Encephalitis: Viral - Diagnosis

Tests for antibodies are only useful in patients who survive the acute attack. They must be performed at the following times:

The first test is taken when the symptoms first occur. At that time, antibody levels are low or absent. Antibodies rise over time.
The next test is taken during convalescence (about 3 to 5 weeks later). For a diagnosis of the virus, antibody levels at that time should be at least four times the initial measurement.

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In the case of West Nile virus, a 2003 study suggested that antibodies may persist a year or more after an initial infection.

Polymerase Chain Reaction (PCR)

A test called the polymerase chain reaction (PCR) is a rapid diagnostic test that is used to detect some viruses:

PCR uses blood, spinal fluid, or any other tissue specimen that may contain the virus.
It replicates a piece of the viral DNA millions of times until the virus is detectable, usually within2 or3 hours.
Sensitivity is almost equal to viral culture and results are much quicker.

PCR and Herpes Simplex Encephalitis. PCR analysis of spinal fluid is particularly important in diagnosing herpes simplex virus encephalitis. It has allowed the identification of even mild and unusual forms, allowing rapid, life-saving treatments. PCR may not always be effective in diagnosing suspected herpes simplex virus encephalitis in infants and should not be used as the sole test in this age group. PCR is also proving to useful in monitoring treatment in these patients.

PCR and Varicella-Zoster Virus (VZV). PCR is also useful for identifying the VZV virus (which is responsible for chicken pox and shingles).

PCR and Arboviruses. PCR may be less useful for identifying arboviruses, although methods are being developed for identifying many of the common ones. One, for example, can detect West Nile virus within5 hours.

Brain Biopsy

If possible, samples of brain tissue are removed for examination and testing for the presence of the virus. Tissue is examined using staining techniques and then viewed under an electron microscope. In a few cases, brain cells are able to be cultured; that is, the viruses can actually be made to replicate in samples. It is the gold standard for diagnosing rabies.

Virus Culture

A viral culture uses specimens taken from various tissue samples. Samples may be taken of blood, spinal fluid, or from the blisters of infections caused by varicella zoster or herpes, or throat washing for those caused by cytomegalovirus or Epstein-Barr virus. Samples are sent to a laboratory where it takes between 1 to 14 days to detect the virus in the preparation made from the specimen. A culture is also sometimes used in vaccinated patients to determine if encephalitis may be caused by a natural virus or by the vaccine.