A review of M. bovis BCG protection against TB in cattle and other animals species

BCG Vaccine-The Road Not Taken

The Bacillus Calmette-Guérin (BCG) vaccine has been used for over one hundred years to protect against the most lethal infectious agent in human history, tuberculosis. Over four billion BCG doses have been given and, worldwide, most newborns receive BCG. A few countries, including the United States, did not adopt the WHO recommendation for routine use of BCG. Moreover, within the past several decades, most of Western Europe and Australia, having originally employed routine BCG, have discontinued its use. This review article articulates the impacts of those decisions. The suggested consequences include increased tuberculosis, increased infections caused by non-tuberculous mycobacteria (NTM), increased autoimmune disease (autoimmune diabetes and multiple sclerosis) and increased neurodegenerative disease (Parkinson's disease and Alzheimer's disease). This review also offers an emerged zoonotic pathogen, Mycobacteriumavium ss. paratuberculosis (MAP), as a mostly unrecognized NTM that may have a causal role in some, if not all, of these diseases. Current clinical trials with BCG for varied infectious, autoimmune and neurodegenerative diseases have brought this century-old vaccine to the fore due to its presumed immuno-modulating capacity. With its historic success and strong safety profile, the new and novel applications for BCG may lead to its universal use-putting the Western World back onto the road not taken.

Development of a diagnostic compatible BCG vaccine against Bovine tuberculosis

Bovine tuberculosis (BTB) caused by Mycobacterium bovis remains a major problem in both the developed and developing countries. Control of BTB in the UK is carried out by test and slaughter of infected animals, based primarily on the tuberculin skin test (PPD). Vaccination with the attenuated strain of the M. bovis pathogen, BCG, is not used to control bovine tuberculosis in cattle at present, due to its variable efficacy and because it interferes with the PPD test. Diagnostic tests capable of Differentiating Infected from Vaccinated Animals (DIVA) have been developed that detect immune responses to M. bovis antigens absent in BCG; but these are too expensive and insufficiently sensitive to be used for BTB control worldwide. To address these problems we aimed to generate a synergistic vaccine and diagnostic approach that would permit the vaccination of cattle without interfering with the conventional PPD-based surveillance. The approach was to widen the pool of M. bovis antigens that could be used as DIVA targets, by identifying antigenic proteins that could be deleted from BCG without affecting the persistence and protective efficacy of the vaccine in cattle. Using transposon mutagenesis we identified genes that were essential and those that were non-essential for persistence in bovine lymph nodes. We then inactivated selected immunogenic, but non-essential genes in BCG Danish to create a diagnostic-compatible triple knock-out ΔBCG TK strain. The protective efficacy of the ΔBCG TK was tested in guinea pigs experimentally infected with M. bovis by aerosol and found to be equivalent to wild-type BCG. A complementary diagnostic skin test was developed with the antigenic proteins encoded by the deleted genes which did not cross-react in vaccinated or in uninfected guinea pigs. This study demonstrates the functionality of a new and improved BCG strain which retains its protective efficacy but is diagnostically compatible with a novel DIVA skin test that could be implemented in control programmes.

Prevalence and Economic Losses Due to Bovine Tuberculosis in Cattle Slaughtered at Bodija Municipal Abattoir, Ibadan, Nigeria

Bovine tuberculosis (BTB) is a zoonotic disease responsible for considerable economic losses; with consequent negative impact on both public health and the livestock industry. However, the burden of this disease and associated economic losses remain un-investigated among slaughtered cattle in Ibadan, the hub of livestock activities in south-western Nigeria. A cross sectional study was conducted over a three-month period to determine the prevalence and economic losses due to BTB among slaughtered cattle at the Bodija Municipal Abattoir, Ibadan, in south-western Nigeria. Individual slaughtered cattle were purposively inspected for the presence of tuberculous lesions, and representative sample of affected organs and associated lymph nodes from the BTB suspected animals were taken. The suspected lesions were processed based on Becton Dickinson digestion and decontamination procedure and the losses due to BTB were estimated mathematically, using a formula. The BTB prevalence of 9.3 % (38/408) was obtained with a significant statistical association (P ≤ 0.05) of the disease with the breeds of cattle slaughtered. Out of the 46 visceral organs condemned: 29 (63 %) were lungs, 12 (26.1 %) livers, 4 (8.7 %) hearts and 1 (2.2 %) kidney. The total estimated annual economic loss (direct and indirect) due to BTB was estimated as Nigerian naria NGN 703,980,070 (EUR 1,725,441.4). This study revealed BTB as endemic and a major cause of concern considering its ill-health and economic effects on both humans and the livestock industry. Efforts are therefore required: to control this disease along the beef value chain in order to safeguard human and livestock health; as well as to limit the economic losses associated with its prevalence.

