Viral encephalitis
Viral encephalitis | |
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Specialty | Infectious diseases |
Viral encephalitis is
Viral encephalitis can be diagnosed based on the individual's symptoms, personal history, such as travel history, and different clinical tests such as
Encephalitic viruses are typically transmitted either from person-to-person or are arthropod-borne viruses, called arboviruses. The young and the elderly are at the highest risk of viral encephalitis. Many cases of viral encephalitis are not identified either because of lack of testing or mild illness, and serological surveys indicate that asymptomatic infections are common. Various ways of preventing viral encephalitis exist, such as vaccines that are either in standard vaccination programs or which are recommended when living in or visiting certain regions, and various measures aimed at preventing mosquito, sandfly, and tick bites in order to prevent arbovirus infection.
Etiology
Many viruses are capable of causing encephalitis during infection, including:[1]
- California encephalitis virus[2]
- Chandipura virus[3]
- Chikungunya virus[4]
- Cytomegalovirus
- Dengue virus
- Eastern equine encephalitis virus
- Enteroviruses
- Epstein-Barr virus
- Herpes simplex virus
- HIV[5]
- Human herpesvirus 6
- Human herpesvirus 7
- Inkoo virus[7]
- Jamestown Canyon virus[8]
- Japanese encephalitis virus
- La Crosse virus
- Lymphocytic choriomeningitis mammarenavirus[9]
- Measles virus
- Mumps virus
- Murray Valley encephalitis virus[10]
- Nipah virus
- Powassan virus[8]
- Rabies virus
- Rubella virus
- SARS-CoV-2[11]
- Snowshoe hare virus[7]
- St. Louis virus
- Tahyna virus[7]
- Tick-borne encephalitis virus
- Varicella-zoster virus, which causes both chickenpox and shingles
- Venezuelan equine encephalitis virus
- West Nile virus
- Western equine encephalitis virus
- Zika virus
Transmission
Encephalitic viruses vary in their manner of transmission. Some are transmitted from person-to-person, whereas others are transmitted by animals, especially bites from arthropods such as mosquitos, sandflies, and ticks, such viruses being called arboviruses.[12] An example of person-to-person transmission is the herpes simplex virus, which is transmitted by means of intimate physical contact.[13] An example of arboviral transmission is the West Nile virus, which usually is incidentally transmitted to people from the bites of Culex mosquitos, especially Culex pipiens.[14]
Pathogenesis
Viruses that cause viral encephalitis first infect the body and replicate outside of the
Diagnosis
Examination
If viral encephalitis is suspected, then questions can be asked about the individual's history and physical examination can be performed. Important aspects of one's history include immune status, exposure to animals, including insects, travel history, vaccination history, geography, and time of year. Symptoms usually occur acutely,
Virus-specific symptoms may also exist or tests may indicate one virus. Specific examples include:[1]
- palsies.
- Epstein-Barr virus encephalitis is usually accompanied by enlargement of the lymph nodes and enlargement of the spleen
- Herpes zoster encephalitis may be accompanied by rash and skin vesicles, and because it involves the frontal lobe and temporal lobe, is often characterized by psychiatric features, memory deficits, and loss of language faculties.
- Many arboviral encephalitides, such as Japanese encephalitis, primarily affect the basal ganglia, sometimes causing motor symptoms such as involuntary movements and movements similar to those observed in Parkinson's disease.
- Nipah virus may produce brainstem and cerebellar signs, hypertension, and segmental myoclonus, or twitching of a group of connected muscles.
- Zika virus characteristically may cause microcephaly among newborn children if a pregnant woman is infected.
Histology
The brain histology of viral encephalitis shows dead neurons with nuclear dissolution and elevated
Clinical evaluation
Virus | Preferred diagnostic test |
---|---|
Cytomegalovirus | CSF PCR or CSF-specific IgM |
Dengue/Chikungunya/Zika | CSF PCR or CSF-specific IgM |
Enterovirus | Stool and throat PCR are preferred over CSF PCR |
Epstein-Barr virus | Serum EBV capsid antigen IgG and IgM (VCA) and EBV nuclear antigen IgG (EBNA) |
Herpes simplex virus | CSF PCR, can be repeated within 2 to 7 days of disease onset if negative with high clinical suspicion; or CSF for HSV-IgG after 10–14 days of disease onset |
HHV-6 | CSF PCR paired with serum PCR to exclude viral integration into host DNA that causes false positives |
Influenza | Culture, antigen test, PCR of respiratory secretions |
Measles | CSF-specific IgG |
Varicella-zoster virus | CSF-specific IgG |
Neuroimaging and
Test results specific to certain viruses include:[1]
- For herpes simplex virus encephalitis, a CT scan may show low-density lesions in the temporal lobe. These lesions usually appear 3 to 5 days after the start of the infection.
