Allergic or Immunological Tests

Allergic or Immunological Tests

The immunological tests are dependent on the reaction between the antigen and the antibody. The important diseases of domestic animals including tuberculosis, paratuberculosis, glanders and brucellosis can be diagnosed in routine practice. The implication of immunological tests is vast and too accurate for the diagnosis of diseases of livestock and poultry.

TUBERCULIN TEST

      1.      Single Intradermal Test (SID):

This test is very easily applicable in cattle and buffalo. The skin of middle neck is preferred. A 2" x 2" area is shaved. The thickness of the skin fold is measured (mm) with a dial or ordinary caliper and 0.1 ml (0.2 ml in positive herd) tuberculin or its PPD (purified protein derivative) is injected intradermally with special syringe and needle. The pressure is applied on the needle at 30⁰ angles with the skin. A small pea sized elevation indicates proper placing of the antigen. The skin fold thickness of the site is noted 72-96 hours (3-4 days) later.

Interpretation: If the thickness increases by 4 mm or more, with or without painful swelling, indicates the test positive. In doubtful case, the test is converted into Stormont Test (ST) or repeated after a month.

      2.      Stormont Test (ST):

The SID test may be converted into Stormont test in less sensitized animals. The first test is conducted as mentioned above. After 7 days, again 0.1 ml tuberculin or PPD (purified protein derivative) is injected intradermally at the same site. The reaction and thickness of the skin is recorded 24 hours later and is interpreted as above. The tested animal gets desensitized for 6 months.

Horse: SID test may be used for tuberculin test but the specificity remains questionable.

Sheep and Goat: In caudal fold, 0.1 ml tuberculin is injected intradermally and read 72 hours later. Precautions: The tuberculin tests employing subcutaneous and intravenous routes are not in routine use as anaphylactic reactions are often observed.

Limitations: Animals get sensitized with other infections like paratuberculosis, liver fluke infestations, skin tuberculosis, saprophytic acid fast bacilli and avian tuberculosis, which can be ruled out by conducting comparative test similar to SID test at two places about 5" down on the same side of the neck of cattle and buffalo. The injection showing more reaction is considered positive.

JOHNIN TEST

It is applicable for the diagnosis of Johne's disease (paratuberculosis) in cattle, buffaloes, sheep and goats. Single intradermal test is used. Johnin 0.1 ml is injected in the skin of neck similar to tuberculin test. Skin fold thickness is measured pre- and 48-72 hours post- infection. A positive test is characterized by oedematous swelling.

For the diagnosis of subclinical Johne's disease, short thermal test has been advised. One ml Johnin, diluted with 9 ml normal saline is injected intravenously. A rise in body temperature by 2⁰ F around 5-8 hours post-inoculation indicates the test positive.

Limitation: Early and very advance cases fail to give positive test.

MALLEIN TEST

It is used for glanders test in horses and mules.

      A.      Intradermopalpebral test:

This test is used widely. The eye is cleaned properly. The lower eyelid is fixed with fingers and 0.1 ml mallein is injected intradermally about 1/2" down the palpebral margin. Development of the severe conjunctivitis or oedema of whole orbit by 24-28 hours, indicate the test positive.

      B.      Subcutaneous test:

One ml diluted mallein (1:9 in normal saline) is injected subcutaneously in the middle of the neck. The body temperature is recorded at 0, 9, 12, 15, 18, 21 and 24 hours post-inoculation. The start of rising in body temperature 18 hours onward and reaching to 103-104⁰ F or more with or without local inflammation indicates the test positive.

      C.      Opthalmic test:

The test is infrequently applied. Few drops of mallein are instilled in the normal conjunctival sac with a suitable dropper or syringe. A positive test is characterized by purulent conjunctivitis, photophobia, and swollen eyelids within 24 hours of instillation, which persists for 48-72 hours.

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