Molecular epidemiology of cattle tuberculosis in Mexico through whole-genome sequencing and spoligotyping

Mycobacterium bovis infection in cattle persists in Mexico, posing a threat to human health. Control of bovine tuberculosis, through the National Program Against Bovine Tuberculosis, has led to the decrease of disease prevalence in most of the country, except for high dairy production regions. Genotyping of M. bovis has been performed mainly by spoligotyping and variable number tandem repeats (VNTR), but higher resolution power can be useful for a finer definition of the spread of the disease. Whole genome sequencing and spoligotyping was performed for a set of 322 M. bovis isolates from different sources in Mexico: Baja California, Coahuila, Estado de Mexico, Guanajuato, Hidalgo, Jalisco, Queretaro and Veracruz, from dairy and beef cattle, as well as humans. Twelve main genetic clades were obtained through WGS and genetic diversity analysis. A clear differentiation of the Baja California isolates was seen as they clustered together exclusively. However, isolates from the central states showed no specific clustering whatsoever. Although WGS proves to have higher resolving power than spoligotyping, and since there was concordance between WGS and spoligotyping results, we consider that the latter is still an efficient and practical method for monitoring bovine tuberculosis in developing countries, where resources for higher technology are scarce.

Differential Cell Composition and Cytokine Expression Within Lymph Node Granulomas from BCG-Vaccinated and Non-vaccinated Cattle Experimentally Infected with Mycobacterium bovis

Cattle vaccination against bovine tuberculosis (bTB) has been proposed as a supplementary method to help control the incidences of this disease. Bacillus Calmette-Guérin (BCG) is currently the only viable candidate vaccine for immunization of cattle against bTB, caused by Mycobacterium bovis (M. bovis). In an attempt to characterize the differences in the immune response following M. bovis infection between BCG-vaccinated and non-vaccinated animals, a combination of gross pathology, histopathology and immunohistochemical (IHC) analyses was used. BCG vaccination was found to significantly reduce the number of gross and microscopic lesions present within the lungs and lymph nodes. Additionally, the microscopically visible bacterial load of stages III and IV granulomas was reduced. IHC using cell surface markers revealed the number of CD68+ (macrophages), CD3+ (T lymphocytes) and WC1+ cells (γδ T cells) to be significantly reduced in lymph node granulomas of BCG-vaccinated animals, when compared to non-vaccinated animals. B lymphocytes (CD79a+) were significantly increased in BCG-vaccinated cattle for granulomas at stages II, III and IV. IHC staining for iNOS showed a higher expression in granulomas from BCG-vaccinated animals compared to non-vaccinated animals for all stages, being statistically significant in stages I and IV. TGFβ expression decreased alongside the granuloma development in non-vaccinated animals, whereas BCG-vaccinated animals showed a slight increase alongside lesion progression. IHC analysis of the cytokines IFN-γ and TNF-α demonstrated significantly increased expression within the lymph node granulomas of BCG-vaccinated cattle. This is suggestive of a protective role for IFN-γ and TNF-α in response to M. bovis infection. Findings shown in this study suggest that the use of BCG vaccine can reduce the number and severity of lesions, induce a different phenotypic response and increase the local expression of key cytokines related to protection.

