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 Michigan's 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.

Use of the Intradermal Tuberculin Test in a Herd of Captive elk (Cervus Elaphus Nelsoni) Naturally Infected with Mycobacterium Bovis

In the United States, tuberculosis of captive cervids, caused by Mycobacterium bovis, attracted attention in 1991 when investigations, prompted by the identification of a tuberculous elk ( Cervus elaphus nelsoni) of U.S. origin exported to Canada, revealed tuberculosis in 10 different elk herds in 8 different states. Based on methods used in cattle, official regulations pertaining to testing and eradication of tuberculosis in captive cervids were added to the U.S. Department of Agriculture bovine tuberculosis eradication effort in 1994. However, little published information exists on the accuracy of intradermal tuberculin testing in naturally infected cervids. Evaluation of a captive herd of 71 animals in Wisconsin included postmortem examination and tissue sample collection from both tuberculin test responders and nonresponders. Within this captive herd, of admittedly small size, results showed the single cervical test to have a sensitivity of 88% and a specificity of 69%. Evaluation of diagnostic tests in the species of interest is important, as extrapolation of data obtained from other species may not be appropriate.

Evaluation of environmental sampling and culture to determine Mycobacterium avium subspecies paratuberculosis distribution and herd infection status on US dairy operations

The objectives of this study were to determine the distribution of Mycobacterium avium subspecies paratuberculosis (MAP) in the environment and assess the relationship between the culture status of MAP in the farm environment and herd infection status. The National Animal Health Monitoring System's Dairy 2002 study surveyed dairy operations in 21 states. One component of the study involved collection and culturing of environmental samples for MAP from areas on farms where manure accumulated from a majority of a herd's cows. Operations were selected for inclusion based on perceived risk factors for MAP infection identified in a previously administered questionnaire. Individual animal and environmental samples were collected and used to determine the efficiency of environmental sampling for determination of herd infection status. Individual animal fecal, serum, and milk samples were used to classify herds as infected or not infected based on the presence of at least one test-positive animal in the herd. A total of 483 environmental samples (approximately 5 per farm) were collected, and 218 (45.1%) were culture-positive for MAP. A similar percentage of environmental cultures collected from all designated areas were positive [parlor exits (52.3%), floors of holding pens (49.1%), common alleyways (48.8%), lagoons (47.4%), manure spreaders (42.3%), and manure pits (41.5%)]. Of the 98 operations tested with the environmental sample culture, 97 had individual serum ELISA results, 60 had individual fecal culture results, and 34 had individual milk ELISA results. Sixty-nine of the 98 operations (70.4%) had at least one environmental sample that was culture-positive. Of the 50 herds classified as infected by fecal culture, 38 (76.0%) were identified by environmental culture. Two of the 10 operations classified as not infected based on individual animal fecal culture were environmental culture-positive. Of the 80 operations classified as infected based on serum ELISA-positive results, 61 (76.3%) were identified as environmental-positive, whereas 20 of the 28 (71.4%) operations identified as infected based on milk ELISA were detected by environmental sampling. Environmental sample culturing is less costly than individual animal sampling, does not require animal restraint, and identified more than 70% of infected operations. Environmental sampling is another diagnostic tool that veterinarians and dairy producers can use to determine herd infection status for MAP.

Recovery of Salmonella, Listeria monocytogenes, and Mycobacterium bovis from cheese entering the United States through a noncommercial land port of entry

A joint multiagency project was initiated in response to a Salmonella outbreak in San Diego County, California, in 2004. Samples of cheese were collected during four 1-day operations at the San Ysidro port of entry, along the United States-Mexico border. Surveyed participants were persons crossing the border as pedestrians or in vehicles who had a minimum of 2.27 kg of cheese, which may suggest a potential diversion to illegal marketing. In addition, data were collected about the cheese to identify risk factors for cheese contamination. Two hundred four cheese samples were submitted to the California Animal Health and Food Safety Laboratory System-San Bernardino Branch and analyzed for potential food pathogens. Ninety-four percent (190 of 203) of the samples tested positive for alkaline phosphatase. Salmonella was detected from 13% (27 of 204) of the samples comprising 11 serogroups and 28 serotypes. Pulsed-field gel electrophoresis DNA fingerprinting analysis, performed following standardized methods, determined that an isolate obtained from this study had an indistinguishable pattern from a recent Salmonella enterica serovar Typhimurium var. Copenhagen epidemic in the San Diego County that was linked to 14 illnesses. Listeria spp. were detected from 4% (8 of 204) of the samples, and of these, half were identified as L. monocytogenes. Escherichia coli O157:H7 was not detected from any of the samples. Mycobacterium bovis was detected from one panela-style cheese sample. Nine additional samples yielded Mycobacterium spp.

