Febrile Antigens are stained bacterial antigen suspensions used to identify and measure antibodies in human sera, following infection. Bacterial infection will cause the body to produce antibodies in response to the invading pathogen. When the serum sample is mixed with a febrile antigen, the solution will agglutinate if antibodies are present, indicating infection. Febrile Antigens are also known as Widal reagents – named after George-Fernand Widal who applied the agglutination reaction (discovered by Gruber and Durham) to test for typhoid fever using human serum. The Widal test became the first example of serum diagnostics, leading the way for blood science.

Rapid Labs offer a range of high density and standard Febrile Antigens for the identification of Salmonella, Proteus and Brucella bacterial infections. High Density Febrile Antigens are typically used in areas which have a low exposure to the disease, whilst Standard Febrile Antigens are more suited to endemic areas with a high incidence/risk of the disease. All our tests are easy-to-use, affordably priced and offer fast results to enable efficient screening for for disease. They are available to use as both slide or tube methods. The slide method provides immediate agglutination, which is useful for obtaining an estimate titre, whilst the tube method can be used to determine the titre and is generally considered a more accurate (albeit less rapid) method.


Brucella Febrile Antigen Range:

Brucella are a group of Gram-negative, rod-shaped bacteria. Infection (Brucellosis) can occur in humans usually by the consumption of unpasteurised milk and/or close contact with infected farm animals. Rapid Labs offer febrile antigens for two of the most common Brucella species that can affect humans: Brucella Abortus and Brucella Melitensis. Brucella Melitensis is the most virulent and invasive species, usually infecting goats and sheep. Brucella Abortus is less virulent and primarily affects cattle. Our febrile antigens are available in 5ml volumes:

Product Name Type Cat. No.
Brucella Abortus Febrile Antigen High Density HF-BAAF
Brucella Abortus Febrile Antigen Standard F-BAAF
Brucella Melitensis Febrile Antigen High Density HF-BMA5
Brucella Melitensis Febrile Antigen Standard F-BMA5


Proteus Febrile Antigen Range

Proteus is a genus of Gram-negative saprophytic bacteria. They are found in decomposing matter, manure soil, faeces and sewage. The OX-2, OX-19 and OX-k strains can cross-react with several species of the Rickettsiae bacteria:

Proteus Strain Rickettsiae Strain Associated Disease
OX-19 Rickettsia typhi Murine Typhus
OX-19 Rickettsia prowazekii Epidemic Typhus
OX-k Orientia tsustsugamushi Scrub Typhus
OX-2 Rickettsia rickettsia Rocky Mountain Spotted Fever
OX-2 Rickettsia africae African Tick-Bite Fever
OX-2 Rickettsia japonica Japanese Spotted Fever


Rapid Labs offers Febrile Antigens in 5ml sizes for the OX-2, OX19 and OX-k strains of Proteus:

Product Name Type Cat. No.
Proteus OX-19 Febrile Antigen High Density HF-POX195
Proteus OX-19 Febrile Antigen Standard F-POX195
Proteus OX-k Febrile Antigen High Density HF-POXK5
Proteus OX-k Febrile Antigen Standard F-POXK5
Proteus OX-2 Febrile Antigen High Density HF-POX25
Proteus OX-2 Febrile Antigen Standard F-POX25


Salmonella Febrile Antigens

Salmonella is a genus of rod-shaped Gram-negative bacteria. There are over 2500 serotypes. Rapid Labs offer a range of Febrile Antigens for the most common serovars tested for in 5ml sizes. Serovars displaying somatic ‘O’ antigens are stained blue, whilst serovars displaying flagella ‘H’ antigens are stained red. The IgM somatic O antibody appears first and represents the initial serologic response in acute typhoid fever, while the IgG flagella H antibody usually develops more slowly but persists for longer:

Antigen Group  Serovars Febrile Antigen Type Cat. No. 
A S. Paratyphi A, S. Paratyphi A var. Durazzo Salmonella O Antigen Group A High Density HF-SOA5
Salmonella O Antigen Group A Standard F-SOA5
Salmonella H Antigen Group A High Density HF-SHA5
Salmonella H Antigen Group A Standard F-SHA5
B S. Paratyphi B, S. Paratyphi B var. Odense, S. Java, S. Limete Salmonella O Antigen Group B High Density  HF-SOB5
Salmonella O Antigen Group B Standard F-SOB5
Salmonella H Antigen Group B High Density HF-SHB5
Salmonella H Antigen Group B Standard F-SHB5
C S. Paratyphi C, S. Choleraesuis, S. Choleraesuis var. Kunzendorf, S. Decatu, S. Typhisuis Salmonella O Antigen Group C High Density HF-SOC5
Salmonella O Antigen Group C Standard F-SOC5
Salmonella H Antigen Group C High Density HF-SHC5
Salmonella H Antigen Group C Standard F-SHC5
D S. Typhi, S. Ndolo Salmonella O Antigen Group D High Density HF-SOD5
Salmonella O Antigen Group D Standard F-SOD5
Salmonella H Antigen Group D High Density HF-SHD5
Salmonella H Antigen Group D Standard F-SHD5


If you would like more information about any of our febrile antigens, or would like to place an order, please get in touch and we’ll be happy to help.

Email: info@rapidlabs.co.uk
Tel: +44 (0) 1206 250484