Abstract

Since its first recognition in North America in 1999, West Nile virus (WNV) has spread rapidly across the continent, but in many communities, rapid diagnostic tests for detection of WNV infection are not fully available. We describe a patient with extrapyramidal movement disorders and changes in the basal ganglia noted on magnetic resonance images that are characteristic of other flavivirus encephalitides and may help in the recognition of patients with West Nile encephalitis. Detailed molecular analysis suggested that, although our patient received a blood transfusion infected with WNV, the virus that caused his initial infection and encephalitis was probably acquired naturally from a mosquito.

West Nile virus (WNV) is a mosquito-borne flavivirus that caused >3800 cases of disease in humans in the United States in 2002 [1–3]. Most humans become infected with WNV after receiving a bite from an infected mosquito, although some have become infected after receiving infected blood products or transplanted organs [4]. West Nile encephalitis typically presents in elderly or immunocompromised patients with fever, a reduced level of consciousness, muscle weakness, and associated features, but in this patient group, the differential diagnosis for such nonspecific features is large. In the United States, WNV infection is usually diagnosed by the IgM ELISA, occasionally by RT-PCR, or by virus isolation from serum or CSF specimens. However, many communities in North America where the virus now circulates do not yet have diagnostic facilities fully established. Even where facilities are available, it may take several days for the results of such investigations to become available. Radiological investigations have the advantage of giving immediate results.

We report the clinical, MRI, and virological findings for an immunosuppressed resident of a WNV-affected area who received WNV-infected blood products and developed West Nile encephalitis characterized by an extrapyramidal movement disorder. Comparison of the patient's radiological and clinical features with those of other flavivirus encephalitides suggests that high signal changes in the basal ganglia may be useful indicators of West Nile encephalitis. Molecular analysis of the virus isolated from his CSF specimen and comparison with the virus detected in the blood products he received and with virus circulating locally in mosquitoes and birds indicated that, although he had received infected blood products, his encephalitis was probably naturally acquired.

Case Report

A 46-year-old man with chronic renal failure presented to the University of Texas Medical Branch at Galveston with a history of increasing fatigue for 1 week and 2 days of fever, rigors, and lethargy. He lived in a rural area of Texas where WNV activity had recently been reported, and he typically spent mornings and evenings on his porch, where he received multiple mosquito bites. He had felt increasing fatigue for 1 week. Two months before hospital admission, the patient had undergone cadaveric renal transplantation and was being treated with mycophenolate, tacrolimus, and prednisone. In the 2 months between transplantation and the current hospital admission, he had been healthy. His medical history included unsuccessful receipt of a renal transplant from a living, related donor 7 years before hospitalization and an episode of cryptococcal meningitis 4 years before hospitalization; the latter was treated successfully, and he had not received any blood products recently.

At examination, the patient was found to have fever (temperature, 40°C) and rigors, and he was lethargic. However, he seemed fully oriented, although his spouse noted that his memory was not quite as good as normal. The general examination revealed nothing remarkable; he had no rash or focal neurological signs. The next day, he became disoriented and had hypotension and diffuse diarrhea. CT of his head revealed nothing abnormal, and a lumbar puncture for detection of opportunistic infections revealed a WBC count of 35 cells/mm3 (predominantly neutrophils), an RBC count of 10 cells/mm3, a glucose level of 68 mg/dL (serum glucose level, 162 mg/dL), and a protein level of 54 mg/dL, but the results of examination were negative for bacteria and fungi. He started receiving the broad-spectrum anti-infective agents vancomycin, ceftriaxone, ampicillin, amphotericin B, and acyclovir.