Short-sequence-repeat analysis of Mycobacterium avium subsp. paratuberculosis and Mycobacterium avium subsp. avium isolates collected from animals throughout the United States reveals both stability of loci and extensive diversity

We analyzed the multilocus short sequence repeats (SSRs) of 211 and 56 isolates of Mycobacterium avium subsp. paratuberculosis and M. avium subsp. avium, respectively. The M. avium subsp. paratuberculosis isolates could be differentiated into 61 genotypes. The M. avium subsp. avium isolates showed limited diversity. These SSRs are stable and suitable for studying the molecular epidemiology of M. avium subsp. paratuberculosis.

Tuberculosis in elephants: antibody responses to defined antigens of Mycobacterium tuberculosis, potential for early diagnosis, and monitoring of treatment

Tuberculosis (TB) in elephants is a re-emerging zoonotic disease caused primarily by Mycobacterium tuberculosis. Current diagnosis relies on trunk wash culture, the only officially recognized test, which has serious limitations. Innovative and efficient diagnostic methods are urgently needed. Rapid identification of infected animals is a crucial prerequisite for more effective control of TB, as early diagnosis allows timely initiation of chemotherapy. Serology has diagnostic potential, although key antigens have not been identified and optimal immunoassay formats are not established. To characterize the humoral responses in elephant TB, we tested 143 serum samples collected from 15 elephants over time. These included 48 samples from five culture-confirmed TB cases, of which four were in Asian elephants infected with M. tuberculosis and one was in an African elephant with Mycobacterium bovis. Multiantigen print immunoassay (MAPIA) employing a panel of 12 defined antigens was used to identify serologic correlates of active disease. ESAT-6 was the immunodominant antigen recognized in elephant TB. Serum immunoglobulin G antibodies to ESAT-6 and other proteins were detected up to 3.5 years prior to culture of M. tuberculosis from trunk washes. Antibody levels to certain antigens gradually decreased in response to antitubercular therapy, suggesting the possibility of treatment monitoring. In addition to MAPIA, serum samples were evaluated with a recently developed rapid test (RT) based on lateral flow technology (ElephantTB STAT-PAK). Similarly to MAPIA, infected elephants were identified using the RT up to 4 years prior to positive culture. These findings demonstrate the potential for TB surveillance and treatment monitoring using the RT and MAPIA, respectively.

Comparison of the recovery of Mycobacterium bovis isolates using the BACTEC MGIT 960 system, BACTEC 460 system, and Middlebrook 7H10 and 7H11 solid media

The BACTEC Microbacteria Growth Indicator Tube (MGIT) 960 system was evaluated to determine how it compares with the BACTEC 460 radiometric system and solid media for recovery of Mycobacterium bovis from tissue samples. A total of 506 bovine lymph node samples were collected from abattoirs in the United States and Mexico between November 2003 and September 2004. Processed samples were inoculated into an MGIT 960 tube, BACTEC 460 vial, and Middlebrook 7H10 and Middlebrook 7H11 solid media. Ziehl-Neelsen slides were prepared to check for contaminants and confirm the presence of acid-fast positive bacilli. Samples containing acid-fast bacilli were confirmed as members of the Mycobacterium tuberculosis complex by a nucleic acid assay. Niacin and nitrate biochemical tests were used to distinguish M. bovis from M. tuberculosis isolates. Statistical analyses were performed to compare recovery rate, mean time to detection, contamination rates, as well as pair-wise comparisons in each category. The results showed that the MGIT 960 system had a higher recovery rate of M. bovis (122/129) than did the BACTEC 460 (102/129) and solid media system (96/129). The average time to detection was 15.8 days for the MGIT 960 system, 28.2 days for the BACTEC 460 system, and 43.4 days for solid media. Contamination rates were 6.9% for the MGIT 960 system, 3.4% for the BACTEC 460 system, and 21.7% for solid media. These results indicate the MGIT 960 system can be used as an alternative to the BACTEC 460 system for recovering M. bovis from tissue samples.

Immune responses to defined antigens of Mycobacterium bovis in cattle experimentally infected with Mycobacterium kansasii

Cross-reactive responses elicited by exposure to nontuberculous mycobacteria often confound the interpretation of antemortem tests for Mycobacterium bovis infection of cattle. The use of specific proteins (e.g., ESAT-6, CFP-10, and MPB83), however, generally enhances the specificity of bovine tuberculosis tests. While genes for these proteins are absent from many nontuberculous mycobacteria, they are present in M. kansasii. Instillation of M. kansasii into the tonsillar crypts of calves elicited delayed-type hypersensitivity and in vitro gamma interferon and nitrite concentration responses of leukocytes to M. avium and M. bovis purified protein derivatives (PPDs). While the responses of M. kansasii-inoculated calves to M. avium and M. bovis PPDs were approximately equivalent, the responses of M. bovis-inoculated calves to M. bovis PPD exceeded their respective responses to M. avium PPD. The gamma interferon and nitrite responses of M. kansasii-inoculated calves to recombinant ESAT-6-CFP-10 (rESAT-6-CFP-10) exceeded corresponding responses of noninoculated calves as early as 15 and 30 days after inoculation, respectively, and persisted throughout the study. The gamma interferon and nitrite responses of M. bovis-inoculated calves to rESAT-6-CFP-10 exceeded the corresponding responses of M. kansasii-inoculated calves beginning 30 days after inoculation. By using a lipoarabinomannan-based enzyme-linked immunosorbent assay, specific serum antibodies were detected as early as 50 days after challenge with M. kansasii. By a multiantigen print immunoassay and immunoblotting, serum antibodies to MPB83, but not ESAT-6 or CFP-10, were detected in M. kansasii-inoculated calves; however, responses to MPB83 were notably weaker than those elicited by M. bovis infection. These findings indicate that M. kansasii infection of calves elicits specific responses that may confound the interpretation of bovine tuberculosis tests.

