Weil-Felix is a nonspecific agglutination test that detects anti-rickettsial antibodies in patients’ serum. Weil-Felix test is based on cross-reactions that occur between antibodies produced in acute rickettsial infections with antigens of OX (OX 19, OX 2, and OXK) strains of Proteusspecies. Dilution of the patient’s serum is tested against suspensions of the different Proteusstrains.
Several rickettsiae, such as Rickettsia prowazekii, Rickettsia tsutsugamushi, and R. rickettsii, possess antigens that cross-react with antigens of OX strains of Proteus vulgaris. ProteusOXK strain agglutinins are produced in scrub typhus and OX 2 and OX 19 agglutinins in other rickettsial diseases, see the table below
Limitation of Weil-Felix test
Both sensitivity and specificity of the Weil-Felix test are low, but its predictive value can be increased by testing both acute and convalescent-phase samples and observing a rise in antibody titre.
Weil-Felix test has low sensitivity, i.e. it gives a high percentage of false-negative results. This is common in the case of scrub typhus.
It also shows low specificity, i.e. false-positive results are obtained in other diseases such as leptospirosis, and relapsing fever (diseases which require differentiating from rickettsial infections), in Proteus infections, brucellosis, and acute febrile illness.
References
- Cox, A. L., Zubair, M., & Tadi, P. (2023). Weil Felix Test. In StatPearls. StatPearls Publishing.
- Amano K. (2005). Nihon rinsho. Japanese journal of clinical medicine, 63 Suppl 7, 146–148.