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Acute Vilyuisk Encephalitis

Viral Encephalitis

Viral encephalitis implies infection of the brain parenchyma by a virus. Seasonal, geographical and immunological factors are all important when differentiating between numerous viral pathogens in the differential diagnosis. Clinical presentation involves the triad of fever, altered consciousness and headache, whereas seizures and various neurological deficits may be encountered. The diagnosis is made through clinical, imaging, laboratory and microbiological findings. Empiric antiviral therapy is the mainstay.


Presentation

The clinical presentation of patients suffering from encephalitis encompasses the triad of headaches, altered level of consciousness and fever. In addition, focal neurological deficits that may range from fronto-temporal signs and aphasia to personality changes can also be seen together with seizures [5]. Cranial nerve deficits, hemiparesis and pyramidal signs may also be encountered [14]. These symptoms are used to distinguish encephalitis from other similar conditions such as ADEM, in which visual disturbances and signs of spinal cord involvement are frequent, and encephalopathy, where fever and focal neurological deficits are rarely present [5]. Additionally, a skin rash may be present in VZV infection, while mucosal lesions are hallmarks of herpes virus encephalitis [14].

Fever
  • The clinical presentation of patients suffering from encephalitis encompasses the triad of headaches, altered level of consciousness and fever.[symptoma.com]
  • Acute disease begins with fever, chills, headache, vomiting and rapid progression to confusion, quadraparesis and death within a few months, with 15% mortality.[virology.ws]
  • Encephalitis and HSV-2 Encephalitis and Myelitis p. 47 Pathogenesis of HSE p. 47 Clinical Evaluation of HSE p. 48 Therapy, Course, and Outcomes p. 54 Systemic Viral Diseases and Encephalitis p. 61 Exanthematous Diseases p. 61 Mumps p. 65 EBV--IM--Glandular Fever[booktopia.com.au]
  • Mountain fever 51. Mountain tick fever 52. Mumps 53. Novacaine drug allergy 54. Peach seed poisoning 55. Penicillin allergy 56. Phenytoin - Teratogenic Agent 57. Polio 58. Polyarteritis nodosa 59. Rat-bite fever 60. Reiter’s syndrome 61.[abovetopsecret.com]
  • Clinical manifestations include CONFUSION, somnolence, FEVER, nuchal rigidity, and involuntary movements. The illness may progress to COMA and eventually be fatal.[bioportfolio.com]
Fatigue
  • […] nasal cavity will be conducted in patients with myalgic Encephalomyelitis/Chronic Fatigue Syndrome (M...[bioportfolio.com]
  • […] febrile illness; Aseptic meningitis; Bornholm disease or epidemic Pleurodynia; Pericarditis and / or myocarditis; Acute hemorrhagic conjunctivitis; herpangina; Foot and mouth disease; Encephalitis; Hepatitis A; poliomyelitis; Polio Syndrome-like; Chronic Fatigue[ivami.com]
  • Chronic Fatigue Syndrome 23. Ciguatera poisoning 24. Coconut crab poisoning 25. Colorado tick encephalitis 26. Crohn's disease 27. Dengue fever 28. Dermatomyositis 29. Dracunculiasis 30. Drug Allergies 31. Ehrlichiosis 32. Erysipelas 33.[abovetopsecret.com]
High Fever
Hunting
  • Why the onset of VE coincides with the subsequent increase in outdoor activities such as fishing, hunting, and herding cattle, is not understood.[virology.ws]
Asymptomatic
  • Many patients who contract some of the viruses that cause encephalitis remain asymptomatic, however, presumably due to strong immune responses, which is why ensuring a strong immune system through regular exercise, as well-balanced diet and reduced contact[symptoma.com]