Growth of Mycobacterium avium subsp. paratuberculosis in the presence of hexadecylpyridinium chloride, natamycin, and vancomycin

A design-of-experiments approach was used to examine the effect of hexadecylpyridinium chloride (HPC), alone or in combination with the antibiotics vancomycin and natamycin, on the growth of Mycobacterium avium subsp. paratuberculosis (MAP). At concentrations above 74.4 microg/ml, HPC had a highly significant detrimental effect on the growth of MAP, whereas natamycin at 10.8 and 21.6 microg/ml and vancomycin at 5.2 and 10.4 microg/ml did not have such an effect. Titration of the amount of HPC tolerated by MAP indicated that growth can occur in the presence of 24.8 microg/ml or lower. Processing of bovine fecal specimens indicated that reducing the concentration of HPC from 32.22 to 1.07 mg/ml during decontamination may improve detection when cultures are grown on solid medium but not when cultures are grown in liquid medium. Further investigation into optimizing HPC concentration during processing of fecal samples is warranted. Natamycin, in conjunction with vancomycin, may be useful for controlling fungal contamination during isolation of MAP from fecal samples.

Effect of egg yolk on the detection of Mycobacterium avium subsp. paratuberculosis using the ESP II liquid culture system

Rapid diagnosis of paratuberculosis in infected cattle is important for the successful control of Johne disease within herds. Thus, improving culture methods for Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis) will aid in the identification of asymptomatic animals. Egg yolk is a component of the media used for growing M. paratuberculosis, but its requirement as a supplement has not been reported. Using the ESP II liquid culture system, 2 different sources and 5 concentrations (3.3%, 1.6%, 0.8%, 0.4%, and 0%) of egg yolk were analyzed. Egg yolk source did not affect either recovery rate or time to detection, but both parameters were significantly improved when the 3.3% egg yolk concentrations (final volume) were used over media containing no egg yolk. This study also assessed the recovery of M. paratuberculosis from fecal samples that were cultured multiple times using Herrold egg yolk agar (HEY). Specimens containing greater than 70 cfu/g feces could routinely be identified as positive for M. paratuberculosis after only 1 culture attempt, whereas specimens with fewer bacteria were only intermittently positive, even after 5 replicate cultures. Therefore, this study indicates that the sensitivity of the Trek Diagnostic ESP II liquid culture system for M. paratuberculosis is affected by egg yolk concentration and that single culture attempts using HEY solid media may not identify specimens containing low numbers of bacteria.

Fatal mycobacteriosis with hepatosplenomegaly in a young dog due to Mycobacterium avium

Cases of disseminated Mycobacterium avium infections in dogs are rare because it appears that the species is innately resistant to infection. A 2-year-old, castrated, 5 kg Shih Tzu-Poodle-cross developed anemia, abdominal pain, lethargy, and splenomegaly. Histological examination of surgically removed spleen indicated marked granulomatous splenitis with myriad intracytoplasmic acid-fast bacterial rods. Ultrastructural examination revealed the presence of 3-4-microm-long mycobacteria in phagolysosomes of epithelioid macrophages. Tissue extract of lightly fixed spleen was positive for M. avium 16S ribosomal RNA and negative for M. tuberculosis complex IS6110 DNA by polymerase chain reaction testing. Anemia was associated with the presence of mycobacteria-infected macrophages in bone marrow. The animal's condition deteriorated, and euthanasia was performed after a clinical course of 2 months. The principal morphological findings at necropsy were severe diffuse granulomatous hepatitis, enteric lymphadenomegaly, and segmental granulomatous enteritis with intralesional mycobacteria present. Mycobacterium avium was cultured from enteric lymph nodes sampled at necropsy. The source of infection was not established but was presumed to be environmental with an enteric portal of entry.

