Distinguishing Extravascular from Intravascular Ferumoxytol Pools within the Brain: Proof of Concept in Patients with Treated Glioblastoma.

BACKGROUND AND PURPOSE: Glioblastoma-associated macrophages are a major constituent of the immune response to therapy and are known to engulf the iron-based MR imaging contrast agent, ferumoxytol. Current ferumoxytol MR imaging techniques for localizing macrophages are confounded by contaminating intravascular signal. The aim of this study was to assess the utility of a newly developed MR imaging technique, segregation and extravascular localization of ferumoxytol imaging, for differentiating extravascular-from-intravascular ferumoxytol contrast signal at a delayed 24-hour imaging time point. MATERIALS AND METHODS: Twenty-three patients with suspected post-chemoradiotherapy glioblastoma progression underwent ferumoxytol-enhanced SWI. Segregation and extravascular localization of ferumoxytol imaging maps were generated as the voxelwise difference of the delayed (24 hours) from the early (immediately after administration) time point SWI maps. Continuous segregation and extravascular localization of ferumoxytol imaging map values were separated into positive and negative components. Image-guided biologic correlation was performed. RESULTS: Negative segregation and extravascular localization of ferumoxytol imaging values correlated with early and delayed time point SWI values, demonstrating that intravascular signal detected in the early time point persists into the delayed time point. Positive segregation and extravascular localization of ferumoxytol imaging values correlated only with delayed time point SWI values, suggesting successful detection of the newly developed extravascular signal. CONCLUSIONS: Segregation and extravascular localization of ferumoxytol MR imaging improves on current techniques by eliminating intrinsic tissue and intravascular ferumoxytol signal and may inform glioblastoma outcomes by serving as a more specific metric of macrophage content compared with uncorrected T1 and SWI techniques.

Anoxic Brain Injury Detection with the Normalized Diffusion to ASL Perfusion Ratio: Implications for Blood-Brain Barrier Injury and Permeability.

BACKGROUND AND PURPOSE: Anoxic brain injury is a result of prolonged hypoxia. We sought to describe the nonquantitative arterial spin-labeling perfusion imaging patterns of anoxic brain injury, characterize the relationship of arterial spin-labeling and DWI, and evaluate the normalized diffusion-to-perfusion ratio to differentiate patients with anoxic brain injury from healthy controls. MATERIALS AND METHODS: We identified all patients diagnosed with anoxic brain injuries from 2002 to 2019. Twelve ROIs were drawn on arterial spin-labeling with coordinate-matched ROIs identified on DWI. Linear regression analysis was performed to examine the relationship between arterial spin-labeling perfusion and diffusion signal. Normalized diffusion-to-perfusion maps were generated using a custom-built algorithm. RESULTS: Thirty-five patients with anoxic brain injuries and 34 healthy controls were identified. Linear regression analysis demonstrated a significant positive correlation between arterial spin-labeling and DWI signal. By means of a combinatory cutoff of slope of >0 and R2 of > 0.78, linear regression using arterial spin-labeling and DWI showed a sensitivity of 0.86 (95% CI, 0.71-0.94) and specificity of 0.82 (95% CI, 0.66-0.92) for anoxic brain injuries. A normalized diffusion-to-perfusion color map demonstrated heterogeneous ratios throughout the brain in healthy controls and homogeneous ratios in patients with anoxic brain injuries. CONCLUSIONS: In anoxic brain injuries, a homogeneously positive correlation between qualitative perfusion and DWI signal was identified so that areas of increased diffusion signal showed increased ASL signal. By exploiting this relationship, the normalized diffusion-to-perfusion ratio color map may be a valuable imaging biomarker for diagnosing anoxic brain injury and potentially assessing BBB integrity.

Increased Notching of the Corpus Callosum in Fetal Alcohol Spectrum Disorder: A Callosal Misunderstanding?