Vomiting
  • Acute disease begins with fever, chills, headache, vomiting and rapid progression to confusion, quadraparesis and death within a few months, with 15% mortality.[virology.ws]
  • […] posted by Agent_USA_Supporter your forgetting one thing on that list Roundworm Infections -Fever -larvae in stool -gas -abdominal pain -diarrhea -vomiting just in case.[abovetopsecret.com]
  • Specialty Neurology, Infectious disease Symptoms Headache, fever, confusion, stiff neck, vomiting [1] Complications Seizures, trouble speaking, memory problems, problems hearing [1] Duration Weeks to months for recovery [1] Types Herpes simplex, West[en.wikipedia.org]
Seizure
  • Patients usually present with a triad of headache, altered consciousness and fever, while additional signs include seizures and various neurological deficits.[symptoma.com]
  • • Permanent brain damage • Post-traumatic epilepsy • Partial emotional seizure • Psychic simple partial seizure • Partial motor seizure • Partial sensory seizure • Pseudo-torch syndrome • Partial somatosensory seizure • Primary angiitis of the central[atozhealthtopics.blogspot.com]
  • Encephalitis p. 31 Common Management Issues p. 31 Antiviral and Immunomodulating Therapy p. 32 Therapy by Type of Encephalitis p. 32 Clinical Evaluation for Acute Management p. 33 Acute Management Decisions p. 34 Reduction of Raised ICP p. 35 Control of Seizures[booktopia.com.au]
  • The clinical presentation often includes disorientation, disinhibition, memory loss, seizures, and behavioral anomalies.[en.wikipedia.org]
  • In addition, early mental status changes often occur as a result of virusencephalitis, beside focal neurological deficiencies, epileptic seizures, cerebral compression, even coma.[ncbi.nlm.nih.gov]
Headache
  • The clinical presentation of patients suffering from encephalitis encompasses the triad of headaches, altered level of consciousness and fever.[symptoma.com]
  • Volume 1 covers the visual sensory system, the autonomic nervous system, the ocular motor system, the eyelid, facial pain and headache, and nonorganic disease. Volume 2 covers tumors, the phacomatoses, and vascular disease.[books.google.com]
  • Acute disease begins with fever, chills, headache, vomiting and rapid progression to confusion, quadraparesis and death within a few months, with 15% mortality.[virology.ws]
  • Specialty Neurology, Infectious disease Symptoms Headache, fever, confusion, stiff neck, vomiting [1] Complications Seizures, trouble speaking, memory problems, problems hearing [1] Duration Weeks to months for recovery [1] Types Herpes simplex, West[en.wikipedia.org]
  • Clinical manifestations include the acute onset of fever, HEADACHE, altered mentation, and SEIZURES followed by coma. The condition is fatal in up to 50% of cases. Recovery may be marked by residual neurologic deficits and EPILEPSY.[bioportfolio.com]
Cerebellar Ataxia
  • Ataxia and Related Syndromes p. 110 Brain Stem ADEM Including Bickerstaff's Brain Stem Encephalitis p. 111 Miller Fisher Syndrome p. 112 ATM p. 112 Acute Hemorrhagic Leukoencephalopathy (Hurst) p. 113 Acute Encephalopathy, Including Reye's Syndrome p[booktopia.com.au]
  • Aniridia cerebellar ataxia mental deficiency. Ankyloglossia. .. Anton- Vogt syndrome. Aortic Aneurysm, Thoracic. Aphasia. .. jumbled speech, unrelated words though clearly articulated, inability to form sentences, difficulty speaking.[gatohez.over-blog.com]
Somnolence
  • Clinical manifestations include CONFUSION, somnolence, FEVER, nuchal rigidity, and involuntary movements. The illness may progress to COMA and eventually be fatal.[bioportfolio.com]