Use of recombinant ESAT-6:CFP-10 fusion protein for differentiation of infections of cattle by Mycobacterium bovis and by M. avium subsp. avium and M. avium subsp. paratuberculosis

Immunological diagnosis of Mycobacterium bovis infection of cattle is often confounded by cross-reactive responses resulting from exposure to other mycobacterial species, especially Mycobacterium avium. Early secretory antigenic target 6 (ESAT-6) and culture filtrate protein 10 (CFP-10) are dominant gamma interferon (IFN-gamma)-inducing antigens of tuberculous mycobacteria, and they are absent from many environmental nontuberculous mycobacteria. Because M. avium exposure is the primary confounding factor in the diagnosis of M. bovis-infected animals, in vitro responses to a recombinant ESAT-6:CFP-10 (rESAT-6:CFP-10) fusion protein by blood leukocytes from cattle naturally exposed to M. avium or experimentally challenged with Mycobacterium avium subsp. avium or Mycobacterium avium subsp. paratuberculosis were compared to responses by M. bovis-infected cattle. Responses to heterogeneous mycobacterial antigens (i.e., purified protein derivatives [PPDs] and whole-cell sonicates [WCSs]) were also evaluated. Tumor necrosis factor alpha (TNF-alpha), IFN-gamma, and nitric oxide responses by M. bovis-infected cattle to rESAT-6:CFP-10 exceeded (P < 0.05) the corresponding responses by cattle naturally sensitized to M. avium. Experimental infection with M. bovis, M. avium, or M. avium subsp. paratuberculosis induced significant (P < 0.05) IFN-gamma and nitric oxide production to WCS and PPD antigens, regardless of the mycobacterial species used for the preparation of the antigen. Responses to homologous crude antigens generally exceeded responses to heterologous antigens. Nitric oxide and IFN-gamma responses to rESAT-6:CFP-10 by blood leukocytes from M. bovis-infected calves exceeded (P < 0.05) the corresponding responses of noninfected, M. avium-infected, and M. avium subsp. paratuberculosis-infected calves. Despite the reported potential for secretion of immunogenic ESAT-6 and CFP-10 proteins by M. avium and M. avium subsp. paratuberculosis, it appears that use of the rESAT-6:CFP-10 fusion protein will be useful for the detection of tuberculous cattle in herds with pre-existing sensitization to M. avium and/or M. avium subsp. paratuberculosis.

Comparison of two DNA extractions and nested PCR, real-time PCR, a new commercial PCR assay, and bacterial culture for detection of Mycobacterium avium subsp. paratuberculosis in bovine feces

In this study, 5 combinations of 2 DNA extractions and 3 polymerase chain reaction (PCR) techniques were compared with culture for the detection of Mycobacterium paratuberculosis directly from bovine feces. These combinations included a new commercial extraction technique combined with a commercial PCR/Southern blot technique, nested PCR (nPCR), or real-time PCR, and a university-developed extraction combined with nPCR or real-time PCR. Four of the 5 combinations had statistically similar sensitivities between 93% and 100% and specificity between 95% and 100%, when compared with culture results from 63 bovine fecal samples. These results indicated that using a commercial extraction with a commercial PCR/Southern blot, nPCR, or real-time PCR, or a university-developed extraction with real-time PCR would result in similar sensitivities to culture for the identification of M. paratuberculosis from bovine feces and are valid alternatives to culture.

Mycobacterial isolations in captive elephants in the United States

Interest in tuberculosis in elephants has been increasing over the past several years in the United States. Several techniques have been used to diagnose mammalian tuberculosis. Currently, the test considered most reliable for diagnosis of TB in elephants is based on the culture of respiratory secretions obtained by trunk washes.

Bovine tuberculosis in Michigan wildlife

White-tailed deer in Michigan are now recognized as a reservoir host of bovine tuberculosis (TB). It has been determined that the most likely cause of bovine TB infection in the deer is from congregating in artificially high numbers at feed sites. The presence of a wildlife reservoir of TB in Michigan poses a serious threat to the control and eradication programs that are now in their final stages in the United States.

Polymerase chain reaction detection of Mycobacterium tuberculosis complex and Mycobacterium avium organisms in formalin-fixed tissues from culture-negative ruminants

In the US eradication program for bovine tuberculosis, a definitive diagnosis depends on the isolation of Mycobacterium bovis. However, in some cases bacterial culture is unsuccessful, even though the tissue is considered suspicious by histopathology because granulomatous lesions and acid-fast organisms are present. The purpose of this study was to determine if polymerase chain reaction (PCR) tests on formalin-fixed tissue would successfully identify the organisms observed in suspect lesions from culture-negative animals. Diagnostic laboratory records were used to select paraffin blocks of tissue from 102 ruminants that had suspect microscopic lesions but no bacterial isolation. Sections from these blocks were examined with PCR primers for IS6110 to detect Mycobacterium tuberculosis complex infection, or with 16S ribosomal RNA and IS900 primers for detection of Mycobacterium avium. The PCR tests successfully identified a mycobacterial infection in 58 of 102 tissues, including 41 M. tuberculosis complex and 17 M. avium (11 subspecies paratuberculosis). These results demonstrate that PCR testing of formalin-fixed tissue, in combination with bacterial culture, may increase the effectiveness of laboratory diagnostic efforts to detect and identify the most common mycobacterial diseases of ruminants.

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.

Naturally occurring tuberculosis in white-tailed deer

OBJECTIVE

To determine the distribution of lesions and extent of tissues infected with Mycobacterium bovis in a captive population of white-tailed deer.

DESIGN

Cross-sectional study.

ANIMALS

116 captive white-tailed deer.

