CLINICAL DESCRIPTION

Viral Encephalitis is divided into two groups, based upon the different causes of each one. The first group, Neurotropic-Virus Encephalitis, occurs in an individual as a primary infection. These viruses affect mostly wild birds and animals and are transmitted to humans through insect vectors. The West Nile, Eastern Equine and St. Louis viruses are examples of infections transmitted to humans through mosquitoes. Ticks are also potential carriers of encephalitis and Russian Spring-Summer Encephalitis is an example of a viral illness transmitted by ticks.

The second type of viral encephalitis occurs as a complication to a primary infection. This type can appear as postinfective encephalitis or postvaccinal encephalitis. Postinfective encephalitis is caused as a complication to other viral infections such as polio, measles, mumps, chickenpox, smallpox, and rubella, to name a few. However, postvaccinal encephalitis occurs as a reaction to vaccines for smallpox or yellow fever. In addition, encephalitis may also appear from exposure to certain bacteria, parasites, harmful chemicals or heavy metal poisoning.

The symptoms of viral encephalitis can range from so mild that it goes unnoticed to life threatening. Mild cases may experience no symptoms or a general ill feeling accompanied with a fever and a persistent headache. More severe cases have many more prominent symptoms, which may include vomiting, lethargy, speech impairment, double vision, seizures and unconsciousness. Suffers of encephalitis may also experience personality changes and mood swings.

CASE CLASSIFICATION

1. CONFIRMED
   
   A clinically compatible case which is laboratory confirmed by:
   • A fourfold or greater change in serum antibody titer, or
   • Isolation of virus from, or demonstration of viral antigen or genomic sequences in, tissue, blood, cerebrospinal fluid (CSF), or other body fluid, or
   • Specific immunoglobulin M (IgM) antibody by enzyme immunoassay (EIA) antibody captured in CSF or serum. Serum IgM antibodies alone should be confirmed by demonstration of immunoglobulin G antibodies by another serologic assay (e.g., neutralization or hemagglutination inhibition).
     
     
2. PROBABLE
   
   A clinically compatible case occurring during a period when arboviral transmission is likely, and with the following supportive serology: a stable (less than or equal to twofold change) elevated antibody titer to an arbovirus (e.g., greater than or equal to 320 by hemagglutination inhibition, greater than or equal to 128 by complement fixation, greater than or equal to 256 by immunofluorescence, and greater than or equal to 160 by neutralization, or greater than or equal to 400 by enzyme immunoassay IgM).
   
   
3. POSSIBLE
   
   Not used