BACKGROUND AND PURPOSE: In the medicolegal literature, notching of the corpus callosum has been reported to be associated with fetal alcohol spectrum disorders. Our purpose was to analyze the prevalence of notching of the corpus callosum in a fetal alcohol spectrum disorders group and a healthy population to determine whether notching occurs with increased frequency in the fetal alcohol spectrum disorders population. MATERIALS AND METHODS: We performed a multicenter search for cases of fetal alcohol spectrum disorders and included all patients who had a sagittal T1-weighted brain MR imaging. Patients with concomitant intracranial pathology were excluded. The corpus callosum was examined for notches using previously published methods. A χ2 test was used to compare the fetal alcohol spectrum disorders and healthy groups. RESULTS: Thirty-three of 59 patients with fetal alcohol spectrum disorders (0-44 years of age) identified across all centers had corpus callosum notching. Of these, 8 had an anterior corpus callosum notch (prevalence, 13.6%), 23 had a posterior corpus callosum notch (prevalence, 39%), and 2 patients demonstrated undulated morphology (prevalence, 3.4%). In the healthy population, the anterior notch prevalence was 139/875 (15.8%), posterior notch prevalence was 378/875 (43.2%), and undulating prevalence was 37/875 (4.2%). There was no significant difference among the anterior (P = .635), posterior (P = .526), and undulating (P = .755) notch prevalence in the fetal alcohol spectrum disorders and healthy groups. CONCLUSIONS: There was no significant difference in notching of the corpus callosum between patients with fetal alcohol spectrum disorders and the healthy population. Although reported to be a marker of fetal alcohol spectrum disorders, notching of the corpus callosum should not be viewed as a specific finding associated with fetal alcohol spectrum disorders.

Defining the Normal Dorsal Contour of the Corpus Callosum with Time.

BACKGROUND AND PURPOSE: Morphological changes of the corpus callosum have been associated with a large number of congenital neurocognitive and psychiatric disorders. Focal defects or notches of the dorsal surface of the corpus callosum have not been well characterized. Our purpose was the following; 1) to characterize the dorsal contour of the corpus callosum during the life span, 2) to characterize the relationship of contour deviations to neighboring vessels, and 3) to determine whether contour deviations are congenital or acquired. MATERIALS AND METHODS: We retrospectively reviewed normal sagittal T1-weighted brain MR images. A "notch" was defined as a concavity in the dorsal surface at least 1 mm in depth. The corpus callosum was considered to be "undulating" if there were >2 notches, including an anterior and posterior notch. The presence of a pericallosal artery and its relationship to a notch were assessed. RESULTS: We reviewed 1639 MR imaging studies, spanning 0-89 years of age. A total of 1102 notches were identified in 823 studies; 344 (31%) were anterior, 660 (60%) were posterior, and 98 (9%), undulating. There was a positive correlation between the prevalence (P < .001) and depth (P = .028) of an anterior notch and age and a negative correlation between the prevalence of a posterior notch and age (P < .001). There was no difference between patient sex and corpus callosum notching (P = .884). Of the 823 studies with notches, 490 (60%) were associated with a pericallosal artery (P < .001). CONCLUSIONS: The prevalence and depth of notches in the anterior corpus callosum increase significantly with age; this finding suggests that most notches are acquired. There is a significant positive association between the presence of a corpus callosum notch and adjacent pericallosal arteries, suggesting that this may play a role in notch formation.

Pulsed arterial spin-labeled MR imaging evaluation of tuberous sclerosis.

BACKGROUND AND PURPOSE: Tuberous sclerosis presents with characteristic cortical hamartomas and subependymal nodules associated with seizures. The purpose of this study was to use pulsed arterial spin-labeling (PASL) to quantify the perfusion of the cortical hamartomas and correlate the perfusion values with seizure frequency. MATERIALS AND METHODS: A retrospective search yielded 16 MR imaging examinations including conventional MR imaging and PASL perfusion performed in 13 patients (age range, 7 months to 23 years) with a history of tuberous sclerosis. The mean perfusion of each cortical hamartoma greater than 5 mm in size localized with conventional MR imaging sequences was obtained with use of manually drawn regions of interest. Cortical hamartomas were classified as normal, hyperperfused, or hypoperfused on the basis of the mean and SD of the unaffected cortex. Correlation was made between perfusion imaging, conventional imaging, and clinical history. RESULTS: Of the 245 cortical hamartomas, 227 (92.7%) were hypoperfused, 10 (4.1%) were hyperperfused, and 8 (3.3%) were unchanged relative to the mean gray matter. One patient had a subependymal giant cell astrocytoma with a mean perfusion of 93.5 mL/100 g tissue/min. There was a statistically significant positive correlation between seizure frequency and the number of hyperperfused cortical tubers (r = 0.51; n = 16; P = .04), with higher seizure frequency associated with a greater number of hyperperfused cortical tubers. There was no significant correlation, however, between seizure frequency and the overall number of cortical tubers (r = 0.20; n = 16; P = .47). CONCLUSIONS: The PASL technique can assess and quantify the perfusion characteristics of a cortical hamartoma. Most lesions are hypoperfused; however, both normally perfused and hyperperfused lesions occur. The presence of hyperperfused cortical tubers was associated with increased seizure frequency.

