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Robert M. Meyer DVM, MS
USDA APHIS Veterinary Services
TB Surveillance in Cattle at Slaughter
Primary surveillance for bovine tuberculosis (TB) in cattle today is largely conducted in slaughter plants as part of federal and state meat inspection programs. New cases of TB may be detected when cattle move to slaughter and are inspected for evidence of disease by federal or state meat inspection personnel. Cattle showing gross signs or lesions of disease suspicious of being TB in lymph nodes or the lungs are sampled, and tissue samples are sent to the laboratory for a definitive diagnosis. Samples found to be positive for TB at the laboratory are then traced by animal health personnel to their herds of origin, and the herd is tested and restricted from further movement.
Surveillance by tuberculin skin testing, including periodic TB testing of cattle on farms throughout the United States, now plays a relatively minor role in detecting TB-infected herds in most parts of the United States. However, periodic skin testing of herds can be a very effective method of detecting infected herds early when it is known that repeated exposure of cattle to TB is occurring. Such is the situation that now exists in northeastern Michigan where the disease is known to be endemic in free-ranging whitetail deer.
Figure 1. Malignant tumor
in the lung resembling TB
The use of slaughter surveillance as the primary method of detecting new cases of TB is economical and effective as long as all suspicious lesions are submitted to detect TB at the very low prevalence that exists today in the national herd. Inspectors in some plants are doing a good job of submitting samples to the lab, but others have become complacent in their support of the program. In recent years the overall numbers of suspicious lesions being submitted for diagnosis from adult slaughter cattle (i.e. cattle over 2 years of age) nationally has decreased. This decrease has led to concern that the current submission rate from adult cattle may not be sufficient to identify the few remaining TB-infected herds in time to reach the national goal of TB eradication in domestic livestock by December 31, 2003.
Since last October, 31 cases of TB have been detected in all classes of slaughter cattle nationwide. This includes 3 cases found in adult cattle (2 years of age and older), and 28 cases in fed or immature cattle. One of the cases found in adult cattle has been determined to be caused by Mycobacterium avium. Therefore, investigation of this case has been concluded. Another case in adult cattle is PCR positive for M. tuberculosis complex, and testing of possible source herds in South Dakota is now in progress to try to find the herd of origin for this animal. The third adult TB case is in a Holstein cow found at slaughter recently in Michigan. Investigation as to the origin for this animal is in progress in both Indiana and Michigan since the cow carried an Indiana backtag at the time it was slaughtered.
Investigations conducted to date in the 28 immature cattle cases have shown that 8 cases likely originated in feeder cattle imported from Mexico. Two cases were determined to be in steers previously used for roping events, and investigations as to their origin and exposure potential continue. One extensive case of TB was found at slaughter in Pennsylvania in a fed heifer originating from northeastern Michigan, and17 other cases from immature cattle are still under investigation.
The fed heifer from Michigan recently detected during slaughter inspection in Pennsylvania requires additional comment. Extensive lesions of tuberculosis were found in the lungs and thoracic lymph nodes of this young, 18 month old heifer. There can be no argument that this animal could effectively spread TB. Animals with lesions such as these represent a significant threat to the health of our country’s livestock industry and to the public health. One can only imagine the severe damage that this heifer would have caused to other herds had it gone into breeding channels rather than to a terminal feedlot. Epidemiologic investigation of the source for this case to date has led to at least 2 Michigan herds infected with TB.
Figure 2. Bovine TB in the lung of a MI-origin
heifer recently detected during slaughter
inspection in Pennsylvania
It is imperative that the submission rate of all suspicious granulomas found at slaughter be increased significantly if newly infected herds are to be detected early. Completion of the national bovine TB eradication program depends on it. Of equal importance is the need to test all herds in northeastern Michigan that are receiving continued exposure from infected deer if TB infection in cattle is going to be contained within the area. It is quite obvious that extensive lesions of TB can develop within months, and if herds are not regularly tested, the disease will spread. Disease investigations now underway in northeastern Michigan suggest that the finding of more infected herds will continue.
The collection and submission of all identification devices along with suspicious samples is key to tracing TB positive samples to their correct herds of origin. Of the 31 TB cases detected so far this year, only 10 (32%) had official eartags or backtags that would allow accurate tracing to herds of origin. Eleven cases in fed cattle presented with plastic bangle tags that allowed tracing to the feedlot only. Tissues for 10 cases (32%) arrived at the laboratory without any identification devices whatsoever. Obviously, this is an area that great improvements need to be made to enhance all of our disease surveillance efforts.
