Poikilocytosis of Angora goats is associated with erythrocyte density and reticulocytosis

Angora goats in South Africa experience several syndromes that result in notable morbidity and mortality in juveniles and adults, but not kids. Insight into their causes is hampered by the lack of normal reference values for this breed, and the present study therefore aimed to characterise (1) differences in the haematology of healthy kids at birth and weaning, and (2) the haematology of apparently healthy yearlings. Selected variables were measured by blood smear analysis, and complete blood counts were performed using an ADVIA 2120i. Variables at 1, 11, and 20 weeks of age were compared using the Friedman test and associations between variables of yearlings were determined by correlation analysis. In kids, red blood cell count, mean corpuscular haemoglobin concentration (MCHC), and poikilocytosis increased over time, while mean corpuscular haemoglobin (MCH) and mean corpuscular volume (MCV) decreased. Yearlings displayed a lower MCHC, and higher haemoglobin distribution width than previously reported for goats, and these were positively correlated with poikilocytosis, as were reticulocyte counts. White cell counts of yearlings exceeded normal values previously reported for goats, with some individuals displaying remarkably high mature neutrophil counts. Changes in haemoglobin variant expression or cation and water fluxes are possible explanations for the findings in kids, while in yearlings, the associations between MCHC, HDW, poikilocytosis, and reticulocytosis suggest alterations in red cell hydration in adulthood that are associated with increased red cell turnover. These findings may prove informative in the further investigation of various clinical syndromes in this population.

Comparison of interferon gamma release assay and CXCL9 gene expression assay for the detection of Mycobacterium bovis infection in African lions (Panthera leo)

Mycobacterium bovis (M. bovis) infection has been identified in both domestic and wild animals and may threaten the conservation of vulnerable species including African lions (Panthera leo). There is a need to develop accurate ante-mortem tools for detection of M. bovis infection in African big cat populations for wildlife management and disease surveillance. The aim of this study was to compare the performances of two immunological assays, the QuantiFERON®-TB Gold Plus (QFT) Mabtech Cat interferon gamma release assay (IGRA) and QFT CXCL9 gene expression assay (GEA), which have both shown diagnostic potential for M. bovis detection in African lions. Lion whole blood (n=47), stimulated using the QFT platform, was used for measuring antigen-specific CXCL9 expression and IFN-γ production and to assign M. bovis infection status. A subset (n=12) of mycobacterial culture-confirmed M. bovis infected and uninfected African lions was used to compare the agreement between the immunological diagnostic assays. There was no statistical difference between the proportions of test positive African lions tested by the QFT Mabtech Cat IGRA compared to the QFT CXCL9 GEA. There was also a moderate association between immunological diagnostic assays when numerical results were compared. The majority of lions had the same diagnostic outcome using the paired assays. Although the QFT Mabtech Cat IGRA provides a more standardized, commercially available, and cost-effective test compared to QFT CXCL9 GEA, using both assays to categorize M. bovis infection status in lions will increase confidence in results.

Combining Analytical Approaches and Multiple Sources of Information to Improve Interpretation of Diagnostic Test Results for Tuberculosis in Wild Meerkats

Diagnostic tests are used to classify individual animals' infection statuses. However, validating test performance in wild animals without gold standard tests is extremely challenging, and the issue is further complicated in chronic conditions where measured immune parameters vary over time. Here, we demonstrate the value of combining evidence from different diagnostic approaches to aid interpretation in the absence of gold standards, large sample sizes, and controlled environments. Over a two-year period, we sampled 268 free-living meerkats (Suricata suricatta) longitudinally for Mycobacterium suricattae (a causative agent of tuberculosis), using three ante-mortem diagnostic tests based on mycobacterial culture, and antigen-specific humoral and cell-mediated immune responses, interpreting results both independently and in combination. Post-mortem cultures confirmed M. suricattae infection in 22 animals, which had prior ante-mortem information, 59% (13/22) of which were test-positive on a parallel test interpretation (PTI) of the three ante-mortem diagnostic assays (95% confidence interval: 37-79%). A similar ability to detect infection, 65.7% (95% credible interval: 42.7-84.7%), was estimated using a Bayesian approach to examine PTI. Strong evidence was found for a near doubling of the hazard of death (Hazard Ratio 1.75, CI: 1.14-2.67, p = 0.01), associated with a positive PTI result, thus demonstrating that these test results are related to disease outcomes. For individual tests, small sample sizes led to wide confidence intervals, but replication of conclusions, using different methods, increased our confidence in these results. This study demonstrates that combining multiple methodologies to evaluate diagnostic tests in free-ranging wildlife populations can be a useful approach for exploiting such valuable datasets.

