Colleen S. Bruning-Fann

Bovine Tuberculosis in Free-Ranging White-Tailed Deer From Michigan

A 4.5 yr-old male white-tailed deer (Odocoileus virginianus) killed by a hunter during the 1994 firearm hunting season in northeastern Michigan (USA) had lesions suggestive of tuberculosis and was positive on culture for Mycobacterium bovis the causative agent for bovine tuberculosis. Subsequently, a survey of 354 hunter-harvested white-tailed deer for tuberculosis was conducted in this area from 15 November 1995 through 5 January 1996. Heads and/or lungs from deer were examined grossly and microscopically for lesions suggestive of bovine tuberculosis. Gross lesions suggestive of tuberculosis were seen in 15 deer. Tissues from 16 deer had acid-fast bacilli on histological examination and in 12 cases mycobacterial isolates from lymph nodes and/or lungs were identified as M. bovis. In addition, lymph nodes from 12 deer (11 females and 1 male) without gross or microscopic lesions were pooled into 1 sample from which M. bovis was cultured. Although more male (9) than female (3) deer had bovine tuberculosis infections, this difference was not statistically significant. Mycobacterium bovis culture positive deer ranged in age from 1.5 to 5.5 yr with a mean of 2.7 yr (median 2.5 yr) for males and 3.2 yr (median 3.5 yr) for females. This appears to be the first epidemic occurrence of M. bovis in free-ranging cervids in North America. A combination of environmental (high deer density and poor quality habit) and management-related factors (extensive supplemental feeding) may be responsible for this epizootic.

Bovine tuberculosis in free-ranging carnivores from Michigan

During a survey of carnivores and omnivores for bovine tuberculosis conducted in Michigan (USA) since 1996, Mycobacterium bovis was cultured from lymph nodes pooled from six coyotes (Canis latrans) (four adult female, two adult male), two adult male raccoons (Procyon lotor), one adult male red fox (Vulpes vulpes), and one 1.5-yr-old male black bear (Ursus americanus). One adult, male bobcat (Felis rufus) with histologic lesions suggestive of tuberculosis was negative on culture but positive for organisms belonging to the Mycobacterium tuberculosis complex when tested by polymerase chain reaction. All the tuberculous animals were taken from three adjoining counties where M. bovis is known to be endemic in the free-ranging white-tailed deer (Odocoileus virginianus) population. There were two coyotes, one raccoon, one red fox, and one bobcat infected in Alpena county. Montmorency County had two coyotes and one raccoon with M. bovis. Two coyotes and a bear were infected from Alcona County. These free-ranging carnivores/omnivores probably became infected with M. bovis through consumption of tuberculous deer. Other species included in the survey were opossum (Didelphis virginiana), gray fox (Urocyon cinereoargenteus), and badger (Taxidea taxus); these were negative for M. bovis.

Comparison of postmortem techniques for the detection of Mycobacterium bovis in white-tailed deer (Odocoileus virginianus)

A retrospective study of various diagnostic postmortem techniques used in a 4-year surveillance program for detection of Mycobacterium bovis infection in wild white-tailed deer (Odocoileus virginianus) was conducted. The tests evaluated were routine histopathology, acid-fast staining, detection of acid-fast bacilli in culture, and an M. tuberculosis group-specific genetic probe applied to pure cultures. Each of these techniques were compared with a reference or “gold standard” of mycobacterial culture and identification. Histopathology, the most rapid form of testing for M. bovis infection in white-tailed deer samples, had a sensitivity of 98% and a specificity of 87%, resulting in a positive predictive value of 94%. The detection of acid-fast bacilli by staining was less sensitive than histopathology (90%), but its higher specificity (97%) resulted in a positive predictive value of 99%. The detection of acid-fast bacilli on culture was both highly specific (93%) and sensitive (100%). The group-specific genetic probe had the highest sensitivity and specificity and produced results in complete agreement with those of mycobacterial culture, suggesting that this technique could be used as the new “gold standard” for this particular wildlife tuberculosis surveillance program.