Workup

Whenever patients present with the mentioned triad of symptoms, immediate diagnostic protocols to exclude or confirm viral encephalitis should be instated. Patient history should be fully obtained, including information regarding recent travel, exposure to animals and mosquitoes,as well as presence of comorbidities that may present as a risk factor (such as HIV infection), followed by a thorough physical examination and neuroimaging studies. MRI is recommended over CT [14], but both are useful in initial evaluation. The importance of brain imaging lies in excluding conditions that may contraindicate lumbar puncture, such as increased intracranial pressure and risk of herniation. Additionally, some MRI findings can point to the underlying cause, such as unilateral frontotemporal changes in herpes simplex encephalitis or thalamic hemorrhage in Japanese encephalitis [14]. Disseminated lesions in the brainstem and basal ganglia are considered as hallmarks of Eastern Equine encephalitis [14]. Once imaging studies have determined that lumbar puncture can be safely performed, CSF examination should be carried out. A high protein and normal glucose content is seen in viral infections of the CNS, together with lymphocytic pleiocytosis [1]. However, neutrophils may predominate in the case of WNV infection and can often mislead the physician toward a bacterial pathogen [1]. For these reasons, the use of all accessible microbiological tests should be advocated, including serology for herpesviruses, Japanese encephalitis virus and arboviruses, whereas polymerase chain reaction (PCR) is a more specific method of viral DNA detection that can be used for virtually all pathogens [7]. Despite the availability of these tests, however, the pathogen remains undiagnosed in up to 60% of patients and the diagnosis, as well as treatment, remains on clinical criteria [7] [12]. Electroencephalography (EEG) and brain biopsy may be performed for further differentiation between causes.

Brain Edema
  • Otherwise, symptomatic therapy that often mandates severe intensive care is necessary, as coma, status epilepticus, respiratory failure and brain edema are not uncommon.[symptoma.com]

Treatment

Symptomatic management is the primary form of therapy for patients with suspected viral encephalitis, because antiviral therapy is available only against herpes viruses, influenza and CMV. Nevertheless, it is recommended to start patients on intravenous acyclovir as soon as a high suspicion toward encephalitis is made [6]. The recommended dosage is 10mg/kg q8h for 2-3 weeks for adults and 20 mg/kg for children under 12 years [6], and it is important to infuse the drug over 1 hour or even more to reduce nephrotoxicity. For CMV infection, valganciclovir 900 mg PO q12h for 2-3 weeks is indicated for milder cases, while ganciclovir 5 mg/kg IV q12h for 2-3 weeks is used in severe cases [12]. Supportive care includes antiepileptic therapy, management of brain edema through administration of mannitol and ensuring adequate tissue oxygenation through assisted ventilation [5], as many patients are in severely comatose states.

Prognosis

The most important factor in determining the prognosis is the causative agent of encephalitis, but in general, fatal outcomes are not uncommon. Mortality rates for WNV are estimated to be around 12%, whereas Japanese encephalitis mortality rates are between 20-30% [13]. Untreated herpes simplex encephalitis has a mortality rate of 70% (compared to 20-30% with therapy) and less than 3% of patients who do survive return to normal daily life, indicating that an early diagnosis may be of life-saving magnitude in some patients [7] [14]. Regardless of the etiology, long-term neurological and psychiatric complications are common, while respiratory failure, coma and status epilepticus may ensue despite adequate supportive care [9]. All of these facts emphasize the striking danger viral encephalitis poses to individuals.

Etiology

Viral encephalitis can be caused by numerous pathogens [1] [2] [5]:

  • Herpesvirus family - The most frequently confirmed etiological agents are HSV-1,HSV-2, and VZV, the causative agent of chickenpox [2]. In fact, VZV has been determined to be the most common cause of viral encephalitis in several studies, indicating that its role in viral encephalitis is perhaps underestimated [5]. CMV is an important member of the herpesvirus family, as it has shown to be one of the most frequent causes of encephalitis in immunocompromised individuals. Human herpesvirus 6 (HHV-6), the causative agent of roseola infantum, can also cause encephalitis after its reactivation from latent stages of the disease.
  • Arthropod-borne viruses (arboviruses) - This group comprises various geographically distinct pathogens that all lead to encephalitis. Japanese encephalitis virus, St. Louis encephalitis virus, Venezuelan and Eastern equine encephalitis viruses and West Nile virus (WNV), which has markedly distributed throughout the world in the past few decades and has become the most common cause of epidemic viral encephalitis in the United States, are all described in literature [6].
  • Enteroviruses - Although poliovirus has been almost eradicated through successful vaccination programs, it has been cited as one of the pathogens, whereas nonpolio enteroviruses such as echoviruses and coxsackie virus can also invade the central nervous system.
  • Rabies - Despite the fact that rabies is a rare occurrence in vaccinated populations, rabies virus causes a universally fatal infection of the central nervous system that eventually manifests with encephalitis.
  • Influenza virus - Aside from respiratory infection, which is the most important clinical feature of influenza, encephalitis has been recognized as a rare but important complication.
  • Rubella virus, Measles virus, Nipah and Hendra viruses, as well as tick-borne encephalitis, Powassan virus and the group of California encephalitis viruses (including La Crosse and Tahyna viruses) are somewhat less common but still important pathogens mentioned in literature [1].

