The Bovine Tuberculosis Eradication Program continued to make strides toward the final eradication of bovine tuberculosis during the past fiscal year. The disease is projected to be eradicated by the end of the 1998 fiscal year. This objective is still a valid one barring any major setbacks.

Four issues that could affect this objective are: 1) tuberculosis in imported Mexican steers, 2) inadequate slaughter surveillance, 3) persistent tuberculosis infection in large dairies, and 4) tuberculosis in captive Cervidae herds. Each of these issues has the potential to setback the date bovine tuberculosis will be eradicated from the United States. The United States Department of Agriculture (USDA), Animal and Plant Health Inspection Service (APHIS), Veterinary Services (VS) is working with other State and Federal regulatory agencies, industry groups, and the Mexican Government to prevent such setbacks.

During 1993, the national status for bovine tuberculosis changed with the addition of Hawaii to the list of States that are Accredited-Free. There were 12 herds infected with bovine tuberculosis this fiscal year; nine were carried over from the previous fiscal year and three were detected during fiscal year 1993. The newly detected herds consisted of two dairy herds in Texas and one game park in Oklahoma. The infection in the Oklahoma game park can be attributed to tuberculosis in the park’s Cervidae population.

Since 1988, VS has conducted over 1,300 investigations of tuberculosis infected feedlot cattle of Mexican origin. These investigations were conducted in 13 States. Since eight of these States are classified as Accredited Free, the possibility of tuberculosis reinfection by Mexican-origin steers is a foremost program issue.

Epidemiologic investigations involving Mexican steers have shown that approximately 67 percent of the infected imports are of the Holstein breed. This information has prompted the Mexican government to temporarily ban the exportation of all Holstein cattle to the United States until they can act to minimize the presence of tuberculosis in such exported animals.

In accordance with the resolutions of the United States Animal Health Association (USAHA) in 1992, APHIS is considering regulations to limit exposure of domestic cattle to infected Mexican imports, to recognize the Mexican blue metal eartag as the official permanent identification for imported Mexican cattle, and to impose movement requirements for Mexican steers that have entered the United States.

Mexico has officially implemented a Bovine Tuberculosis Eradication program. A joint United States-Mexico Tuberculosis Committee has been formed to support initiatives aimed at disease eradication in both countries. In support of Mexico’s tuberculosis efforts, APHIS has sponsored cooperative training programs in the areas of post-mortem inspection, laboratory procedures, and field testing. Slaughterhouse findings of tuberculosis in Mexican steers and related traceback information is shared with Mexican disease control officials. Additionally, APHIS has provided the Mexican Government with laboratory supplies and equipment for a regional tuberculosis laboratory.

The submission of thoracic granulomas from slaughter animals is the principle method of tuberculosis surveillance in the United States. Federal meat inspection personnel are the cornerstone of this surveillance. VS has determined that the optimal submission rate for adequate surveillance is one sample per 2,500 animals slaughtered or one sample per 2,000 adult animals slaughtered. During fiscal year 1992, the national average for slaughter submissions was approximately 35 percent of the optimal submission rate, the highest ever achieved. This granuloma submission data reflects inherent problems in the existing surveillance program for tuberculosis. Since this submission rate has never exceeded 35 percent of the optimum rate, meat inspection personnel must be encouraged to submit more granulomas for surveillance purposes. The goal of one sample per 2,500 animals slaughtered is also too general to be an accurate measure of slaughter surveillance. These figures must also be reevaluated to establish equitable rates throughout every region of the United States, and for every type of slaughter operation.

The inclusion of individual animal identification with slaughter samples is essential for the traceback of tuberculosis infected animals to their herds of origin. Meat inspection personnel provided identification on 1,028 (25 percent) of the 4,040 samples submitted for tuberculosis surveillance in fiscal year 1993. Of the 327 tuberculosis investigations conducted on feedlot animals of Mexican origin, 100 (31 percent) had Mexican eartags submitted with the slaughter samples. Mexico’s improved animal identification and computerized record keeping systems now permits the traceback of these animals to their Mexican herd of origin. Proper identification substantially increase the likelihood of a successful tuberculosis investigation. The USDA, Food Safety and Inspection Service (FSIS) is working with VS to increase the submission of identification devices with surveillance samples collected by its inspectors.

Bovine tuberculosis continues to persist at a very low level in some large dairy operations in the El Paso milkshed. Total depopulation of such large herds is the most effective method for eliminating the disease, but is rarely an economically acceptable option for either the Government or the herd owner. In recognition of this, a tuberculosis eradication initiative has been implemented for large dairy operations of this area. This initiative includes a Regional Tuberculosis Epidemiologist stationed in El Paso, Texas to develop individual herd clean-up plans and employment of new testing methods and schedules meant to enhance the eradication of tuberculosis in these large dairies. Total herd depopulation is still considered to be the most effective method to eradicate tuberculosis from affected herds. The re-appearance of tuberculosis in herds previously released from quarantine by testing has long been recognized as a deterrent to eradication. The rate of reinfection in such herds is estimated at 33 percent and appears to increase as herd size increases.

Uniform Methods and Rules (UM&R) for Cervidae have been developed in response to resolutions of the USAHA tuberculosis committee. These rules provide for accredited cervid herds, official tuberculosis tests, and requirements for interstate movement. The UM&R represents a cooperative effort between USDA, State regulatory agencies, the cervid industry, and USAHA. The cervid industry has also proposed an industry supported fund to indemnify cervid owners with herds affected with tuberculosis. This would be a significant step toward reducing the financial burden of owners and accelerating the eradication of the disease in Cervidae.

There has been a rekindling of interest in tuberculosis research in recent years that will help the program to continue its progress. Agricultural Research Service of USDA, Colorado State University, Cornell University, Iowa State University, and Texas A&M University have ongoing research programs in bovine tuberculosis. APHIS continues to support these efforts by providing diagnostic specimens and reagents to these institutions. The Scientific Advisory Subcommittee of the Tuberculosis Committee (TBSAS) that was established by USAHA during fiscal year 1993 provides a means for unbiased evaluations of scientific issues relevant to the national tuberculosis program. This subcommittee has been charged with the analysis of data from a joint United States-Canada project to evaluate the Blood Tuberculosis Test (BTB). The TBSAS has also been charged with the evaluation of the gamma interferon assay. Their reports should be available during the fiscal year 1994.