Evaluation of the immunogenicity and diagnostic interference caused by M. tuberculosis SO2 vaccination against tuberculosis in goats

The immunogenicity and diagnostic interference caused by M. tuberculosis SO2, a prototype vaccine first time tested in goats was evaluated. Tuberculosis-free goats were distributed in four groups: [1], non-vaccinated; [2], subcutaneously (SC) BCG vaccinated; [3], intranasally (IN) SO2 vaccinated and [4], SC SO2 vaccinated. Intradermal tuberculin and IFN-γ tests using PPDs and alternative antigenic cocktails containing mainly ESAT-6 and CFP-10 (E/C) were applied at different times post-vaccination. Results showed a significant (p<0.05) increase in the number of reactors detected using both PPD-based intradermal and IFN-γ tests at different times in all the vaccinated groups. No intradermal reactivity was detected in the vaccinated goats using a cocktail containing E/C, Rv3615c and Rv3020c. A higher overall reactivity was observed in the group [4] in comparison with the other vaccinated groups. Results showed that antigens used to differentiate BCG vaccinated animals could be potentially used to differentiate SO2 vaccinated ones.

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.

Comparison of PCR versus culture for detection of Mycobacterium bovis after experimental inoculation of various matrices held under environmental conditions for extended periods

The purpose of this study was to compare the performance of a molecular detection technique (nested PCR) with that of mycobacterial culture in the detection of Mycobacterium bovis DNA in a set of 687 samples of experimentally inoculated environmental substrates (hay, soil, corn, water) exposed to natural weather conditions in Michigan. Four replicates of each substrate were used; half were autoclaved for sterilization, all were inoculated with 50,000 CFU of M. bovis isolated from Michigan livestock, and all were placed in outdoor enclosures, with half under shade and the other half exposed to direct sunlight. Samples were tested for the presence of M. bovis during one 12-month period, with monthly sample testing and during three 12-week periods (winter, spring, summer) with weekly sample testing. Samples were subjected to mycobacterial culture for isolation of M. bovis and a nested PCR with two primer sets targeting IS6110 to detect M. bovis DNA. In 128 samples tested during the 12-month period, M. bovis was not detectable by culture after 2 months but M. bovis DNA was detectable by PCR for at least 7 months. Of the 559 samples tested during the 12-week periods, PCR detected M. bovis DNA for up to 88 days in all of the sample types. There were no significant differences in the detection of M. bovis between shade and sun samples or between sterile and unsterilized samples, regardless of the detection method (PCR or culture). For use in epidemiologic investigations, the PCR assay was more rapid than mycobacterial culture, was not hindered by contaminating organisms, and detected M. bovis DNA in environment samples much longer after initial contamination than mycobacterial culture did.

Sustained protection against tuberculosis conferred to a wildlife host by single dose oral vaccination

BACKGROUND

Vaccination of wildlife against bovine tuberculosis (TB) is being considered by several countries to reduce the transmission of Mycobacterium bovis infection to livestock. In New Zealand, where introduced brushtail possums (Trichosurus vulpecula) are the major wildlife hosts, we have previously shown that repeat applications of a lipid-encapsulated oral bacille Calmette-Guerin (BCG) vaccine reduce the incidence of naturally acquired TB in wild possums. Here we extend this conceptual demonstration to an operational level, assessing long-term protection against TB conferred to free-living possums by a single oral immunisation.

METHODS

Possums in a non-TB area were randomly allocated to receive lipid-formulated BCG vaccine or remained unvaccinated. After initial trials to assess vaccine immunogenicity and establishment of protection within the first year post-vaccination, 13 individuals of each treatment group were relocated to a biosecurity facility and challenged (at 28 months post-vaccination) by subcutaneous injection of virulent M. bovis.

RESULTS

Vaccine immunogenicity and short-term protection were confirmed at 2 months and 12 months post-vaccination, respectively. In the long-term assessment, vaccinated possums had significantly reduced bacterial counts in peripheral lymph nodes compared to controls, with 0.6-2.3 log(10)-fold reductions in M. bovis burdens.

DISCUSSION

The magnitude of protective response by possums to experimental challenge at 28 months post-vaccination is known to equate to a high degree of protection against natural infection in this species. With techniques for oral bait delivery well advanced, the longevity of protection demonstrated here shows that an operable wildlife vaccine against TB is feasible.

