Evaluation of two cocktails containing ESAT-6, CFP-10 and Rv-3615c in the intradermal test and the interferon-γ assay for diagnosis of bovine tuberculosis.

The intradermal tuberculin tests and the interferon-gamma (IFN-γ) assay are the principal tests used worldwide for the ante-mortem diagnosis of bovine tuberculosis. The conventional reagent currently in use in these tests is purified protein derivative (PPD) tuberculin obtained from Mycobacterium bovis culture. The components of PPD are poorly characterized and difficult to standardize. To overcome this issue, antigens specific to the Mycobacterium tuberculosis complex are being studied. Here we have assessed the biological potency of ESAT-6, CFP-10 and Rv-3615c presented as peptide or recombinant protein cocktails in comparison with the standard bovine PPD used routinely in Spanish eradication campaigns. The study was performed in cattle (n=23) from a herd with natural M. bovis infection. Animals were simultaneously injected with PPD and the peptide and protein cocktails. The percentages of cattle reacting positively to single intradermal test were 60.9% (bovine PPD), 47.8% (peptide cocktail) and 60.9% (protein cocktail), with no significant difference between the actual skin fold thickness increases (p>0.05). The IFN-γ assay detected 60.9% of animals when stimulation was performed with bovine PPD, but decreased to 52.2% when stimulation was performed with the peptide cocktail and to 47.8% when stimulation was performed with the protein cocktail. However, no significant differences were found between IFN-γ responder frequencies (p>0.05). These results show a potential use of these defined reagents for in vivo tuberculosis diagnosis.

Epidemiological investigation of a Mycobacterium avium subsp. hominissuis outbreak in swine.

Mycobacterium avium subsp. hominissuis (MAH) infection in swine may cause granulomatous lesions in lymph nodes that must undergo differential diagnosis with those caused by M. tuberculosis complex members. Moreover, MAH outbreaks can lead to severe economic losses due to condemnation of carcasses. A number of potential sources of infection for animals can usually be identified in contaminated farms. This report describes the application of several molecular characterization techniques in order to identify the possible environmental sources of MAH infection in an outbreak involving four breeding farms and six fattening farms. Molecular profiles obtained from MAH strains suggested a likely epidemiological link between clinical and environmental isolates cultured from sawdust and cooling systems from one breeding farm. These results highlight the potential risk posed by these environmental elements in the spread of infection and the need for implementation of adequate management practices in order to minimize this risk.

Factors influencing the performance of an interferon-γ assay for the diagnosis of tuberculosis in goats.

The interferon-gamma (IFN-γ) assay is an effective tool for the diagnosis of tuberculosis (Tb) in goats. The objectives of this study were to evaluate factors that might affect assay performance: (1) the phenol concentration of the purified protein derivative (PPD, tuberculin) used; (2) dialysis of PPD; and (3) delaying antigenic stimulation of blood samples for 8, 16 and 24h after collection. The assay was performed in duplicate with two cut-off points. Dialysis of PPD reduced test sensitivity, whereas the concentration of phenol did not significantly affect test outcome. Delaying antigenic stimulation of samples >8h resulted in a reduction in test sensitivity, compromising the capacity of the assay to detect infected animals. Performing the assay in duplicate was unnecessary, which has implications for reducing assay costs. These findings will facilitate the effective application of the IFN-γ assay as an ancillary test in Tb eradication programmes in goats.

Ante-mortem testing wild fallow deer for bovine tuberculosis.

This study aimed to maximize the sensitivity of bovine tuberculosis detection in living wild fallow deer (Dama dama) under field conditions. We evaluated the rapid test (RT; CervidTB STAT-PAK Assay, Chembio Diagnostic Systems, Inc., USA) in comparison with the comparative cervical skin test (CCT). A total of 134 fallow deer were captured between January and March 2008. At time 0, 0.1 ml of avian purified protein derivative (avian PPD; Cooper-Zeltia, Spain), 0.1 ml bovine PPD (Cooper-Zeltia, Spain), 0.1 ml negative control PBS and 0.1 ml of a positive control (the mitogen phytohaemagglutinin, PHA; containing 250 mg PHA, diluted in PBS) were injected intradermally at four shaved sites in the neck. The skin fold thickness at each injection site was measured at time 0 and 72 h (3 repeats each time). Animals with a skin test response of 2mm or more at the bovine PPD injection site and animals with any visible reactivity in the RT were necropsied and tissues submitted for culture and for histopathology. A total of 36 fallow deer were considered reactors to bovine PPD or to the RT (apparent prevalence 27%). Regarding both bovine PPD reactivity and the skin fold increase at the PHA injection site, we found significant effects of age and sex by age interaction. Adult males had the largest responses. Mycobacterium bovis was isolated from lymphoid tissues of 21 fallow deer. Skin test sensitivity, as compared to M. bovis culture confirmed deer, was 80.1% (17/21). But, the CCT alone would have missed 4 of 21 culture confirmed animals. RT sensitivity, based on culture confirmed deer, was also 80.1% (17/21). Similarly, the RT alone would have missed another 4 of 21 culture confirmed deer. However, combining the CCT and the RT allowed for detecting all 21 culture positive fallow deer. We conclude that the combined application of the RT and the skin testing can maximize the sensitivity of bTB detection in living fallow deer, thus facilitating control programs for wildlife disease surveillance.