During last year, 1,028 lesions suspicious of being TB were sent to USDA’s National Veterinary Services Laboratories for diagnosis from all classes of cattle slaughtered at plants throughout the United States. 436 of these submissions came from nearly 6 million adult cattle slaughtered. Last year’s national lesion submission rate of 0.76 per 10,000 adult cattle slaughtered is less than 1/5th of what program officials feel is adequate to detect the few remaining TB herds quickly. Figure
3. National Rates of Submission of TB Suspicious Tissues to NVSL
The lesion submission rate from adult cattle so far this year of 1.93 is encouraging, and suggests that efforts now being made to improve this rate are beginning to work. The submission of 555 tissues from adult cattle so far this fiscal year already exceeds last year’s total, but the submission rate is still less than half the target of 5 submissions for every 10,000 head of adult cattle killed.
Regional differences in the suspicious lesion submission rate for adult cattle exist.
Figure 4. Regional TB Granuloma Submission
Rates (FY2000)
Last year adult submission rates per 10,000 adult cattle killed ranged from 1.08 in the western portion of the U.S. to 0.24 in the southeast.
So far this year, regional submission rates for adult cattle have improved in the western, central, and northeastern portions of the U.S. to 3.17, 1.43, and 2.18 respectively.
Figure 5. Regional TB Granuloma Submission
Rates (FY2001 2nd Quarter)
But more improvement is needed for surveillance in adult cattle to be considered optimal. The rate of .36 in the southeastern portion of the country is significantly different from other parts of the country (p < .0001), and certainly does not give one much confidence of an effective surveillance program in that region.
In relation to the continuing bovine TB outbreak in Michigan, it is critical to examine the efficacy of slaughter surveillance being conducted in those states that receive Michigan cattle.
Adult cattle originating from Michigan are mostly killed in plants located in Michigan, Wisconsin, Pennsylvania, and Ohio. Submission rates for adult cattle slaughtered in plants in each of these states range from 22.6 per 10,000 adult cattle killed in Michigan to 1.05 in Wisconsin. Considering that the majority of Michigan-origin, adult cattle go to 6 large slaughter plants in Wisconsin and Pennsylvania, it is imperative that rates of suspicious lesions being submitted be improved if infected herds are to be found.
Figure 6. TB Granuloma Submission Rates in States That Receive the
Majority of Michigan Adult Slaughter Cattle
Since the finding of the infected heifer at slaughter in Pennsylvania, efforts in that state have been intensified to increase the lesion submission rate by placing animal health personnel in plants to assist meat inspectors with the packaging and shipping of samples to the lab. As a result, the sample submission rate for adult cattle is now 5.5 in Pennsylvania. APHIS appreciates the good efforts that most FSIS personnel in Pennsylvania are now making to enhance surveillance.
Figure
7. Distribution of TB Submissions from Adult Cattle in WI Plants
In Wisconsin, efforts of a few inspectors have significantly increased the submission of samples in plants where they have been assigned. However, others appear to be reluctant to support the submission of all granulomatous pathology unless they are truly convinced it is TB. One Wisconsin plant accounted for 72% of all submissions made from all Wisconsin plants last year, and 65% so far this year. It is clear that more uniformity in sampling is needed among these Wisconsin plants.
Submission of suspicious lesions from adult cattle provides epidemiologists with the best opportunity for locating new herds infected with TB. Older cattle often have official eartags or other types of individual identification that greatly assists with tracing to their herds of origin. Therefore, it is understandable and important that emphasis be placed on enhancing the lesion submission rate in plants killing this type of cattle. Only 40 plants kill over 90% of the nearly 6 million adult cattle slaughtered in the United States today. Special efforts to enhance surveillance are now focused particularly on these plants.
To date, these efforts have included personal visits to the plants by animal health personnel to discuss the TB slaughter surveillance program, meetings with USDA’s Food Safety Inspection Service to communicate program needs & concerns, training programs for meat inspectors, and the development of a TB surveillance newsletter. Improvements have also been made to APHIS’ TB Performance Awards program that rewards federal meat inspectors who make significant efforts and contributions to the TB slaughter surveillance program.