PROCEDURE

Deer were euthanatized, and postmortem examinations were performed. Tissues with gross lesions suggestive of tuberculosis were collected for microscopic analysis and bacteriologic culture. Tissues from the head, thorax, and abdomen of deer with no gross lesions were pooled for bacteriologic culture. Tonsillar, nasal, oral, and rectal swab specimens, fecal samples, and samples of hay and pelleted feed, soil around feeding sites, and water from 2 natural ponds were collected for bacteriologic culture.

RESULTS

Mycobacterium bovis was isolated from 14 of 116 (12%) deer; however, only 9 of 14 had lesions consistent with tuberculosis. Most commonly affected tissues included the medial retropharyngeal lymph node and lung. Five of 14 tuberculous deer had no gross lesions; however, M bovis was isolated from pooled tissue specimens from the heads of each of these deer. Bacteriologic culture of tonsillar swab specimens from 2 of the infected deer yielded M bovis. Mean (+/- SEM) age of tuberculous deer was 2.5 +/- 0.3 years (range, 0.5 to 6 years). Mycobacterium bovis was not isolated from feed, soil, water, or fecal samples.

CONCLUSIONS AND CLINICAL RELEVANCE

Examination of hunter-killed white-tailed deer for tuberculosis commonly includes only the lymph nodes of the head. Results of such examinations may underestimate disease prevalence by as much as 57%. Such discrepancy should be considered when estimating disease prevalence.

Identification of tuberculosis in cattle slaughtered in Mexico

OBJECTIVES

To determine epidemiologic factors associated with tuberculosis (TB) in dairy cattle slaughtered in 6 important regions for milk production in Mexico.

ANIMALS

2,500 cattle.

PROCEDURE

Tissue specimens with lesions typical of TB were obtained during routine inspection of carcasses at abbatoirs between July 1996 and January 1997. Infection with Mycobacterium organisms was confirmed by histologic examination and bacteriologic culture. Species identification was made by use of selective growth medium, conventional biochemical tests, and radiometric procedures. Epidemiologic information for affected cattle was obtained by personal interviews with cattle dealers and owners.

RESULTS

400 (16%) of 2,500 cattle carcasses had gross lesions typical of TB. Of the 400 infected cattle, 336 (84%) had lesions in > or = 1 lymph node. Infection was confirmed in 87% of cattle with gross lesions by histologic examination, in 77% by bacteriologic culture at a laboratory in the United States, and in 59% by bacteriologic culture at a laboratory in Mexico. Most cattle were adult females in fair to good body condition that came from large herds (> 500 cattle) and were not included in the Mexican TB control program.

CONCLUSIONS AND CLINICAL RELEVANCE

Mean prevalence of lesions typical of TB in dairy cattle at 6 locations in Mexico was 16%. Mycobacterium infection was confirmed by various techniques in most lesions. Recognition of typical gross lesions at slaughter may expedite TB control procedures.

Molecular epidemiologic analysis of Mycobacterium bovis isolates from Mexico

OBJECTIVE

To assess phylogenetic relationships among Mycobacterium bovis isolates by use of random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) fingerprinting and to relate genetic profiles of isolates to epidemiologic characteristics.

ANIMALS

400 cattle with tuberculosis.

PROCEDURE

Mycobacterium bovis was isolated from various organs of cattle slaughtered in 6 geographic regions of Mexico. Most cattle were adult Holsteins from large herds that did not participate in a tuberculosis control program. Four random primers and 2 selected primers were used in RAPD-PCR fingerprinting of 88 isolates. Pairwise genetic distance between isolates was obtained and subjected to cluster analysis with bootstrapping to test for levels of support.

RESULTS

98 different fragments were obtained; there was broad genetic diversity among isolates, and each isolate had a unique RAPD-genotype, including those originating from the same herd. Clustering by geographic location, affected organ, or severity of lesion was not detected. Linkage disequilibrium analysis suggested that M. bovis was highly clonal and that mutations develop at a rapid rate among isolates.

CONCLUSIONS AND CLINICAL RELEVANCE

Use of RAPD-PCR could not differentiate M. bovis isolates by epidemiologic characteristics or identify common sources of infection.

Inflammatory pseudotumor in a cat with cutaneous mycobacteriosis

A 5-year-old, castrated male, domestic Shorthair Cat had an ulcerated mass with fistulous tracts on the left hind paw. Homogeneous tan tissue diffusely infiltrated the dermis and subcutis of the paw and extended proximally so that, short of amputation, complete excision was not feasible. Biopsy specimens consisted of granulation tissue with marked proliferation of spindle cells. Neutrophils and histiocytic cells were scattered among the spindle cells. The histiocytic cells had abundant foamy or vacuolated cytoplasm, but features of granulomatous inflammation, such as epithelioid macrophages or granuloma formation, were not observed. The initial impression was inflammatory granulation tissue, but the degree of fibroplasia prompted inclusion of fibrosarcoma in the differential diagnosis. Cutaneous mycobacteriosis was diagnosed when numerous acid-fast bacteria were identified with Kinyoun's stain; Mycobacterium avium was subsequently cultured. The cat was euthanatized because of lack of response to enrofloxacin therapy. At necropsy, lesions were localized to the hind limb. Not only is mycobacteriosis an uncommon cause of cutaneous masses in cats, but this case was unusual because of the lack of granuloma formation and the similarity of the mass to a spindle cell tumor.

