Detection of Viral Infections

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Detection of Viral Infections
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Major Factors that DriveLaboratory Diagnosis of
Viral Infection

• Risk to patient or an unborn fetus
• Availability of FDA-Licensed Antiviral Drugs for
  treatment of certain viral infections
• Availability of rapid assays that possess high
  specificity and sensitivity
• Availability of reliable immunologic and
  molecular assays that enhance definitive
  identification of viruses.

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Well-Defined Indicator for Laboratory Diagnosis
of Viral Infections

• Viral infections that occur during pregnancy
  ExamplesRubella virus infection HSV-1/HSV-2
  genitalis
• Viral infections that occur in immuno-compromised
  patients ExamplesMeasles or Varicella in
  inpatient cancer treatment centers.
• Viral infections that partially mimic bacterial
  infections ExampleMeningitis.

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• Viral infections for which there are established
  drug treatment regimens ExamplesHIV-1, HSV-2,
  Influenza Viruses A/B, HPV, HCMV
• Viral infections that pose potential public
  health risks ExamplesInfluenza A virus,
  Ebola or Marburg Virus, Dengue virus, HAV,
  HBV, HCV
• Virus infections caused by emerging or
  re-emerging viral pathogens
• Viral infections that can be controlled by rapid
  post-exposure immunization Examplerabies virus
  infection

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Indirect versus Direct Methods for Detection of
Viral Infections

• Vast majority of indirect methods are based on
  the use of viral antigen(s) to detect evidence of
  a specific humoral response ExampleELIASA
  tests, Immunofluorescence tests, Western Blot
  tests, RIBA procedures
• Direct methods for viral detection are generally
  based on the use of selected cell cultures for in
  vitro isolation of virions Classic
  ExamplesHSV-2 in Vero Cell Cultures or specific
  antibody to capture viral antigen(s) Rotavirus
  (fecal specimen), Influenza A virus (bronchial
  lavage)

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• Non-routine methods that are used to detect
  and/or confirm viral infections include
• PCR
• Reverse Transcription PCR
• Dot Blots
• Southern Blot
• Northern Blot
• Electron Microscopy

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Key Parameters of the Reliability of Laboratory
Tests

• Specificity and Sensitivity describe the
  performance and value of the test
• Sensitivity Percentage of those with the disease
  or infection who are positive, e.g., a certain
  E/A method that is used to screen a population
  for HIV-antibody may display a sensitivity of
  98, i.e.98/100 will be correctly diagnosed and
  2/100 will be missed. (The false-negative rate
  2.)

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• Specificity Percentage of those without
  infection who are negative, e.g. the same E/A
  method used above to measure HIV-1 antibody may
  have a specificity of 97, i.e. 97/100 uninfected
  people will be correctly diagnosed, but 3/100
  will be incorrectly scored as infected. (The
  false-positive rate 3.)

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Table of Possible Test Results