Page 942 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

CHAPTER 72: Encephalomyelitis 673

■ NONPOLIO ENTEROVIRUSES ■ RUBELLA VIRUS

Echovirus, coxsackievirus, and other numbered enteroviruses belong Encephalitis is an extremely rare postinfectious complication of rubella.
to this group and are associated with a wide spectrum of CNS disease Rubella virus infection causes a benign disease, and neurological
such as aseptic meningitis, encephalitis, acute poliomyelitis–like ill- complications are rare. The onset of viral encephalitis most frequently
ness, optic and cranial neuritis. They account for more than 80% of occurs within 1 to 8 days after the development of the typical rash.
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cases of aseptic meningitis, but less than 5% of all cases of encephalitis. The main neurologic findings are headache, ataxia, and hemiplegia.
Enterovirus encephalitis occurs during late summer and early fall and Diagnosis of rubella encephalitis is generally confirmed by determin-
affects mostly children and young adults. The spectrum of illness can ing the presence of rubella antibodies in CSF serum by ELISA, though
range from mild encephalitis to severe disease with seizures, paresis, rarely the virus can be isolated from CSF. Guillain-Barré syndrome and
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and coma. Enterovirus 71 has been associated with a severe form of acute postinfectious demyelinating encephalomyelitis have also been
brain stem encephalitis presenting with myoclonus, tremors, ataxia, described. Rubella encephalitis is generally self-limiting, with about an
and cranial nerve defects, often with fatal outcomes. 70,71 CSF cell count 80% recovery rate without any sequelae. The treatment is supportive.
is usually 10 to 500/µL with a lymphocytic predominance. CSF glucose The case fatality rate has been found to vary between 0% and 30%. A
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concentration is often normal with a normal or slightly elevated pro- rubella SSPE-like syndrome occurs mainly in young adults, as opposed
tein concentration. The sensitivity of CSF PCR to detect enteroviruses to measles-associated SSPE, which tends to occur in children.
ranges from 66% to 90%. A CSF culture for enteroviruses is less sensi-
tive than PCR. MRI of the brain in encephalitis due to enterovirus RHABDOVIRIDAE
71 may show increased signal abnormalities in midbrain, pons, and
medulla. At the present time, no approved antiviral agents are avail- ■ RABIES VIRUS
able for the treatment. In majority of cases, the illness is benign and Rabies is one of the oldest described in human history and causes highly
the treatment is supportive. Intraventricular γ-globulin therapy can fatal encephalitis. Rabies virus is a bullet-shaped RNA virus, transmitted
be considered for chronic or severe enteroviral encephalitis in patients to humans usually by saliva from infected animal bites. Other modes
with agammaglobulinemia. 47,72 of transmission include scratches, respiratory droplets, contact with
infected secretions, and through corneal transplants. Domestic animals
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BUNYAVIRIDAE (dogs, cats) account for only 10% of human exposures, whereas wild
animals account for the other 90% (skunks, foxes, raccoons, and bats).
In the Bunyaviridae family, the viruses belonging to the California
encephalitis group, La Crosse virus and Jamestown Canyon virus, are Dogs are still the primary source in underdeveloped countries, while
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responsible for disease in the United States, with La Cross virus being bats are the major source in the United States. Rabies is a neurotropic
responsible for the majority of cases. Another member of this group, virus that spreads from site of contact through peripheral nerves to the
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Tahyna virus, is predominantly seen in Russia. brain, ultimately leading to fatal encephalomyelitis. Rabies can present
as either a classical encephalitic form or much less common paralytic
■ LA CROSSE VIRUS form. An asymptomatic incubation period of 20 to 90 days is followed by
La Crosse virus (LACV), a bunyavirus, is a leading cause of pediatric a prodrome of nonspecific flu-like symptoms. Tingling and paresthesia
at the site of bite are reliable symptoms of a rabid bite. Eventual acute
arboviral encephalitis in the Midwestern United States and is transmitted neurologic syndrome is characterized by manic behavior with agita-
primarily by the eastern tree hole mosquito (Ochlerotatus triseriatus). tion, dysarthria, dysphagia, diplopia, vertigo, nystagmus, seizures, and
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Though initially confined to Midwest area, it has recently been reported hallucinations. Hydrophobia with hypersalivation secondary to painful
in the southeastern United States. Most human LACV infections contractions of pharyngeal muscles is unique sign of rabies. Ultimately
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occur in summer and in children under the age of 15. LACV encepha- coma, generalized flaccid paralysis, and death occur due to vascular and
litis is the most common presentation, with nonspecific findings such respiratory collapse. The case fatality rate with rabies is 100%. The par-
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as fever, headache, altered mental status, vomiting, and stiff neck. alytic form is characterized by flaccid paralysis in the bitten limb, which
Approximately half of the cases of LACV encephalitis manifest seizures ascends symmetrically or asymmetrically. A diagnosis of rabies needs a
during the acute illness. Persistent paresis, learning disabilities, cogni- high index of clinical suspicion and good history, even in the absence
tive defects, and neurobehavioral disorders such as attention deficits of a definitive history of an animal bite. Rabies can be diagnosed by
and hyperactivity are some of the rare sequelae seen with LACV. This detecting virus-specific fluorescent material in skin biopsy, isolation of
encephalitis rarely results in death with a case-fatality rate of about the virus from patient saliva, or presence of antirabies antibodies in the
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0.3%. Currently, there is no standard therapy for LACV encephalitis; serum or CSF of nonimmunized patients. Rabies is a disease of preven-
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however, ribavirin has been shown to inhibit LACV infection by inhib- tion, with effective immunization of domestic animals, avoiding contact
iting RNA polymerase. 76 with wild animals and postexposure prophylaxis (active vaccination and
passive immunoglobulins). High-risk groups likely to be exposed to
TOGAVIRIDAE rabid animals like lab personnel, veterinarians, and travelers to endemic
■ WESTERN, EASTERN, AND VENEZUELAN EQUINE countries need preexposure prophylaxis. Treatment is supportive, but
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the outcome is dismal. Patients should be isolated and caregivers should
ENCEPHALITIS VIRUSES take precautions to avoid exposure to their body fluids. 87
WEEV, EEEV, and VEEV are alphaviruses that cause encephalitis in
horses and humans. The primary amplifying vector for these viruses ORTHOMYXOVIRIDAE
primarily by mosquitoes in the genera Culex, Culiseta, and Aedes. ■ INFLUENZA VIRUS
includes birds, rodents, and horses. These viruses are transmitted
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EEEV is the most virulent, but has lowest incidence of human cases. Influenza-associated acute encephalopathy/encephalitis (IAE) is an
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In contrast, VEEV is the least virulent, more transmissible in humans, uncommon but serious complication with high mortality and neurologi-
and capable of producing epidemics. Case fatality rates for WEEV fall cal sequelae. It is a rapidly progressive encephalopathy seen in the early
between those of EEEV and VEEV. Detection of virus-specific IgM, phase of influenza infection, affecting mostly children under the age
virus isolation, and viral nucleic acid helps in diagnosis. Currently, there of 5 years, and is caused by influenza A, B, and C viruses, including the
are no vaccines against WEEV, EEEV, or VEEV that are effective in novel H1N1. There is no CNS inflammation in IAE. Along with the flu
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humans; however, several are under development. symptoms, the neurologic manifestations include altered mental status,

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