Eurasian wild boar response to skin-testing with mycobacterial and non-mycobacterial antigens.

Eurasian wild boar (Sus scrofa) are able to maintain bovine tuberculosis (bTB) in the wild and are most probably able to transmit the disease to other species, thus acting as a true wildlife reservoir. Translocation of wild boar is a common practice in European countries. Therefore, identifying effective tools for bTB diagnosis in living wild boar is crucial for the implementation of control measures. We describe for the first time the sex and origin related differences in the skin-test response to mycobacterial antigens (bPPD and aPPD) and to a non-mycobacterial antigen (PHA, a plant derived mitogen) in wild and farmed wild boar, and used a small sample of known M. bovis infected wild boar to establish whether skin-testing is an option for bTB diagnosis in living wild boar. The highest skinfold increase response was detected at the PHA injection site, evidencing that the PHA test could be useful in monitoring cell mediated immunity (CMI) in wild boar populations. A clear age-increasing trend of the PHA response indicated that age should be taken into account when measuring CMI in wild boar. Origin related differences in the response against mycobacterial antigens could reflect differential exposure to mycobacterial antigens. Skin testing in BCG immunized wild boar showed low sensitivity (43-57%), while the sensitivity was good in the culture positive controls (75-100%), depending on the reading criterion. Specificity improved when the criterion was a response to bPPD larger than 2 mm and bPPD response larger than aPPD response (77%). Although a limited sample, our results indicated the potential of skin test as a bTB diagnostic tool in Eurasian wild boar. However, handling of wild boar is dangerous, specificity is low, and more effort is needed in order to define the sensitivity of this technique.

Experimental infection of Eurasian wild boar with Mycobacterium avium subsp. avium.

The Eurasian wild boar (Sus scrofa) is increasingly relevant as a host for several pathogenic mycobacteria. We aimed to characterize the first experimental Mycobacterium avium subsp. avium (MAA) infection in wild boar in order to describe the lesions and the immune response as compared to uninfected controls. Twelve 1-4-month-old wild boar piglets were housed in class III bio-containment facilities. Four concentrations of MAA suspension were used: 10, 10(2) and 10(4) mycobacteria (2 animals each, oropharyngeal route) and 2.5 x 10(6) mycobacteria (2 animals each by the oropharyngeal and nasal routes). No clinical signs were observed and pathology evidenced a low pathogenicity of this MAA strain for this particular host. Bacteriological and pathological evidence of successful infection after experimental inoculation was found for the group challenged with 2.5 x 10(6) mycobacteria. These four wild boar showed a positive IFN-gamma response to the avian PPD and the real-time RT-PCR data revealed that three genes, complement component C3, IFN-gamma and RANTES, were significantly down regulated in infected animals. These results were similar to those found in naturally and experimentally M. bovis-infected wild boar and may constitute biomarkers of mycobacterial infection in this species.

PCR amplification and high-resolution melting curve analysis as a rapid diagnostic method for genotyping members of the Mycobacterium avium­intracellulare complex.

Some of the members of the Mycobacterium avium­intracellulare (MAI) complex are recognized as human pathogens in both immunocompromised and immunocompetent patients. The current molecular methods that are available for genotyping the MAI complex members can be both expensive and technically demanding. In this report, we describe for the first time the application of a real-time PCR and high-resolution melt approach to differentiate between the complex members by targeting a member of the Pro- Pro-Glu gene family, MACPPE24. To this end, reference strains of the M. avium subspecies and Mycobacterium intracellulare were used to optimize the technique. Then, this real-time PCR­high-resolution melt approach was used to distinguish ten M. avium ssp. hominissuis field isolates from the M. intracellulare reference strain.