With time and with more attention to certain constraints that now affect program operations and progress, surveillance for TB in cattle at slaughter should continue to improve. However, APHIS will need to provide FSIS with continual feedback and support, and FSIS will need to better communicate to their field offices that TB surveillance is an activity for which they have a great responsibility.
Attention and commitment to improving TB surveillance is long overdue. And, it certainly suggests the need to critically review other animal disease surveillance methods and activities.
Surveillance for TB in Free-Ranging Wildlife in Michigan
Since disclosure of bovine tuberculosis in a hunter-killed whitetail deer in northeastern Michigan in 1994, the Michigan Department of Natural Resources has conducted statewide surveys to determine the extent of their tuberculosis problem. 340 cases of bovine TB have been found in nearly 64,000 free-ranging whitetail deer examined since 1995. Twenty-three (23) cases have been discovered in such scavenger species as bear, coyote, fox, raccoon, bobcat, and opossum. One case each was also disclosed in an elk and a semi-feral, domestic cat last year. At least 13 cattle herds and one captive cervid herd to date have become infected as a result of exposure to infected, free-ranging whitetail deer. Figure
8. Bovine Tuberculosis Survey Results
Seventy five percent (75%) of all positive deer cases have been found in portions of four counties that are considered to be the core area for the outbreak. However, cases of TB in deer have been found in outlying counties that are a considerable distance from the core.
Figure 9. Apparent TB Prevalence in White-tail
Deer
Since 1996, the apparent prevalence of TB in free-ranging deer within the core area generally ranged from 1.5% to 3.3% depending upon which particular part of the core area that was sampled. However, targeted sampling in certain townships has shown that several “hot zones” for the disease exist with prevalence levels over 7%. Figure
10. Apparent TB Prevalence in Core Area by County 1996-2000
Surveillance for TB in Free-Ranging Wildlife in States Other Than Michigan
During the past 10 years, surveys looking specifically for bovine tuberculosis in wildlife, mainly free-ranging deer and elk, have been conducted in various states outside of Michigan. Many of these reports have been somewhat anecdotal in nature, and no effort, to date, has been made to consolidate the information. In preparation for this meeting, I asked state and federal animal health officials and certain wildlife officials to provide information regarding details of wildlife surveys looking specifically for TB that have been conducted in their states in the past 10 years. Responses have been obtained from 36 states to date. Therefore, this report should be considered a “work in progress” at this point since all the information from all states may not yet be in. But, I will attempt to report to you today what information I have received to date.
Previously I have reported on the results of an epidemiological investigation for bovine TB in wildlife on the island of Molokai, Hawaii. This investigation has continued during this past year, and, since 1998, a total of 389 axis deer, 276 feral swine, 72 feral goats, and 41 mongoose have been sampled. No additional cases of bovine TB have been found in any animal species on Molokai since my report last year.
Since 1992, annual surveys for TB have been conducted in Wyoming in free-ranging elk originating from the southern portions of Yellowstone National Park and Grand Teton National Park. Samples from 2,298 elk shot by hunters have been collected by wildlife biologists with the Wyoming Game & Fish Department and the National Park Service as the elk migrated from their traditional summer ranges in the parks to their winter range at the National Elk Refuge in Jackson, Wyoming. Microscopic examination of tissue submitted from these elk has been conducted at the Wyoming State Diagnostic Laboratory in Laramie. To date, only 1 case of mycobacteriosis has been found in samples examined, and further tests conducted on tissues from this elk have shown that it is not bovine-type TB. Figure
11. 2,298 elk sampled since 1992; 1 case of mycobacteriosis; NOT
bovine TB In November, 2000, a buffalo taken from this same area (Teton County, WY) showed granulomatous pathology with acid-fast organisms in the lung. However, PCR tests conducted at USDA’s National Animal Disease Laboratory indicated that the lesions were caused by Mycobacterium avium – not bovine TB. There is no evidence to suggest that bovine TB exists in wildlife in the Greater Yellowstone area at this time.
Surveys for TB have been conducted in free-ranging Wisconsin deer each year since 1997. Lymph nodes in the heads of 4,161 hunter-killed deer have been examined for evidence of TB over the past 4 years, and no evidence of TB has been detected.
Ohio has conducted three surveys in whitetail deer during 1996, 1998, and 2000. A total of 1,581 deer have been sampled, and no TB has been detected in samples examined to date.