Hypercapnia-induced cerebral hyperperfusion: an underrecognized clinical entity.

BACKGROUND AND PURPOSE: The incidence of cerebral hyperperfusion and hypoperfusion, respectively, resulting from hypercapnia and hypocapnia in hospitalized patients is unknown but is likely underrecognized by radiologists and clinicians without routine performance of quantitative perfusion imaging. Our purpose was to report the clinical and perfusion imaging findings in a series of patients confirmed to have hypercapnic cerebral hyperperfusion and hypocapnic hypoperfusion. MATERIALS AND METHODS: Conventional cerebral MR imaging examination was supplemented with arterial spin-labeled (ASL) MR perfusion imaging in 45 patients during a 16-month period at a single institution. Patients presented with an indication of altered mental status, metastasis, or suspected stroke. Images were reviewed and correlated with arterial blood gas (ABG) analysis and clinical history. RESULTS: Patients ranged in age from 1.5 to 85 years. No significant acute findings were identified on conventional MR imaging. Patients with hypercapnia showed global hyperperfusion on ASL cerebral blood flow (CBF) maps, respiratory acidosis on ABG, and diffuse air-space abnormalities on same-day chest radiographs. Regression analysis revealed a significant positive linear relationship between cerebral perfusion and the partial pressure of carbon dioxide (pCO(2); beta, 4.02; t, 11.03; P < .0005), such that rates of cerebral perfusion changed by 4.0 mL/100 g/min for each 1-mm Hg change in pCO(2). CONCLUSIONS: With the inception of ASL as a routine perfusion imaging technique, hypercapnic-associated cerebral hyperperfusion will be recognized more frequently and may provide an alternative cause of unexplained neuropsychiatric symptoms in hospitalized patients. In a similar fashion, hypocapnia may account for a subset of patients with normal MR imaging examinations with poor ASL perfusion signal.

Migraine associated cerebral hyperperfusion with arterial spin-labeled MR imaging.

We present a case series demonstrating abnormal regional cerebral hyperperfusion associated with migraine headache using arterial spin-labeling (ASL). In 3 of 11 patients, regional cortical hyperperfusion was demonstrated during a headache episode that corresponded to previous aura symptoms.

Anoxic injury-associated cerebral hyperperfusion identified with arterial spin-labeled MR imaging.

BACKGROUND AND PURPOSE: Anoxic brain injury is a devastating result of prolonged hypoxia. The goal of this study was to use arterial spin-labeling (ASL) to characterize the perfusion patterns encountered after anoxic injury to the brain. MATERIALS AND METHODS: Sixteen patients with a history of anoxic or hypoxic-ischemic injury ranging in age from 1.5 to 78.0 years (mean, 50.3 years) were analyzed with conventional MR imaging and pulsed ASL 1.0-13.0 days (mean, 4.6 days) after anoxic insult. The cerebral perfusion in each case was quantified by using pulsed ASL as part of the standard stroke protocol. Correlation was made among perfusion imaging, conventional imaging, clinical history, laboratory values, and outcome. RESULTS: Fifteen of the 16 patients showed marked global hyperperfusion, and 1 patient showed unilateral marked hyperperfusion. Mean gray matter (GM) cerebral blood flow (CBF) in these patients was 142.6 mL/100 g of tissue per minute (ranging from 79.9 to 204.4 mL/100 g of tissue per minute). Global GM CBF was significantly higher in anoxic injury subjects, compared with age-matched control groups with and without infarction (F(2,39) = 63.11; P < .001). Three patients had global hyperperfusion sparing areas of acute infarction. Conventional imaging showed characteristic restricted diffusion in the basal ganglia (n = 10) and cortex (n = 13). Most patients examined died (n = 12), with only 4 patients surviving at the 4-month follow-up. CONCLUSION: Pulsed ASL can dramatically demonstrate and quantify the severity of the cerebral hyperperfusion after a global anoxic injury. The global hyperperfusion probably results from loss of autoregulation of cerebral vascular resistance.