First data on Eurasian wild boar response to oral immunization with BCG and challenge with a Mycobacterium bovis field strain.

The Eurasian wild boar (Sus scrofa) is considered a reservoir for bovine tuberculosis (bTB) caused by Mycobacterium bovis and closely related members of the Mycobacterium tuberculosis complex in south-central Spain. The vaccination of wildlife with BCG offers an alternative to culling and to movement restriction for the control of bTB among wildlife reservoirs. In this study, we hypothesized that oral BCG immunization of wild boar would affect the expression of immunoregulatory genes and confer protection against M. bovis. Three groups were used to describe the infection, pathological findings and gene expression profiles in wild boar: BCG-vaccinated and M. bovis-challenged (vaccinated challenged group; N=6), non-vaccinated and M. bovis-challenged (non-vaccinated challenged group; N=4), and non-vaccinated and mock-infected (control group; N=2) animals. M. bovis was isolated from 50% (3/6) and 75% (3/4) of vaccinated challenged and non-vaccinated challenged animals, respectively. All four wild boar from the non-vaccinated challenged group developed bTB-compatible lesions 114 days after challenge. In contrast, only 50% of vaccinated challenged wild boar developed lesions. The PBMC mRNA levels of IL4, RANTES, C3, IFN-gamma and methylmalonyl-CoA mutase (MUT) were analyzed at several days post-vaccination (dpi). When vaccinated challenged animals were compared to controls, all five genes were significantly upregulated at the time of M. bovis infection at 186dpi but IFN-gamma levels were also upregulated at 11 and 46dpi. The C3 and MUT mRNA levels were higher at 46dpi, and 11 and 186dpi, respectively, in vaccinated protected wild boar when compared to non-vaccinated challenged animals. At the end of the experiment (300dpi), the mRNA levels of selected genes were lower in non-vaccinated challenged animals when compared to control wild boar. Exposing wild boar to a dose of 10(4)cfu of M. bovis by the oropharyngeal route is an adequate protocol to produce an infection model in this species. Our results suggested that oral BCG immunization of wild boar results in the upregulation of immunoregulatory genes that may be associated with protective response to M. bovis infection in this species. More studies on vaccine efficacy, delivery, and safety will be needed to confirm if oral vaccination with BCG could be used in bTB control programs for reducing M. bovis infection and clinical disease in wild boar.

Mycobacterium peregrinum infection in farmed European tench (Tinca tinca L.).

This work is the first description of Mycobacterium peregrinum as an etiological agent for mycobacteriosis in farmed fishes. We report the mycobacterial infection in farmed European tench (Tinca tinca L.) which was confirmed by culture, molecular identification methods (PCRs aimed at 16S rRNA, rpobeta and hsp65 sequencing), and histopathology. Since M. peregrinum infection has been described in humans, their clinical significance in fishes should be considered of healthcare interest. With this case report, we also show that a multidisciplinary approach was needed to overcome difficulties associated to diagnosis of piscine mycobacteriosis.

Polymorphisms in gyrA and gyrB genes among Mycobacterium avium subsp. paratuberculosis type I, II, and III isolates.

The analysis of the gyrA and gyrB genes of a panel of Mycobacterium avium subsp. paratuberculosis isolates from types I, II, and III detected type-specific single nucleotide polymorphisms. Based on these results, we developed a PCR and restriction enzyme analysis to discriminate type I and III isolates. The application of this technique would be the unique strategy to characterize these strains when there is not enough bacterial growth to perform pulsed-field gel electrophoresis and IS900 restriction fragment length polymorphism.

Molecular epidemiology of Types I/III strains of Mycobacterium avium subspecies paratuberculosis isolated from goats and cattle.

Molecular characterization of Mycobacterium avium subsp. paratuberculosis (M. a. paratuberculosis) isolates classifies them into three groups: cattle or Type II, sheep or Type I, and intermediate or Type III. To avoid problems associated with characterization of extremely slow growth strains, PCR-based techniques that divide the M. a. paratuberculosis strains in two main groups (cattle or Type II, and sheep or Types I/III) can be performed. The objectives of this study were to characterize the M. a. paratuberculosis isolates identified by different PCR-based tests (IS1311-PCR and restriction endonuclease analysis, PCR test based on a DNA sequence difference, and a PCR aimed at three Type I-specific loci), and to determine the clinical and epidemiological implications of Types I/III M. a. paratuberculosis strains in livestock. One hundred and fifty-eight M. a. paratuberculosis strains from domestic ruminants were analyzed. One hundred and six M. a. paratuberculosis isolates (61 from goats and 45 from cattle) were classified as Type II strains; and 52 (29 from cows, 20 from goats, and three from sheep) were included in the Types I/III. The Types I/III M. a. paratuberculosis strains were associated to Spanish native breeds. The majority of these animals had not been in direct or indirect contact with sheep flocks infected with M. a. paratuberculosis. This fact should be taken into account when implementing paratuberculosis control programs.

