Study of the immunological profile towards Mycobacterium bovis antigens in naturally infected cattle

A number of studies have determined the contribution of Th1 and Th2 responses to the protective immunity and pathology of Mycobacterium bovis infection. However, much of that information is derived from experimentally infecting cattle with M. bovis and few data from naturally infected animals are available. The aim of this study was to characterize the immunological profile towards M. bovis antigens of naturally infected cattle by measurement of cytokine mRNA expression in PBMC, and to determine which lymphocyte subsets are involved in recall responses of PBMC from M. bovis infected cattle to M. bovis antigens. Consistent with data from cattle experimentally infected with M. bovis , naturally infected animals were found to display a Th1 cytokine profile in response to M. bovis PPDB stimulation. Production of IFN-γ mRNA by PBMC after PPDB stimulation statistically distinguishes between infected and healthy herds, suggesting that this molecule is usable as an M. bovis -infection marker. As happens in experimentally infected cows, CD4, CD8 and γδTCR cells from a herd naturally infected with M . bovis are the predominant T cell subsets expanded in response to PPDB.     

Tick-borne diseases in ruminants of Central and Southern Italy: epidemiology and case reports

Sera and blood from cattle and sheep were examined for the presence of Babesia and Theileria spp by microscopy and serology at the Parasitology Department of the Istituto Zooprofilattico Sperimentale of Abruzzo and Molise (IZSAM). Of the 47 bovine herds (323 animals) tested, 15 were found positive for Babesia bigemina and 1 for Babesia bovis. Two outbreaks occurred, one caused by B. bigemina and one by B. bovis. The B. bigemina outbreak occurred in Abruzzo and has been followed for two years. The isolate of B. bigemina was very pathogenic leading to the death of two cows out of 57. The vector responsible of the transmission appeared to be Rhipicephalus bursa. Parasites were observed in the erythrocytes for 30 days whereas sera were positive to indirect immunofluorescence (IFA) for at least one year. The B. bovis outbreak occurred in the province of Mantova (Northern Italy) in a group of 70 beef cattle imported from France. The infection resulted in the death of 5 animals and severe illness in another 6. In contrast with what occurred for Babesia infection, no clinical cases were recorded in cattle when species of Theileria were detected by microscopy. Of the 24 bovine herds (252 animals) tested for Theileria, 21 were found positive for the T. "sergenti"/buffeli/orientalis group. Single and mixed infection of T. "sergenti" and T. buffeli/orientalis were detected in herds of cross-bred cattle from Abruzzo and Marche. The parasites were identified by using a polymerase chain reaction which amplified DNA encoding p32/34. Most of the collected ticks (90%) were adults of R. bursa whereas the others were adults of Hyalomma detritum. During the period the animals have been observed (18 months), no clinical cases have been recorded and no associations have been found between blood abnormalities and animals found infected with Theileria. Prevalences of subclinically infected carriers increased from February till December (95.4%) even if the animals were indoors and no ticks were present. The prevalence then dropped dramatically six months later (76.7%). In calves less than 1 year old, the prevalence of infection significantly (p<0.05) increased with age, however intraerythrocytic stages of Theileria were found in the blood of three newborn calves (<7 days of age). Of the 18 ovine flocks tested for Babesia spp. (150 animals examined), 1 was positive for B. ovis and 2 for B. motasi. B. motasi infection was not associated with symptoms, while an outbreak of babesiosis caused by B. ovis occurred in Abruzzo. The infection resulted in the death of 3 animals (0.75% of the flock), two rams (20% of the total number) and a ewe, and severe illness in another 5 ewes (2% of the flock). Specimens of R. bursa and R. turanicus were collected from the infected animals. Of the 18 flocks (150 animals) examined, 12 were microscopically positive for Theileria spp. No clinical cases were recorded and identification at species level was not possible on the basis of morphological criteria. The prevalence distribution of infected herds and infected animals within herds and flocks have been calculated by a Monte Carlo simulation model, running 10,000 iterations. The most likely levels of prevalence of infected herds and infected animals within herds found for the species observed were as follows: 20% for B. bigemina with a prevalence within herd of 27%, 11% for B. bovis (18% within herd), 10% for Babesia ovis (19% within herd), 10% for B. motasi (17.5% within herd), 63% for Theileria in cattle (66% within herd) and 51% for Theileria in sheep (55% within herd).     