Epidemiology

Epidemiological studies suggest that the incidence rate of viral encephalitis (based on clinical criteria only) ranges between 3.5-7.4 per 100,000 patients per year, but significant variations exist [10]. In the United States, isolated reports are closer to the upper border of 7.4 per 100,000 individuals per year,and approximately 20 000 cases are reported on an annual basis [2], whereas research conducted in England showed an incidence rate of 1.5 per 100 000 individuals per year [11]. Numerous studies have determined a much higher incidence rate in children, up to 22.5 per 100 000 individuals per year, indicating that young age is a significant risk factor for this form of infection [10]. On the other hand, a second peak in the elderly has been observed, especially for WNV [11]. Across all studies, however, the reports seem to underestimate the actual number of patients who suffered from viral encephalitis, primarily due to lack of confirmation [5] [11] [12]. In the lack of diagnostic tools to determine the exact viral pathogen, epidemiological information regarding recent travel, vector exposure, immune status and seasonal development of infection are considered to be of vital importance. Exposure to specific mosquito species (for ex. Aedes sp.) puts the patient at significant risk for contraction of WNV, equine encephalitis viruses and Japanese encephalitis, which is estimated to cause infection in almost 70,000 individuals every year [13]. Rodents (tick-borne encephalitis, LCMV), horses (several equine encephalitis viruses), woodchucks (Powassan virus), bats, dogs, skunks (all carrying rabies) and birds are all vectors of transmission and direct contact with these animals significantly increases the risk of contracting the viruses they respectfully carry [1]. Some viruses are endemic for certain regions of the world (Africa is endemic for Rift Valley fever virus, whereas Japanse and tick-borne encephalitis are restricted primarily to Asia). On the other hand, WNV is distributed through practically all parts of the globe [1]. Finally, immunodeficiency either by HIV, corticosteroid therapy due to organ transplantation or malignancy has shown to be a risk factor for encephalitis caused by HSV or VZV [3].

Sex distribution
Age distribution

Pathophysiology

The pathogenesis model significantly varies across different pathogens, as various modes of replication and further dissemination into host central nervous tissue has been established. Viruses that cause encephalitis are neurotropic, meaning that they invade and replicate within the nervous system. They exhibit variations in potency of CNS invasion [3], meaning that not all virions are equally dangerous and harmful for the human host. Routes include hematogenous and direct invasion of the neural network, which is the case of herpes viruses [10]. Viruses can pass through the blood-brain barrier, usually being situated inside macrophages and other leukocytes and trigger their replication once they reach the CNS. In addition to viral replication, significant damage on the parenchyma of the brain occurs as a result of severe pro-inflammatory events, the primary reason why patients often suffer from severe and long-term consequences of this disease.

Prevention

Prevention measures may include avoiding exposure and direct contact to mosquitoes and animals that are known to be vectors of transmission as well as management of underlying immunocompromised conditions that puts the patient at increased risk for infection. Many patients who contract some of the viruses that cause encephalitis remain asymptomatic, however, presumably due to strong immune responses, which is why ensuring a strong immune system through regular exercise, as well-balanced diet and reduced contact with harmful vectors could be the optimal strategy for prevention.