Arterial spin-labeling in routine clinical practice, part 3: hyperperfusion patterns.

Arterial spin-labeled (ASL) perfusion imaging can be implemented successfully into a routine clinical neuroimaging protocol and can accurately demonstrate alterations in brain perfusion. We have observed patterns of focal, regional, and global hyperperfusion in a wide variety of disease processes. The causes of hyperperfusion at clinical ASL have not been previously characterized. Focal lesions such as brain tumors and vascular malformations with increased perfusion can be well depicted by ASL. More global causes of hyperperfusion, including postanoxia vasodilation and hypercapnia, may go undetected on conventional MR images, whereas the regional hyperperfusion, which may occur in reversible encephalopathies and luxury perfusion, has been consistently illustrated on ASL cerebral blood flow maps at our institution.

Arterial spin-labeling in routine clinical practice, part 2: hypoperfusion patterns.

Arterial spin-labeling (ASL) is a powerful perfusion imaging technique capable of quickly demonstrating both hypo- and hyperperfusion on a global or localized scale in a wide range of disease states. Knowledge of pathophysiologic changes in blood flow and common artifacts inherent to the sequence allows accurate interpretation of ASL when performed as part of a routine clinical imaging protocol. Patterns of hypoperfusion encountered during routine application of ASL perfusion imaging in a large clinical population have not been described. The objective of this review article is to illustrate our experience with a heterogeneous collection of ASL perfusion cases and describe patterns of hypoperfusion. During a period of 1 year, more than 3000 pulsed ASL procedures were performed as a component of routine clinical brain MR imaging evaluation at both 1.5 and 3T. These images were reviewed with respect to image quality and patterns of hypoperfusion in various normal and disease states.

Arterial spin-labeling in routine clinical practice, part 1: technique and artifacts.

The routine use of arterial spin-labeling (ASL) in a clinical population has led to the depiction of diverse brain pathologic features. Unique challenges in the acquisition, postprocessing, and analysis of cerebral blood flow (CBF) maps are encountered in such a population, and high-quality ASL CBF maps can be generated consistently with attention to quality control and with the use of a dedicated postprocessing pipeline. Familiarity with commonly encountered artifacts can help avoid pitfalls in the interpretation of CBF maps. The purpose of this review was to describe our experience with a heterogeneous collection of ASL perfusion cases with an emphasis on methodology and common artifacts encountered with the technique. In a period of 1 year, more than 3000 pulsed ASL cases were performed as a component of routine clinical brain MR evaluation at both 1.5 and 3T. These ASL studies were analyzed with respect to overall image quality and patterns of perfusion on final gray-scale DICOM images and color Joint Photographic Experts Group (JPEG) CBF maps, and common artifacts and their impact on final image quality were categorized.

Multifocal variant of heterotopic ossification.

In this case report, we present a 25 year follow-up of a single patient with a previously undescribed multifocal variant of heterotopic ossification. The patient presented with multiple occurrences of lesions similar to myositis ossificans atraumatica as well as some lesions resembling exostoses/osteochondromas. Several images and histological sections show the range of appearances and locations of her somewhat disparate lesions, including an exostosis with intraspinal extension. Until additional similar cases are brought forward, we consider this a unique variant of heterotopic ossification. The precise aetiology of this patient's condition is unknown.

Experimental exposure of cattle to a precise aerosolised challenge of Mycobacterium bovis: a novel model to study bovine tuberculosis.

