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Transcript of weilfelixtest-120213194736-phpapp02
Dr.T.V.Rao MD
WEIL – FELIX TEST
DR.T.V.RAO MD 1
• 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
DR.T.V.RAO MD 2
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)
DR.T.V.RAO MD 3
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 DR.T.V.RAO MD 4
• 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
DR.T.V.RAO MD 5
• 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
DR.T.V.RAO MD 6
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. DR.T.V.RAO MD 7
WEIL-FELIX TEST
INDICATED 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)..
DR.T.V.RAO MD 8
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.
DR.T.V.RAO MD 9
• 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
DR.T.V.RAO MD 10
• 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
DR.T.V.RAO MD 11
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.
DR.T.V.RAO MD 12
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 infections Test may be negative in 50 percent scrub typhus
DR.T.V.RAO MD 13
DR.T.V.RAO MD 14
WEIL FELIX TEST AND
CONCENTRATION CAMPS
DR.T.V.RAO MD 15
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.
DR.T.V.RAO MD 16
• 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
DR.T.V.RAO MD 17
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.
DR.T.V.RAO MD 18
• Created by Dr.T.V.Rao MD for Medical
and Paramedical Students in the
Developing World
DR.T.V.RAO MD 19