Field evaluation of the protective efficacy of Mycobacterium bovis BCG vaccine against bovine tuberculosis

The protective efficacy of Mycobacterium bovis BCG (1 x 10(6) single dose) was evaluated under field conditions. A total of 140 male Holstein Friesian calves, one to two week-old were selected. Two groups of 70 each were formed, one group was vaccinated and the other was injected with a placebo during their second week of age and followed until 12 months of age. The study considered a positive case of tuberculosis to be an animal that had a positive reaction to the three following tests in a row: tuberculin, IFNgamma PPD-B and IFNgamma ESAT6-CFP10 during the 12 months of exposure. The results showed a 59.4% efficacy (IC95%: 47.64-71.16). The non-vaccinated calves were 2.4 times more at risk of becoming infected (IC95%: 1.07-5.68) compared to vaccinated animals. As a complementary test a PCR test was performed using nasal exudates in some animals from both groups using a Mycobacterium complex detection kit. All the positive PCR reactions (5/44) were found in the non-vaccinated animals. These findings suggest that the use of the BCG vaccine, even though it is not capable of protecting 100%, does prevent TB vaccinated animals from excreting bacilli in their nasal secretions at their first year of age.

Oral vaccination against bovine tuberculosis with Mycobacterium bovis BCG

The use of a bacillus Calmette-Guerin (BCG)-based vaccine could represent a viable strategy for controlling bovine tuberculosis (TB), principally in those cases where a wildlife disease vector exists. This article focuses on recent progress in animal TB vaccinology, outlining that oral-route vaccination represents the most feasible means of distributing a vaccine to control disease in wildlife. Drawing on historical successes of previous wildlife vaccination programs, the article suggests how, and in what form, an oral-delivery BCG-based vaccine might become operational, considering the wide diversity of TB reservoir species and the inherent problems associated with field delivery of a live-attenuated microbial vaccine.

Is interleukin-4delta3 splice variant expression in bovine tuberculosis a marker of protective immunity?

Splice variants of the interleukin-4 (IL-4) cytokine gene have been described for humans, mice, and cattle. IL-4 splice variants have been shown to inhibit IL-4-mediated cellular responses and thus act as IL-4 antagonists. Recent work has highlighted the possibility of a correlation between IL-4 splice variants and protection against clinical tuberculosis. In this study we investigated the potential role of IL-4 splice variants IL-4delta2 and IL-4delta3 in cattle with bovine tuberculosis, using quantitative real-time reverse transcription-PCR. For this analysis we used naturally exposed tuberculin skin test-positive field reactor cattle, uninfected control cattle, and cattle from two experimental models of protective immunity against Mycobacterium bovis: (i) vaccination with M. bovis BCG and challenge with virulent M. bovis and (ii) infection with M. bovis and treatment with isoniazid (INH) prior to rechallenge. The cytokine levels of field reactor cattle were compared to the levels of uninfected controls, while in kinetic studies of BCG vaccination and INH treatment we compared pre-experimental values with sequential samples for each individual animal. The data revealed a significant increase in IL-4delta3 mRNA expression in field reactor cattle, which had no visible pathology compared to cattle with gross pathology typical of bovine tuberculosis. Increased IL-4delta3 expression in both cattle models of protective immunity (BCG vaccination and INH treatment) was transient over time, reaching significance in the INH treatment model. Our results support the hypothesis that IL-4delta3 is involved in protective immunity against M. bovis infection in cattle and are in accordance with clinical studies that have suggested a role for IL-4 splice variants in protective immunity in tuberculosis.