Ability of T cell subsets and their soluble mediators to modulate the replication of Mycobacterium bovis in bovine macrophages

Peripheral blood mononuclear cells (PBMCs) from cattle vaccinated with Bacillus Calmette-Guerin (BCG) were obtained and expanded in vitro by incubation with purified protein derivative. The ability of these cells to modulate the replication of virulent Mycobacterium bovis in autologous-infected macrophages was compared to cells from non-vaccinated controls. Cells from non-vaccinated animals were shown to confer a significant degree of mycobacteriostatic activity to autologous-infected macrophages. This activity was not inhibited by including a neutralizing antibody versus interferon-gamma (IFN-gamma), and was dependent on direct contact between PBMCs and infected macrophages. Addition of autologous PBMCs from BCG-vaccinated cattle was shown to significantly enhance macrophage resistance to M. bovis, and this increased macrophage resistance was partly abrogated by including a neutralizing antibody to IFN-gamma. Addition of T cells from non-vaccinated animals to infected macrophages was associated with a modest increase in macrophage release of TNF-alpha and nitric oxide, whereas PBMCs from vaccinated animals increased very significantly the release of these factors. Neutralization of nitric oxide (NO), by inclusion of monomethyl-L-arginine, significantly diminished the ability of PBMCs from vaccinated animals to enhance macrophage resistance to M. bovis, but had no impact on the ability of T cells from naive animals to modulate macrophage function. The ability of naive cells to increase macrophage anti-M. bovis activity was largely mediated by CD4+ T cells, whereas both CD4+ T cells and CD8+ T cells conferred macrophage resistance to M. bovis in vaccinated animals. These data highlight the role of IFN-gamma and NO in the immune resistance of cattle to M. bovis.     

Antigen recognition and immunomodulation by gamma delta T cells in bovine tuberculosis

This report describes the in vitro proliferative responses of peripheral blood gammadelta T cells to defined mycobacterial protein Ags and the immunomodulatory effect of gammadelta T cells in cattle infected with Mycobacterium bovis. gammadelta T cell responses were specific to M. bovis infection because they were detected in cattle either experimentally or naturally infected with M. bovis, but were not present in uninfected controls. Proliferating gammadelta T cell cultures produced enhanced levels of IFN-gamma and TGF-beta, but not IL-2 in response to the more immunodominant mycobacterial AGS: Depletion of gammadelta T cells from PBMC resulted in an increased Ag-specific proliferation in half the animals tested, indicating a suppressive effect of gammadelta T cells upon other (alphabeta) T cell responses. Because gammadelta T cells constitute a major T cell population in the peripheral blood of cattle, the activities of gammadelta T cells described in this report could make a significant contribution to the immune response in bovine tuberculosis.     

Serological differences in Neospora caninum-associated epidemic and endemic abortions.

A sandwich enzyme-linked immunosorbent assay (ELISA) for the sensitive and specific detection of bovine antibodies to Neospora caninum was developed and evaluated using sera from cattle experimentally infected with N. caninum, Toxoplasma gondii, Sarcocystis cruzi, Sarcocystis hominis, Sarcocystis hirsuta, Eimeria bovis, Cryptosporidium parvum, Babesia divergens, and field sera from naturally exposed animals. Field sera were classified using a gold standard that included the results from an indirect fluorescent antibody test (IFAT) and an immunoblot (IB). Based on these gold standard results, i.e., IFAT-IB results, an equal relative sensitivity and specificity of 94.2%(theta0) was reached when a cutoff of 0.034 (d0) was employed. The analysis of IFAT-IB-positive field sera showed that within groups of aborting and nonaborting dams, the animals from herds with endemic N. caninum-associated abortions had significantly higher ELISA indices than animals from herds with N. caninum-associated epidemic abortions. By contrast, IFAT-IB-positive aborting dams from herds with endemic N. caninum-associated abortions had significantly lower IFAT titers than IFAT-IB-positive aborting dams from herds with epidemic N. caninum-associated abortions. This is the first time that statistically significant serological differences between herds exhibiting epidemic and endemic N. caninum-associated abortions are described.     

