Viral Encephalitis PDF

Viral Encephalitis · Acute viral encephalitis (AVE) is defined as a rapid-onset, febrile inflammatory disease of the brain as a result of direct viral invasion or an immunologic reaction initiated by a virus. o The infection may be focal (i.e., located in only...

Viral Encephalitis · Acute viral encephalitis (AVE) is defined as a rapid-onset, febrile inflammatory disease of the brain as a result of direct viral invasion or an immunologic reaction initiated by a virus. o The infection may be focal (i.e., located in only one region) or diffuse (i.e., widespread). o Acute viral encephalitis is often accompanied by viral meningitis and is considered a neurologic emergency. o Although encephalitis can also be caused by bacteria, fungi, or other microorganisms, it is most commonly the result of a VIRUS · Herpes simplex virus (HSV) encephalitis is the most common type of AVE and has an incidence of 2 cases per 1 million people per year. o HSV encephalitis accounts for approximately 10% of all cases of AVE in the United States. o Although children and young adults are the most commonly infected populations, infants and elderly patients often have a more serious clinical course. o In 2002, the largest encephalitis outbreak in U.S. history (3800 cases and 225 deaths) was attributed to West Nile virus. · Although most cases of AVE are mild in nature, the infection can be life-threatening and cause permanent damage to the central nervous system (CNS). o Mortality rate (MR) depends largely on the specific etiologic agent. o Viruses that carry high mortality rates include; rabies rhabdovirus (virtually 100% MR) HSV (70% MR) eastern equine alphavirus (35% MR) St. Louis flavivirus (20% MR in the elderly). · Causes and Risk Factors: o Many types of viruses cause AVE. o Most cases in the United States are caused by: § Enteroviruses (particularly coxsackievirus and echovirus) § HSV § a bite from a rabid animal (i.e., rabies virus), arboviruses. § Arboviruses are transmitted from infected animals to humans through the bite of an infected tick, mosquito or other blood-sucking insect. · Acute viral encephalitis takes two forms: o primary and secondary (or postinfectious) disease. o Primary encephalitis occurs when a virus directly invades the brain. § This can happen at any time of year (sporadic encephalitis) or be part of an outbreak (epidemic encephalitis). § Viruses that commonly cause epidemics in the United States include: § arbovirus § poliovirus § echovirus § coxsackievirus.  o Sporadic encephalitis is usually caused by: § HSV § varicella/zoster § mumps viruses · Pathophysiology Exposure to viruses that cause AVE can occur through: o insect and animal bites o sexual contact o food or drink contamination o inhalation of respiratory droplets (e.g., from coughing or sneezing) from an infected person, or skin contact. o Microbes can spread through contact with saliva, nasal discharge, feces, respiratory and throat secretions, and through kissing or sharing drinking glasses, eating utensils or such personal items as toothbrushes, lipstick, or cigarettes. o People sharing a household, at a daycare center, or in a classroom with an infected individual are at risk for infection. · In rural areas, viruses that cause AVE are often carried by: o mosquitoes and ticks. o The specific pathophysiology varies with the viral family. · Viruses access the CNS through two distinct routes: o Hematogenous o Neuronal retrograde dissemination. · Patients generally experience signs and symptoms of leptomeningeal irritation—headache, photophobia (i.e., extreme sensitivity of the eyes to light), and neck stiffness. o They also develop focal neurologic signs, seizures, and alterations of consciousness beginning with confusion and progressing to lethargy, stupor, and occasionally coma. Behavioral and speech disturbances are common and abnormal movements may be seen. o Other clinical manifestations include general malaise, vomiting, memory loss, and paralysis.