- Japanese encephalitis often has distinct EEG patterns, including diffuse delta activity with spikes, diffuse continuous delta activity, and alpha coma activity.
Differential diagnosis
A broad differential diagnosis can be performed that looks at many potential causes of the encephalitis, infectious and noninfectious. Potential alternatives to viral encephalitis include malignancy, autoimmune or paraneoplastic diseases such as anti-NMDA receptor encephalitis, a brain abscess, tuberculosis or drug-induced delirium, exposure to certain drugs or toxins, neurosyphilis, vascular disease, metabolic disease, or encephalitis from infection caused by a bacterium, fungus, protozoan, or parasitic worm.[1][6][13] In children, differential diagnosis may not be able to distinguish between viral encephalitis and immune-mediated inflammatory CNS diseases, such as acute disseminated encephalomyelitis, as well as immune-mediated encephalitis, so other diagnostic methods may need to be used.[4]
Treatment
Treatment of viral encephalitis is primarily supportive with intravenous antiviral therapy due to there being no specific medical therapy for most viral infections involving the central nervous system. Individuals may require intensive care for frequent neurological exams or respiratory support, and treatment for electrolyte disturbance, autonomic disregulation, and renal and hepatic dysfunction, as well as for seizures and non-compulsive status epilepticus.[1][4]
A very specific exception is herpes simplex virus (HSV) encephalitis, which can be treated with
Serial intracranial pressure (ICP) is important to monitor as elevated ICP is associated with poor prognosis. Elevated ICP can be relieved with steroids and
Prognosis
If treated, most individuals recover from viral encephalitis without long-term problems related to the illness. Mortality rates vary for those who do not receive treatment, for example being about 70% for herpes encephalitis
- For Eastern equine encephalitis, some children may experience seizures, severe intellectual disability, and various forms of paralysis.
- For Japanese encephalitis, extrapyramidal symptoms relating to motor function may remain.
- For St. Louis encephalitis, low blood sodium level and excess, unsuppressable release of antidiuretic hormone
- For Western equine encephalitis, some children may experience seizures and behavioral changes.
- For pregnant women infected with Zika virus, the newborn child may have microcephaly.
Other potential complications following viral encephalitis include:[1]
- Encephalopathy
- Flaccid paralysis
- Impaired intelligence
- Low blood sodium level
- Mononeuropathy
- Mood and behavioral changes
- Residual neurological deficits
Epidemiology
While the etiology of many cases of encephalitis is unknown, viruses account for about 70% of confirmed encephalitis cases, with the herpes simplex virus being the most common cause at about 50% of encephalitis cases.
Prevention
As many encephalitic viruses are transmitted by mosquitos, many prevention efforts revolve around preventing mosquito bites. In areas where such arboviruses are widespread, people should use protective clothing and should sleep under a mosquito net. Removing containers of stagnant water and spraying insecticides can be beneficial. Activities that increase the likelihood of tick bites should be avoided. Vaccines against some arboviruses that cause viral encephalitis exist, such as those against Eastern equine encephalitis, Western equine encephalitis, and Venezuelan equine encephalitis. Although these vaccines are not perfectly effective, they are recommended for people who live in or travel to high-risk areas.[1][6] Some vaccines that are included in standard vaccination programs, such as the MMR vaccine, which prevents measles, mumps, and rubella, are also capable of preventing viral encephalitis.[15]
See also
- List of central nervous system infections
References
- ^ PMID 29262035. Retrieved 28 March 2020.
- PMID 13009479.
- PMID 28731002.
- ^ PMID 31513761.
- PMID 30967139.
- ^ a b c d "Understanding encephalitis -- the basics". WebMD. 26 March 2019. Retrieved 27 March 2020.
- ^ PMID 30882310.
- ^ PMID 26903031.
- PMID 26631809.
- PMID 29044370.
- S2CID 226200547.
- ^ a b "Encephalitis, Viral". World Health Organization. Archived from the original on May 16, 2006. Retrieved 27 March 2020.
- ^ PMID 27106239.
- ^ "West Nile Virus". World Health Organization. 3 October 2017. Retrieved 27 March 2020.
- ^ "Understanding encephalitis -- prevention". WebMD. 26 March 2019. Retrieved 27 March 2020.