Mycobacterium bovis in wildlife in France

In early 2001, tuberculosis-like lesions were detected in three hunter-killed red deer (Cervus elaphus) in the Brotonne Forest (Normandy, France), and Mycobacterium bovis was isolated. In subsequent hunting seasons, two surveys were conducted in the area. In the first survey (2001-02 hunting season), nine (13%) of 72 red deer sampled were positive for M. bovis. In the 2005-06 hunting season, the prevalence of M. bovis infection increased to 24% (chi2=3.85, df=1, P=0.05; 33 positive among 138 sampled). The prevalence remained stable in juveniles, but it increased significantly in adults: from 13% in 2001-02 to 32% in 2005-06 (chi2=5.13, df=1, P=0.02). Wild boar (Sus scrofa) were heavily infected in both surveys. One roe deer (Capreolus capreolus) and one red fox (Vulpes vulpes) also tested positive in the second survey. Mycobacterium bovis was not isolated from Eurasian badgers (Meles meles). Spoligotyping and mycobacterial interspersed repetitive unit-variable number tandem repeat analysis demonstrated that all M. bovis strains isolated from wildlife were of the same genotype. Thus, the wildlife outbreak involved only a single strain, and this strain was the same as that circulating in nearby cattle herds since 1995. Sensitivity, specificity, and predictive values of the presence of macroscopic lesions as a diagnostic criterion were evaluated from the data obtained from red deer. Necropsy seems to be satisfactory as a routine tool to monitor the disease in wild red deer populations in which bovine tuberculosis has become established.     

Chorioptic Mange (Acarina: Psoroptidae) in Domestic and Wild Ruminants in Israel

In a 20-year-survey, 9364 dairy cattle in 324 herds kept under a zero-grazing management, 1252 beef cattle in 46 herds grazing all the year round, 3347 sheep in 134 herds (only 26 are grazing herds), and 872 goats in 47 herds (only 20 are grazing) were examined. The mites collected from cattle were identified as Chorioptes texanus only, and those from sheep, goats and gazelles were identified as C. bovis. Chorioptic mange was not diagnozed in grazing beef cattle, ibexes and housed animals (as compared to grazing herds), and in rams and billy goats. Holstein-Israeli bulls kept in insemination centres were not clinically infested, whereas four Charolais bulls were infested with chorioptic mange. Infestation rate was higher in older animals than in younger ones. Hoggets and young goats over 10 months and heifers over 13 months were found clinically infested with Choriopic mites. Lesions were not usually extensive and occurred mainly in predilection sites. The ocular form in sheep and the groin form in goats are very uncommon and apparently are reported for the first time. Chorioptic mange was recorded generally throughout the year. In our study seasonal distribution could not be demonstrated in cattle, while in sheep and goats the highest infestation rate occurred in February to March and the lowest in August and September.     

Cloning, sequencing, and expression of interferon-gamma from elk in North America

Eradication of Mycobacterium bovis relies on accurate detection of infected animals, including potential domestic and wildlife reservoirs. Available diagnostic tests lack the sensitivity and specificity necessary for accurate detection, particularly in infected wildlife populations. Recently, an in vitro diagnostic test for cattle which measures plasma interferon-gamma (IFN-gamma) levels in blood following in vitro incubation with M. bovis purified protein derivative has been enveloped. This test appears to have increased sensitivity over traditional testing. Unfortunately, it does not detect IFN-gamma from Cervidae. To begin to address this problem, the IFN-gamma gene from elk (Cervus elaphus) was cloned, sequenced, expressed, and characterized. cDNA was cloned from mitogen stimulated peripheral blood mononuclear cells. The predicted amino acid (aa) sequence was compared to known sequences from cattle, sheep, goats, red deer (Cervus elaphus), humans, and mice. Biological activity of the recombinant elk IFN-gamma (rElkIFN-gamma) was confirmed in a vesicular stomatitis virus cytopathic effect reduction assay. Production of monoclonal antibodies to IFN-gamma epitopes conserved between ruminant species could provide an important tool for the development of reliable, practical diagnostic assays for detection of a delayed type hypersensitivity response to a variety of persistent infectious agents in ruminants, including M. bovis and Brucella abortus. Moreover, development of these reagents will aid investigators in studies to explore immunological responses of elk that are associated with resistance to infectious diseases.     