Non-aerosol models of bovine tuberculosis are limited in reproducibility and relevance to natural cases seen in farmed animals. Therefore, there is a need for aerosol models of infection in cattle that can reproduce bovine tuberculosis as seen in natural cases of the disease. This manuscript describes a cattle tuberculosis model based on the inhalation of a precisely defined dose of Mycobacterium bovis in aerosol form, and defines those sites of M. bovis deposition following aerosol inhalation. The dissemination of bacilli and the resultant pathological change following infection is also described. Cattle aged 4-5 months, were infected with approximately 10(4) colony forming units (CFU), using a Madison chamber that had been modified to deliver aerosols to calves. In Experiment 1, calves were examined for gross pathology at post mortem (PM) examination at 93 and 132 days post-infection (PI), respectively. In Experiment 2, pairs of calves were examined for gross pathology at PM examination at 1 day PI and 7 days PI, respectively. At PM examination, samples were taken for bacteriology. Retrospective counts showed that the calves inhaled between 3 x 10(4) and 8 x 10(4)CFU of M. bovis. In Experiment 1, pathology indicative of tuberculosis and detection of M. bovis by qualitative bacteriology was found throughout the lower respiratory tract (LRT). In Experiment 2, pathology was only observed in a single site of one calf at day 7 PI. Samples positive for M. bovis by bacteriology were predominantly in the LRT. The numbers of M. bovis CFU recovered and the distributions of positive sites were greater at day 7 PI than day 1 PI. This study describes an aerosol exposure method that can deliver a defined dose of M. bovis almost exclusively to the LRT. The distribution of M. bovis and lesions indicative of tuberculosis suggests this aerosol method replicates the primary mode of tuberculosis transmission in cattle.

The immunology of bovine tuberculosis and progression toward improved disease control strategies.

Failure to remove cattle diseased with Mycobacterium bovis has immense financial implications for disease control, animal health and agricultural trade as well as the zoonotic risk to human health. Current disease control strategies based on DTH skin testing fail to detect all diseased cattle and additional measures are urgently needed to improve detection of disease and to prevent naïve animals becoming exposed to infection. Experimental models of bovine TB traditionally based on intra-nasal instillation, intra-tracheal inoculation or placed in-contact with infected cattle, have been further developed using aerosolised bacteria delivered to the respiratory tract, allowing field-like bovine TB to be recreated under controlled, experimental conditions. Experimental infection models have already been used to improve diagnostic tests. Specificity of DTH skin testing can be improved under experimental conditions, using recombinant ESAT-6, while laboratory assays such as IFN-gamma release have benefited from the use of defined proteins to improve assay specificity. In combination, antigen cocktails may also improve test sensitivity. There is a concerted international effort to evaluate vaccines for use in cattle populations and to define vaccination strategies which will eliminate disease from infected herds. DNA, protein and genetically modified vaccines inoculated in a single dose, given as prime-boost or injected concurrently, will elicit significant protection against challenge with M. bovis under controlled conditions. However, vaccines and vaccination strategies require evaluation under field conditions. Furthermore, complementary strategies are under development to differentiate immune responses that follow vaccination from those following disease. This paper describes those recent advances which may lead to the introduction of improved disease control strategies.

Optimizing antigen cocktails for detection of Mycobacterium bovis in herds with different prevalences of bovine tuberculosis: ESAT6-CFP10 mixture shows optimal sensitivity and specificity.

Bovine tuberculosis is a major problem in many countries; hence, new and better diagnostic tools are urgently needed. In this work, we have tested ESAT6, CFP10, PE13, PE5, MPB70, TB10.4, and TB27.4 for their potentials as diagnostic markers in field animals from Northern Ireland, Mexico, and Argentina, regions with low, medium, and high prevalences of bovine tuberculosis, respectively. At all three sites, ESAT6 and CFP10 were superior diagnostic antigens, while their combination performed even better at the two sites where the combination was tested, providing the best coverage for the detection of diseased populations. The high sensitivity in the skin test reactor groups, combined with the high specificity in the tuberculosis-free groups, indicated that a diagnosis could correctly be made for 85% of the infected animals, based on their responses to these two antigens. Furthermore, TB10.4, PE13, and PE5 have the potential to supplement ESAT6 and CFP10 in a future five-component diagnostic cocktail.

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.

Early antibody responses to experimental Mycobacterium bovis infection of cattle.