Summary

Encephalitis is a term encompassing inflammation of the brain parenchyma that may occur due to infectious, autoimmune and paraneoplastic causes [1]. Viral pathogens, however, are hypothesized to be one of the most common causes of this syndrome. A myriad of viruses have been described as potential causes, depending on factors such as geographical location, season and immune status of the individual. Herpes simplex 1 and 2 (HSV-1 and HSV-2) viruses, as well as Varicella zoster virus (VZV) are considered to be one of the most frequently confirmed viral pathogens when it comes to encephalitis [2], whereas numerous arboviruses (including West Nile virus (WNV), Venezuelan and Japanese encephalitis viruses, as well as several other), Human herpesvirus type 6 (HHV-6), Rabies virus, Lymhpocytic choriomeningitis virus (LCM), cytomegalovirus (CMV), but also tick borne-encephalitis, influenza and several other are listed as potential causes [1]. Risk factors are geographical presence, level of virulence, but also immune status of the individual, since immunocompromised patients, for ex. those suffering from human immunodeficiency virus (HIV) infection, are at a significantly higher risk for infection by HSV and CMV [3]. Transmission of viruses that cause encephalitis usually requires the presence of a vector, with mosquitoes being responsible in the majority of cases [4]. Other vectors, however, are rodents, horses, skunks, swine, birds and bats [1], each being responsible for transmission of one or more viruses. Depending on the geographical region and distribution of vectors, different pathogens may be encountered at various parts of the globe. For example, Japanese encephalitis virus is one of the most important causative agents of encephalitis in Asia with more than 15000 deaths every year, whereas St. Louis encephalitis virus is restricted to the central and eastern part of the United States [5]. Although viral pathogens are widely distributed throughout the world and exposure cannot be avoided, not all patients suffer from a symptomatic infection. In fact, only a very small number of individuals develop some form of illness and a fraction of these individuals develop severe brain infection. An example includes the estimation that up to 1 million people in the United States have contracted WNV, but only about 20,000-30,000 cases have been documented [1] [6]. The clinical presentation comprises the triad of fever, altered consciousness and headache, while accompanying features that distinguish viral encephalitis from other similar conditions such as acute disseminated encephalomyelitis (ADEM) and encephalopathy are neurological deficits and differences in cerebrospinal fluid (CSF) findings [5]. Whenever this triad is confirmed in patients, all attempts to obtain a detailed patient history regarding recent travel and exposure to potential vectors should be made. Prior to obtaining a lumbar puncture and performing CSF analysis, computed tomography (CT) or magnetic resonance imaging (MRI) should be done first to rule out the presence of tumors or brain herniation, as lumbar puncture can cause further deterioration of the patient under such circumstances. In the case of viral encephalitis, CSF panel shows lymphocytic pleocytosis (although neutrophils may be present in WNV and several other) [1], normal glucose and elevated protein levels, together with negative cultures [5]. Various serological and molecular tests exist for identifying viral pathogens, but studies have determined that the diagnosis is not confirmed in up to 60% of patients [7]. For these reasons, the importance of empiric therapy is detrimental and should be based on on patient history and laboratory results. Unfortunately, scarce options exist when it comes to antiviral therapy, and the empiric regimen consists of acyclovir, primarily used for herpes encephalitis [8]. In immunocompromised patients, gancyclovir may be given due to strong suspicion toward CMV, while oseltamivir can be effective against influenza but only if administered during the first few days [1] [7]. Otherwise, symptomatic therapy that often mandates severe intensive care is necessary, as coma, status epilepticus, respiratory failure and brain edema are not uncommon [9]. The prognosis can be fatal despite all therapeutic measures and mortality rates range from 20-70%, depending on the pathogen and attempted treatment.