Proteomic and transcriptomic analyses of differential stress/inflammatory responses in mandibular lymph nodes and oropharyngeal tonsils of European wild boars naturally infected with Mycobacterium bovis

Differential stress/inflammatory responses were characterized at the mRNA and protein levels in mandibular lymph nodes (MLN) and oropharyngeal tonsils of European wild boars (Sus scrofa), naturally infected with Mycobacterium bovis. Suppression-subtractive hybridization combined with immunohistochemistry and/or quantitative real-time RT-PCR were used to identify and characterize abundant stress/inflammatory gene sequences differentially expressed in tuberculous (TB+) wild boars. Genes identified in MLN and tonsils corresponded to serum amyloid A, arginase I, osteopontin, lysozyme, annexin I, and heat shock proteins, respectively. Global protein patterns in MLN and tonsils were compared between TB+ and nontuberculous (TB-) boars by 2-DE and MALDI-TOF MS. Five proteins, including stress/inflammatory proteins annexin V, serum albumin, and apolipoprotein A1 were found at lower levels in MLN of TB+ boars. Manganese superoxide dismutase was found up-regulated in MLN of TB+ boars. Five proteins, including creatine kinase and MHC class II antigens were found up-regulated in tonsils of TB+ boars. These results demonstrated differential stress/inflammatory responses in wild boars naturally infected with M. bovis and suggest possible markers of tuberculosis in this species that may prove useful for future studies of host-pathogen interactions and for diagnostics and vaccine development.

Farm husbandry and the risks of disease transmission between wild and domestic mammals: a brief review focusing on bovine tuberculosis in badgers and cattle

Where wildlife act as a reservoir of disease for domestic mammals, measures solely based on management of either in isolation are unlikely to resolve the problem. Many such diseases can have serious economic implications for farmers and the economy and their management can present considerable challenges. Traditionally, wildlife populations have been culled in attempts to reduce the risks of disease transmission to livestock (e.g. bovine tuberculosis in European badgers and brushtail possums). However, this may be both undesirable and potentially counter-productive in some circumstances. Consequently, in recent years increasing attention has focused on changing livestock husbandry and farm management practices so as to reduce risks of disease transmission from wildlife to livestock. Here we present a brief review of husbandry and farm management practices that may influence disease transmission risks from wild to domestic mammals, with particular attention to bovine tuberculosis in the UK. We conclude that the manipulation of farming practices could potentially make a significant contribution to disease risk management. However, there are currently scant empirical data on risk reduction methods and further information will undoubtedly be required to inform husbandry best-practice.

Mycobacterium bovis DeltaleuD auxotroph-induced protective immunity against tissue colonization, burden and distribution in cattle intranasally challenged with Mycobacterium bovis Ravenel S

Bovine tuberculosis is a chronic granulomatous disease caused by Mycobacterium bovis. Lack of definitive diagnostics and effective vaccines for domestic animals are major obstacles to the control and eradication of bovine tuberculosis. Auxotrophic mutants of Mycobacterium tuberculosis have shown promise as vaccine candidates for preventing human tuberculosis. Similarly, we constructed a leucine auxotroph of M. bovis, by using allelic exchange to delete leuD (encoding isopropyl malate isomerase), creating a strain requiring exogenous leucine for growth in vitro. We vaccinated 10 cattle subcutaneously with 10(9)CFU of M. bovis DeltaleuD and 10 age-matched, gender-matched controls were injected with phosphate-buffered saline. Vaccinated cattle had significantly increased in vitro antigen-specific T-cell-mediated responses. All cattle were challenged intranasally on day 160 post-immunization with 10(6)CFU of virulent M. bovis Ravenel S. On day 160 post-challenge vaccinated cattle had significantly reduced tissue mycobacterial burdens and 6 of 10 had complete clearance of the challenge strain and histopathological lesions were dramatically less severe in the vaccinated group. Thus, a single subcutaneous immunization of the M. bovis DeltaleuD mutant produced highly significantly protective immunity as measured by a reduction in tissue colonization, burden, bacilli dissemination, and histopathology caused by virulent M. bovis Ravenel S challenge.

