Factors affecting red deer skin test responsiveness to bovine and avian tuberculin and to phytohaemagglutinin

Comparative cellular immune responses in calves after infection with Mycobacterium avium subsp. paratuberculosis, M. avium subsp. avium, M. kansasii and M. bovis

In the present study, calves were infected with Mycobacterium avium subsp. paratuberculosis (MAP), Mycobacterium avium subsp. avium (M. avium), Mycobacterium kansasii (M. kansasii), or Mycobacterium bovis (M. bovis) to determine differences in cellular immunity. Comparative cellular responses were assessed upon stimulation of cells with mycobacterial whole cell sonicates respective of each infection group. Antigen-specific whole blood interferon gamma (IFN-γ) responses were observed in all infection groups compared to noninfected control calves, however, responses were more robust for M. bovis calves. Upon antigen stimulation of PBMCs, secretion of IFN-γ and IL-10 was higher for M. bovis calves compared to other infection groups. In contrast, IL-12 secretion was lower for M. bovis calves compared to MAP infected calves. Within the total PBMC population, higher numbers of CD4+, CD8+, and γδ TCR + T cells were observed for MAP and M. avium calves compared to M. bovis calves. This aligned with higher expression of CD26 on these subpopulations for MAP and M. avium calves, as well. In contrast, greater expression of CD25 was observed on CD4+ and γδ TCR + T cells and natural killer cells for M. bovis calves. Overall, similarities in cellular immune responses were observed between the closely related MAP and M. avium during infection of calves. In contrast, significant differences were noted between calves infected with MAP and M. bovis. This suggests that host immune responses to different mycobacteria may impact interpretation of diagnostic tools based upon their cellular immunity.

Diagnosis of tuberculosis in wildlife: a systematic review

Animal tuberculosis (TB) is a multi-host disease caused by members of the Mycobacterium tuberculosis complex (MTC). Due to its impact on economy, sanitary standards of milk and meat industry, public health and conservation, TB control is an actively ongoing research subject. Several wildlife species are involved in the maintenance and transmission of TB, so that new approaches to wildlife TB diagnosis have gained relevance in recent years. Diagnosis is a paramount step for screening, epidemiological investigation, as well as for ensuring the success of control strategies such as vaccination trials. This is the first review that systematically addresses data available for the diagnosis of TB in wildlife following the Preferred Reporting Items of Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The article also gives an overview of the factors related to host, environment, sampling, and diagnostic techniques which can affect test performance. After three screenings, 124 articles were considered for systematic review. Literature indicates that post-mortem examination and culture are useful methods for disease surveillance, but immunological diagnostic tests based on cellular and humoral immune response detection are gaining importance in wildlife TB diagnosis. Among them, serological tests are especially useful in wildlife because they are relatively inexpensive and easy to perform, facilitate large-scale surveillance and can be used both ante- and post-mortem. Currently available studies assessed test performance mostly in cervids, European badgers, wild suids and wild bovids. Research to improve diagnostic tests for wildlife TB diagnosis is still needed in order to reach accurate, rapid and cost-effective diagnostic techniques adequate to a broad range of target species and consistent over space and time to allow proper disease monitoring.

No effect of inoculation site and injection device on the skin test response of red deer to the intradermal injection of Mycobacterium avium-derived purified protein derivative (PPD)

Mycobacterial diseases are important health issues in farmed deer. The single intradermal tuberculin test is the standard test for tuberculosis testing in deer. We studied two factors which might influence the response of deer to skin testing: the inoculation site and the injection device. Deer included in this study were 2.5 years old farmed red deer (Cervus elaphus) hinds (n = 80). Two areas of 3 cm × 3 cm were shaved at the left side of the neck. Site A (SA) was situated about 10 cm caudal to the head, while site B (SB) was 10 cm caudal to SA. All hinds received at the same time two 0.1 ml inoculations of Mycobacterium avium derived purified protein derivative (aPPD). One inoculation was made by syringe and the other one with the needle-free syringe Dermojet. To test the inoculation site effect, half of the animals were inoculated by Dermojet in SA and by syringe in SB to compare with the inoculation in SA by syringe and Dermojet in SB in the other half. No differences were recorded for the injection device nor for the inoculation site. Ten hinds had a skinfold increase larger than 30 tenths of mm by any injection device and inoculation site. Seven (9%) and 6 (8%) hinds were classified as positive by syringe and Dermojet, and at the anterior or posterior inoculation site, respectively. The distribution of skinfold thickness increases did not differ by injection device. Our findings support the needle-free Dermojet syringe as a suitable tool for skin-testing in red deer and suggest no relevant effect of the position of the inoculation site along the neck in red deer.

