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An Overview of Viral Encephalitis |
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| Specific agents: |
All of the viral agents causing encephalitis are arboviruses: requiring transmission by an insect or an arachnid. The vectors are either culicine mosquitoes or ticks.
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| Other causes: |
Differential diagnosis may have to include a number of viral or bacterial infections including:
Other possible causes include a number of hemorrhagic fevers or stroke. |
| Risk groups: | Groups most at risk of complications and mortality are the pre-adolescent children and the elderly. The effect is most marked for West Nile virus for which these two groups are most at risk. For the equine encephalitis viruses there is no particular age group at risk, but those who work with horses or live near them are at a greater risk of infection |
| First indications: | An increase in in absenteeism because of headaches or the number of people reporting to emergency rooms or primary care physicians with severe persistent headaches, |
| Surge period: |
These diseases have incubation periods in the range 3 - 21 days although 5-15 days after inoculation is when most cases are likely to develop. In an attack that is a single point event there is likely to be a surge of cases within 2-3 days of the first cases that will peak after about a week to 10 days. If the attack is conducted by release of infected mosquito or tick vectors the surge may be slower to appear and longer lasting. |
| Animal indicators: |
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Coordination between public health, agricultural, veterinary, and wildlife services is essential in responding to outbreaks of viral encephalitis. |
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| Main treatment options: | Treatment is symptomatic. There are no specific treatments for any of the viruses. |
| Essential medical supplies: |
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| Symptoms: | Most viral encephalitides viruses show a wide range of severity. Clinically significant symptoms can occur in less than 1% of cases, e.g. Japanese encephalitis virus; for the equine encephalitis viruses, fatality rates can reach over 10% of cases. It may be useful to look at the incidence of subclinical cases, such as a spike in absenteeism because of headaches or flu-like symptoms, when the first clinically significant cases appear. |
| Subclinical to mild: | Headache, non-specific "flu-like" symptoms. |
| Treatment of subclinical cases: | In a large-scale outbreak, otherwise healthy adults with subclinical to mild symptoms and no other risk factors that may lead to further development of the disease may have to be sent home with an information sheet to release resources for more severe cases. |
| Mild to moderate: | Fever, nausea (lightheadedness, dizziness), anorexia |
| Moderate to severe: | Vomiting, diarrhea, disorientation, stiff neck, aseptic meningitis, lethargy, meningitis, meningoencephalitis |
| Severe to fatal: |
Extreme neurological and behavioral symptoms including:
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| Sequelae: | Long-term neurological, neuromuscular, or psychiatric defects are common in survivors of severe cases of viral encephalitis. |
| Precautions for health care personnel: |
Standard or universal precautions for personnel dealing with patients. Risk of secondary infection from victims of the preliminary attack is low. Biological samples for laboratory diagnosis and body fluids should be handled at the highest level of biological containment available. |
| Vector control: |
Most of these agents are carried by mosquitos or ticks. Sample collection and screening should begin as soon as an attack is suspected. In the case of lymphocytic choriomeningitis, rodent screening will be needed. Instructions on minimizing the risk of mosquite or tick bites should be disseminated through news outlets. |
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