Bovine tuberculosis persists as a costly zoonotic disease in numerous countries despite extensive eradication and control efforts. Sequential serum samples obtained from Mycobacterium bovis-infected cattle were evaluated for seroreactivity to mycobacterial antigens. Animals received M. bovis by aerosol, intratonsil, intranasal, or intratracheal inoculation. Assays included the multiantigen print immunoassay for determination of antigen recognition patterns, immunoblot analysis for sensitive kinetic studies, and the VetTB STAT-PAK test, a novel, rapid test based on lateral-flow technology. Responses to MPB83 were detected for all M. bovis-infected animals regardless of the route or strain of M. bovis used for inoculation. Other less commonly recognized antigens included ESAT-6, CFP-10, and MPB70. Responses to MPB83 were detectable as early as 4 weeks after inoculation, were boosted upon injection of purified protein derivatives for skin testing, and persisted throughout the course of each of the four challenge studies. MPB83-specific immunoglobulin M (IgM) was detected prior to MPB83-specific IgG detection; however, early IgM responses rapidly waned, suggesting a benefit of tests that detect both IgM- and IgG-specific antibodies. The VetTB STAT-PAK test detected responses in sera from 60% (15/25) of the animals by 7 weeks after challenge and detected responses in 96% (24/25) of the animals by 18 weeks. These findings demonstrate the potential for new-generation antibody-based tests for the early detection of M. bovis infection in cattle.

Progress in the development of vaccines and diagnostic reagents to control tuberculosis in cattle.

The sharp rise of bovine tuberculosis (TB) in Great Britain and the continuing problem of wild life reservoirs in countries such as New Zealand and Great Britain have resulted in increased research efforts into the disease. Two of the goals of this research are to develop (1) cattle vaccines against TB and (2) associated diagnostic reagents that can differentiate between vaccinated and infected animals (differential diagnosis). This review summarises recent progress and describes efforts to increase the protective efficacy of the only potential TB vaccine currently available, Mycobacterium bovis BCG, and to develop specific reagents for differential diagnosis. Vaccination strategies based on DNA or protein subunit vaccination, vaccination with live viral vectors as well as heterologous prime-boost scenarios are discussed. In addition, we outline results from studies aimed at developing diagnostic reagents to allow the distinction of vaccinated from infected animals, for example antigens that are not expressed by vaccines like Mycobacterium bovis Bacille-Calmette-Guérin, but recognised strongly in Mycobacterium bovis infected cattle.

Pathogenesis of bovine tuberculosis: the role of experimental models of infection.

In many countries, test-and-slaughter policies based on tuberculin skin testing have made a significant impact on the control of bovine tuberculosis (caused by infection with Mycobacterium bovis). However, in some countries these policies have not proved as effective and improved disease control strategies are required (including improved diagnostic tests and development of vaccines). The host pathogen interactions in bovine tuberculosis are very complex. While studies of the disease in naturally infected field cases of bovine tuberculosis have provided valuable information, detailed knowledge can also be gained through studies of disease models. A number of studies have developed M. bovis infection models employing a range of routes and challenge doses. An early objective was assessment of vaccine efficiency, and models of infection remain central to current work in this area. Development of the intra-nasal and intra-tracheal models have also advanced our understanding of the kinetics of the immune response. In many of these studies, understanding of pathogenesis has been improved by definition of the cells that respond to infection and those that are instrumental in modulation of host responses. Experimental models of infection have been adapted to study cattle to cattle transmission, modeling one of the fundamental routes of infection. This review provides a historical perspective on the types of experimental models used in over 100 years of research and outlines new opportunities to refine those methods for bovine and human tuberculosis and to contribute to improved diagnostics, advanced understanding of immunology and vaccine design.

Shedding of Mycobacterium bovis in the nasal mucus of cattle infected experimentally with tuberculosis by the intranasal and intratracheal routes.

Four groups of six calves were infected experimentally with either a low dose of approximately 10(4) colony-forming units (cfu) or a high dose of approximately 10(6) cfu of Mycobacterium bovis. Each dose was delivered by the intranasal and intratracheal routes. More severe disease was observed in the groups inoculated with the high dose. Visible lesions were identified in 21 of the 24 animals, all of which also gave positive skin tests and interferon-gamma (IFN-gamma) responses. Nasal shedding was detected in 15 of the 24 animals and the frequency of shedding was influenced by both the route and the dose of infection; no shedding was observed in the group infected intratracheally with the low dose. Two of the 15 confirmed shedders had no visible lesions at postmortem examination; both of these calves gave IFN-gamma responses but only one was skin test positive.