Macroimmunology: The drivers and consequences of spatial patterns in wildlife immune defence

The prevalence and intensity of parasites in wild hosts varies across space and is a key determinant of infection risk in humans, domestic animals and threatened wildlife. Because the immune system serves as the primary barrier to infection, replication and transmission following exposure, we here consider the environmental drivers of immunity. Spatial variation in parasite pressure, abiotic and biotic conditions, and anthropogenic factors can all shape immunity across spatial scales. Identifying the most important spatial drivers of immunity could help pre-empt infectious disease risks, especially in the context of how large-scale factors such as urbanization affect defence by changing environmental conditions. We provide a synthesis of how to apply macroecological approaches to the study of ecoimmunology (i.e. macroimmunology). We first review spatial factors that could generate spatial variation in defence, highlighting the need for large-scale studies that can differentiate competing environmental predictors of immunity and detailing contexts where this approach might be favoured over small-scale experimental studies. We next conduct a systematic review of the literature to assess the frequency of spatial studies and to classify them according to taxa, immune measures, spatial replication and extent, and statistical methods. We review 210 ecoimmunology studies sampling multiple host populations. We show that whereas spatial approaches are relatively common, spatial replication is generally low and unlikely to provide sufficient environmental variation or power to differentiate competing spatial hypotheses. We also highlight statistical biases in macroimmunology, in that few studies characterize and account for spatial dependence statistically, potentially affecting inferences for the relationships between environmental conditions and immune defence. We use these findings to describe tools from geostatistics and spatial modelling that can improve inference about the associations between environmental and immunological variation. In particular, we emphasize exploratory tools that can guide spatial sampling and highlight the need for greater use of mixed-effects models that account for spatial variability while also allowing researchers to account for both individual- and habitat-level covariates. We finally discuss future research priorities for macroimmunology, including focusing on latitudinal gradients, range expansions and urbanization as being especially amenable to large-scale spatial approaches. Methodologically, we highlight critical opportunities posed by assessing spatial variation in host tolerance, using metagenomics to quantify spatial variation in parasite pressure, coupling large-scale field studies with small-scale field experiments and longitudinal approaches, and applying statistical tools from macroecology and meta-analysis to identify generalizable spatial patterns. Such work will facilitate scaling ecoimmunology from individual- to habitat-level insights about the drivers of immune defence and help predict where environmental change may most alter infectious disease risk.

A new test to detect antibodies against Mycobacterium tuberculosis complex in red deer serum

Red deer (Cervus elaphus) farming is a growing economic activity worldwide. However, the capacity of this species to act as reservoir of animal tuberculosis (TB) poses a threat to other wildlife and to livestock. Diagnostic assay accuracy in this species is therefore highly relevant for prevention and control measures. Our aim was to evaluate the diagnostic performance of the protein complex P22, obtained from Mycobacterium bovis derived purified protein derivative (bPPD), as a candidate antigen for the detection of antibodies against Mycobacterium tuberculosis complex (MTC). We assessed the performance of this new antigen in indirect enzyme-linked immunosorbent assays (ELISA) in TB-positive and TB-negative red deer, in comparison with a bPPD-based ELISA. The P22 ELISA achieved a higher specificity (Sp) and similar sensitivity (Se) in comparison with the bPPD ELISA at all the cut-off points considered. The P22 ELISA yielded optimal Sp (99.02%; 95% confidence intervals [CI_95%]: 96.5-99.8) and appropriate Se (70.1%; CI_95%: 63.6-76) at the selected cut-off point of 100%. These results suggest that P22 can be used as an alternative antigen in the immunodiagnosis of animal TB through the use of an ELISA-type detection of antibodies against MTC in red deer, thus contributing to the diagnosis of animal TB in this species as a measure for further disease prevention and control programs.