Shedding of Mycobacterium bovis in respiratory secretions of free-ranging wild dogs (Lycaon pictus): Implications for intraspecies transmission

It has recently been discovered that Mycobacterium bovis (M. bovis) causes disease in the endangered African wild dog (Lycaon pictus) in areas endemic for bovine tuberculosis (bTB), including the Kruger National Park (KNP). However, information on M. bovis infection dynamics within this species is limited and requires investigation as M. bovis can cause conservation consequences due to movement restrictions, crucial for genetic management. This study had two aims: firstly, to investigate mycobacterial shedding in free-ranging wild dogs from KNP by culturing oropharyngeal swab (OS) and bronchoalveolar lavage (BAL) samples. Secondly, to determine the relationship between ante-mortem culture and interferon gamma release assay (IGRA) results as well as agreement between OS culture and BAL culture results. Mycobacterial culture revealed that 6 of 173 (3.5%) OS samples and 1 of 32 (3.1%) BAL samples (from 7 different wild dogs) were M. bovis culture positive, suggesting that wild dogs can shed M. bovis through respiratory secretions. However, the possibility of contamination by ingestion of infected prey cannot be excluded in wild dogs with positive OS culture results. Furthermore, the test outcomes between IGRA and culture (OS and BAL) differed substantially. Samples from 172 wild dogs were available for IGRA screening and 134 had positive results (detectable M. bovis immune sensitization). Seven wild dogs had culture-positive results, which included one additional wild dog that did not have an IGRA result (total 173 wild dogs). Out of these 7 M. bovis culture-positive wild dogs, 3 were IGRA positive initially, however, after repeat sampling and testing, 5 out of 7 were IGRA positive. These findings suggest that intraspecies transmission of M. bovis may be possible among wild dogs. Although the risk of intraspecies transmission is currently unknown, this knowledge is important for assessing the risk of M. bovis transmission from infected wild dogs to uninfected populations during translocations.

Development of a cytokine gene expression assay for the relative quantification of the African elephant (Loxodonta africana) cell-mediated immune responses

Immunological assays are the basis for many diagnostic tests for infectious diseases in animals and humans. Application in wildlife species, including the African elephant (Loxodonta africana), is limited however due to lack of information on immune responses. Since many immunoassays require both identified biomarkers of immune activation as well as species-specific reagents, it is crucial to have knowledge of basic immunological responses in the species of interest. Cytokine gene expression assays (GEAs) used to measure specific immune responses in wildlife have frequently shown that targeted biomarkers are often species-specific. Therefore, the aim of this study was to identify elephant-specific cytokine biomarkers to detect immune activation and to develop a GEA, using pokeweed mitogen stimulated whole blood from African elephants. This assay will provide the foundation for the development of future cytokine GEAs that can be used to detect antigen specific immune responses and potentially lead to various diagnostic tests for this species.

Review of Diagnostic Tests for Detection of Mycobacterium bovis Infection in South African Wildlife

Wildlife tuberculosis is a major economic and conservation concern globally. Bovine tuberculosis (bTB), caused by Mycobacterium bovis (M. bovis), is the most common form of wildlife tuberculosis. In South Africa, to date, M. bovis infection has been detected in 24 mammalian wildlife species. The identification of M. bovis infection in wildlife species is essential to limit the spread and to control the disease in these populations, sympatric wildlife species and neighboring livestock. The detection of M. bovis-infected individuals is challenging as only severely diseased animals show clinical disease manifestations and diagnostic tools to identify infection are limited. The emergence of novel reagents and technologies to identify M. bovis infection in wildlife species are instrumental in improving the diagnosis and control of bTB. This review provides an update on the diagnostic tools to detect M. bovis infection in South African wildlife but may be a useful guide for other wildlife species.