By day 4 of hospitalization, the patient had become obtunded. His eyes opened spontaneously, with continuous conjugate nystagmus, both in the primary position and on lateral and vertical gaze that was at times vertical and at times horizontal. The findings of a cranial nerve examination were otherwise unremarkable. He would intermittently obey commands. Peripheral examination revealed a marked generalized stiffness of his axial musculature, with increased limb tone and brisk deep-tendon reflexes but flexor plantars. On this day, he experienced intermittent limb tremors, and, in response to pain, he developed rhythmic jerking of the limbs (myoclonus). An electroencephalogram showed global suppression of activity with low-amplitude theta and beta waves, and MRI revealed nothing abnormal. His hemoglobin level had decreased to 6.6 mg/dL, and he receiving a transfusion with 2 U of packed RBCs, with an additional 5 U being transfused during the next 3 weeks. He underwent intubation for airway protection, and Pseudomonas aeruginosa was cultured from a bronchoalveolar lavage specimen.

Examination of a second lumbar puncture specimen revealed a WBC count of 6 cells/mm3, now predominantly lymphocytes. All antirejection medications were withdrawn to prevent an overwhelming infection. By day 10 of hospitalization, the patient had developed rhythmic stereotyped chewing movements (bruxism). Additional MRI performed at this time revealed increased signal intensity on T2-weighted and fluid-attenuated inversion recovery images in both thalami, in the right caudate nucleus, and in the periventricular gray matter of the fourth ventricle at the vermis of the cerebellum (figure 1). Because of the possibility that these lesions represented lymphoma, a magnetic resonance spectroscopy study was performed. However, this did not reveal the depressed N-acetyl aspartate peak or a reversal of Hunter's angle, which would have been consistent with CNS lymphoma.

Figure 1

Fluid-attenuated inversion recovery images for a patient with West Nile encephalitis on day 10 of hospitalization showing increased signal intensity in the periventricular gray matter of the fourth ventricle at the vermis of the cerebellum (A and B) and increased signal intensity in both thalami and the right caudate nucleus (C and D).

Figure 1

Fluid-attenuated inversion recovery images for a patient with West Nile encephalitis on day 10 of hospitalization showing increased signal intensity in the periventricular gray matter of the fourth ventricle at the vermis of the cerebellum (A and B) and increased signal intensity in both thalami and the right caudate nucleus (C and D).

During the next 30 days, the patient's condition stabilized, and 2 separate MRIs (obtained on days 18 and 37 of hospitalization) showed that the high signal intensities were resolving. Subsequently, the bruxism, tremors, and hypertonia resolved, although the nystagmus persisted. The patient remained ventilator dependent, and although he was able to respond to the command to close his eyes, his limbs were flaccid and areflexic and had no power. He died on day 54 of hospitalization as preparations were being made to transfer him to a hospice. Samples of brain and spinal cord tissue were obtained at autopsy.

Virological Investigations

A sample of the first CSF specimen, obtained the day after hospital admission, caused cytopathic effects when inoculated into cultures of monkey kidney Vero cells. The virus isolate was subsequently confirmed to be WNV by an indirect fluorescent antibody test that used a WNV monoclonal antibody (H5-46), complement fixation test, and RT-PCR. No other virus isolates were recovered from the patient's serum, CSF, or brain tissue samples or from any of the 7 donor blood units (table 1). RT-PCR was performed on RNA extracted from the patient samples and from the donor blood units using primers for the 3′ half of the WNV envelope (E) protein (WN1751 and WN2504A) [5] and AMV reverse transcriptase (Roche). The products were cloned into pGEM-T Easy (Promega) and sequenced as described elsewhere [5]. In addition, the complete premembrane-envelope (PrM/E) gene region of the WNV isolated from the patient's CSF was sequenced directly. One of the donor blood units given on the 17th day of hospitalization and a serum sample obtained from the patient 6 days after that transfusion tested positive for WNV by RT-PCR. Nucleotide sequencing of these products confirmed their identity as being from lineage I WNV and showed that they were identical throughout the region analyzed. Analysis of the sequence of the CSF isolate and viral RNA extracted from brain tissue at autopsy showed that these too belonged to lineage I but differed from the blood product and serum virus. Therefore, the sequences were compared with those of bird and mosquito isolates obtained from southeast Texas during June through August 2002.

Table 1

Results of investigations for West Nile virus (WNV) infection.

Table 1

Results of investigations for West Nile virus (WNV) infection.

