Laboratory Activities 6 and 7 – Widal Test Flashcards
is a pathologic process brought about by pathogenic microorganisms in which an extremely high fever is a characteristic manifestation.
Febrile disease
An example of febrile illness is [?] caused by microorganisms under the genus Salmonella.
typhoid fever
Widal test is a method that qualitatively detects and quantitatively measures the antibodies in the serum of a patient with typhoid fever. This test includes Salmonella species other than Salmonella typhi by the use of a variety of Salmonella O and H antigens.
During the disease, the body responds to this antigenic stimulation by producing antibodies with titers that [?] in early stages to a peak and then [?] until it is undetectable.
increase slowly
gradually fall
Diseases characterized by fever caused by bacterial microorganisms that include:
o Typhoid fever o Paratyphoid fever o Brucellosis o Tularemia o Typhus
Antibodies to Salmonella may be detected in the patient’s serum from the
second week after the onset of infection
are antibodies produced in response to various fever-producing bacteria
Febrile agglutinins
Febrile Diseases
Includes the following conditions
TYPHOID FEVER
TYPHUS FEVER
Salmonella infection
TYPHOID FEVER
Rickettsial infection (Typhus, Rocky Mountain spotted fever, other rickettsial infections)
TYPHUS FEVER
Transmission: Ingestion of contaminated food or food products
TYPHOID FEVER
TYPHUS FEVER
Associated conditions:
o Gastroenteritis
o Bacteremia and extraintestinal infections
o Enteric fever (Typhoid fever)
TYPHOID FEVER
TYPHUS FEVER
Standard technique for the diagnosis of typhoid fever
Culture method
TYPHOID FEVER
Laboratory diagnosis:
a. Culture method
b. Widal agglutination test
TYPHOID FEVER
Laboratory diagnosis:
TYPHUS FEVER
Laboratory diagnosis:
a. Weil-Felix Agglutination
b. Rickettsial antibodies
a. Culture method Specimens
blood, urine, stool
Principle: Bacterial agglutination that detects antibodies in typhoid fever, tularemia, and brucellosis
Widal agglutination test
o Antibody of the patient’s serum is measured by adding a constant amount of antigen (i.e., Salmonella species antigens) to serially diluted serum ® After appropriate incubation, the tubes are examined for visible agglutination
Widal agglutination test: Bacterial agglutination
Widal agglutination test
Measures the presence of anti-O and anti-H antibodies using bacterial suspensions using:
o Killed Salmonella typhi and Salmonella paratyphi that have been treated to retain O and H antigens
o Brucella abortus (for tularemia and brucellosis)
Measures the presence of anti-O and anti-H antibodies using bacterial suspensions
Widal agglutination test
Widal agglutination test
Antibodies detected:
o Antibodies to O = _______________ (IgG or IgM?)
o Antibodies to H = _______________ (IgG or IgM?)
o Antibodies to O = _______________ (IgG or IgM?)
o Antibodies to H = _______________ (IgG or IgM?)
Widal agglutination test
Interpretation of results:
0
1+
2+
3+
4+
0 No agglutination
1+ 25% agglutination
2+ 50% agglutination
3+ 75% agglutination
4+ 100% agglutination
Note: A single rapid slide test is NOT considered positive unless a value of at least [?] is assigned in a sample taken in the [?] of infection
2+
first 2-3 weeks
• Qualitative test to detect IgM and IgG antibodies in the serum of a patient with typhoid fever
Typhidot
• Detects serum antibody to antigen dotted on a nitrocellulose membrane
Typhidot
• Non-specific rickettsial test based on cross-reacting antibodies induced by some rickettsiaeb.
Weil-Felix Agglutination
• Antibodies generated from rickettsial infection cross-react with polysaccharide O antigens of some Proteus species
Weil-Felix Agglutination
Weil-Felix Agglutination
Proteus species:
o Proteus OX2 and Proteus OX19:
o Proteus OXK:
gold standard for diagnosis of TYPHUS FEVER
Rickettsial antibodies
o Various antigens can be employed in slide agglutination tests to screen for febrile agglutinins
Serological Tests for Febrile Agglutinins
o If a febrile agglutinin is found, it can be titrated by doubling dilutions of the patient’s serum (i.e., 1:20 through 1:320) and adding a constant amount of bacterial antigen
Serological Tests for Febrile Agglutinins
Serological Tests for Febrile Agglutinins
Three controls should be run simultaneously:
(1) antigen control
(2) known positive serum control
(3) known negative serum control
