Proteus OX-19 is one of the somatic antigens produced by the Proteus vulgaris bacteria. An antigen is a molecule foreign to the body that the system recognizes as a threat, generating an immune response in the form of antibodies.
If we take serum from that person's blood and mix it with Proteus OX19 concentrate, a precipitate or agglutination will be obtained. This is because both organisms have similar antigen groups.
Typhus
Typhus is a disease caused by the bacterium Rickettsia prowazekii, an obligate intracellular parasite. This bacterium is transmitted by the louse (Pediculus humanus), which contracts it by biting a sick person, being able to infect a healthy host by defecating on their skin at the time of the bite.
The infected person maintains the bacteria for life, which can multiply under conditions of depressed immune system.
Symptoms
Typhus symptoms include severe headaches, sustained high fever and prostration, bronchial disease, cardiovascular abnormalities, bleeding at different levels, mental confusion, and stupor.
On the fifth day the rash appears (a skin rash all over the body except the soles of the feet and palms). This rash is maculopapular (discolored patches of skin and small bumps). Neurological complications and even coma can occur.
Diagnosis
The Weil-Felix (WF) test is based on the fact that several Proteus species have receptors for antibodies of the immune system, the same as those present in members of the genus Rickettsia. The only exception is the species Rickettsia akari.
The Weil-Felix agglutination test is not very sensitive and can frequently give false positives, so it is not considered a reliable test. However, the use of the Weil-Felix test is acceptable in conditions where definitive investigations are not possible.
The test must be interpreted in the correct clinical context. That is, the patient's symptoms and whether she comes from a region where typhus is known to exist must be taken into account.
In addition to other general information such as trips to endemic areas, contact with reservoir animals, camping history and professional environment.
Classic test
In basic terms, the test consists of the following steps:
1- The serum is extracted from the blood of the patient with rickettsiosis by centrifugation.
2- An extract of fresh Proteus vulgaris OX-19 cells is prepared (or the commercially ready antigen is used).
3- In an agglutination tube, prepare a mixture of 0.5 ml of serum and 0.5 ml of antigen, in a battery of dilutions.
4- They are incubated at 37 ° C for two hours and left in the refrigerator until the next day at 8-10 ° C.
5- The degree of agglutination that occurs is recorded. In complete agglutination, a precipitate separates and the supernatant should be totally clear.
The slide test
There is also a variant in a slide (a rectangular glass sheet measuring 75 by 25 mm and approximately 1 mm thick).
In this case, a drop of blood from the patient's finger is applied to the slide and a drop of concentrated and preserved Proteus vulgaris OX-19 solution. The result is read with the naked eye according to the intensity and speed of the agglutination.
The slide test is designed for mass examinations under field conditions. The results appear to be favorably comparable to those obtained in agglutination tube tests.
Results
Values between 1:40 and 1:80 are considered negative, while results between 1: 160 (in endemic or epidemic areas) and 1: 320 (in isolated areas) can be considered positive.
References
- Cohen SS (1945) The chemical alteration of a bacterial surface, with special reference to the agglutination of B. Proteus OX-19. Journal of Experimental Medicine. 82 (2): 133-142.
- Falkinham JO and PS Hoffman. (1984) Unique Developmental Characteristics of the Swarm and Short Cells of Proteus vulgaris and Proteus mirabilis. Journal of Bacteriology. 158 (3): 1037-1040.
- Felix A (1944) Technique and interpretation of the Weil-Felix test in typhus fever. Transactions of the Royal Society of Tropical Medicine and Hygiene. 37 (5): 321-341.
- Mahajan SK, R Kashyap, A Kanga, V Sharma, BS Prasher and LS Pal. (2006) Relevance of Weil-Felix Test in Diagnosis of Scrub Typhus in India. The Journal of the Association of Physicians of India 54: 619-621.
- Welch H. and IA Bengtson. (1946) Techniques for the laboratory diagnosis of Typhus and other rickettsiasis Translated into Spanish by Dr. JA Montoya, Epidemiologist of the Pan American Sanitary Bureau, from the work “Diagnostic Procedures & Reagents,” 2a. ed., pp. 232-246, by permission of the American Public Health Association Publishing House, 1790 Broadway, New York 19, NY, USA
- Ziolkowski A, AS Shashkov, AS Swierzko, SN Senchenkova, FV Toukach, M Cedzynski and YA Knirel. (1997) Structures of the O-antigens of Proteus bacilli belonging to OX group (serogroups O1-O3) used in Weil-Felix test. FEBS Letters, 411 (2-3): 221–224.