In vitro T-cell activation of monocyte-derived macrophages by soluble messengers or cell-to-cell contact in bovine tuberculosis.

The macrophage plays a dual role in tuberculosis, promoting not only protection against mycobacteria, but also survival of the pathogen. Macrophages inhibit multiplication of mycobacteria but also act in concert with lymphocytes through presentation of antigens to T cells. Studies in animal and human infections have suggested a correlation of in vitro growth rates of mycobacteria with in vivo virulence, using uracil uptake to assess mycobacterial metabolism. This study found that blood-derived, non-activated bovine macrophages were capable of controlling Mycobacterium bovis bacillus Calmette-Gurin growth for up to 96 hr, but were permissive to intracellular growth of virulent M. bovis. The present investigation compared the in vitro modulation of these macrophage activities by cytokine-rich T-cell supernatants or cell-to-cell contact. On the one hand, treatment of cultured monocytes with mitogen-produced T-cell supernatants promoted morphological changes suggestive of an activation status, enhanced the antigen presentation capabilities of monocytes and up-regulated major histocompatibility complex class II expression. However, this activation was not associated with enhanced anti-M. bovis activity. On the other hand, incubation of infected monocytes with T-cell populations resulted in proportionally increased inhibition of M. bovis uracil uptake. This inhibition was also seen using cells from uninfected animals and indicated the necessity for cell-to-cell contact to promote antimycobacterial capability.

Bovine tuberculosis and the endangered Iberian lynx.

We report the first case of bovine tuberculosis in a free-living Iberian lynx (Lynx pardina), an extremely endangered feline, from Doñana National Park in Spain. The isolate (Mycobacterium bovis) correlates by molecular characterization with other isolates from wild ungulates in the park, strongly suggesting an epidemiologic link. Mycobacterium bovis infects many animal species, with wild and free-ranging domestic ungulates being the main reservoirs in nature (1).

Cellular interactions in bovine tuberculosis: release of active mycobacteria from infected macrophages by antigen-stimulated T cells.

The outcome of Mycobacterium bovis infections depends on the interactions of infected macrophages with T lymphocytes. Several studies in humans and in mouse models have suggested an important role for cytotoxicity in the protective immune response to mycobacterial infections, and both CD4+ and CD8+ T cells have been shown to elicit appropriate cytolytic activity. The present study investigated in vitro interactions of T cells with M. bovis-infected macrophages in bovine tuberculosis. The results showed that following interaction with antigen-stimulated peripheral blood mononuclear cells (PBMC) from infected cattle, there was an increased presence of M. bovis in the extracellular compartment of infected macrophage cultures, as measured by incorporation of [3H]uracil into mycobacterial RNA. Furthermore, out of a panel of T-cell clones from infected cattle, it was found that a higher proportion of CD8+ clones produced an increase in the number of metabolically active extracellular M. bovis organisms compared with CD4+ clones. Finally, a positive correlation between percentage of antigen-dependent release of mycobacteria and total uracil uptake by M. bovis within culture systems was detected. This could be regarded as an indication of preferential intracellular control of mycobacteria by activated macrophages.

Mycobacterium tuberculosis subsp. caprae subsp. nov.: a taxonomic study of a new member of the Mycobacterium tuberculosis complex isolated from goats in Spain.

Isolates from the Mycobacterium tuberculosis complex cultured from caprine pathological tissue samples were biochemically and genetically characterized. The isolates were negative for nitrate reduction and niacin accumulation, they weakly hydrolysed Tween 80, were sensitive to pyrazinamide (50 micrograms ml-1) and were resistant to 1 and 2 micrograms tiophene-2-carboxylic acid hydrazide ml-1 but not to 5 or 10 micrograms tiophene-2-carboxylic acid hydrazide ml-1. Sequencing of the pncA gene revealed a polymorphism characteristic of M. tuberculosis, whereas oxyR, katG and gyrA sequences were characteristic of Mycobacterium bovis. The fingerprinting patterns obtained with IS6110, direct repeats and polymorphic G+C-rich sequence-associated RFLP and direct variable repeat-spacer oligonucelotide typing (spoligotyping) segregated these isolates from the other members of the complex. The results of this testing, together with the repeated association of this micro-organism with goats, suggest that a new member of this taxonomic complex not matching any of the classical species had been identified. This unusual mycobacterium may play a role in the epidemiology of animal and human tuberculosis in Spain. The name Mycobacterium tuberculosis subsp. caprae subsp. nov. is proposed for these isolates. The type strain of Mycobacterium tuberculosis subsp. caprae subsp. nov. is gM-1T (= CIP 105776T).