Optimisation of the tuberculin skin test for detection of Mycobacterium bovis in African buffaloes (Syncerus caffer)

Effective screening methods are critical for preventing the spread of bovine tuberculosis (bTB) among livestock and wildlife species. The tuberculin skin test (TST) remains the primary test for bTB globally, although performance is suboptimal. African buffaloes (Syncerus caffer) are a maintenance host of Mycobacterium bovis in South Africa, tested using the single intradermal tuberculin test (SITT) or comparative test (SICTT). The interpretation of these tests has been based on cattle thresholds due to the lack of species-specific cut-off values for African buffaloes. Therefore, the aims of this study were to calculate buffalo-specific thresholds for different TST criteria (SITT, SICTT, and SICTT_72h that calculates the differential change at 72 h only) and compare performance using these cut-off values. The results confirm that 3 mm best discriminates M. bovis-infected from unexposed control buffaloes with sensitivities of 69 % (95 % CI 60-78; SITT and SICTT) and 76 % (95 % CI 65-83; SICTT_72h), and specificities of 86 % (95 % CI 80-90; SITT), 96 % (95 % CI 92-98; SICTT_72h) and 97 % (95 % CI 93-99; SICTT), respectively. A comparison between TST criteria using buffalo-specific thresholds demonstrates that the comparative TST performs better than the SITT, although sensitivity remains suboptimal. Therefore, further research and the addition of ancillary tests, such as cytokine release assays, are necessary to improve M. bovis detection in African buffaloes.

The Xpert MTB/RIF Ultra assay detects Mycobacterium tuberculosis complex DNA in white rhinoceros (Ceratotherium simum) and African elephants (Loxodonta africana)

The study describes the novel use of the Xpert MTB/RIF Ultra assay for detection of Mycobacterium tuberculosis complex (MTBC) DNA in samples from white rhinoceros (Ceratotherium simum) and African elephants (Loxodonta africana). Culture negative respiratory sample matrices were spiked to determine if the Ultra could detect MTBC DNA in rhinoceros and elephant samples. Rhinoceros bronchial alveolar lavage fluid (BALF) was found to have an inhibitory effect on the Ultra. In this study, the limit of detection (LOD) of M. tuberculosis H37Rv in all spiked animal samples were 2 CFU/ml compared to 15.6 CFU/ml for humans, while the LOD for M. bovis SB0121 was 30 CFU/ml compared to 143.4 CFU/ml for M. bovis BCG in humans. Screening was performed on stored tissue and respiratory samples from known MTBC-infected animals and MTBC DNA was detected in 92% of samples collected from six rhinoceros and two elephants. Conversely, 83% of culture-negative tissue and respiratory samples from uninfected animals tested negative on the Ultra. In conclusion, the Ultra assay appears to be a sensitive and rapid diagnostic test for the detection of MTBC DNA from tissue and respiratory samples collected from African elephants and rhinoceros. Furthermore, the Ultra assay could provide a new tool for the detection of MTBC in various sample types from other wildlife species.

The VetMAX™ M. tuberculosis complex PCR kit detects MTBC DNA in antemortem and postmortem samples from white rhinoceros (Ceratotherium simum), African elephants (Loxodonta africana) and African buffaloes (Syncerus caffer)

BACKGROUND

Bovine tuberculosis and tuberculosis are chronic infectious diseases caused by the Mycobacterium tuberculosis complex members, Mycobacterium bovis and Mycobacterium tuberculosis, respectively. Infection with M. bovis and M. tuberculosis have significant implications for wildlife species management, public health, veterinary disease control, and conservation endeavours.

RESULTS

Here we describe the first use of the VetMAX™ Mycobacterium tuberculosis complex (MTBC) DNA quantitative real-time polymerase chain reaction (qPCR) detection kit for African wildlife samples. DNA was extracted from tissues harvested from 48 African buffaloes and MTBC DNA was detected (test-positive) in all 26 M. bovis culture-confirmed animals with an additional 12 PCR-positive results in culture-negative buffaloes (originating from an exposed population). Of six MTBC-infected African rhinoceros tested, MTBC DNA was detected in antemortem and postmortem samples from five animals. The PCR was also able to detect MTBC DNA in samples from two African elephants confirmed to have M. bovis and M. tuberculosis infections (one each). Culture-confirmed uninfected rhinoceros and elephants' samples tested negative in the PCR assay.