Cattle lice (Anoplura, Mallophaga) in New York: seasonal population changes, effects of housing type on infestations of calves, and sampling efficiency

A year-long survey was made of commercial dairy herds in New York for cattle lice (Anoplura and Mallophaga). All herds were infested with lice. The cattle bitting louse, Bovicola bovis (L.), accounted for about 90% of the observed infestations; infestations of mature animals were most common during the winter months, especially March (26% infested); and infestation rates of calves were high (30-45%) from January through June. Cows that were housed in stanchion barns were about twice as likely to be infested (24.7%) as were those in free stalls (11.1%). Calves housed in individual outdoor hutches had substantially lower infestation rates (4.5%) than calves maintained inside barns in collective stalls and pens (46.0%).     

Evaluation of susceptibility of Mycobacterium bovis to antituberculous drugs by radiometric BACTEC 460TB system

Susceptibility of Mycobacterium bovis strains to antituberculous drugs (isoniazid and rifampin) was detected by radiometric BACTEC 460TB system. M.bovis strains were isolated from tissue samples showing tuberculous lesions collected at an abbattoir from cattle belonging to 47 tuberculosis outbreaks occurring in Northern Italy in 1995-1999. Forty-six out of 61 strains (75.4%) resulted susceptible to both isoniazid and rifampin. Thirteen strains (21.3%) were resistant to isoniazid only. No strains showed resistance to rifampin only. Two strains (3.3%) resulted resistant to both drugs, showing antituberculous multidrug-resistance. Given the compulsory eradication program of bovine tuberculosis by elimination of infected animals and the ban on antituberculous drug treatments in animals, detection of resistant M. bovis strains appears of great interest.     

Experimental inoculation of meadow voles (Microtus pennsylvanicus), house mice (Mus musculus), and Norway rats (Rattus norvegicus) with Mycobacterium bovis

Mycobacterium bovis has a wide host range that includes several wildlife species, and this can hamper attempts to eradicate bovine tuberculosis from livestock. The purpose of this study was to determine if common rodent species, namely meadow voles (Microtus pennsylvanicus), house mice (Mus musculus), and Norway rats (Rattus norvegicus), that inhabit the bovine tuberculosis endemic area of Michigan, can be experimentally infected with M. bovis. The objectives of the study were: 1) to determine if these rodent species can be infected, and if so, to document attendant pathologic processes/pathogenesis; 2) to detect any fecal shedding of M. bovis; and 3) to evaluate the relative susceptibility of the three species to M. bovis infection. For each species (n=36) there were two treatment (n=12/group) and one or two control groups depending on species (n=6-12/group); the maximum study duration was 60 days. The meadow vole treatments consisted of high dose inocula that were given by oral or intranasal routes, whereas the house mice and Norway rats were given only oral inocula at either a high or low dose. Of the three species, meadow voles were most susceptible to M. bovis infection. Upon intranasal inoculation, all 12 voles were infected as determined by gross and microscopic lesions and culture of M. bovis from tissue and feces. Seven of the 12 meadow voles inoculated orally were infected. House mice also were susceptible; M. bovis was isolated from 14 of 24 animals. Only one Norway rat in the high dose treatment group was positive by culture and this was the only animal from which minimal attendant lesions were observed. Results of this study indicate that meadow voles and house mice can be infected with M. bovis and might serve as spillover hosts. Concerted efforts should, therefore, be made to reduce or eliminate these rodents on premises where M. bovis-infected livestock are present.     

Antimicrobial use in organic and conventional dairy herds

Use of antimicrobials for food-producing animals is a major public concern due to the risk of antimicrobial resistance. Although dairy production has a relatively low usage of antimicrobials, the potential for further reduction should be explored. The objective of the study was to estimate the current differences in antimicrobial use in Danish organic and conventional dairy herds and to describe the differences between them. Based on data from three different sources, 2604 herds (306 organic and 2298 conventional) were identified for the study. These herds had been either organic or conventional for the entire period from 2015 to 2018. Antimicrobial use was calculated as the treatment incidence in Animal Daily Doses (ADDs)/100 animals/day for three age groups: adult cattle, young stock and calves. For adult cattle, the ratio of median treatment incidence between conventional and organic production ranged from 2.8 : 1 to 3.4 : 1, depending on the specific year. For cows, 25% of the organic herds had a higher treatment incidence than the 25% of conventional herds with the lowest treatment incidence. Antimicrobial use for young stock was low and at a similar level in both the organic and conventional production systems. For calves, the median treatment incidence was 1.2 times higher in conventional herds and 1.6 times higher for the 75th percentile. Analyses of treatment incidence in adult cattle showed an overall decrease from 2015 to 2018 in both organic and conventional herds. The decrease was greater for the conventional herds (0.12 ADD/100 animals/day) compared to the organic herds (0.04 ADD/100 animals/day) over the 4-year period. In addition, herd size was an important risk factor for treatment incidence in conventional herds, increasing by 0.07 ADD/100 animals/day per 100 cows, whereas herd size had a minor influence on the treatment incidence in organic herds. The results of this study demonstrate the large variation in antimicrobial use within both organic and conventional herds, suggesting that further reduction is possible. Furthermore, herd size appears to be a risk factor in conventional herds but not in organic herds – an aspect that should be studied in more detail.     