Restriction fragment length polymorphism and spacer oligonucleotide typing: a comparative analysis of fingerprinting strategies for Mycobacterium bovis.

The combination of conventional investigation and DNA fingerprinting is yielding important insights into the epidemiology of Mycobacterium bovis infections. Various genetic markers used in restriction fragment length polymorphism (RFLP) have recently been exploited for fingerprinting of M. bovis isolates. The newly developed spacer oligonucleotide typing aimed to investigate the polymorphism of M. tuberculosis in the DR locus, has also been applied to the molecular typing of M. bovis isolates. This work compared the performance of the insertion sequence (IS) IS6110, IS1081 and the genetic elements polymorphic G + C-rich repeat (PGRS) and direct repeat (DR) used in RFLP analysis with spoligotyping using a group of 128 Spanish M. bovis isolates. In this study, the most sensitive technique for identifying polymorphism in M. bovis was PGRS-RFLP, closely followed by IS6110-RFLP. We propose several schemes for fingerprinting of these isolates, however, the clear geographical variations found by different authors makes the study of each local situation indispensable. An international consensus in the methods used would be desirable for efficient interlaboratory comparison of strains.

Evaluation of the gamma-interferon assay for eradication of tuberculosis in a goat herd.

OBJECTIVE: To evaluate the usefulness of the gamma-interferon assay in the diagnosis of caprine tuberculosis in comparison with a single intradermal tuberculin test, and to obtain a group of animals free from this infection in a herd with a high prevalence. DESIGN: An immunological study involving four serial comparative gamma-interferon and single intradermal tuberculin tests. ANIMALS: A herd of 87 goats of Guadarrama breed. PROCEDURE: Serial testing and segregation of animals. RESULTS: We found that the number of infections detected by the gamma-interferon test was considerably greater than the number detected by the single intradermal tuberculin test. A group of 10 animals was negative to both tests in two consecutive rounds and three kids were negative in the last round of testing. CONCLUSIONS: Gamma-interferon assay is appropriate for diagnosis and eradication of tuberculosis in goats. This test is able to detect early Mycobacterium bovis infection. Avian reactors with simultaneous increased reaction to bovine PPD in the gamma-interferon assay (designated as avian reactors) should be considered test positive for M bovis. By serial testing with the gamma-interferon and the single intradermal tuberculin tests, and a policy of segregation of kids at birth, it is possible to achieve a group of animals test negative for tuberculosis from a herd of goats with high immunoreactivity to this infection.

Evaluation of four DNA typing techniques in epidemiological investigations of bovine tuberculosis.

DNA fingerprinting techniques were used to type 273 isolates of Mycobacterium bovis from Australia, Canada, the Republic of Ireland, and Iran. The results of restriction fragment length polymorphism (RFLP) analysis with DNA probes from IS6110, the direct repeat (DR), and the polymorphic GC-rich sequence (PGRS) were compared with those of a new PCR-based method called spacer oligonucleotide typing (spoligotyping) developed for the rapid typing of Mycobacterium tuberculosis (J. Kamerbeek et al., J. Clin. Microbiol. 35:907-914, 1997). Eighty-five percent of the isolates harbored a single copy of IS6110, and 81.5% of these carried IS6110 on the characteristic 1.9-kb restriction fragment. RFLP analysis with IS6110 identified 23 different types, RFLP analysis with the DR probe identified 35 types, RFLP analysis with the PGRS probe identified 77 types, and the spoligotyping method identified 35 types. By combining all results, 99 different strains could be identified. Isolate clusters were frequently associated within herds or were found between herds when epidemiological evidence confirmed animal movements. RFLP analysis with IS6110 was sufficiently sensitive for the typing of isolates with more than three copies of IS6110, but RFLP analysis with the PGRS probe was the most sensitive typing technique for strains with only a single copy of IS6110. Spoligotyping may have advantages for the rapid typing of M. bovis, but it needs to be made more sensitive.