Question

Widal test is used for susceptibility of
(a) Malaria
(b) Cholera
(c) Yellow fever
(d) Typhoid

Answer 1

Typhoid fever is usually confirmed by analysing samples of blood, stools or urine. There are six types of tests for diagnosing malaria. The diagnosis of cholera is confirmed by isolating V. cholerae from stool cultures. The blood itself will reveal the yellow fever virus and if it doesn’t then antibodies and other substances specific to the virus can be detected.

Complete Answer:
Widal test is an indirect agglutination test for enteric fever or undulant fever. Enteric fever or typhoid fever, also known as typhoid, is a disease caused by Salmonella serotype typhi bacteria. In the test, the bacteria causing typhoid is mixed with a serum containing specific antibodies obtained from an infected individual. It is basically a dot ELISA kit that detects IgM (immunoglobulin M) and IgG (immunoglobulin G) antibodies against the outer membrane protein of the Salmonella typhi. The test becomes positive within 2-3 days of infection and separately identifies IgM and IgG antibodies. Typically, typhoid is accompanied by diarrhea, progressive fever and rose colored rashes on the body. The Widal test is both quantitative as well as qualitative and it can show the titres of specific antibodies. IgM shows any recent infection whereas IgG signifies remote infections. The test gives results as either positive or negative.
The main principle of widal test is that if any homologous antibody is present in the patient's serum, it will react with the respective antigen present in the reagent and give visible clumping on the test card and agglutination in the tube. The antigens used in the test are “H” and “O” antigens of Salmonella typhi and “H” antigen of S. paratyphi.

Therefore option d, is the correct answer

Note:
Widal test is also used to check undulant fever or brucellosis which is a highly contagious zoonosis caused by the ingestion of unpasteurized milk or undercooked meat from infected animals, or close contact with their secretions. It is also known as Malta fever or Mediterranean fever. The dot enzyme-linked immunosorbent assay (Dot-ELISA) is a solid-phase immunoassay for antibody or antigen detection which uses minute amounts of reagent dotted onto solid surfaces such as nitrocellulose and other paper membranes which avidly bind proteins.