By Dr. Richard D. Hull
Illinois Department of Agriculture

In the past decade, the nation has shown great progress in the eradication of bovine Brucellosis. That eradication was greatly accelerated after the initiation of the Rapid Completion for Brucellosis Eradication Plan. The goal set by this plan was that within five years from approval, all states would be Class Free or qualifying for Class Free status. If we were in full compliance with that plan, we would have today attained the goal of eradication.

As of February 1994, there are still 229 quarantined herds in the nation with 59 percent of these in Texas. The basic plan for the Brucellosis clean-up program adopted some 25 years ago, consisted of three essential prerequisites - surveillance, prevention and eradication. Figures 1, 2, and 3 illustrate Illinois’ progress in their cleanup program.

Now that we are approaching the beginning of that end, the surveillance now is the most important prerequisite. Today, surveillance has been classified into primary and secondary. Primary surveillance includes: (1) Market Cattle Identification (MCI); (2) Brucellosis Ring Test (BRT); and (3) large scale area testing. Secondary surveillance procedures are initiated following the disclosure of an infected herd. These would include: (1) area circle testing; (2) epidemiological tracebacks; and (3) diagnostic testing. Post-quarantine testing could also be included in this category.

The MCI testing includes auction market testing, change of ownership testing, and tests at slaughter. The slaughter plant testing represents approximately 50 percent of MCI testing. This total number has remained relatively consistent since 1979 and represents about 6 million cattle a year.

From 1975 through 1985, approximately 20 million cattle were tested each year with 12 million collections by MCI disclosing an average ranch testing). From 1986 to 1993, there were only 16 million cattle tested, yet MCI collections remained at 12.5 million. The percentage of reactors found by MCI has increased steadily and at present, 75 percent of the reactors disclosed are from MCI surveillance and only 25 percent by farm and ranch testing.

Another method of surveillance used to monitor for Brucella abortus infection in dairy cattle is the Brucellosis Ring Test (BRT). With the implementation of this surveillance, from 1975 to 1985, an average of 225 infected herds were disclosed annually. The BRT samplings peaked in 1981 with almost five million samples, and from 1973 to 1985, the trace to infected herds was about 415 herds per year. For the years of 1984 to 1991, the number of samplings dropped to about two million and has since been declining . The number of tracebacks of infected herds have also been declining from a high of 641 herds in 1975 to only five herds in 1993. The BRT testing in Illinois has followed a similar pattern, (Figure 4).

Another form of herd surveillance is the Certified Brucellosis Free herd testing program. In checking Illinois records, we find that the number of herds and the number of cattle fulfilling test requirements for this classification has not varied in the past 12 years -- not even since Illinois was declared Brucellosis Class-Free in 1992.

The Brucellosis calfhood vaccination program has been helpful in preventing animals from becoming infected, but it has also resulted in many tracebacks to negative herds. Last year, Illinois had three positive animals in separate herds in which Strain 19 was isolated. We are now seeing a steady decline in the number of calfhood vaccinated animals. Nationally there was a 24 percent reduction this past year in the number of animals vaccinated. Illinois has also experienced a corresponding decline (Figure 5). The reduction in the maximum age for heifer vaccinations and the decline in the number of heifers being vaccinated will help to reduce the number of these positives tracebacks to a negative herd.

As we near our goal of total eradication of cattle Brucellosis, we dare not become complacent and lose sight of our final objective. With 32 Free states and the possibility of three other states attaining that goal before the end of this year, there would only be 15 states remaining in the Class-A category. There has been little change in our surveillance in the past 15 years, both state and nationwide. If this surveillance was adequate to cleanup and eradicate Brucellosis in some 35 states, total eradication should be obtained if this surveillance program and the Uniform Method & Rules (UM&R) guidelines are strictly followed.

But as we seek to obtain the eradication of that last infected herd, there are indications that changes may occur that could lessen the requirements of the UM&R by extending the investigation period of MCI traceback tests; extending the time required for epidemiology investigations; and by lengthening the period in approving action plans that require testing of potentially exposed herds from an infected herd.

Now is not the appropriate time to sacrifice proper surveillance that will identify these remaining infected herds. Dr. Frank Mulhern presented an inspiring paper at the 1983 Annual LCI meeting, titled "Let’s Clean Up 40 States" which warned of regulatory and producer apathy. Dr. Granville Frye has suggested bovine Brucellosis should be managed similar to a Foreign Animal Disease. This eradication program has been a costly, both in man-hours and in dollars. Let’s follow Dr. Mulhern’s advise and not become complacent in the final stages of eradication.