Eliminating the Card Test

By Dr. Richard E. Breitmeyer, Director
Division of Animal Industry
California Department of Food and Agriculture

The final stages of the brucellosis eradication program require highly sensitive diagnostic tests. The card test is an easy, inexpensive, rapid and highly sensitive presumptive test for brucellosis. However, the card test has many false positive results because it lacks specificity. This is particularly a problem when testing populations where most cattle are vaccinated with Strain 19, and the true disease prevalence is extremely low.

Supplemental tests with higher specificity are available to reclassify cattle found positive on presumptive tests for brucellosis. However, we cannot currently reclassify cattle testing positively on the card test as negative following negative supplemental tests. The inability to reclassify cattle causes unjustified marketing restrictions, and has caused markets and states to stop using the card test.

In June 1994 we removed the card test from the cattle brucellosis testing protocols in California because of the inability to reclassify cattle. The card test is no longer included in the routine testing procedures for health certification, interstate shipments, disease investigations, or diagnostic samples. The card test is only conducted when required for export shipments and when specifically requested.

An easy, inexpensive, rapid and highly sensitive presumptive test for brucellosis should not be abandoned from the brucellosis program because cattle cannot be reclassified. Designated Brucellosis Epidemiologists should be able to reclassify card positive cattle using supplemental tests and epidemiologic information from the animal and herd of origin.

Resolved that the USAHA recommends that the USDA change the wording for the card test in the Brucellosis Eradication Uniform Methods and Rules, p. 24.

c. Card Test - results are recorded as either negative or positive. The card test is to be used as an official test to classify cattle and/or bison [as reactors] only under the following circumstances:

(1) When conditions and time are such that no other test is available; or

(2) When the owner and/or his or her agent request it because of time or situation constraints; or

(3) In stockyards when the State animal health official specifically designates the card test as the official test. No other test except the BAPA is to be used in stockyards as an official test in those States. (The CITE test can also be used on all cattle and/or bison as a supplemental test whenever the card test is used.); or

(4) In stockyards, when the State animal health official designates the card test as the official test for nonvaccinates, the card test will be the only official diagnostic test for nonvaccinated cattle and/or bison (except that the CITE® test can be used on all cattle and/or bison as a supplemental test whenever the card test is used). The card test may be used in conjunction with the standard plate test (STP) or rivanol test as supplemental tests on vaccinated cattle and/or bison. Vaccinated cattle and/or bison that are positive to the card test must be classified as reactors or suspects if all supplemental tests completed support suspicious or reactor classifications. Card test positive cattle and/or bison may be classified negative only by a Designated Brucellosis Epidemiologist provided all supplemental tests are negative and additional documented information supports such action.