Modelling the variation in skin-test tuberculin reactions, post-mortem lesion counts and case pathology in tuberculosis-exposed cattle: Effects of animal characteristics, histories and co-infection

Correctly identifying bovine tuberculosis (bTB) in cattle remains a significant problem in endemic countries. We hypothesized that animal characteristics (sex, age, breed), histories (herd effects, testing, movement) and potential exposure to other pathogens (co-infection; BVDV, liver fluke and Mycobacterium avium reactors) could significantly impact the immune responsiveness detected at skin testing and the variation in post-mortem pathology (confirmation) in bTB-exposed cattle. Three model suites were developed using a retrospective observational data set of 5,698 cattle culled during herd breakdowns in Northern Ireland. A linear regression model suggested that antemortem tuberculin reaction size (difference in purified protein derivative avium [PPDa] and bovine [PPDb] reactions) was significantly positively associated with post-mortem maximum lesion size and the number of lesions found. This indicated that reaction size could be considered a predictor of both the extent (number of lesions/tissues) and the pathological progression of infection (maximum lesion size). Tuberculin reaction size was related to age class, and younger animals (<2.85 years) displayed larger reaction sizes than older animals. Tuberculin reaction size was also associated with breed and animal movement and increased with the time between the penultimate and disclosing tests. A negative binomial random-effects model indicated a significant increase in lesion counts for animals with M. avium reactions (PPDb-PPDa < 0) relative to non-reactors (PPDb-PPDa = 0). Lesion counts were significantly increased in animals with previous positive severe interpretation skin-test results. Animals with increased movement histories, young animals and non-dairy breed animals also had significantly increased lesion counts. Animals from herds that had BVDV-positive cattle had significantly lower lesion counts than animals from herds without evidence of BVDV infection. Restricting the data set to only animals with a bTB visible lesion at slaughter (n = 2471), an ordinal regression model indicated that liver fluke-infected animals disclosed smaller lesions, relative to liver fluke-negative animals, and larger lesions were disclosed in animals with increased movement histories.

Development and evaluation of an interferon gamma assay for the diagnosis of tuberculosis in red deer experimentally infected with Mycobacterium bovis

BACKGROUND

Red deer (Cervus elaphus) is regarded as an epidemiologically relevant host for Mycobacterium bovis (M. bovis) and closely related members of the Mycobacterium tuberculosis complex that cause animal tuberculosis (TB). The standard antemortem screening test for the detection of TB in deer is the intradermal tuberculin skin test, but the detection of interferon-gamma (IFNγ) produced by white blood cells exposed to M. bovis antigens can be used as an alternative or supplemental assay in most TB eradication/control programs. This study aims to develop an in-house sandwich ELISA for deer IFNγ, based on the cross-reactivity of the antibodies to both cervid and bovine IFNγ, and to evaluate the potential of this assay to detect M. bovis-infected red deer in response to the in vitro stimulation of whole-blood cells with bovine purified protein derivative (bPPD), p22 protein complex derived from bPPD or using the specific tuberculous mycobacterial proteins ESAT-6/CFP-10, Rv3615c and Rv3020c. The positive control stimulant used in this study was pokeweed mitogen, which resulted in a consistent induction of IFNγ in samples from red deer, thus allowing the interpretation of the assay.

RESULTS

The percentage of animals correctly classified by this technique as M. bovis non-infected was 100%. The detection of infected animals as positive was high and ranged widely depending upon the antigen and the cut-off value applied, as well as the time after infection. Our findings indicate that this protocol may serve as a reliable assay for the antemortem diagnosis of TB from the initial stage of M. bovis-infection, and may also be adequately sensitive.

CONCLUSIONS

The suggested optimal antigens and cut-off are bPPD, p22 and the combination of ESAT-6/CFP-10 and Rv3020c with a 0.05 Δ optical density, which yielded a up to 100% correct classification of TB positive and negatve red deer under our experimental conditions. This technique will aid in TB testing of farmed and translocated deer. Future studies should evaluate the ability of this IFNγ assay to detect specific responses under field conditions.

Effects of repeated comparative intradermal tuberculin testing on test results: a longitudinal study in TB-free red deer

BACKGROUND

Diagnosing tuberculosis (TB) in farmed red deer (Cervus elaphus) is challenging and might require combining cellular and humoral diagnostic tests. Repeated skin-testing with mycobacterial purified protein derivatives (PPDs) might sensitize or desensitize the subjects to both kinds of diagnostic tools. We evaluated the effect of repeated (every 6 months) comparative tuberculin skin testing on skin test and ELISA responsiveness in farmed red deer hinds from a TB-free herd. Eighteen 8-month old hinds were inoculated with bovine and avian PPDs and the mitogen phytohaemagglutinin (PHA), as positive control and concurrently tested by ELISA for antibodies against avian (avian PPD, aPPD and protoplasmatic antigen 3, PPA3) and bovine antigens (bPPD and MPB70). Blood serum was also sampled three weeks after each skin testing round and tested for antibodies against aPPD and bPPD, in order to detect eventual antibody level boosts. Testing took place every six months from winter 2012 until winter 2015.