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 north-eastern portion of Michigan's 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 (Procyon lotor), red fox (Vulpes vulpes), bobcat (Felis rufus), and badger (Taxidea taxus).

Restriction fragment length polymorphism analysis of Mycobacterium bovis isolates from captive and free-ranging animals

Mycobacterium bovis isolates from cattle, captive elk, and free-ranging mule deer and coyotes were examined by restriction fragment length polymorphism (RFLP) analysis. DNA extracted from each isolate was digested with restriction endonucleases AluI and PvuII. DNA probes used for Southern hybridizations were a 37-base oligonucleotide and a 123-base-pair sequence specific for the insertion sequence IS6110 and a plasmid, pTBN12, which contains a polymorphic GC-rich repetitive sequence present in several species of mycobacteria. Generally, M. bovis isolates originating from a single herd of either cattle or captive elk had identical RFLP patterns, whereas isolates from unrelated sources had distinct patterns. The RFLP patterns for M. bovis isolates from free-ranging mule deer and coyotes were identical to patterns observed for isolates from a captive elk herd that was located in the area where the free-ranging animals were found. These results indicate that the captive elk herd may have been the source of M. bovis that infected the free-ranging animals. Results of this study show that RFLP analysis is a useful tool for differentiation of M. bovis isolates and for molecular epidemiology studies to determine possible sources of infection in outbreaks of tuberculosis in animals.

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.

Survey of free-ranging elk from Wyoming and Montana for selected pathogens

From December 1991 through January 1995, a disease survey was conducted on herds of free-ranging, hunter-killed elk (Cervus elaphus nelsoni) from three areas in proximity to Yellowstone National Park (YNP), Wyoming (USA), after tuberculosis caused by Mycobacterium bovis was discovered in a captive herd of elk in the area. Complete or partial sets of specimens from 289 elk collected between December 1991 and January 1993 were examined histologically; no mycobacterial lesions were observed. Lesions of tuberculosis were not detected in tonsils or lymph nodes of the head from an additional 99 hunter-killed, adult elk from one area (area 2) collected in January 1995. Neither M. bovis nor M. paratuberculosis were isolated from any of the specimens cultured. Antibodies to Brucella abortus were detected in serum samples from 0%, 1%, and 1% of elk from three areas sampled (areas 1, 2 and 3), respectively. Brucella abortus biovar 1 was isolated from multiple tissues from one seropositive animal from area 3. Larvae with morphology consistent with Dictyocaulus sp. were found in 12%, 14%, and 0% of fecal specimens tested from areas 1, 2, and 3, respectively. Pasteurella multocida and Actinomyces pyogenes were isolated from a lung with purulent bronchopneumonia and abscesses.

Molecular epidemiology of Mycobacterium bovis in Texas and Mexico

Seventy-nine Mycobacterium bovis isolates recovered from Mexican and Texas cattle were categorized into 16 and 25 distinct types on the basis of IS6110 and direct-repeat fingerprint patterns, respectively. By using a combination of both fingerprint patterns, 30 distinct restriction fragment length polymorphism types were defined. Fifty-eight of 79 isolates (73%) were distributed among nine clusters. Clustered isolates were identified within herds, as well as in geographically disperse herds in Texas and Mexico. This observation is consistent with active transmission within herds and among herds, presumably as a result of active or historical cattle movements. The majority of bovine isolates (64 of 79) exhibited a single copy of IS6110. Interestingly, in contrast to previous studies, a high percentage of bovine isolates (15 of 79) exhibited multiple IS6110 copies (two to five) distributed among 11 different restriction fragment length polymorphism types. It is speculated that transmission from noncattle sources may be responsible. Continued fingerprinting of isolates originating from nonbovine sources and herd surveys is expected to provide useful information regarding the epidemiology of tuberculosis in this region.

A comparison of gross pathology, histopathology, and mycobacterial culture for the diagnosis of tuberculosis in elk (Cervus elaphus)