Patient Information

Viral encephalitis is a term that implies infection of the brain by a virus. Most important viral agents include the herpes virus family (herpes simplex type 1 and 2, varicella zoster virus and cytomegalovirus), West Nile virus (WNV) and several other arthropod-borne viruses (or arboviruses, named after the fact that mosquitoes transmit viruses to humans) and a myriad of other pathogens (such as influenza, measles, rabies, etc.). Their occurrence may significantly depend on geography and presence of animals that transmit the particular virus, such as Japanese encephalitis, which is exclusively seen in Asia, or Eastern Equine encephalitis virus, as its presence is restricted to southern and eastern parts of the United States. Numerous animals, in addition to mosquitos, have been established as potential vectors - bats, skunks, dogs, woodchucks, horses and rodents, making direct contact with these animals a risk factor for this infection. Age extremes (less than 10 years and more than 65 years of age) are shown to possess highest rates of infection, whereas travel to endemic areas and an immunocompromised status (such as human immunodeficiency virus - HIV infection or corticosteroid therapy) are also established risk factors. Patients usually present with a triad of headache, altered consciousness and fever, while additional signs include seizures and various neurological deficits. To make the diagnosis, imaging studies such as magnetic resonance imaging (MRI) or computed tomography (CT scan) are initially performed to investigate the presence of brain lesions that may suggest the causative agent, but also to ensure that a lumbar puncture may be performed. This procedure comprises drawing a sample of cerebrospinal fluid (CSF) from the spine and its subsequent examination. Changes in content of the CSF can indicate whether the infection is of viral, bacterial or some other origin, but more importantly, microbiological investigation of this material may provide valuable results in determining the exact virus that caused symptoms. Despite numerous advances in techniques used for confirmation, however, the final diagnosis is not made in up to 60% of patients, and clinical criteria are used for initiation of treatment. Unfortunately, antiviral therapy currently exists for only herpes viruses and a few other, shifting the focus of treatment on symptomatic measures. The prognosis of patients suffering from viral encephalitis is not good, as up to a third of patients do not survive infections by West Nile virus and Japanese encephalitis virus. Similar mortality rates are observed with herpes viruses, but the percentage rises to 70% in untreated patients, which is why administration of acyclovir is indicated in those in whom viral encephalitis is suspected, in the attempt to reduce mortality rates. However, only 3% of individuals return to their normal function and many develop long-term neurological and psychiatric complications. These facts show that viral encephalitis is a devastating and often life-threatening disease that necessitates improvement in diagnostic and therapeutic fields in order to reduce very high mortality rates.

References

Article

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  2. Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson J, Loscalzo J. eds. Harrison's Principles of Internal Medicine, 18e. New York, NY: McGraw-Hill; 2012.
  3. Kennedy PG. Viral encephalitis. Journal of neurology. 2005;252(3):268-272.
  4. Murray PR, Rosenthal KS, Pfaller MA. Medical Microbiology. Seventh edition. Philadelphia: Elsevier/Saunders; 2013.
  5. Kennedy P. Viral encephalitis: Causes: Causes, differential diagnosis, and management. J Neurol Neurosurg Psychiatry. 2004;75(1):i10-i15.
  6. Davis LE, DeBiasi R, Goade DE, et al. West Nile virus neuroinvasive disease. Annals of neurology. Sep 2006;60(3):286-300.
  7. Chan BK, Wilson T, Fischer KF, Kriesel JD. Deep Sequencing to Identify the Causes of Viral Encephalitis. Plos One. 2014;9(4):e93993.
  8. Gilbert DN, Chambers HF, Eliopoulos GN, Saag MS. The Sanford Guide to Antimicrobial Therapy 2015. 45th ed. Antimicrobial Therapy, Inc, Sperryville, VA; 2015.
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  10. Misra UK, Tan CT, Kalita J. Viral encephalitis and epilepsy. Epilepsia. 2008;49(6):13-18.
  11. Granerod J, Cousens S, Davies NWS, Crowcroft NS, Thomas SL. New estimates of incidence of encephalitis in England. Emerg Infect Dis [Internet]. 2013 Sep [cited Aug 04, 2016].
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Last updated: 2019-07-11 20:21