Weil Felix
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Serological agglutination test used historically to aid in the diagnosis of rickettsial infections
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🧪 What is the Weil-Felix Test?
The Weil-Felix test is a serological agglutination test used historically to aid in the diagnosis of rickettsial infections. It detects antibodies in the patient's serum that cross-react with certain strains of Proteus bacteria (OX19, OX2, OXK), which share antigens with Rickettsia species.
❓ Why is the Test Done?
To:
- Support the diagnosis of rickettsial infections such as:
- Typhus (epidemic and murine)
- Spotted fever group rickettsioses (e.g., Rocky Mountain spotted fever)
- Scrub typhus (OXK antigen)
- Aid diagnosis when more specific tests (e.g., PCR, immunofluorescence) are unavailable
📊 Normal Range / Interpretation
Result | Interpretation |
|---|---|
Negative (low titers) | No significant rickettsial infection |
Positive (significant titers) | Suggests current or recent rickettsial infection |
📈 Interpretation of Results
Antigen Used | Positive Agglutination Titers | Associated Infection |
|---|---|---|
OX19 | ≥ 1:80 (varies by lab) | Epidemic typhus, Rocky Mountain spotted fever |
OX2 | ≥ 1:80 | Spotted fever group rickettsiae |
OXK | ≥ 1:80 | Scrub typhus |
Rising titers in paired sera confirm diagnosis.
🧠 Associated Conditions
Condition | Details |
|---|---|
Epidemic typhus | Caused by Rickettsia prowazekii |
Murine typhus | Caused by Rickettsia typhi |
Scrub typhus | Caused by Orientia tsutsugamushi |
Rocky Mountain spotted fever | Caused by Rickettsia rickettsii |
🔄 Related / Follow-Up Tests
- Immunofluorescence assay (IFA) – gold standard for rickettsial antibodies
- PCR for rickettsial DNA – early diagnosis
- Clinical assessment – rash, fever, exposure history
✅ Fasting Required?
Test | Fasting Required |
|---|---|
Weil-Felix Test | ❌ No |
📝 Summary Table
Parameter | Details |
|---|---|
What | Serological test detecting cross-reacting antibodies to Proteus antigens in rickettsial infections |
Why | Support diagnosis of typhus and spotted fevers |
Normal Result | Negative or low titers |
Positive Result | Elevated titers indicating rickettsial infection |
Associated Conditions | Epidemic typhus, murine typhus, scrub typhus, RMSF |
Follow-up Tests | IFA, PCR, clinical correlation |
Fasting Required | ❌ No |
How our test process works!
