What testing method is used for diagnosing Tuberculosis (Tb) in animals?

The caudal fold test is the correct method for diagnosing Tuberculosis (Tb) in animals, particularly in cattle. This test involves the intradermal injection of a tuberculin agent into the skin of the animal's caudal fold (located at the base of the tail). A positive reaction, indicated by swelling or inflammation at the injection site after a specified duration, suggests exposure to the tuberculosis bacterium.

This method is specifically designed for large animals and is part of standard screening protocols in livestock to identify potentially infected animals. The sensitivity and specificity of the caudal fold test make it a preferred option for on-farm testing, helping to control and manage the spread of tuberculosis in animal populations.

Other methods mentioned, such as the Elsa test, chest X-ray, and blood culture, do not serve as primary tools for diagnosing tuberculosis in animals. While the Elsa test is primarily used for certain viral diseases in different contexts, chest X-rays are used for human diagnosis rather than for animals, and blood cultures, while they can identify bacterial infections, are not a practical or commonly used method for detecting tuberculosis in animal populations. Thus, the caudal fold test is specifically tailored to the needs of animal health surveillance for Tuberculosis.