CONCLUSIONS

These results suggest this new detection kit is a sensitive screening test for the detection of MTBC-infected African buffaloes, African elephants and white rhinoceros.

Test Characteristics of Assays to Detect Mycobacterium bovis Infection in High-Prevalence African Buffalo (Syncerus caffer) Herds

A herd of African buffaloes (Syncerus caffer) was tested for Mycobacterium bovis infection using three cytokine release assays. All animals were subsequently euthanized and mycobacterial culture determined the infection prevalence (52%) and diagnostic characteristics. Sensitivities were lower than previously reported and results provide new insight into the practical utility of these assays.

Parallel measurement of IFN-γ and IP-10 in QuantiFERON®-TB Gold (QFT) plasma improves the detection of Mycobacterium bovis infection in African buffaloes (Syncerus caffer)

The QuantiFERON®-TB Gold (QFT) stimulation platform for cytokine release is a novel approach for diagnosis of bovine tuberculosis in wildlife species. Plasma interferon gamma (IFN-γ) is routinely measured to detect immune sensitization to Mycobacterium bovis. However, the cytokine interferon gamma-inducible protein 10 (IP-10) has been proposed as an alternative, more sensitive, diagnostic biomarker. In this study, we investigated the use of the QFT system with measurement of IFN-γ and IP-10 in parallel to identify M. bovis-infected African buffaloes. The test results of either biomarker in a cohort of M. bovis-unexposed buffaloes (n = 70) led to calculation of 100% test specificity. Furthermore, in cohorts of M. bovis culture-positive (n = 51) and M. bovis-suspect (n = 22) buffaloes, the IP-10 test results were positive in a greater number of animals than the number based on the IFN-γ test results. Most notably, when the biomarkers were measured in parallel, the tests identified all M. bovis culture-positive buffaloes, a result neither the single comparative intradermal tuberculin test (SCITT) nor Bovigam® IFN-γ release assay (IGRA) achieved, individually or in parallel. These findings demonstrate the diagnostic potential of this blood-based assay to identify M. bovis-infected African buffaloes and a strategy to maximise the detection of infected animals while maintaining diagnostic specificity and simplifying test procedures.

A commercial ELISA for detection of interferon gamma in white rhinoceros

Bovine tuberculosis (bTB), caused by Mycobacterium bovis, is endemic in Kruger National Park, South Africa, home to the largest population of white rhinoceros (Ceratotherium simum) in the world. In 2016, the first cases of naturally occurring bTB were reported in white rhinoceros; however, there is a lack of understanding of infection and disease process in this species. Prevention and control of transmission depends on the availability of accurate tools to detect M. bovis infection. Interferon gamma (IFN-γ) assays are a reliable detection method for TB in other animal species, and studies have indicated that these tests can be used in white rhinoceros. We sought to screen and optimize a commercial IFN-γ enzyme-linked immunosorbent assay (ELISA) to detect endogenous white rhinoceros IFN-γ in mitogen-stimulated whole blood as a basis for developing a test for M. bovis infection. Optimizations included identifying ELISA antibodies and determining the effect of sample matrix, ELISA plate incubation temperature, ELISA linearity, assay reproducibility, and the assay's limit of quantification. The optimized assay employed an equine IFN-γ antibody pair that was used to create a commercial ELISA kit. This ELISA had a linear response to recombinant equine and endogenous rhinoceros IFN-γ (range: 7.8-125 pg/mL). When incubated at 37°C, the ELISA was highly reproducible, with an optimal recovery and a low limit of quantification, indicating that the Mabtech equine IFN-γ ELISA^PRO kit is a robust assay for measuring white rhinoceros IFN-γ.

