Transcript Weil Felix test

BRUCELL
WEIL FELIX TEST
WIDAL TEST
BRUCELL
• Gram negative small coccobacilli.
• Non- motile.
• None encapsulated.
• Fastidious, need special media with CO2 and
anaerobic condition for growth these media
called as Castenada media.
• facultative intracellular parasites causing
chronic disease
• Cause brucellosis disease or undulating fever.
Species of Brucella:
• Brucella abortus
• Brucella melitinsis
• Brucella bovis
• Brucella suis.
Mode of transmission:
• Brucellosis is a zoonotic disease transmitted by:
• Ingesting infected food by Brucella bacteria.
• Direct contact with infected animals.
• Inhalation of aerosols.
• Consumption of unpasteurized milk products.
• Transmission from human to human, through sexual
contact or from mother to child, is rare but possible.[1]
Symptoms:
• Signs and symptoms are similar to those of the flu and include:
• Fever
• Chills
• Sweats
• Weakness
• Fatigue
• Joint, muscle and back pain
• Headache
• Brucellosis symptoms may disappear for weeks or months and then
return. In some people, brucellosis becomes chronic, with symptoms
persisting for years, even after treatment. Long-term signs and
symptoms include fatigue, fevers, arthritis and spondylitis — an
inflammatory arthritis that affects the spine and adjacent joints.
• The infection can usually be treated successfully with antibiotics.
Treatment takes several weeks, however, and relapses are common.
Diagnosis :
• Blood culture in first week of infection.
• Brucella is isolated from a blood culture on Castenada medium.
Prolonged incubation (up to 6 weeks) may be required as they're slowgrowing, but on modern automated machines the cultures often show
positive results within seven days. On Gram stain they appear as dense
clumps of Gram-negative coccobacilli and are exceedingly difficult to see.
• Animal inoculation test.
• Serology test.
• Serology for brucellosis is a blood test to look for antibodies against
Brucella, the bacteria that causes the disease brucellosis. The blood is
then tested in a laboratory to look for antibodies. For Brucella, the serum
agglutination test (SAT) is the simplest and most widely used testing
method. This test done after 2 weeks (10 days) of fever.
• The CDC/Council of State and Territorial Epidemiologists case
definition for human brucellosis states that the laboratory
criteria for diagnosis includes
• 1) Isolation of Brucella species from a clinical specimen,
• 2) Four-fold or greater rise in Brucella agglutination titer between acute-
and convalescent-phase serum specimens drawn >2 weeks apart and
studied at the same laboratory, or
• 3) Demonstration by immunofluorescence of Brucella species in a clinical
specimen.
Normal results:
• A normal result shows no antibodies to Brucella. However,
during the first few days to weeks of exposure to an antigen,
there may be very little antibody production. As brucellosis
progresses, more antibodies will be present. If the health care
provider suspects brucellosis, you may need to have the test
repeated 10 days to 2 weeks after the first test to watch for this
rise.
• Negative to a titer of > or =1:40 can be seen in the normal,
healthy population. A titer of > or =1:80 is often considered
clinically significant;(1) however, a 4-fold or greater increase in
titer between acute and convalescent phase sera is required to
diagnose acute infection.
• Prozone phenomena:
• The presence of high antibody titer that lead to Ag block and hence false
negative results are obtained. Dilution will resolve this problem.
Note:
• A normal (negative) result usually means you have not come in contact
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with the bacteria that causes brucellosis. However, this test may not
detect the disease at an early stage. Your doctor may have you come
back for another test in 10 days to 3 weeks.
Brucella antibody have long lifespan may reach one year.
Infection with other bacteria, such as Yersinia , Francisella , and Vibrio ,
and certain immunizations can cause false-positive results.
Normal value ranges may vary slightly among different laboratories.
Some labs use different measurements or test different samples. Talk to
your doctor about the meaning of your specific test results.
An abnormal (positive) results usually means you have come in contact
with the bacteria that causes brucellosis. However, this does not mean
that you have an active infection. Your doctor will repeat the test after a
few weeks to see if the test result increases. This is more likely to be a
sign of a current infection.
OX- 19
( WEIL FELIX TEST )
Rickettsia
• Obligately intracellular
• grown in embryonated eggs or tissue culture
• Gram-negative
• Small, pleomorphic coccobacilli
• Transmitted by arthropod vectors (ticks, lice, fleas,
mites, chiggers).
• Include the genera Rickettsiae, Ehrlichia, Orientia,
and Coxiella.
• zoonotic pathogens cause infections that disseminate
in the blood to many organs.
Complications:
• Lymphocytosis
• Leukopenia
• Thrombocytopenia
• Anemia, in some cases hemoglobin may increase as
result of hemoconcentration.
• Urine analysis will show high RBCs, cast may be
present, high protein .
• Increase blood urea and creatinine.
INVESTIGATIONS
• PCR – Amplification of O tsutsugamushi DNA from the
blood of febrile patients.
SEROLOGICAL TESTS such as
• Indirect Flourescent antibody test (IFA) test ( Titer ≥ 1:
200 ),
• the Complement Fixation Test.
