A 7-year-old boy is brought to the emergency department due to fever, headache, vomiting, and confusion. He has no prior medical conditions and is up to date with immunizations. The patient has not traveled recently, and his parents report no exposure to individuals with similar symptoms or ingestion of anything out of the ordinary. They recently noticed several dead birds around their neighborhood. Temperature is 39 C (102.2 F). Physical examination shows neck rigidity and right lower extremity weakness with fasciculations. Cerebrospinal fluid analysis shows a leukocyte count of 200/mm3 with 20% neutrophils and 80% lymphocytes. Which of the following pathogens is most likely responsible for this patient's condition?
West Nile virus | |
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West Nile virus is an enveloped RNA virus that is found in warm climates worldwide. The virus replicates extensively within birds and is passed to mosquitos (Culex species) during blood feeding. Viral accumulation in mosquito salivary glands can lead to human transmission.
Most infected patients develop low-level viremia that is neutralized within a week by the immune system; these individuals typically remain asymptomatic. However, a minority of patients (particularly the young, elderly, or immunosuppressed) are unable to mount an effective immune response and develop significant clinical manifestations, including:
West Nile fever – a self-limited, flu-like illness that is often associated with a maculopapular rash
Neuroinvasive disease – the virus is neurotropic and often causes meningitis (eg, fever, headache, neck stiffness), encephalitis (eg, confusion, tremors, seizures), and/or flaccid paralysis (eg, asymmetric weakness of limbs, fasciculations). Cerebrospinal fluid usually shows a lymphocytic pleocytosis.
Most patients recover completely with supportive care, but neuroinvasive disease may lead to long-term neurologic sequelae or death.
(Choice A) Cryptococcus neoformans, a fungus found in bird feces, can cause meningoencephalitis. However, the vast majority of infections occur in those with severe immunosuppression (eg, advanced AIDS). In addition, most patients with Cryptococcus meningitis have slowly progressive headache, lethargy, personality changes, and memory impairment (not focal neurologic deficits with fasciculations).
(Choice B) Herpes simplex virus is a leading cause of sporadic encephalitis; it is usually characterized by confusion, focal neurologic deficits (eg, hemiparesis, dysphagia, cranial nerve defects), and seizures. It is not harbored in birds; cerebrospinal fluid usually shows elevated erythrocytes (in addition to lymphocytic pleocytosis); lower-motor neuron signs (eg, fasciculations) would not be seen.
(Choice C) Nonpolio enteroviruses (eg, Coxsackievirus, echovirus) often cause aseptic (viral) meningitis and can occasionally cause encephalitis. However, these viruses are not associated with bird vectors and do not typically cause lower-motor neuron signs.
(Choice D) Although polio virus is a common cause of acute, asymmetric flaccid paralysis, patients that have received age-appropriate vaccinations are very unlikely to develop the infection.
Educational objective:
West Nile virus is harbored in birds and transmitted to humans by mosquitos. Most patients are asymptomatic, but the virus can cause an influenza-like illness or neuroinvasive disease with meningitis, encephalitis, and flaccid paralysis.