SEROLOGICAL DIAGNOSIS OF INFECTIOUS DISEASES (Typhoid fever)

Question 1

Causative agent of typhoid fever:

Answer 1

Salmonella typhi

Question 2

Most common cause of Salmonellosis in North America:

Answer 2

Salmonella entiritidis

Question 3

A protein produced by S. typhi which inhibits fusion of lysosomes with the phagosome (resists phagocytosis):

Answer 3

SPIC (Salmonella Pathogenicity Island-Chaperone) protein

Question 4

Antibodies against S. typhi appear ______ days after infection

Answer 4

7-10 days after infection

Question 5

Antigens of S. typhi:

Answer 5

O Antigen
H antigen
Vi antigen

Question 6

Thermostable somatic antigen; It is a polysaccharide in nature and is an endotoxin:

Answer 6

O antigen

Question 7

Flagellar antigen; protein in nature:

Answer 7

H antigen

Question 8

Capsular antigen; second somatic antigen that can occur independently of the O antigen; associated with virulent strains; indicative of carrier state

Answer 8

Vi antigen

Question 9

Gold standard for diagnosing S. typhi infection:

Answer 9

Bacterial culture

Question 10

Serological tests for S. typhi:

Answer 10

1. Widal test
2. Typhidot test
3. Tubex

Question 11

Test principle of Widal test:

Answer 11

Direct agglutination

Question 12

Serological test for S. typhi that uses somatic antigens (O, H, A, B)

Answer 12

Widal test (febrile agglutination test)

Question 13

Reporting of Widal test; which scale should be the one reported?

Answer 13

The smallest quantity of the serum that exhibits a 2+ of 50% agglutination is considered the titer and should be the one reported

Important note: A fourfold rise in the titer is more significant than a single determination

Question 14

A titer of 1:80 Somatic O Abs in Nonvaccinated patients:

Answer 14

1:80 titer is suspected of the presence S. typhi infection

Question 15

A titer of 1:160 Somatic O Abs in Nonvaccinated patients:

Answer 15

1:160 titer strongly suggestive for the presence of S. typhi infection

Question 16

A titer of 1:40 Flagellar H in Nonvaccinated patients:

Answer 16

1:40 Flagellar H titer suspects for the presence of the infection

Question 17

A titer of 1:160 Flagellar H in Nonvaccinated patients:

Answer 17

1:160 strongly suggestive for the presence of the infection

Question 18

Somatic O Abs and Flagellar H titer in Vaccinated, Carrier, and Reinfection:

Answer 18

1:160

Question 19

Dot enzyme immunoassay which detects serum antibody to antigen dotted on a nitrocellulose membrane

Answer 19

Typhidot test

Question 20

Typhidot
IgM (+) and IgM/IgG (+/-):

Answer 20

• Definite typhoid fever
• Acute typhoid fever

NOTE: Tyophidot-M is a dot enzyme immunoassay for the detection of specific IgM to Salmonella typhi

Question 21

Typhidot
IgG (+)

Answer 21

• Previously successfully treated case of typhoid fever
• Reinfection with typhoid fever
• Typhoid carrier

NOTE: Tyophidot-M is a dot enzyme immunoassay for the detection of specific IgM to Salmonella typhi

Question 22

Typhidot
IgM and IgG

Answer 22

• Not typhoid fever OR
• Ongoing typhoid infection

NOTE: Tyophidot-M is a dot enzyme immunoassay for the detection of specific IgM to Salmonella typhi