A 68-year-old woman is brought to the emergency department due to confusion and lower extremity weakness. Her symptoms began 2 days ago with fever, headache, malaise, and myalgias. Today, the patient became confused and had difficulty ambulating due to left lower extremity weakness. The patient has a history of lymphoma in remission, hypertension, and type 2 diabetes mellitus. She drinks alcohol socially but does not use tobacco or recreational drugs. She is visiting her family in Texas for the summer and has never traveled outside the United States. Temperature is 38.3 C (101 F), blood pressure is 130/70 mm Hg, and pulse is 96/min. The patient is oriented to place and person only and has a coarse hand tremor. There is flaccid paralysis of the left lower extremity with preserved sensation. CT scan of the head shows no abnormalities. Lumbar puncture is performed, and cerebrospinal fluid analysis shows lymphocytic pleocytosis and elevated protein. Cerebrospinal fluid polymerase chain reaction testing yields viral RNA. The infectious agent responsible for this patient's current condition is most likely transmitted via which of the following mechanisms?
West Nile virus | |
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This patient has acute confusion associated with fever and asymmetric lower extremity paralysis, consistent with neuroinvasive West Nile virus (WNV) infection. WNV is a positive-sense, single-strand RNA flavivirus transmitted by female mosquitoes (Culex spp), most commonly in the summer in warmer regions (eg, southern United States, Latin America, Africa). Most WNV infections are asymptomatic or present with a flu-like illness (fever, headache, myalgias), often with a maculopapular or morbilliform rash on the back and chest.
Neuroinvasive infection is an uncommon complication of WNV but has a 10% fatality rate. It occurs most commonly in older patients and those with a history of malignancy or organ transplant, and is characterized by meningitis (ie, headache, meningismus) and/or encephalitis (altered mental status). The presence of acute-onset asymmetric flaccid paralysis is highly suggestive of WNV, particularly if the patient demonstrates concurrent parkinsonian features (eg, rigidity, bradykinesia, tremor, postural instability).
(Choices A and D) HIV, cytomegalovirus, and Epstein-Barr virus can be transmitted via blood transfusion or sexual contact, whereas herpes simplex virus 1 and 2 are transmitted through sexual or oral contact. Although these viruses can cause aseptic meningitis and encephalitis, asymmetric flaccid paralysis and concurrent tremor are more suggestive of WNV.
(Choice C) Varicella, mumps, and adenoviruses are spread via respiratory secretions (eg, droplets, aerosols) and are capable of causing aseptic meningitis or encephalitis, but paralysis is rare. Hemophilus influenzae and Mycoplasma pneumoniae are associated with Guillaine-Barre syndrome, which can cause ascending paralysis; however, Guillaine-Barre is not typically associated with fever at the time of symptom onset or viral RNA in the CSF.
Educational objective:
West Nile virus is a single-strand flavivirus transmitted by mosquitoes, most commonly in the summer. Most infections are asymptomatic or may present with a flu-like illness (West Nile fever), often with a maculopapular or morbilliform rash. Neuroinvasive disease manifests as meningitis, encephalitis, or asymmetric flaccid paralysis; patients may have parkinsonian features (eg, tremor).