Immunofluorescence staining for detection of variola virus

Area of Science:

• Virology
• Epidemiology
• Public Health

Background:

• In 1975, Bangladesh was the last country with endemic variola major smallpox, nearing eradication.
• Existing diagnostic methods included immunodiffusion and embryonated egg culture.
• A rapid and accurate laboratory diagnostic method was needed.

Purpose of the Study:

• To evaluate the effectiveness of a new immunofluorescence (IF) staining technique for diagnosing smallpox.
• To assess the sensitivity and specificity of IF compared to clinical diagnosis and reference laboratory testing.

Main Methods:

• Collected laboratory specimens (scabs, vesicular/pustular impressions) from suspected smallpox patients.
• Performed immunofluorescence (IF) staining on specimens.
• Reinvestigated IF-positive cases and sent subsamples to a WHO reference laboratory for confirmation.

Main Results:

• Out of 144 specimens, 78 tested IF positive for smallpox.
• The IF technique demonstrated 100% sensitivity (no false negatives) for variola major.
• A high rate of false-positive results was observed with the IF technique.

Conclusions:

• The immunofluorescence (IF) technique is highly sensitive for detecting variola major.
• The high false-positive rate of IF precludes its recommendation as a routine screening test for smallpox.
• Accurate laboratory diagnostics are crucial for disease eradication campaigns.