History and Basis For Test
The basis of the test is the presence of antigenic cross-reactivity between Rickettsia spp. and certain serotypes of non-motile Proteus spp., a phenomenon first published by Edmund Weil and Arthur Felix in 1916. The serum of patients diagnosed with epidemic typhus was found to agglutinate in the presence of bacteria now known as Proteus vulgaris. Ensuing work elucidated that it was in fact the somatic (O) antigen that cross-reacted with anti-rickettsial antibodies, and furthermore, that different Proteus O antigens would cross-react with different species of Rickettsia.
Typhus group rickettsiae (Rickettsia prowazekii, R. typhi) react with P. vulgaris OX19, and scrub typhus (Orientia tsutsugamushi) reacts with P. mirabilis OXK. The spotted fever group rickettsiae (R. rickettsii, R. africae, R. japonica, etc.) react with P. vulgaris OX2 and OX19, to varying degrees, depending on the species.
The Weil–Felix test suffers from poor sensitivity and specificity, with a recent study showing an overall sensitivity as low as 33% and specificity of 46%. Other studies have had similar findings. As a result, it has largely been supplanted by other methods of serology, including indirect immunofluorescence antibody (IFA) testing, which is the gold standard. However, in resource-limited settings, it still remains an important tool in the diagnosis and identification of public health concerns, such as outbreaks of epidemic typhus.
Read more about this topic: Weil-Felix Test
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