Mycobacterium bovis in Coyotes from Michigan

During a survey for tuberculosis in wild carnivores and omnivores, Mycobacterium bovis was cultured from pooled lymph nodes of three adult female coyotes (Canis latrans) harvested by hunters in Michigan (USA). No gross or histologic lesions suggestive of tuberculosis were seen in these animals. One coyote was taken from Montmorency county and two coyotes from Alcona county located in the northeastern portion of Michigans Lower Peninsula where free-ranging white-tailed deer (Odocoileus virginianus) have been found infected with bovine tuberculosis. It is thought that these coyotes became infected with M. bovis through the consumption of tuberculous deer. Other species included in the survey were the opossum (Didelphis virginiana), raccoon (Procyonlotor), red fox (Vulpes vulpes), bobcat (Felis rufus), and badger (Taxidea taxus).

The sensitivity of gross necropsy, caudal fold and comparative cervical tests for the diagnosis of bovine tuberculosis

Bovine tuberculosis (bTb) was diagnosed in 22 cattle herds in the northeast corner of Michigans lower peninsula. Of these 22 herds, 494 animals in 7 herds were examined by gross necropsy, histopathologic exam, mycobacterial culture, and polymerase chain reaction (PCR) assay performed only on samples that were histologically compatible for bTb. Results of culture and PCR assay interpreted in parallel were used as the reference test for calculation of the sensitivity of 1) the caudal fold test (CFT), 2) the caudal fold and comparative cervical skin tests used in series (CFTCCTSER), and 3) gross necropsy. Mycobacterium bovis was isolated from 43 animals. Using all 7 herds, the sensitivities of the CFT, the CFTCCTSER, and gross necropsy were 93.02%, 88.37%, and 86.05%, respectively. When the data were stratified by low- and moderate-prevalence herds, the sensitivities were 83.33%, 75.0%, and 83.33% in low-prevalence herds and 96.77%, 93.55%, and 87.10% in moderate-prevalence herds. The sensitivities of the 2 skin tests were slightly higher when 2 or more gross lesions were present, and the sensitivity of gross necropsy was significantly higher (P = 0.049). The sensitivity of the CFT was found to be notably higher than most estimates in other studies; however, a direct comparison was not possible because the amount of purified protein derivative and the reference methods were different in this study compared with other published studies. Although the sensitivities are high, 2 of the 7 herds (29%) would have had 1 or more positive animals left in the herd if a test-and-removal program had been used. This suggests that when positive herds are identified, selective culling of skin test reactors is a less acceptable disease control strategy than is complete depopulation.

Descriptive Epidemiology of Bovine Tuberculosis in Michigan (1975–2010): Lessons Learned

Despite ongoing eradication efforts, bovine tuberculosis (BTB) remains a challenge in Michigan livestock and wildlife. The objectives of this study were to (1) review the epidemiology of BTB in Michigan cattle, privately owned cervids, and wildlife between 1975 and 2010 and (2) identify important lessons learned from the review and eradication strategies. BTB information was accessed from the Michigan BTB Eradication Project agencies. Cattle herds (49), privately owned deer herds (4), and wild white-tailed deer (668) were found infected with BTB during the review period. BTB has occurred primarily in counties located at the northern portion of the states Lower Peninsula. Currently used BTB eradication strategies have successfully controlled BTB spread. However additional changes in BTB surveillance, prevention, and eradication strategies could improve eradication efforts.

The use of epidemiological concepts and techniques to discern factors associated with the nitrate concentration of well water on swine farms in the USA

This epidemiological study investigates the relationship between various factors associated with swine farms and the nitrate concentration of well water in the USA. Through a random sampling procedure, 605 swine farms located in 18 states were selected for inclusion in this study. A total of 631 well water samples were collected from these farms and tested for a variety of elements and compounds. The concentrations of nitrate, nitrite, sulfate, chloride, sodium, potassium, ammonia, fluoride, bromide and lithium were determined by an ion chromatograph while an inductively coupled argon plasma emission spectrophotometer was used to determine the concentrations of calcium, magnesium, barium, zinc, iron and phosphate. Data concerning various farm factors were gathered via a personally administered questionnaire. The data were examined using both multiple linear regression and logistic regression. Results indicate that 53.6% (338/631) of the wells contained detectable levels of nitrate, 11.7% (74/631) had nitrate levels exceeding 45 ppm and 4.3% (27/631) exceeded 100 ppm. Logistic models demonstrated an association between nitrate concentrations > 45 ppm, increasing water potassium levels and wells < 100 ft deep. Nitrate levels > 100 ppm were related to increasing water concentrations of potassium, magnesium, barium and zinc, wells 6-10 years old, increasing distance from the study farm to the nearest cattle farm and a greater distance to the nearest waterway located off the study farm. A negative association was seen between nitrate concentrations > 100 ppm, the water level of sulfate, and the use of the same well to supply both the household and livestock. Multiple linear regression models revealed a positive association between increasing nitrate concentration and the water levels of chloride, calcium, zinc and the greater number of miles from the study farm to the nearest farm with cattle or sheep. A negative association was noted between the concentration of well water nitrate and the water levels of sulfate and ammonia, the use of water treatment, the number of miles to the nearest farm with poultry, the employment of water treatment and the use of the same well to supply water to both livestock and the household.

