Literature Commentary by Dr. John G. Bartlett: Viral Infections, January 2008

John G. Bartlett, MD


January 09, 2008

West Nile Virus

Sejvar JJ. The long-term outcomes of human West Nile virus infection. Clin Infect Dis. 2007;44:1617-1624. The author is from the Division of Vector-Borne Infectious Diseases at the CDC and provides an authoritative review of the neurologic complications of West Nile virus (WNV) infection. It should be emphasized that only approximately 20% of persons who have serologic evidence of WNV infection have reported clinical symptoms, which are usually characterized by abrupt onset of fever, headache, malaise, anorexia, and nausea. These acute symptoms generally resolve in 2-6 days, but what is perhaps less well known and understood is that many or most have persistent symptoms of "extreme fatigue." This applies to young patients as well as the more vulnerable elderly patients. In fact, 96% of patients with WNV in one series described fatigue that persisted for a median of 36 days.[6] The self-assessment in these patients indicate high rates of fatigue, weakness, and problems with concentration.[7,8]

Neurologic Disease: About 20% of patients with WNV infection show symptomatic disease, and about 1% of all patients (presumably 5% of the 20%) have West Nile neuroinvasive disease (WNND). These are divided into 3 syndromes which have substantial overlap and include West Nile meningitis (WNM), West Nile encephalitis (WNE), and West Nile poliomyelitis (WNP). See Table 3 .

West Nile Meningitis: This category accounts for about 40% of the neuroinvasive complications of WNV infection. The accompanying symptoms and median age of patients are similar to those with West Nile fever (WNF). Hospitalization is required more frequently, but primarily for pain control for the headache or rehydration due to nausea, vomiting, and poor oral intake.[9] These patients often have persistent fatigue and problems with concentration and memory, as noted with patients with WNF.[10]

West Nile Encephalitis: This occurs primarily in persons over 55 years of age and occurs with immunosuppression. WNE is associated with substantial short-term and long-term morbidity and mortality.[11] The mortality rate is generally reported to be approximately 20% and is usually attributed to acute respiratory failure or cardiac complications.[12,13] The neurologic sequelae often involve movement disorders and extrapyramidal involvement that may be transient or may last for days, weeks, or even years. The frequency among those with WNE is reported at 20% to 40%, although many of these symptoms are often mild and not disabling.[7,9] However, a substantial number of these patients also require rehabilitation services with physical, occupational, or speech therapy.[14] It should be noted that the severity of initial neurologic symptoms may not reflect the ultimate functional outcome.

West Nile Poliomyelitis: This is the flaccid paralysis or poliomyelitis that results from involvement of the lower motor neurons or anterior horn cells of the spinal cord as seen with polio virus infection. It is associated with substantial morbidity and mortality. The current estimate is that it accounts for about 10% of persons hospitalized with WNND.[12] Some will have respiratory failure and require prolonged intubation; the mortality rate in this subset may exceed 50%, and most of the strength that can be recovered will be noted in the first 6-8 months. Again, the severity of the initial paralysis does not necessarily predict outcome, and some patients with severe quadriplegia have had complete recovery.

Summary: The author notes that through November 2006 there have been more than 23,500 cases of WNV in the United States, including 9700 cases of neuroinvasive disease and 904 fatalities. However, he concludes that the acute morbidity and mortality is the "tip of the iceberg" with respect to the long-term consequences of this infection. Even those with mild cases of WNF will frequently have subjective somatic complaints for prolonged periods that include profound fatigue, cognitive complaints, and problems with memory and concentration, although these have been not documented extensively with normal testing. Many with neuroinvasive disease will have some substantial morbidity and mortality. WNE survivors will have relatively high rates of subsequent movement disorders that sometimes require long-term rehabilitation services. Those with WNP have high mortality rates and sequelae analogous to the experience with paralytic polio.


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