Weil – felix test

DR.T.V.RAO MD 1

Dr.T.V.Rao MD

WEIL – FELIX TEST

DR.T.V.RAO MD 2

• Gram-negative, obligate intracellular coccobacilli bacteria that infect mammals and arthropods

• Rickettsia are transmitted in the arthropods, which serves as both vector and reservoir

• Contain Both DNA and RNAIs sensitive to antibiotics.

RICKETTSIA GENERAL INTRODUCTION

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CATEGORY OF RICKETTSIA• Genus

Rickettsia, Coxiella ,Orientia,Ehrlichia Bartonella

• Species

Rickettsia prowazekii (epidemic typhus), Rickettsia typhi (endemic typhus), Rickettsia rickettsii (spotted fever), Rochalimaea Quintana (trench fever), Coxiella burnetii (Q fever)

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RICKETTSIA AND SEROLOGY• Rickettsiae is a genus of motile, Gram-negative,

non-spore forming, highly pleomorphic bacteria that can present as cocci (0.1 μm in diameter), rods (1–4 μm long) or thread-like (10 μm long). Obligate intracellular parasites

• Because of this, Rickettsiae cannot live in artificial nutrient environments and are grown either in tissue or embryo cultures (typically, chicken embryos are used).

• Still we have to dependent on Weil Felix test

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• The agglutination reactions, based on antigens common to both organisms, determine the presence and type of rickettsial infection

• Because Rickettsia are both fastidious and hazardous, few laboratories undertake their isolation and diagnostic identification

• Weil-Felix test that is based on the cross-reactive antigens of OX-19 and OX-2 strains of Proteus vulgaris.

WEIL-FELIX A HETEROPHILE AGGLUTINATION TEST

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• In 1915, Weil and Felix showed that serum of patients infected with any member of the typhus group of diseases contains agglutinins for one or more strains of O X Proteus. In cases of typhus fever the reaction usually appears before the sixth day and reaches its height in the second week.

WEIL AND FELIX CONTRIBUTE FOR TESTING

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BASIS OF THE WEIL-FELIX 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 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.

WEIL-FELIX TESTINDICATED IN WHEN PATIENTS PRESENT WITH

RASHES

• Test for diagnosis of typhus and certain other rickettsial diseases. The blood serum of a patient with suspected rickettsial disease is tested against certain strains of (OX-2, OX-19, OX-K)..

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DR.T.V.RAO MD 9

WEIL-FELIX REACTION – A HETEROPHILE AGGLUTINATION

TEST

• A Weil-Felix reaction is a type of agglutination test in which patients serum is tested for agglutinins to O antigen of certain non-motile Proteus and rickettsial strains (OX19, OX2, OXK)

• OX19, OX2 are strains of Proteus vulgaris.OXK is the strain of Proteus mirabilis.

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• The Weil-Felix Test can be done as either a slide or a tube test. The antigens necessary (OX2, OX19, and OXK) can be obtained commercially.

PROCEDURE OF WEIL -FELIX TEST

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• On a solid surface (glass slide, tile, card), a small amount (50-100 μL) of the patient’s serum is placed. A single drop of the desired antigen is added, and the resulting suspension is mixed and then rotated for one minute. Visible agglutination is indicative of a positive result, and corresponds roughly to a titre of 1:20. Positive results can be further titrated using the tube method, which is more labour-intensive.

SLIDE METHOD

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TUBE METHOD• Using 0.25% phenol saline as a diluent, a series of

tubes containing twofold dilutions of patient serum are made with a final volume of 1 mL. A drop of antigen suspension is added to each tube, and the mixture is incubated at 50-55 °C for 4-6 hours. A positive tube would show visible flocculation or granulation, which is accentuated when the tube is gently agitated. The titre corresponds to the most dilute tube in the series that still shows positivity. Generally, a titre of ≥1:320 is considered diagnostic.

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INTERPRETATIONS IN WEIL-FELIX REACTION

• Sera from endemic typhus agglutinate OX19, OX2.Tick borne spotted fever agglutinate OX19, OX2.

• Scrub Typhus agglutinate OXK strain

• Test is negative in rickettsialpox, trench fever and Q-fever.False positive reaction may occur in urinary or other Proteus infectionsTest may be negative in 50 percent scrub typhus

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WEIL FELIX TEST AND CONCENTRATION CAMPS

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WEIL-FELIX TEST POSITIVITY SAVES FROM NAZIS

• In Poland, during World War II, where a pair of quick-thinking doctors used a little-known organism to keep the Nazis at bay.

The microorganisms is Proteus OX19. . Its one remarkable feature is that human antibodies for Proteus OX19 cross-react with the antibodies for Rickettsia – the bacterium responsible for the deadly disease typhus. Blood from a patient infected with Proteus Ox19 will give a false-positive in the most common typhus screening method, the Weil-Felix test.

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• While the Polish doctors could, and did, inject a number of other people with Proteus to induce positive Weil-Felix results, an on-site Nazi medical team could well have proved their undoing. Fortunately, ingenuity and a good dose of hospitality and alcohol prevented them from being

uncovered. ( From the British Medical Journal)

HOW THEY MADE WEIL-FELIX TEST POSITIVE

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LIMITATION OF WEIL-FELIX TEST• 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.

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• Created by Dr.T.V.Rao MD for Medical and Paramedical Students in the

Developing World• Email

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