• The Weil Felix Test
• Scrub IgM ELISA Test: Highly specific test
Weil Felix test
• Reckettsial infection (typhus fever) will cause
heterolphilic antibodies that agglutinate some strains
of Proteus.
• The agglutination reactions, the basis of the test is the
sharing of an Alkali stable carbohydrate antigen of
rickettsia and by certain strains of Proteus.
• Slide and tube method.
• Test is negative in rickettsialpox,
• False positive reaction may occur in urinary or other
Proteus infections.
• Typhus group rickettsiae
• (Rickettsia prowazekii, R. typhi) react with P. vulgaris OX19,
• scrub typhus (Orientia tsutsugamushi) reacts with P.
mirabilis OXK. T
• 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.[2]
Diagnosis of Rickettsiosis (typhus fever ) :
• difficult to diagnose both clinically and in the laboratory.
• Cultivation requires viable eukaryotic host cells, such as
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antibiotic-free cell cultures, embryonated eggs, and susceptible
animals.
Confirmation of the diagnosis requires comparison of acuteand convalescent-phase serum antibody titers.
If OX-19 test is positive, this result is due to infection with
Proteus or Rickettsia.
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%.
As a result, it has largely been supplanted by other methods of
serology, including indirect immunofluorescence antibody (IFA)
testing, which is the gold standard.
Slide method (Laboratory Test)
1. On a solid surface (glass slide, tile, card), a small
amount (50–100 μL) of the patient’s serum is
placed.
2. A single drop of the desired antigen is added, and
the resulting suspension is mixed and then rotated
for one minute.
3. Visible agglutination is indicative of a positive result,
and corresponds roughly to a titre of 1:20.
4. Positive results can be further titrated using the
tube method, which is more labour-intensive.
Tube method (Laboratory Test)
1. Using 0.25% phenol saline as a diluent, a series of
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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
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 titer corresponds to the most dilute tube in the
series that still shows positivity.
Generally, a titre of ≥1:320 is considered diagnostic.
• To differentiate between Proteus infection and
Rickettsial infection:
Proteus
Positive
Rickettsia
Negative
Total WBC
Increased
(leukocytosis)
Decreased
(leukopenia)
WBC differentiation
Neutrophillia
lymphocytosis
Culture from ear
discharge and urine
WIDAL TEST
• Use to diagnosis of typhoid fever which caused by
Salmonella.
• In diagnosis of typhoid fever, patient serum is tested
for salmonella O and H antibodies against Ag
suspension.
• The test is done after 2-3 weeks of infection or after
10 days of fever.
• There are two species of Salmonella :
• Salmonella typhi
• Salmonella paratyphi
• S. paratyphi A
• S. paratyphi B
• S. paratyphi C
• Both typhi and paratyphi have two types of antigen:
• Somatic ( O ) antigen, and that is thermostable.
• Flagellar( H ) antigen, and that is thermolabile.
• Salmonella can be isolated from GIT, urine, blood, bile,
bone marrow, sputum, food products, and milk.
• The confirmatory test for Salmonella is stool culture at
the first week of infection.
Antigenic structure of Salmonella
H( flagel) antigens
O (somatic) antigens
Vi (Virulence) capsular
polysaccharide antigens
Principle of test:
• Patients suffering from enteric fever would possess
antibodies in their sera which can react and
agglutinate serial doubling dilutions of killed colored
Salmonella antigens in a tube agglutination test.
Procedures: Slide method
• A slide widal test is more popular among diagnostic
laboratories as it gives rapid results.
• Qualitative test: One drop each of undiluted patients’ serum
samples for the four antigens are placed on the circled card and
one drop of each of the four Salmonella antigens are added
separately and gently rotated for one minute. Appearance of
agglutination gives qualitative results. To know the titer for
each of the antigens, the test is repeated with dilutions of
serum.
• Quatitative test: 80 μl, 40 μl, 20 μl, 10 μl and 5 μl of patient’s
serum each for the four antigens are placed on the circled card.
To each series of serum
• specimen, one drop of specific antigen is added to each, mixed
and rotated for one minute. Agglutination in each of these is
noted.
• 80 μl corresponds to 1/20 dilution, 40 μl to 1/40, 20 μl to 1/80,
10 μl to 1/160 and 5 μl corresponds to 1/320 titre.
Incubated in water bath at 370C overnight
Procedures:
• Tube method:
Reading the results:
• The control tubes must be examined first, where they
should give no agglutination.
• The agglutination of O antigen appears as a “matt” or
“carpet” at the bottom.
• Agglutination of H antigens appears loose, wooly or
cottony.
• The highest dilution of serum that produces a positive
agglutination is taken as titer.
• The titers for all the antigens are noted.
Other Methods:
 Typhiod Rapid IgM-Assay
 Detects specific IgM and IgG antibodies to S. Typhi
 PCR
 The PCR technology has an unparalleled sensitivity and
specificity for the diagnosis of typhoid
Rapid IgM Kit
 HBSAG
 HCV
 HIV
 HPYLORI
 MALARIA
 TYPHIDOT
 TOXOPLASMA
Rapid IgM Kit
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