West Nile virus infection can have serious, long-term effects

Neuroinvasive disease can cause poliomyelitis, cognitive disorders and lingering clinical syndromes.

Issue: July 2007

Long-term effects of West Nile virus neurovasive disease, including parkinsonism tremors, poliomyelitis, meningitis and cognitive disorders, may occur in more than one third of patients with confirmed infections.

“Although the vast majority of the people who are infected with the virus do fine, you don’t want to take that chance of ending up having persistent, lingering problems,” said James J. Sejvar, MD, a neuroepidemiologist at the CDC Division of Vector-Borne Infectious Diseases and Viral Rickettsial Diseases of the National Center for Zoonotic Vector-Borne and Enteric Diseases. “Physicians need to be aware of these potential persistent problems following initial recovery and should remain cognizant of them as they follow up patients.”

Many people go on to recover fully from West Nile virus, but data suggests 30% to 50% who develop severe neuroinvasive disease have persistent problems that limit both functional abilities and quality of life. Since its emergence in the United States in 1999, more than 23,500 cases of human West Nile virus infection have been reported as of November 2006. Of those, 9,800 patients have neuroinvasive disease and 943 died as a result of West Nile virus infection.

The most common lingering effects are subjective, including overwhelming fatigue, difficulty with concentration and sleep disorders.

“It’s a smaller percentage who have the severe movement disorders and tremors, but all of them can be relatively functionally impairing,” Sejvar said.

Physicians should extend follow-up for patients with confirmed West Nile virus infection, including those with apparently mild acute cases, to assess impaired neurological and motor functions.

Sejvar based his recommendations on a summary he wrote on long-term outcomes of West Nile Virus infection. His summary, one of the first on long-term effects of West Nile virus, was published in Clinical Infectious Diseases.

Disease outcomes

West Nile meningitis accounts for about 40% of cases of West Nile virus neuroinvasive disease. Median patient age is usually similar to those with febrile illness. People with meningitis frequently have persistent fatigue, weakness and difficulties with concentration.

West Nile encephalitis occurs most frequently in people older than 55 and in those with compromised immunity. Fatality rates in hospital are estimated at 20% from West Nile encephalitis. Patients who survive acute illness with West Nile encephalitis can develop persistent neurologic sequelae. In one study, six (38%) of 16 patients with West Nile virus infection from the 2002 Louisiana epidemic had tremors and parkinsonism eight months after recovery from acute illness. In a North Dakota study, new or persistent tremor occurred in 20% of patients a year after acute illness, and tremors persisted more than 1.5 years in 18% of patients with confirmed West Nile neuroinvasive disease in a northern Colorado study cohort.

Poliomyelitis rates due to West Nile virus infection have been difficult to assess, but researchers in one study estimated poliomyelitis occurred in about 10% of patients hospitalized with neuroinvasive disease. Acute neuromuscular respiratory failure, the most severe manifestation of poliomyelitis in West Nile virus patients, is associated with high mortality estimated at greater than 50%. Facial nerve palsy, which could be estimated to occur in up to 70% of patients with West Nile poliomyelitis, is also of concern.

Outbreak predictions

West Nile virus peak years may be difficult to predict, but the geographical prevalence of the virus can be mapped and measured.

“It is notable that West Nile is endemic in most of the United States and there are certain regions that continue to experience hot spots or epidemics, especially in the Midwest and the western United States,” Sejvar said. The Northwestern part of the United States also showed West Nile epidemic last year.

There is no definitive treatment for most of the sequelae of West Nile neuroinvasive disease. The management of the conditions such as fatigue, movement disorders and polio is through supportive physical and occupational therapy.

Medicines provided to treat Parkinson’s disease elicit poor response in post encephalitic Parkinsonism patients, so people with West Nile virus neuroinvasive diseases would likely not benefit from Parkinson-specific medications. There have not been any randomized, controlled assessments of these treatments for West Nile virus.

“West Nile virus is a preventable disease and although the overall risk for developing lingering and ongoing problems is relatively small, it does occur and you don’t want to take that chance,” Sejvar said. – by Kirsten H. Ellis

For more information:

Sejvar JJ. The long-term outcomes of human West Nile virus infection. Clin Infect Dis. 2007;44:1617-1624.