Using the isolation of Mycobacterium bovis as the reference standard, this study evaluated the sensitivity, specificity and kappa statistic of gross pathology (abattoir postmortem inspection), histopathology, and parallel or series combinations of the two for the diagnosis of tuberculosis in 430 elk and red deer. Two histopathology interpretations were evaluated: histopathology I, where the presence of lesions compatible with tuberculosis was considered positive, and histopathology II, where lesions compatible with tuberculosis or a select group of additional possible diagnoses were considered positive. In the 73 animals from which M. bovis was isolated, gross lesions of tuberculosis were most often in the lung (48), the retropharyngeal lymph nodes (36), the mesenteric lymph node (35), and the mediastinal lymph nodes (16). Other mycobacterial isolates included: 11 M. paratuberculosis, 11 M. avium, and 28 rapidly growing species or M. terrae complex. The sensitivity estimates of gross pathology and histopathology I were 93% (95% confidence limits [CL] 84.97%) and 88% [CL 77.94%], respectively, and the specificity of both was 89% [CL 85.92%]). The sensitivity and specificity of histopathology II were 89% (CL 79.95%) and 77% (CL 72.81%), respectively. The highest sensitivity estimates (93-95% [CL 84.98%]) were obtained by interpreting gross pathology and histopathology in parallel (where an animal had to be positive on at least one of the two, to be classified as combination positive). The highest specificity estimates (94-95% [CL 91-97%] were generated when the two tests were interpreted in series (an animal had to be positive on both tests to be classified as combination positive). The presence of gross or microscopic lesions showed moderate to good agreement with the isolation of M. bovis (Kappa = 65-69%). The results showed that post-mortem inspection, histopathology and culture do not necessarily recognize the same infected animals and that the spectra of animals identified by the tests overlaps.

Determination of stability of Brucella abortus RB51 by use of genomic fingerprint, oxidative metabolism, and colonial morphology and differentiation of strain RB51 from B. abortus isolates from bison and elk

Brucella abortus RB51 and isolates from cattle, bison, and elk were characterized by pulsed-field gel electrophoresis and standard techniques for biotyping Brucella species, which included biochemical, morphological, and antigenic techniques, phage susceptibility, and antibiotic resistance. The objectives were to ascertain the stability of RB51 and to differentiate RB51 from other brucellae. Genomic restriction endonuclease patterns produced by pulsed-field gel electrophoresis demonstrated a unique fingerprint for RB51 relative to other brucellae. Comparisons of the oxidative metabolic profiles of RB51 after time in vivo (14 weeks) and in vitro (75 passages) showed no change in characteristic patterns of oxygen uptake on selected amino acid and carbohydrate substrates. Strain RB51 was biotyped as a typical rough B. abortus biovar 1 (not strain 19) after animal passage or a high number of passages in vitro and remained resistant to rifampin or penicillin and susceptible to tetracycline. No reactions with A or M antiserum or with a monoclonal antibody to the O antigen of Brucella lipopolysaccharides were detected; however, RB51 agglutinated with R antiserum. The results indicate that the genomic fingerprint and rough colonial morphology of RB51 are stable characteristics and can be used to differentiate this vaccine strain from Brucella isolates from cattle, bison, and elk.

Comparison of the sensitivity of the caudal fold skin test and a commercial gamma-interferon assay for diagnosis of bovine tuberculosis

A study to determine and compare the sensitivity of the caudal fold tuberculin test (CFT) and a commercial gamma-interferon (gamma-IFN) assay for diagnosis of bovine tuberculosis was conducted. A dairy herd with approximately a third of the cattle infected with Mycobacterium bovis was chosen for this study. All cattle from this herd were slaughtered, and tissue specimens for bacteriologic culturing and histologic examination were collected. Results of the CFT and gamma-IFN assay were compared with results of bacteriologic culturing and histologic examination to determine test sensitivity. Results were analyzed, using each of the following 4 standards to classify cattle as infected: positive test result by bacteriologic culturing only; histologic examination only; bacteriologic culturing and histologic examination; and bacteriologic culturing or histologic examination. Sensitivity of the CFT ranged from 80.4 to 84.4%, depending on the standard of comparison. Sensitivity of the gamma-IFN assay ranged from 55.4 to 97.1%, depending on the standard of comparison and on the method of interpretation. The CFT was significantly (P < 0.001) more sensitive than the gamma-IFN assay for diagnosis of bovine tuberculosis when the gamma-IFN assay was conducted and interpreted as instructed by the manufacturer. Maximum overall sensitivity was achieved when results of the CFT and gamma-IFN assay were interpreted in parallel.

Application of pulsed-field gel electrophoresis for differentiation of vaccine strain RB51 from field isolates of Brucella abortus from cattle, bison, and elk

Restriction endonuclease patterns of genomic fragments separated by use of pulsed-field gel electrophoresis were used to differentiate Brucella abortus strain RB51, a rifampin-resistant mutant of the standard virulent strain 2308, from other brucellae. Results were compared with results obtained by use of standard methods for characterizing brucellae. Electrophoretic patterns of the ATCC type strains allowed identification of the strains to the level of species. Genomic profiles of B abortus biovars 1, 2, and 4 were similar, as were those of biovars 5, 6, and of biovar 3 was similar to that of biovars 5, 6, and 9, except for a missing band at 93 kb and additional bands at 65 and 67 kb. A different fingerprint was detected in B abortus strain RB51, using the pulsed-field gel electrophoresis patterns of genomic DNA digested with restrictive endonuclease Xba I. The profile of B abortus strain RB51 contained a band at 104 kb, as opposed to a 109-kb fragment within profiles of B abortus isolates from naturally infected cattle, bison, and elk. Despite known biochemical and biological differences between RB51 and its parent strain (2308), restriction endonuclease analysis results were similar.

