all age groups usually have persistent weakness (Saad et al. 2005). From 16 WNV seropositive patients (West Nile meningitis, encephalitis and acute flaccid paralysis patients), 11 (68.75%) were discharged home, functionally independent, 3 (18.75%) were discharged home but dependent, 1 (6.25%) required rehabilitation, and 1 (6.25%) died (Sejvar et al. 2003a). Symptoms that still persisted in a follow-up study of these 15 WNV seropositive survivors at 8 months after discharge were fatigue (66.7%), myalgias (20%), and headaches (13.3%) (Sejvar et al. 2003a). At 8 months after discharge, 4 (50%) of 8  WN encephalitis patients showed persistent cognitive deficits (Sejvar et al. 2003a). All patients with WN meningitis reported normal or near-normal functioning at 8-month follow-up, while 62.5% of patients with severe WN encephalitis achieved previous functional levels within 4 months of illness (Sejvar et al. 2003a). Neurologic sequelae have been reported to cause complications in 31% of a cohort of elderly WN meningoencephalitis survivors (Berner et al. 2003), but may affect as many as 50% (Weiss et al. 2001, Petersen and Marfin 2002).

      Pediatric cases with clinical manifestations are relatively rare (Yim et al. 2004), and severe neurologic disease is more common among adults than children (Hayes and O’Leary 2004). In the few reports of pediatric cases, symptoms usually resolved in 5 to 6 days (Yim et al. 2004). There is one report of an 11-year-old girl with previous history of seizures who had mental status changes that persisted for more than 6 months and is still far from her baseline function (Yim et al. 2004). Another patient, a 9-year-old girl, required 6 months for complete recovery of her vision (Yim et al. 2004), but other than these few reports, clinical descriptions of WNV infection in children are scarce, and seem not no present substantial morbidity.

Epidemiology

Symptoms

Risk Factors

Morbidity
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References

Asnis, D.S., R. Conetta, G. Waldman, and A. A. Teixeira. 2001. The West Nile Virus Encephalitis Outbreak in the United States (1999-2000) – From Flushing, New York, to beyond its borders. Ann. N. Y. Acad. Sci. Dec 2001, 951: 161-171.

Berner, Y.N., R. Lang, and M.Y. Chowers. 2003. Outcome of West Nile Fever in Older Adults. J. Am. Geriatr. Soc. 51: 1844-1846.

Granwehr, B.P., K.M. Lillibridge, S. Higgs, P.W. Mason, J.F. Aronson, G.A. Campbell, and A.D.T. Barrett. 2004. West Nile virus: where are we now? Lancet Infect. Dis. 4: 547-556.

Hayes, E.B. and D.R. O’Leary. 2004. West Nile virus infection: a pediatric perspective. Pediatrics. 113: 1375-1381.

Nash, D., A. Labowitz, B. Maldin, D. Martin, F. Mostashari, A. Fine, J.T. Roehrig, G. Campbell, and M. Layton. 2001. A follow-up study of persons infected with West Nile Virus during a 1999 outbreak in the New York City Area. Abstracts of the IDSA 39th Annual Meeting. Clinical Infectious Diseases 33(7):1092.

Pepperell, C., N. Rau, S. Krajden, R. Kern, A. Humar, B. Mederski, A. Simor, D.E. Low, A. McGeer, T. Mazzulli, J. Burton, C. Jaigobin, M. Fearon, H. Artsob, M.A. Drebot, W. Halliday, and J. Brunton. 2003. West Nile virus infection in 2002: morbidity and mortality among patient admitted to hospital in southcentral Ontario. CMAJ. 168(11): 1399-1405.

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

Petersen, L.R., A.A. Marfin, and D.J. Gubler. 2003. West Nile Virus. JAMA 290(4): 524-528.

Saad, M., S. Youssef, D. Kirschke, M. Shubair, D. Haddadin, J. Myers, and J. Moorman. 2005. Acute flaccide paralysis: the spectrum of a newly recognized complication of West Nile virus infection. J. Infec. 51: 120-127.

Sejvar, J.J., M.B. Haddad, B.C. Tierney, G.L. Campbell, A.A. Marfin, J.A. Van Gerpen, A. Fleischauer, A.A. Leis, D.S. Stokic, and L.R. Petersen. 2003a. Neurologic manifestations and outcome of West Nile virus infection. JAMA 290(4): 511-515.

Sejvar, J.J., A.A. Leis, D.S. Stokic, J.A. Van Gerpen, A.A. Marfin, R. Webb, M.B. Haddad, B.C. Tierney, S.A. Slavinski, J.L. Polk, V. Dostrow, M. Winkelmann, and L.R. Petersen. 2003b. Acute Flaccid Paralysis and West Nile Infection. Emerg. Infect. Dis. 9(7): 788-793.

Watson, J.T., P.E. Pertel, R.C. Jones, A.M. Siston, W.S. Paul, C.C. Austin, and S. I. Gerber. 2004. Clinical characteristics and functional outcomes of West Nile fever. Ann. Inter. Med. 141: 360-365.

Weiss, D., D. Carr, J. Kellachan, C. Tan, M. Philips, E. Bresnitz, and M. Layton. 2001. Clinical findings of West Nile virus infection in hospitalized patients, New York and New Jersey, 2000. Emerg. Infec. Dis. 7(4): 654-658.

Yim, R., K.M. Posfay-Barbe, D. Nolt, G. Fatula, and E.R. Wald. 2004. Spectrum of clinical manifestations of West Nile virus infection in children. Pediatrics. 114(6): 1673-1675.
 
 
 
 
 
 

       
Although we provide general information on West Nile Virus (WNV), this web site is designed primarily to provide information on human-health and ecological risk assessments of WNV and tactics used for mosquito management.