Mallein test

Mallein test is a diagnostic procedure used in veterinary medicine to detect the presence of Glanders, a contagious and potentially fatal disease primarily affecting horses, but also capable of infecting donkeys, mules, and humans. The disease is caused by the bacterium Burkholderia mallei. The mallein test, similar in principle to the Tuberculin skin test used in diagnosing tuberculosis in humans, involves the intradermal injection of mallein, a glycerin extract of cultures of Burkholderia mallei. The test is based on the principle of delayed hypersensitivity; animals infected with the bacterium will exhibit a swelling at the site of injection, typically within 24 to 48 hours.

Procedure

The mallein test can be administered in several forms, including the ophthalmic test, where mallein is applied to the conjunctiva of the eye, and the more commonly used palpebral and subcutaneous tests. In the palpebral form, mallein is injected into the lower eyelid, while in the subcutaneous test, it is injected beneath the skin of the neck. The site of injection is observed for signs of inflammation and swelling, which, if present, indicate a positive reaction suggesting the animal is infected with Burkholderia mallei.

Interpretation

A positive mallein test is characterized by significant swelling, heat, and possibly discharge at the site of injection, along with systemic signs of fever and lethargy. However, false positives can occur, and further diagnostic testing, including bacterial culture and PCR (Polymerase Chain Reaction), may be necessary to confirm the diagnosis of glanders.

Regulation and Use

Due to the serious nature of glanders and its potential as a bioterrorism agent, the use of the mallein test is strictly regulated in many countries. It is an essential tool in the control and eradication programs for glanders, especially in regions where the disease is endemic. Quarantine and euthanasia of positive animals are common control measures to prevent the spread of the disease.

History

The mallein test was first developed in the late 19th century and has since been a critical component in the fight against glanders. Its development paralleled that of the tuberculin test, reflecting a significant advancement in veterinary diagnostics and infectious disease control.

Limitations

While the mallein test is valuable for screening purposes, it is not without limitations. False positives and negatives can occur, and the test's interpretation can be subjective. Additionally, the test does not differentiate between current and past infections, which can complicate efforts to control the disease in endemic areas.

Conclusion

The mallein test remains a cornerstone in the diagnosis and control of glanders in equine populations. Despite its limitations, when used alongside other diagnostic methods, it provides valuable information for managing this dangerous disease.