Fatal Tuberculosis in a Free-Ranging African Elephant and One Health Implications of Human Pathogens in Wildlife

Tuberculosis (TB) in humans is a global public health concern and the discovery of animal cases of Mycobacterium tuberculosis (Mtb) infection and disease, especially in multi-host settings, also has significant implications for public health, veterinary disease control, and conservation endeavors. This paper describes a fatal case of Mtb disease in a free-ranging African elephant (Loxodonta africana) in a high human TB burden region. Necropsy revealed extensive granulomatous pneumonia, from which Mtb was isolated and identified as a member of LAM3/F11 lineage; a common lineage found in humans in South Africa. These findings are contextualized within a framework of emerging Mtb disease in wildlife globally and highlights the importance of the One Health paradigm in addressing this anthroponotic threat to wildlife and the zoonotic implications.

Measuring antigen-specific responses in Mycobacterium bovis-infected warthogs (Phacochoerus africanus) using the intradermal tuberculin test

BACKGROUND

Bovine tuberculosis (bTB) caused by Mycobacterium bovis has previously been diagnosed in warthogs and infection can be highly prevalent (> 30%) in endemic areas. Thus, warthogs could potentially be an important species to consider as sentinels for disease surveillance. However, disease surveillance is dependent on availability of accurate diagnostic assays and only a few diagnostic tests have been investigated for warthogs. Furthermore, the tests that have been used in this species require laboratory equipment and trained personnel to obtain results. Therefore, this study investigated the use of the intradermal tuberculin test (ITT) to screen warthogs for bTB, which can be done with minimal equipment and under field conditions by most veterinarians and other qualified professionals. Changes in skin fold thickness measurements at the bovine purified protein derivative (PPD) administration site, between 0 and 72 h, were compared with differential changes between the bovine and avian PPD sites, for 34 warthogs, to evaluate the performance when different interpretation criteria for the ITT was used.

RESULTS

Using an increase of 1.8 mm or more at the bovine PPD site as a cut-off for positive responders, 69% of 16 M. bovis culture-positive warthogs had a positive test result, with 100% of the 18 culture-negative warthogs considered as test negative. When a differential of 1.2 mm or more in skin fold thickness at the bovine PPD compared to the avian PPD site was used as a cut-off for the comparative ITT, 81% of culture-positive warthogs were considered as test positive, with 100% of culture-negative warthogs considered as test negative.

CONCLUSION

The findings in this study suggest that the ITT is a promising tool to use when screening warthogs for M. bovis infection.

IP-10: A potential biomarker for detection of Mycobacterium bovis infection in warthogs (Phacochoerus africanus)

Bovine tuberculosis (bTB) is endemic in several areas of South Africa and has been reported in multiple species, including common warthogs (Phacochoerus africanus). Limited diagnostic tests and disease control programs exist for African wildlife. Thus, there is a need to develop techniques for bTB detection in species such as warthogs to assess their role in disease maintenance and spread in multi-host ecosystems. In this study, we obtained blood samples from warthogs in bTB endemic areas to investigate biomarkers for detection of Mycobacterium bovis infection. Warthog whole blood was incubated in QuantiFERON^® TB Gold In-Tube tubes and pathogen specific release of interferon gamma (IFN-γ) and interferon gamma induced protein 10 (IP-10) was measured by a sandwich enzyme-linked immunosorbent assay. Although we were unable to measure IFN-γ, we could successfully measure IP-10. The IP-10 assay was able to distinguish between M. bovis-infected and M. bovis-culture negative warthogs, within bTB endemic areas, with an assay specific sensitivity of 68% and specificity of 84%. Of the 88 M. bovis-exposed warthogs screened, 42% were IP-10 test positive. These results indicate warthogs develop a measurable cell-mediated immune response after antigen stimulation of whole blood, which can distinguish between M. bovis-infected and M. bovis-culture negative animals. Thus, the IP-10 assay shows promise as an ante-mortem test to diagnose bTB in warthogs.