RESULTS

The skin test response to both PPDs peaked during the second and third test round, returning to standard values thereafter. Individual variability was particularly high at the first year and early second year testing rounds (first intradermal test and blood sampling; first winter). The antibody response to avian antigens increased through time, while no such increase was recorded for bovine antigens. The antibody boost three weeks after skin testing was more marked for avian PPD. However, there was no consistent trend in the boosting response through time.

CONCLUSION

Repeated comparative skin testing at six month intervals did not cause progressive increments in skin test responsiveness or antibody production. Specifically, we observed no loss of the skin test response to bPPD and also no progressive loss of the boosting effect in the ELISA responses. However, we recorded increases through time in the antibody levels against avian mycobacterial antigens, possibly due to the progressive exposure to MAP or to other cross-reacting environmental mycobacteria. These findings should be taken into account in designing and interpreting TB testing schemes in farmed deer.

Application of Concanavalin A during immune responsiveness skin-swelling tests facilitates measurement interpretation in mammalian ecology

The skin‐swelling test is a simple and widespread method used in field ecological research to estimate cellular immune responsiveness in animals. This immunoecological test is based on measuring the magnitude of tissue swelling response at specific times following subcutaneous application of an experimental pro‐inflammatory stimulant. In the vast majority of studies across vertebrate taxa, phytohemagglutinin (PHA) is used as a universal stimulant. Given the complexity of immune response activation pathways of PHA, however, interpretation of test results can be ambiguous. Goal of this study was to improve methodology of the skin‐swelling test to decrease this ambiguity. Here, we present an alternative protocol aimed at facilitating interpretation of skin‐swelling data for mammals. Based on previous evidence suggesting that mammalian T cells are readily activated by Concanavalin A (ConA) in vitro, we compared cellular immune responses in vivo to PHA and ConA as an alternative pro‐inflammatory stimulant in mice. We measured magnitude of tissue swelling and compared it with intensity of blood cell infiltration into tissue over a 72‐hour interval. Our results corroborate that PHA and ConA show important differences in both dynamics and response amplitude in rodents. ConA induces stronger swelling with a distinct leukocyte activity pattern and higher pro‐inflammatory cytokine (interleukin 6 [IL‐6] and interferon gamma[IFN‐γ]) expression than PHA during peak response (24‐h post‐treatment). Furthermore, unlike PHA, magnitude of swelling was positively associated with cellular activity (number of neutrophils infiltrating tissue) following ConA injection. We conclude that ConA is the more suitable stimulant for skin‐swelling tests in mammals. This is because of the molecular binding specificity in the two lectins, that is, ConA specifically activates T cells while PHA also triggers erythroagglutination. We propose that ConA be used in all future ecological testing in mammals as it exhibits better performance and its application facilitates immunological interpretation of skin‐swelling test results.

Oral administration of heat-inactivated Mycobacterium bovis reduces the response of farmed red deer to avian and bovine tuberculin

Orally delivered mycobacterial antigens may not sensitize the immunized animals causing a positive tuberculin skin test response. As the first step to address this critical issue, we characterized the response of farmed red deer (Cervus elaphus) to orally delivered heat-inactivated Mycobacterium bovis. Thirty-two adult red deer hinds from a farm known to be free of tuberculosis (TB) were randomly assigned to two different treatment groups, immunized (n=24) and control (n=8). Immunized hinds were dosed orally with 2 ml of PBS containing 6 × 10(6) heat-inactivated M. bovis. The mean skin test response of immunized deer to both avian purified protein derivative (aPPD) and bovine PPD (bPPD) was consistently lower in immunized than in control hinds. One year after immunization, immunized hinds had a significant reduction in the skin test response to aPPD and in the ELISA antibody levels against both aPPD and bPPD (24-36% reduction; P<0.05). By contrast, no significant change was observed in the skin test response to phytohaemagglutinin, or in the ELISA antibody levels against the M. bovis specific antigen MPB70. The mRNA levels for C3, IFN-γ and IL-1β and serum protein levels for IFN-γ and IL-1β did not vary between immunized and control deer. However, serum C3 protein levels were significantly higher (P=0.001) in immunized than in control deer six months after immunization. These results confirm that oral heat-inactivated M. bovis does not sensitize farmed red deer and therefore does not cause false-positive responses in the tuberculin skin test. The absence of sensitization in orally immunized deer opens the possibility of testing the vaccine in deer and possibly other ruminants without the risk of causing false-positive reactions in TB-tests. This study also provided the first evidence that orally-delivered inactivated mycobacterial antigens elicit some kind of immune response in a ruminant.