Previous analysis has shown that strains circulating within this region could be distinguished into 2 distinct genetic variants—one circulating in the Houston metropolitan area, and the other isolated from Bolivar Peninsula—that differ at 9 signature nucleotides (encoding 3 amino acid changes) in the PrM/E gene region [5]. The sequence of the patient's CSF isolate and virus identified in the brain at autopsy by RT-PCR was identical to Bolivar Peninsula isolates, whereas the E protein gene fragment sequences from the donor blood unit and the patient's posttransfusion serum sample were identical to the Houston metropolitan area consensus sequence (table 2). The patient's CSF and serum samples (including 2 from June 2002, which were obtained at the time of his renal transplantation) were also tested for the presence of antibody to flavivirus by hemagglutination inhibition, complement fixation, and plaque reduction neutralization assays; IgM and IgG ELISAs were also done (performed by a commercial laboratory) (table 1). These showed that the patient's serum was still negative for antibody on day 8 of hospitalization but tested positive by day 20. The donor blood sample that tested positive for WNV by RT-PCR was also tested for WNV antibodies using the hemagglutination inhibition test, but the result was negative, which was also the case for a subsequent sample we requested from the donor. A blood sample obtained from the patient's wife also tested negative.

Table 2

Molecular comparison of West Nile virus strains.

Table 2

Molecular comparison of West Nile virus strains.

Discussion

WNV first appeared in the United States in New York in 1999. Although the number of patients in the initial year was not large, the virus spread across the continent and, in 2002, caused its largest recorded outbreak, with >3800 cases and 225 deaths [1, 2]. WNV is a mosquito-borne member of the genus Flavivirus, family Flaviviridae. Serologically and genetically, it is a member of the Japanese encephalitis (JE) serogroup. This serogroup includes St. Louis encephalitis (SLE) virus, which causes sporadic disease and occasional epidemics in the United States, Murray Valley encephalitis (MVE) virus, which causes occasional outbreaks in Australia and New Guinea, and JE virus, which is found in the Asia-Pacific region and is numerically the most important member of the group, causing an estimated 30,000–50,000 cases of encephalitis annually, with 10,000–15,000 deaths [6].

To date, most patients with West Nile encephalitis in the United States have been elderly or immunocompromised, as was our patient. The diagnosis of a nervous system infection in such patients is particularly difficult to make, because the clinical features may be nonspecific and the differential is large. Traditionally, flavivirus infections have been diagnosed by serological tests or virus isolation, both of which have their practical limitations. After the arrival of WNV into the United States, newer diagnostic tests, such as IgM and IgG capture ELISA, RT-PCR, and kinetic quantitative PCR (TaqMan), have been used in diagnostic and reference laboratories [7–9]. However, these tests have limited availability in many local hospitals and communities where the disease is now occurring. Moreover, some immunosuppressed patients may not make antibody until late in the course of illness. Therefore, clinical and radiological features that suggest WNV infection may be useful.

Flaccid limb weakness is one such feature that was recognized during the first New York outbreak of infection in 1999. Although originally described as Guillain-Barré syndrome [10], a reexamination of the electrophysiological data suggested that the paralysis in cases of West Nile encephalitis was probably the result of anterior horn cell damage in the spinal cord [4]. A poliolike syndrome caused by damage to these cells has been described previously for infections due to other flaviviruses, including JE, SLE, and MVE viruses, and also WNV infection [11, 12]. The radiological signs associated with extrapyramidal movement disorders have not previously been emphasized as possible pointers to WNV infection. Our patient had many of the features suggestive of extrapyramidal motor involvement—axial rigidity, tremors, stereotypic orofacial dyskinesias, myoclonus, and ocular bobbing movements reminiscent of opsoclonus myoclonus—that have been seen in other flaviviral encephalitides, particularly those associated with JE [13] and SLE [14] viruses. In these 2 conditions, the extrapyramidal movement disorders have been associated with abnormalities in the basal ganglia (especially the thalamus and substantia nigra), both radiologically and pathologically [13–15].