Helminth parasites of intermingling axis deer, wild swine and domestic cattle from the island of Molokai, Hawaii

Helminth infections of axis deer (Cervus axis), wild swine (Sus scrofa) and domestic cattle (Bos taurus) were studied among intermingling herds on the Puu-O-Hoku Ranch, Molokai, Hawaii. Twenty-four species of helminths were collected from the 10 deer, 10 swine and 10 cattle. Capillaria bovis, Cooperia punctata, Haemonchus contortus and Trichostrongylus axei infected both axis deer and cattle, whereas Gongylonema pulchrum infected both axis deer and wild swine. None of the species of helminths occurred in both wild swine and cattle nor was any species found in all three hosts. Wild swine and domestic cattle supported separate and distinct helminth communities. In contrast, the helminth community of axis deer appeared to be derived from the helminth communities of cattle and wild swine and consisted only of those species capable of parasitizing either a broad range of ruminants or many mammalian taxa.     

Targeting of Mycobacterium tuberculosis heparin-binding hemagglutinin to mitochondria in macrophages

Mycobacterium tuberculosis heparin-binding hemagglutinin (HBHA), a virulence factor involved in extrapulmonary dissemination and a strong diagnostic antigen against tuberculosis, is both surface-associated and secreted. The role of HBHA in macrophages during M. tuberculosis infection, however, is less well known. Here, we show that recombinant HBHA produced by Mycobacterium smegmatis effectively induces apoptosis in murine macrophages. DNA fragmentation, nuclear condensation, caspase activation, and poly (ADP-ribose) polymerase cleavage were observed in apoptotic macrophages treated with HBHA. Enhanced reactive oxygen species (ROS) production and Bax activation were essential for HBHA-induced apoptosis, as evidenced by a restoration of the viability of macrophages pretreated with N-acetylcysteine, a potent ROS scavenger, or transfected with Bax siRNA. HBHA is targeted to the mitochondrial compartment of HBHA-treated and M. tuberculosis-infected macrophages. Dissipation of the mitochondrial transmembrane potential (ΔΨ(m)) and depletion of cytochrome c also occurred in both macrophages and isolated mitochondria treated with HBHA. Disruption of HBHA gene led to the restoration of ΔΨ(m) impairment in infected macrophages, resulting in reduced apoptosis. Taken together, our data suggest that HBHA may act as a strong pathogenic factor to cause apoptosis of professional phagocytes infected with M. tuberculosis.     

Use of IgG avidity ELISA to differentiate acute from persistent infection with Salmonella Dublin in cattle