Herd outbreak of bovine tuberculosis illustrates that route of infection correlates with anatomic distribution of lesions in cattle and cats

An outbreak of bovine tuberculosis (TB) in a Michigan dairy herd resulted in quarantine, depopulation, pathology, and epidemiologic investigations. This herd, compared to other TB-infected herds in Michigan, was unusual in the long-term feeding of waste milk to its replacement calves. The herd had 80 cattle with positive results on caudal fold test or gamma interferon testing, which were reclassified as suspects because the herd had never been known to be tuberculous previously. Autopsy revealed striking variation in the anatomic distribution of gross anatomic lesions, microscopic lesions, and culture-positive lymph nodes between the adult cattle, the calves, and the domestic cats present on the farm. Adult cattle had lesions and culture-positive lymph nodes predominantly within the thoracic lymph nodes, whereas cats had 50% of their lesions and culture-positive lymph nodes in their abdomens, and 50% of positive calves had culture-positive lymph nodes in their abdomens. This difference in anatomic distribution correlated with the likely routes of infection, which are believed to be by direct airborne transmission in adult cattle and indirect ingestion of contaminated milk in both calves and cats. Although TB literature over the past 100-plus years states that the route of infection may manifest itself in differences in lesion anatomic distribution, our team has been working with TB for over 20 years, and we have never encountered such striking variation between different groups of animals on the same farm.

Use of whole-genome sequencing and evaluation of the apparent sensitivity and specificity of antemortem tuberculosis tests in the investigation of an unusual outbreak of Mycobacterium bovis infection in a Michigan dairy herd

OBJECTIVE To describe use of whole-genome sequencing (WGS) and evaluate the apparent sensitivity and specificity of antemortem tuberculosis tests during investigation of an unusual outbreak of Mycobacterium bovis infection in a Michigan dairy herd. DESIGN Bovine tuberculosis (bTB) outbreak investigation. ANIMALS Cattle, cats, dog, and wildlife. PROCEDURES All cattle in the index dairy herd were screened for bTB with the caudal fold test (CFT), and cattle ≥ 6 months old were also screened with a γ-interferon (γIFN) assay. The index herd was depopulated along with all barn cats and a dog that were fed unpasteurized milk from the herd. Select isolates from M bovis-infected animals from the index herd and other bTB-affected herds underwent WGS. Wildlife around all affected premises was examined for bTB. RESULTS No evidence of bTB was found in any wildlife examined. Within the index herd, 53 of 451 (11.8%) cattle and 12 of 21 (57%) cats were confirmed to be infected with M bovis. Prevalence of M bovis-infected cattle was greatest among 4- to 7-month-old calves (16/49 [33%]) followed by adult cows (36/203 [18%]). The apparent sensitivity and specificity were 86.8% and 92.7% for the CFT and 80.4% and 96.5% for the γIFN assay when results for those tests were interpreted separately and 96.1% and 91.7% when results were interpreted in parallel. Results of WGS revealed that M bovis-infected barn cats and cattle from the index herd and 6 beef operations were infected with the same strain of M bovis. Of the 6 bTB-affected beef operations identified during the investigation, 3 were linked to the index herd only by WGS results; there was no record of movement of livestock or waste milk from the index herd to those operations. CONCLUSIONS AND CLINICAL RELEVANCE Whole-genome sequencing enhanced the epidemiological investigation and should be used in all disease investigations. Performing the CFT and γIFN assay in parallel improved the antemortem ability to detect M bovis-infected animals. Contact with M bovis-infected cattle and contaminated milk were major risk factors for transmission of bTB within and between herds of this outbreak.