In our patient with West Nile encephalitis, high—signal intensity changes on MRI in the thalamus and caudate nucleus were very similar to those seen in patients infected with other flaviviruses. Such changes have not been mentioned in recent descriptions of West Nile encephalitis [16, 17]. Although, in our patient, the changes were originally suspected of being due to lymphoma, the magnetic resonance spectroscopy pattern was not that of lymphoma. Moreover, the fact that the abnormalities resolved with receipt of supportive therapy alone as the patient's neurological condition stabilized makes it likely that they were indeed caused by WNV infection. Additional studies will be needed to determine the sensitivity and specificity of these findings for WNV infection.

The clinical and laboratory findings for our patient are similar to those described recently for other immunosuppressed patients [18], including one who developed fatal West Nile encephalitis and for whom the virus was also isolated from blood and CSF samples [19]. Both our patient and the patient described elsewhere had a delayed immune response, as measured by the appearance of antibody, suggesting that immunosuppressed patients may be unable to mount a rapid immune response to WNV infection, resulting in a more severe illness or death. In cases of JE infection, the failure to mount an immune response is also associated with virus isolation and an increased risk of fatal disease [4, 20].

Most WNV infections occur after receipt of a bite from an infected mosquito. However, during the summer of 2002, it became apparent that nosocomial transmission of WNV can occur from transplanted organs or blood products already infected with the virus [21]. Although our patient had received a kidney transplant 2 months before his hospital admission, there is little to suggest that he was infected in this way: he remained relatively healthy after the transplantation, and retrospective serological testing of blood specimens obtained after transplantation showed no evidence of WNV infection. The same cannot be said of the blood transfusions he received. Of the 7 U he received, 1 was shown by RT-PCR to contain WNV RNA, and 6 days later, WNV RNA with an identical sequence was detected in the patient's blood.

At face value, these findings would seem to support a possible transfusion-related infection. However, sequencing of the virus initially isolated from the patient's CSF specimen and the viral RNA found in his brain at autopsy indicated that the virus that had caused the encephalitis was a different genetic variant. The latter was genetically almost identical (in the region sequenced) to those circulating naturally in the Bolivar Peninsula, which is geographically close to the patient's home, whereas the strain detected in the sample of transfused blood was identical to the viruses circulating naturally in the Houston metropolitan area, the area from which the donor originated. Of interest, the follow-up sample reported to have come from the donor tested negative for antibody, but our attempts to pursue this further were hampered by confidentiality issues. The fact that our patient received transfusions after he became encephalopathic and that his PCR-positive serum sample already contained antibodies to WNV also argues against the transfused virus being responsible for his disease.

Our findings suggest that, even when a patient with West Nile encephalitis has received an infected blood product, one should be cautious before assuming that this product was responsible for the disease—especially for patients who come from areas where WNV is circulating. In many areas, a kinetic quantitative PCR assay (TaqMan) is being used to look for evidence of WNV infection in blood products and patients. Although this test is very sensitive, it does not normally yield a PCR product with a sequence (and, therefore, origins) that can be determined. Viral culture and RT-PCR with detailed molecular analysis of the virus strains detected, as described here, may be needed to supplement the findings of the kinetic quantitative PCR assay to help resolve such questions in the future.

In summary, the clinical and radiological features of West Nile encephalitis described in our patient, although not well recognized in the West Nile encephalitis literature to date, may be important indicators that an encephalopathic patient is infected with WNV. Determining the source of infection for patients from areas where WNV is endemic who have also received infected blood transfusions may be difficult, but molecular analysis may help.

Acknowledgments

We thank Greg Chaljub and Rajeev Shah, for radiological assistance; Jack Alperin and Alexander Indrikous, for support from the transfusion service; and Deborah A. Payne, Candace Sanders, and Dana Vanlandingham, for virological assistance.

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Financial support: National Institutes of Health (grants AI-10984 and T32 AI07536), Texas Higher Education Coordinating Board Advanced Research Program, Centers for Disease Control and Prevention (cooperative agreement U90/CCU 620916-01), and a Wellcome Trust Career Development Award (to T.S.).

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