DNA vaccine using Mycobacterium bovis Ag85B antigen induces partial protection against experimental infection in BALB/c mice

Bovine tuberculosis is a major cause of economic loss in countries where it is endemic, and in some countries, it may be a significant zoonotic disease problem. Therefore, new strategies for vaccine development are required, and among them, genetic immunization has potential value. The main goal of this study was to test the Mycobacterium bovis Ag85B gene as a DNA vaccine following challenge with an M. bovis virulent strain (ATCC 19274). Groups of BALB/c mice (n = 10) were immunized four times intramuscularly with the pCI-Ag85B construct or the pCI vector alone as the control. High titers of total immunoglobulin G (IgG), IgG1, and IgG2a anti-Ag85B were measured in pCI-Ag85B immunized mice when compared to the pCI control group. Regarding cellular immunity, significant levels of gamma interferon (IFN-gamma) (1,100 +/- 157 pg/ml) and tumor necrosis factor alpha (650 +/- 42 pg/ml) but not interleukin-4 were detected in splenocyte culture supernatants of pCI-Ag85B-vaccinated mice following stimulation with recombinant Ag85B. Further, the main source of IFN-gamma is CD8(+) T cells, as demonstrated by intracellular cytokine staining. As far as protection, a significant reduction in bacterial load in spleens (P < 0.05) was detected in pCI-Ag85B-immunized mice compared to the pCI vector control group. The results obtained here suggest that use of the Ag85B DNA vaccine is a promising strategy to control M. bovis infection due to its ability to induce a Th1 type of immune response. However, protective efficacy needs to be improved, since partial protection was achieved in spleens but not in lungs of vaccinated mice.

The safety and immunogenicity of Bacillus Calmette-Guérin (BCG) vaccine in European badgers (Meles meles)

European badgers (Meles meles) are a wildlife reservoir for Mycobacterium bovis (M. bovis) in Great Britain (GB) and the Republic of Ireland and therefore constitute a potential source of infection for cattle. Reduction of badger densities in the Republic of Ireland has resulted in an associated reduction in the risk of a herd break-down with bovine tuberculosis and a study to determine whether this is also the case in GB has been running since 1997. If badgers are a significant source of M. bovis infection for cattle, vaccinating badgers with Bacillus Calmette-Guérin (BCG) might prove to be a long term, cost-effective strategy for controlling bovine tuberculosis whilst preserving badger populations. As a first step towards BCG vaccination of wild badgers, it was necessary to demonstrate safety of the vaccine in captive badgers. Therefore, captive badgers were vaccinated with a commercial source of BCG that is already licensed for administration to humans in GB-BCG Danish SSI. Using a protocol prescribed by the Veterinary Medicines Directorate (VMD) of GB, badgers were vaccinated with two consecutive doses of BCG via either the subcutaneous (s.c.) or intra-muscular (i.m.) routes. The first dose was high, ranging from 16 to 22 x 10(7) colony-forming units (CFU), and was followed 15 weeks later by a lower dose in the range of 4-7 x 10(5)CFU. Local reaction at the site of injection and general responses (body temperature, haematology and blood serum chemistry), behaviour and excretion of BCG were monitored for 28 weeks from the time of the first vaccination. The only side-effect observed was the occurrence of localised swelling at the site of BCG injection that disappeared 48 days after i.m. vaccination but persisted longer in the group vaccinated by the s.c. route. Immunological responses were measured at regular intervals. Strong cellular responses were observed 13 days after the first vaccination, which persisted for 76 days. The lower dose induced a weaker and shorter-lived response.

Characterization of selected genes upregulated in non-tuberculous European wild boar as possible correlates of resistance to Mycobacterium bovis infection

Bovine tuberculosis (bTB), caused by Mycobacterium bovis (Mycobacterium tuberculosis complex), is a zoonotic disease that affects cattle and wildlife worldwide. These animal hosts can serve as reservoirs of infection, thus increasing the risk of human exposure and infection. In this study we quantified by RNA macroarray fluorescent hybridization and real-time RT-PCR the mRNA levels of genes differentially expressed in oropharyngeal tonsils and mandibular lymph nodes of three and seven individual non-tuberculous and tuberculous wild boars naturally exposed to M. bovis, respectively. These results demonstrated upregulation of two genes, complement component 3 (C3) and methylmalonyl-CoA mutase (MUT), in the non-tuberculous wild boars. These upregulated genes may contribute to resistance of wild boars to bTB by modifying the innate immunity, which limits the ability of the mycobacterium to infect and persist within macrophages. The C3 and MUT genes, therefore, are likely to be good candidates to study as markers of bTB resistance using functional genomics in animal model systems. Identification of genes upregulated in wild animals resistant to bTB contributes to our understanding of the mechanisms of protective immunity and resistance to mycobacterial organisms.