In 1999, 953 deer in Illinois were examined, and no lesions of bovine TB were detected.
Figure 12. TB in Ohio, Wisconsin, Indiana and
Illinois
Indiana initiated a program during the past year that is based on the recognition of suspicious pathology found by workers in deer processing plants or by taxidermists. Fifteen deer were reported as having suspicious pathology, and samples from 13 of these deer were submitted for laboratory examination. No TB has been detected in results received to date.
During the 1997-98 New Jersey hunting season, 506 whitetail deer more than 1.5 years of age were examined for evidence of bovine TB. Forty-five exhibited lesions determined to be actinobacillosis or actinomycosis, and 3 deer showed granulomas and microgranulomas in lymph nodes not caused by bovine TB.
Tissue samples from 100 deer from Gettysburg National Park in Pennsylvania were collected as part of deer population reduction efforts, and examined both histologically and by culture in 1996-97. All samples tested negative for bovine TB. Figure
13. TB in New Jersey, Pennsylvania, Virginia and West Virginia
In 1994, a TB survey involving 30-40 whitetail deer was conducted in Virginia. These deer were taken from areas surrounding a farm containing cattle that had recently been diagnosed with TB. No evidence of TB was found in this relatively small sampling of deer.
Five deer per year for the past ten years have been examined grossly for evidence of TB in West Virginia. No suspicious lesions have been noted.
From 1997 to 2000 a total of 1,756 whitetail deer and certain species of exotic hoofstock have been surveyed for TB in 5 large hunting ranches and 6 state wildlife management areas located in 12 counties throughout Texas. Only 20 animals exhibited any gross pathology that was later determined not to be bovine TB by laboratory examination. Smaller land mammals and birds have also been examined around dairies near El Paso, Texas that have historically had problems with TB, and no evidence of bovine TB has been found in these animals either.
During the 2000 hunting season in Kansas, 351 deer heads were examined for evidence of disease. 218 heads came from whitetail deer and 133 heads from mule deer. Seven whitetail deer heads showed granulomatous pathology in the cervical lymph nodes and were examined in the laboratory. No evidence of TB was detected. Figure
14. TB in Kansas, Mississippi, Texas and North Dakota
In 1999, North Dakota collected samples from 300 whitetail deer taken from areas adjacent to a dairy that was found to have M. bovis infection that same year. All deer tested negative for TB by examination on culture.
From 1998-2000, nearly 300 wild deer have been examined for gross evidence of TB by animal health and wildlife personnel in Mississippi. No evidence of TB has been noted.
In 1997, 231 mule deer and 96 whitetail deer originating mostly from 28 counties in western Nebraska were examined for evidence of TB. No TB was found.
Montana wildlife and animal health officials have conducted several TB surveys over the past several years in wildlife surrounding previously infected captive cervid facilities located mostly in eastern Montana. From 1993-96, 204 mule deer, 25 whitetail deer, 22 elk, and 29 coyotes were sampled. M. bovis was cultured from one mule deer and one coyote both of which would have had likely exposure to animals on the TB-infected game farm. Forty-four deer and 1 elk were sampled in follow-up surveys conducted in 2000. Figure
15. TB in Montana, Oregon and Nebraska
One hundred thirty-seven free-ranging elk have also been tuberculin tested negative in Oregon before being trans-located to the eastern United States.
Nineteen of the 36 states that have responded with information to date indicated that no surveys have been conducted with the express purpose of looking only for TB. These states include Alabama, Delaware, Maryland, Washington, North Carolina, Minnesota, Oklahoma, Missouri, Tennessee, Louisiana, Idaho, New York, Arizona, and the six New England states. However, several of these states did indicate that animals are often examined by wildlife agencies as part of other types of wildlife disease surveys.
For example, since 1990 the Southeastern Cooperative Wildlife Disease Study in Athens, Georgia has performed 184 necropsies of deer to determine their cause of death and has examined 902 more as part of regular deer herd health checks. Most of these deer came from states in the southeastern U.S. No evidence of TB has been discovered.
Acknowledgements
The author greatly appreciates the help received from the many USDA, APHIS and FSIS personnel who provided data and expertise used to compile this report. Thanks also go to the Southeastern Cooperative Wildlife Disease Study, the Michigan Department of Natural Resources, and the Wyoming Department of Game and Fish for the information and photographs they provided.
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