AIMS: To investigate whether an immunoglobulin (Ig)G avidity ELISA can be used to differentiate between acute and persistent infection with Salmonella (S.) Dublin in cattle. To determine whether the IgG isotype, IgG(1) and IgG(2) responses in acute and persistent infections differ. METHODS AND RESULTS: Animals were selected from two herds with long-term infection (years) and two herds recently infected (<3 months). Forty-seven animals were categorized into groups based on the persistence of their antibody level in milk. Based on titre from two serial dilutions the avidity index (AI) was calculated for IgG (IgG-AI), IgG(1) (IgG(1)-AI) and IgG(2) (IgG(2)-AI). The mean IgG-AI for suspected carrier animals with either persistently high (group 1) or persistently high to medium high (group 2) antibody levels was significantly (P = 0.003) higher (32.1% and 38.4%) than for acutely infected animals (21.7% and 22.3%). The probability of being a suspect carrier was associated with IgG-AI, antibody level in the sample and age. However, the effect of age could be the result of a biased sample selection. Specificities and sensitivities were calculated at a range of cut-off values for IgG-AI and IgG(1)-AI. Overall, IgG(2)-AI was high compared with IgG(1)-AI, and there was no difference in IgG(2)-AI between infection groups. There was no difference in the ratio IgG(2):IgG(1) for acute and persistent infection groups. CONCLUSIONS: Assuming that a persistently high antibody response is indicative of persistent infection with S. Dublin in cattle, it can be concluded that the IgG-AI can aid in differentiating between acute and long-term infection on herd level. However, for the test to be useful as an alternative tool to repeated sampling over time for detection of persistently infected carriers during control strategies in cattle herds, the test needs to be optimized and studied further in a larger sample of well-characterized infections in cattle. The affinity of IgG(2) is higher than IgG(1) early in the S. Dublin infection. There appears to be no difference in the IgG(2)-AI between the acute and chronic infection stages. SIGNIFICANCE AND IMPACT OF THE STUDY: For decades the strategies for detection of persistently infected cattle in S. Dublin infected herds have involved repeated bacteriological culture of faecal samples or repeated antibody measurements over several months. Both methods are time consuming and costly, leaving a new method for detection of carrier animals based on a single sampling highly desirable. This study illustrates a tool, IgG-AI, which may prove useful, although more validation of the method is required before it is used in practice.     

Immune responses to the enduring hypoxic response antigen Rv0188 are preferentially detected in Mycobacterium bovis infected cattle with low pathology

The DosR regulon and the Enduring Hypoxic Response (EHR) define a group of M. tuberculosis genes that are specifically induced in bacilli exposed in vitro to conditions thought to mimic the environment encountered by Mycobacteria during latent infection. Although well described in humans, latent mycobacterial infection in cattle remains poorly understood. Thus, the aim of this study was to identify antigens that may potentially disclose cattle with latent M. bovis infection. To this end, we initially screened 57 pools of overlapping peptides representing 4 DosR regulon and 29 EHR antigens for their ability to stimulate an immune response in whole blood from TB-reactor cattle using IFN-γ and IL-2 as readouts. All 4 DosR regulon proteins were poorly recognized (maximum responder frequency of 10%). For the EHR antigens, both IFN-γ and IL-2 revealed similar response hierarchies, with responder frequencies ranging from 54% down to 3% depending on the given EHR antigen. Furthermore, these results demonstrated that responses in the infected cattle were largely IFN-γ biased. To support the concept for their role in latency, we evaluated if EHR antigen responses were associated with lower pathology. The EHR antigen Rv0188 was recognised predominantly in animals presenting with low pathology scores, whereas responses to ESAT-6/CFP-10 or the other EHR antigens tested were prevalent across the pathology spectrum. However, when we determined the production of additional cytokines induced by the M. bovis antigens PPD-B or ESAT-6/CFP-10, we detected significantly greater PPD-B-induced production of the pro-inflammatory cytokine IL-1β in animals recognizing Rv0188 (i.e. those with limited or no pathology). Thus, these results are consistent with the idea that responses to Rv0188 may identify a subset of animals at early stages of infection or in which disease progression may be limited.     

Potential Benefits of Cattle Vaccination as a Supplementary Control for Bovine Tuberculosis

Vaccination for the control of bovine tuberculosis (bTB) in cattle is not currently used within any international control program, and is illegal within the EU. Candidate vaccines, based upon Mycobacterium bovis bacillus Calmette-Guérin (BCG) all interfere with the action of the tuberculin skin test, which is used to determine if animals, herds and countries are officially bTB-free. New diagnostic tests that Differentiate Infected from Vaccinated Animals (DIVA) offer the potential to introduce vaccination within existing eradication programs. We use within-herd transmission models estimated from historical data from Great Britain (GB) to explore the feasibility of such supplemental use of vaccination. The economic impact of bovine Tuberculosis for farmers is dominated by the costs associated with testing, and associated restrictions on animal movements. Farmers’ willingness to adopt vaccination will require vaccination to not only reduce the burden of infection, but also the risk of restrictions being imposed. We find that, under the intensive sequence of testing in GB, it is the specificity of the DIVA test, rather than the sensitivity, that is the greatest barrier to see a herd level benefit of vaccination. The potential negative effects of vaccination could be mitigated through relaxation of testing. However, this could potentially increase the hidden burden of infection within Officially TB Free herds. Using our models, we explore the range of the DIVA test characteristics necessary to see a protective herd level benefit of vaccination. We estimate that a DIVA specificity of at least 99.85% and sensitivity of >40% is required to see a protective benefit of vaccination with no increase in the risk of missed infection. Data from experimentally infected animals suggest that this target specificity could be achieved in vaccinates using a cocktail of three DIVA antigens while maintaining a sensitivity of 73.3% (95%CI: 61.9, 82.9%) relative to post-mortem detection.     

