1. Should this patient be isolated? 

No. He is not infectious. However, at presentation you would not know the diagnosis, would consider enterovirus as a possible cause, and would therefore place the patient in enteric isolation.

2. What is known about the pathogenesis of the infection? 

Infection of the human by a biting, infected arthropod is followed by viremia, which is apparently amplified by extensive virus replication in the reticuloendothelial system and vascular endothelium. After replication, the virus becomes localized in various target organs, depending on its tropism, and illness results. The viruses produce cell necrosis with resultant inflammation which leads to fever in nearly all infections. If the major viral tropism is for the central nervous system (CNS), virus reaching this site by crossing the blood-brain barrier or along neural pathways can cause meningeal inflammation (aseptic meningitis) or neuronal dysfunction (encephalitis). The CNS pathology consists of meningeal and perivascular mononuclear cell infiltrates, degeneration of neurons with neuronophagia, and occasionally destruction of the supporting structure of neurons.

3. Describe how the viral infection was detected? Prior to the serology, what key laboratory findings pointed to a viral encephalitis?

Specific diagnosis is usually accomplished by serologic techniques using acute and convalescent sera. The arboviruses may be isolated in various culture systems (but not in most hospital laboratories); for most agents, however, isolation is by intracerebral inoculation of newborn mice, which often results in encephalitis and death. The viruses may be found in the blood (viremia) from a few days before onset of symptoms through the first 1 to 2 days of illness; attempts at isolation from the blood are generally useful only when viremia is prolonged, as in dengue, Colorado tick fever, and some of the hemorrhagic fevers. Virus is not present in the stool and is rarely found in the throat; viral recovery from cerebrospinal fluid is also unusual. Virus can be isolated readily from affected tissue during the acute phase of illness, but this approach is seldom practical in diagnosis.

Various diagnostic serologic tests have been used including hemagglutination inhibition, complement fixation, virus neutralization methods, and enzyme immunoassay. Early rapid presumptive diagnosis can sometimes by made by the detection of IgM-specific antibodies that often appear within a few days of onset and persist 1 to 2 months, but these tests are not generally commercially available.

The presence of 90% lymphocytes in the LP is consistent with a viral encephalitis

4. What is the appropriate treatment for this infection?

Supportive care only. No specific treatment is available.

5. Are there any long term consequences associated with this viral infection?

No. Recovery is generally complete with lasting immunity. However, patients with eastern equine encephalitis may have poorer outcome with long-term neurologic sequelae.