Wildlife and paratuberculosis: a review

Paratuberculosis (PTB) is an infectious granulomatous enteritis caused by Mycobacterium avium paratuberculosis (MAP) causing significant economic losses in livestock. However, PTB in free-living and captive wildlife has not been as extensively studied as in livestock. We reviewed the existing literature references on MAP to (i) determine the potential impact of MAP infection in wildlife species; (ii) analyze whether wildlife reservoirs are relevant regarding MAP control in domestic ruminants; (iii) assess the importance of MAP as the cause of potential interferences with tuberculosis diagnosis in wildlife. The mean MAP prevalence reported in wildlife was 2.41% (95% confidence interval 1.76-3.06). Although MAP should be considered an important disease in farmed cervids, its impact on free-ranging species is questionable. MAP reservoirs may exist locally but their significance for PTB control in livestock is quite limited. The most critical aspect derived of MAP infection in wildlife is the interference with tuberculosis diagnosis.

Performance of immunochromatographic and ELISA tests for detecting fallow deer infected with Mycobacterium bovis

Fallow deer (Dama dama) are widely distributed as natural or naturalised populations, as well as in game parks and deer farms. We used 157 fallow deer sampled in populations considered to be Mycobacterium tuberculosis complex (MTC) free and 73 Mycobacterium bovis-infected fallow deer confirmed postmortem by culture to evaluate the diagnostic performance of two tests for the detection of anti-mycobacterial antibodies: the dual path platform (DPP) VetTB assay and the bovine purified protein derivative (bPPD) ELISA. We also compared their sensitivity with that of the skin test, analyzed the effect of haemolysis degree on the antibody detection and described the relationship between the test readings and presence/absence of gross tuberculosis (TB) compatible lesions. Sensitivity of bPPD ELISA was 51% at a specificity of 96%. Depending on the cut-off value selected, the sensitivity of DPP VetTB ranged from 62 to 71%, while its specificity was 88-95%. In the subgroup of M. bovis-infected deer for which the skin test data were available (33 of 73); this method detected 76% of culture-positive animals, although the specificity of the intradermal test was not determined in this study. When the DPP VetTB and skin test data were combined, the resulting sensitivity obtained in this sub-group of M. bovis-infected deer increased to 97%. Gross pathology identified TB compatible lesions (TBL) in 89% culture-confirmed fallow deer. The infected animals with visible lesions had significantly higher readings in the DPP VetTB, but not in the bPPD ELISA. Only high levels of haemolysis decreased antibody test sensitivity and this effect was more evident for the bPPD ELISA. The results allowed inferring a number of management recommendations for rapid detection of MTC infection in live fallow deer and in surveys on hunter-harvested cervids.

The testing season affects red deer skinfold increase in response to phytohaemagglutinin

Red deer (Cervus elaphus) have a pronounced seasonality in their physiology. The aim of this study was to assess the effect of the season on red deer responsiveness to skin testing with the phytohaemagglutinin (PHA) mitogen. Study subjects included 270 farmed adult red deer (19 stags and 251 hinds). The skin testing was carried out between January 2009 and August 2010. The animals were injected intradermally with a 0.1 ml volume containing 250 μg of PHA diluted in phosphate buffered saline. The skinfold thickness was measured immediately prior to injection and 72 h after administration, always by the same person and with three repeats per measurement. Single effects of sex and time on skin test responsiveness were significant (p < 0.001) as well as their interaction (p < 0.001). In winter (January), and considering the average of two years, the skinfold increase in response to the intradermal injection of 250 μg PHA was 2.1 times larger in stags and 1.4 times in hinds than in summer (August). While stags had 1.3 times larger responses than hinds in winter, the inverse occurred in summer, with 1.1 times larger responses in hinds. We also evidenced a limited inter-annual variation of skinfold increase in response to PHA in red deer. These findings have important consequences regarding the interpretation of skin test results in the ante-mortem diagnosis of tuberculosis and paratuberculosis, at least in deer.

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.

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.