Is Mycobacterium bovis in the environment important for the persistence of bovine tuberculosis?

Mycobacterium bovis is the causative agent of bovine tuberculosis (bTB) in cattle and wildlife. Direct aerosol contact is thought to be the primary route of infection between conspecifics, whereas indirect transmission via an environmental reservoir of M. bovis is generally perceived not to be a significant source for infection. Here, we report on the application of molecular technology (PCR) to quantify the prevalence of M. bovis in the environment and to explore its epidemiological significance. We show that the detectability of viable M. bovis at badger setts and latrines is strongly linked to the frequency of M. bovis excretion by infected badgers, and that putative M. bovis in the environment is prevalent on a large proportion of endemic cattle farms in Britain. These results raise important questions about the role of an environmental reservoir in bTB persistence.     

Development of vaccines to control bovine tuberculosis in cattle and relationship to vaccine development for other intracellular pathogens

Vaccination of cattle against bovine tuberculosis could be an important strategy for the control of disease either where there is a wildlife reservoir of Mycobacterium bovis infection or in developing countries where it is not economically feasible to implement a 'test and slaughter' control program. Advances in the understanding of protective immune responses to M. bovis infection in cattle and the advent of new molecular biological techniques, coupled with the sequencing of the M. bovis genome have provided opportunities for the rational development of improved tuberculosis vaccines. A number of new tuberculosis vaccines including attenuated M. bovis strains, killed mycobacteria, protein and DNA vaccines are under development and many are being assessed in cattle. Recent results have revealed several promising vaccine candidates and vaccination strategies. Ways of distinguishing between vaccinated and infected cattle are becoming available and the possibility of new approaches to the eradication of tuberculosis from domestic livestock is discussed. Similarities between the mechanisms of protective immunity against M. bovis and against other intracellular parasites continue to be found and discoveries from vaccine studies on bovine tuberculosis may provide helpful insights into requirements for vaccines against other intracellular pathogens.     

Transmission of Mycobacterium tuberculosis between Farmers and Cattle in Central Ethiopia

Background

Transmission of Mycobacterium tuberculosis (M. tuberculosis) complex could be possible between farmers and their cattle in Ethiopia.

Methodology/Principal Findings

A study was conducted in mixed type multi-purposes cattle raising region of Ethiopia on 287 households (146 households with case of pulmonary tuberculosis (TB) and 141 free of TB) and 287 herds consisting of 2,033 cattle belonging to these households to evaluate transmission of TB between cattle and farmers. Interview, bacteriological examinations and molecular typing were used for human subjects while comparative intradermal tuberculin (CIDT) test, post mortem and bacteriological examinations, and molecular typing were used for animal studies. Herd prevalence of CIDT reactors was 9.4% and was higher (p<0.01) in herds owned by households with TB than in herds owned by TB free households. Animal prevalence was 1.8% and also higher (p<0.01) in cattle owned by households with TB case than in those owned by TB free households. All mycobacteria (141) isolated from farmers were M. tuberculosis, while only five of the 16 isolates from cattle were members of the M. tuberculosis complex (MTC) while the remaining 11 were members of non-tuberculosis mycobacteria (NTM). Further speciation of the five MTC isolates showed that three of the isolates were M. bovis (strain SB1176), while the remaining two were M. tuberculosis strains (SIT149 and SIT53). Pathology scoring method described by “Vordermeier et al. (2002)” was applied and the average severity of pathology in two cattle infected with M. bovis, in 11 infected with NTM and two infected with M. tuberculosis were 5.5, 2.1 and 0.5, respectively.

Conclusions/Significance

The results showed that transmission of TB from farmers to cattle by the airborne route sensitizes the cows but rarely leads to TB. Similarly, low transmission of M. bovis between farmers and their cattle was found, suggesting requirement of ingestion of contaminated milk from cows with tuberculous mastitis.