Since its inception in 1917, the National Cooperative State-Federal Bovine Tuberculosis Eradication Program has brought us successfully to the point of virtual eradication of this formidable disease in the United States. The program began with eradication as the goal. This goal has never been abandoned but now must be refaced. The most rapid program progress occurred in its first two decades during which the disease prevalence was reduced from five percent in the nation’s cattle (15 percent in swine) to less than onr percent. By 1940, the entire nation achieved Modified-Accredited status for tuberculosis when the prevalence of bovine tuberculosis in all states dropped to 0.5 percent or less. We experienced a transient but serious regression during World War II and its aftermath. Further reductions proved increasingly difficult but persisted to modern times. Beginning in the mid 1970s, the prevalence of tuberculosis entered a steady state, maintaining itself at a very low, apparently irreducible level.

Since 1985, we have averaged 11 herds newly detected with tuberculosis each year since 1985. During that same period an average of 260 tuberculous carcasses were detected per year. Combining these data, we estimate conservatively the prevalence of tuberculosis in our cattle and bison population at 0.002 percent.

Bovine tuberculosis has been eradicated from swine. Our last case of M. bovis in swine on farms occurred in Spokane, Washington in 1982. We have not confirmed M. bovis in sheep, goats, or horses on farms for at least 30 years. M. bovis infection however does exist in the captive cervid industry in the United States and has been confirmed in some species of exotic bovidae (antelope), camelidae, cervidae, goats, and swine in a few zoos and exotic animal collections.

In the past decade, three issues have emerged having the potential for regressing program progress. These are the importing of increasing numbers of tuberculosis infected animals from Mexico, bovine tuberculosis in large dairy herds and tuberculosis in our captive cervid industry.

U.S. wildlife has remained remarkably free of M. bovis infection. Only two situations are known of sustained infection in wildlife species; M. bovis in feral swine in California and in feral swine, axis deer and feral cattle on the Hawaiian island of Molokai. Both M. bovis outbreaks were eliminated (California during the 1960s; Molokai during the 1980s by "focal depopulation" i.e. sustained hunting and trapping of target species on selected properties known to have been occupied by infected cattle.

Current Status

Forty-two states plus the U.S. Virgin Islands currently have Accredited-Free status, having experienced at least five years freedom of tuberculosis. Many of these states had not experienced M. bovis infection in cattle for 30 or more years. Eight states have Modified-Accredited status. Three of these states will soon be eligible for advancing to Free status.

Figure 1 shows the distribution of these states by status and the infected herds encountered during fiscal year (FY) 1994. The eleven infected herds included six newly detected herds and five herds carried over from previous years. Only three of these herds were depopulated, all small beef herds together numbering about 1,400 cattle. The herds not depopulated were for the most part large dairy herds altogether containing about 20,000 cattle. These herds are located in the New Mexico and Texas areas of the El Paso milkshed, a 60 mile, narrow strip of land containing about 50 diaries. Fifteen of these dairies have been discovered with tuberculosis since 1985, of which seven were depopulated. The remaining eight have been carried over some having been released from quarantine two or more times only to be found again to be infected.

Feeder cattle from Mexico have accounted for the great share of tuberculosis cattle detected on slaughter inspection since 1982. Since 1978, the overall average of 72 percent of all tuberculous feedlot cattle detected at slaughter were traced back to Mexico. Feedlot cattle account for 95 percent of all tuberculous cattle detected at slaughter. We detect about 12 adult tuberculosis cases annually. Slaughter surveillance data provides one of our best indications of disease prevalence.

Figure 2 shows total submissions of suspicious tuberculosis lesions by year since 1985 and the number of cases found laboratory positive. FY 1995 figures have been extrapolated from data obtained to the end of the second quarter. In 1995, a reduction of 75 percent is shown from the 1992 high of 613 tuberculous carcasses. This reduction reflects changes in U.S. regulations dealing with cattle importation from Mexico and the beneficial effects of Mexico’s National bovine tuberculosis eradication program which was implemented in June 1993. The U.S. change in regulations prohibits the entry of Holstein steers and spayed heifers from Mexico. These classes of cattle accounted for almost 70 percent of the tuberculous cattle seen here, but made up only seven percent of the total exports.

We have been concerned with M. bovis infection in captive Cervidae since 1991. During FY 1994 we encountered a total of 11 M. bovis infected cervid herds, of which six were newly discovered and five were carried over from previous years (Figure 3).

Since January 1991, we have confirmed M. bovis infection in a total of 29 cervid herds (Figure 4). Nineteen of these herds (66 percent) were depopulated by the owner without compensation; four have been released from quarantine following a testing program with elimination of reactors and six remain under quarantine today.

To date, at the completion of the first half of FY 1995. We have as yet to detect our first newly infected herd. Perhaps more significantly, neither has the first adult bovine been detected with tuberculosis on slaughter inspection. Also, no new cervid herds have been confirmed with M. bovis infection this FY.

Numerous wildlife surveys conducted since 1991 in areas surrounding private premises with M. bovis infected Cervidae have to date revealed confirmed M. bovis infection in a single free ranging mule deer (Montana), a situation best described as "environmental spillover." Recently, M. bovis was cultured from a hunter killed deer in Michigan. The records show a similar case had occurred in the same area in 1975. These findings are being assessed and appropriate follow-up is underway in Michigan.

Over all, the tuberculosis situation in the United States appears to have significantly improved. The reasons are favorable developments supporting resolution of the Mexican tuberculosis issue and our improved ability to deal with the cervid problem.

However important the encouraging figures indicators, M. bovis can be grossly misleading. For example, the cervid arena. Although the U.S. has adopted a Uniform Methods and Rules, Tuberculosis Eradication in Cervidae (May 1994), there are still no provisions for indemnity for Cervidae destroyed for tuberculosis. Experience has shown that in the absence of compensation for owners, epidemiological investigations for disease cannot function at high efficiency.

The announced goal of tuberculosis eradication by 1998 may be more realistic than previously believed. The most significant cause for our failure to meet this goal is our inability to deal with the large infected dairy herd problem, being unable to free them of disease or to depopulate them. As the result, a reservoir of approximately 30,000 tuberculosis exposed cattle has been accumulated over the past decade which by all rational reasoning should be depopulated.

Herein lies the issue of refacing our program philosophy of eradication versus control. Eradication would require that all exposed animals be destroyed to prevent future outbreaks of bovine tuberculosis made likely by their survival. Control philosophy would permit their survival, leading eventually but assuredly to widespread dissemination of tuberculosis exposed animals. Eradication, with all its benefits; economic, public health, world trade and prestige (?) , is attainable, possibly as early as 1998, but at the cost of depopulating thousands of tuberculosis exposed animals; the cost seemingly high but realistically modest.

Never in the programs history has there been the need for a more strategically important decision. The decision for bovine tuberculosis eradication with all its lasting benefits, is within the grasp and power of the industry, state and federal animal health agencies.