Characteristics of a Brucella species from a bottlenose dolphin (Tursiops truncatus)

A culture isolated from an aborted fetus of a bottlenose dolphin (Tursiops truncatus) was characterized. The isolate was a gram-negative coccobacillus, and the colonial morphology was typical of a smooth Brucella. The isolate was positive for catalase, oxidase, nitrate reduction, and urease. Hydrogen sulfide was not produced. It grew in air at 37 C but required 72 hours for good growth. There was growth on media containing basic fuchsin, thionin, thionin blue, penicillin, and erythritol. The M antigen was dominant, and the isolate was lysed by 4 of 10 brucellaphages tested. The oxidative metabolic profile of the isolate was similar to that for B. abortus but differed in utilization of L-asparagine, L-glutamic acid, and DL-citrulline. Whole-cell lysates were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The protein profiles were markedly different from the protein profiles of reference strains of Brucella species. Biochemical and oxidative metabolism profiles indicated that the isolate belongs in the genus Brucella but did not match the profiles of any established species or biovars. This isolate may be an atypical strain of a recognized Brucella species or a new biovar or species of Brucella.

Abortion caused by Brucella abortus biovar 1 in a free-ranging bison (Bison bison) from Yellowstone National Park

A near-term aborted bison (Bison bison) fetus was collected near Old Faithful geyser in Yellowstone National Park, Wyoming (USA). On necropsy, the fetus liver had a small capsular tear, and there was a small quantity of blood in the peritoneal cavity. Microscopic lesions included mild, purulent bronchopneumonia and mild, multifocal, interstitial pneumonia. Brucella abortus biovar 1 was isolated from fetal abomasal contents, lung, and heart blood.

Results of using histologic examination and acid-fast staining to confirm a diagnosis of swine mycobacteriosis made on the basis of gross examination

Overall, 74% of the tissue specimens that meat inspectors at a large Pennsylvania packing plant identified as lesions of swine mycobacteriosis yielded Mycobacterium avium on bacteriologic culture. Histopathologic lesions compatible with mycobacteriosis were identified in 83% of the specimens; only 12% of the specimens had acid-fast staining organisms.

Comparison of phenotypic characteristics of Salmonella spp isolated from healthy and ill (infected) chickens

Phenotypic characteristics of 12 paired, Salmonella serotypes isolated from healthy and ill chickens were compared. Variables compared included antibiotic resistance profiles, production of colicins and siderophores, mannose-sensitive hemagglutination of erythrocytes, resistance to serum complement, carbon source utilization, presence and transmissibility of R plasmids, and invasiveness in primary chicken kidney cell culture. Differences were found between pairs for utilization of carbon sources, mannose-sensitive hemagglutination of erythrocytes, and invasiveness in cell culture.

Characteristics of Salmonella spp. and Escherichia coli isolated from broiler flocks classified as "good" or "poor" producers

Cecal samples from 100 broiler flocks were cultured for Escherichia coli and Salmonella. Samples were selected from flocks classified as either "good" or "poor" producers by a production formula. In an attempt to identify predictors of flock productivity, isolates were studied for differences in antibiotic resistances, hemagglutination of erythrocytes, production of colicins, production of siderophores, type of hemolysis, resistance to host complement, and presence of plasmids. S. typhimurium (copenhagen) was isolated from one poor producing flock and three good producers. Salmonella isolates showed no significant differences in the parameters studied. The E. coli isolates showed significant differences only for the presence of plasmids. These data indicate that differences in host intestinal E. coli from good and poor producing flocks do not predict flock productivity.

Identification of Brucella abortus strain 19 by decreased ability to utilize erythritol as determined by gas liquid chromatography

A method to identify Brucella abortus strain 19 by erythritol utilization using gas liquid chromatography (GLC) was developed. A total of 69 strains of B. abortus (41 virulent field strain isolates and 28 strain 19 isolates) were tested. Following incubation of the isolate with a standard amount of erythritol, the erythritol present in the cell suspension was acetylated and measured by GLC. Field strains of B. abortus utilized an average of 90.9% of the erythritol, whereas vaccine strains utilized an average of 42.4%. This difference in erythritol utilization will allow a more rapid identification of B. abortus strain 19.

Effect of environmental-genetic interactions on Mycobacterium avium challenge infection

Chickens from lines selectively bred for either a high-antibody (HA) or low-antibody (LA) response to sheep erythrocytes were injected intravenously with Mycobacterium avium while being held in low, medium, or high levels of social stress for 5 days (first environment). During the remaining 6 weeks, they were held under either low or medium levels of social stress (second environment). Infection led to lesions consisting of granulomas, some of which had necrotic centers. There was a positive correlation between numbers of lesions with necrotic centers and M. avium cells recovered from livers. The numbers and nature of lesions were influenced by both genetic and environmental factors. Numbers of necrotizing lesions increased with stressfulness of the first environment. Total numbers of lesions were reduced by the medium-stress second environment, and the total number of necrotizing lesions was reduced among LA chickens in the low-stress second environment.