Genetic resistance to bovine tuberculosis in the Iberian wild boar

Bovine tuberculosis (bTB) is an important re-emerging zoonotic disease, causing major economic losses and constraining international trade of animals and their products. Despite eradication programmes, some countries continue to encounter outbreaks, mainly due to wildlife acting as primary hosts or reservoirs. While the genetic component of tuberculosis in humans and cattle is well documented, the role of genetic factors as modulators of bTB resistance remains unclear for natural populations. To address this issue, we investigated the relative contribution of host genetic variability to susceptibility to bTB infection and disease progression in wild boars from southern Spain. We found that genetic heterozygosity is an important predictor of bTB, not only modulating resistance to infection but also influencing containment of disease progression in infected individuals. Our results provide further evidence that host genetic variability plays a central role in natural populations. Testing each marker separately reveals evidence of both general and single-locus associative effects on bTB and several loci reveal high homology to regions of the genome with known immune function. Our results may prove to be crucial for understanding outbreaks of bTB in wildlife that could potentially affect domestic livestock and humans.

Combined DNA vaccine encapsulated in microspheres enhanced protection efficacy against Mycobacterium tuberculosis infection of mice

In a study to develop novel vaccination strategies against tuberculosis, we encapsulated DNA encoding Ag85B, MPT-64 and MPT-83 antigens mixed with dimethyldioctyldecyl ammonium bromide (DDA) into biodegradable poly(dl-lactide-co-glycolide, PLGA) microspheres. Scanning electron microscopy (SEM) analysis demonstrated a uniform microsphere population with a mean diameter of <5microm. Using RT-PCR we were able to demonstrate antigen gene expression in selected tissue. Moreover, in mice injected with PLGA encapsulated DNA, the levels of expression appeared to be higher comparing to those injected with non-encapsulated DNA. Also, C57BL/6 mice immunized with a single dose of PLGA encapsulated DNA produced increased levels of IFN-gamma in the supernatant of spleen cells when cultured in the presence of the recombinant antigens. High levels of specific IgG antibody against the three antigens were also observed. In vaccine/challenge experiments, mice receiving a single dose of PLGA encapsulated DNA were protected against Mycobacterium tuberculosis challenge at levels comparable to groups of mice immunized with three doses of non-encapsulated DNA vaccine or with Mycobacterium bovis BCG.

Combined DNA vaccines formulated either in DDA or in saline protect cattle from Mycobacterium bovis infection

We tested the effectiveness of combined DNA vaccines encoding antigens Ag85B, MPT64 and MPT83 from Mycobacterium tuberculosis on cattle. Our results showed that calves treated with combined DNA vaccines in the presence of dimethyldioctyldecyl ammonium bromide (DDA) or saline elicited a strong gamma interferon (IFN-gamma) response 1 or 2 months after the third vaccination. All three antigens induced substantial levels of IFN-gamma production 1 month after the bacterial challenge, when the BCG-driven IFN-gamma levels dropped to less than one third of their peak values. Animals receiving combined DNA vaccines produced highest amounts of IgG antibody titer 2 months after the third vaccination. Steady state low IgG levels were found 2 months after bacterial challenge. A few small lung and lymph node lesions were detected in 1/5 animals treated with combined DNA vaccines, whereas 3/5 of BCG-treated and 5/5 of vector-control calves showed larger and significantly more lesions. About 70- to 100-fold fewer bacteria were found in the lungs and lymph nodes of combined DNA vaccine-treated animals compared to those of the control group. Histopathological analyses showed that vaccinated calves possessed substantially improved post-infection lung and lymph node pathology relative to the controls. Our data indicate that combined DNA vaccines may be used in cattle to combat bovine tuberculosis.