Antigen-specific interferon-gamma release is decreased following the single intradermal comparative cervical skin test in African buffaloes (Syncerus caffer)

Effective disease management of wildlife relies on the strategic application of ante-mortem diagnostic tests for early identification and removal of M. bovis-infected animals. To improve diagnostic performance, interferon-gamma release assays (IGRAs) are often used in conjunction with the tuberculin skin test (TST). Since buffaloes are major maintenance hosts of M. bovis, optimal application of bovine TB diagnostic tests are especially important. We aimed to determine whether the timing of blood collection relative to the TST has an influence on IFN-γ production and diagnostic outcome in African buffaloes. Release of IFN-γ in response to bovine purified protein derivative (PPD), avian PPD and PC-HP^® and PC-EC^® peptides was measured by Bovigam^® and an in-house IGRA in a group of Bovigam^®-positive and - negative buffaloes at the time the TST was performed and three days later. There was significantly lower IFN-γ release in response to these antigens post-TST in Bovigam^®-positive buffaloes, but no significant changes in Bovigam^®-negative buffaloes. Also, a significantly greater proportion of buffaloes were Bovigam^®-positive prior to the TST than three days later. We therefore recommend that blood samples for use in IGRAs be collected prior to or at the time the TST is performed to facilitate the correct identification of greater numbers of IGRA-positive buffaloes.

Seroprevalence of Mycobacterium bovis infection in warthogs (Phacochoerus africanus) in bovine tuberculosis-endemic regions of South Africa

Bovine tuberculosis (bTB), caused by Mycobacterium bovis (M. bovis), has been reported in many species including suids. Wild boar are important maintenance hosts of the infection with other suids, that is domestic and feral pigs, being important spillover hosts in the Eurasian ecosystem and in South Africa, warthogs (Phacochoerus africanus) may play a similar role in M. bovis-endemic areas. However, novel diagnostic tests for warthogs are required to investigate the epidemiology of bTB in this species. Recent studies have demonstrated that serological assays are capable of discriminating between M. bovis-infected and uninfected warthogs (Roos et al., ). In this study, an indirect ELISA utilizing M. bovis purified protein derivative (PPD) as a test antigen was used to measure the prevalence and investigate risk factors associated with infection in warthogs from uMhkuze Nature Reserve and the southern region of the Greater Kruger National Park (GKNP). There was a high overall seroprevalence of 38%, with adult warthogs having a higher risk of infection (46%). Seroprevalence also varied by geographic location with warthogs from Marloth Park in the GKNP having the greatest percentage of positive animals (63%). This study indicates that warthogs in M. bovis-endemic areas are at high risk of becoming infected with mycobacteria. Warthogs might present an under-recognized disease threat in multi-species systems. They might also serve as convenient sentinels for M. bovis in endemic areas. These findings highlight the importance of epidemiological studies in wildlife to understand the role each species plays in disease ecology.

The Kinetics of the Humoral and Interferon-Gamma Immune Responses to Experimental Mycobacterium bovis Infection in the White Rhinoceros (Ceratotherium simum)

Mycobacterium bovis is the cause of tuberculosis (TB) in a wide range of species, including white rhinoceroses (Ceratotherium simum). Control of the disease relies on the indirect detection of infection by measuring pathogen-specific responses of the host. These are poorly described in the white rhinoceros and this study aimed to characterize the kinetics of immune responses to M. bovis infection in this species. Three white rhinoceroses were infected with M. bovis and their immune sensitization to this pathogen was measured monthly for 20 months. Cell-mediated immunity was characterized in whole blood samples as the differential release of interferon-gamma in response to bovine purified protein derivative (PPDb) and avian PPD (PPDa) as well as the release of this cytokine in response to the M. bovis proteins 6 kDa early secretory antigenic target (ESAT-6)/10 kDa culture filtrate protein (CFP-10). Humoral immunity was quantified as the occurrence or the magnitude of antibody responses to the proteins ESAT-6/CFP-10, MPB83, MPB83/MPB70, and PPDb. The magnitude and duration of immune reactivity varied between individuals; however, peak responses to these antigens were detected in all animals circa 5-9 months postinfection. Hereafter, they gradually declined to low or undetectable levels. This pattern was associated with limited TB-like pathology at postmortem examination and appeared to reflect the control of M. bovis infection following the development of the adaptive immune response. Measurement of these markers could prove useful for assessing the disease status or treatment of naturally infected animals. Moreover, immune responses identified in this study might be used to detect infection; however, further studies are required to confirm their diagnostic utility.

Antigen-Specific IP-10 Release Is a Sensitive Biomarker of Mycobacterium bovis Infection in Cattle

The most widely used ante-mortem diagnostic tests for tuberculosis in cattle are the tuberculin skin test and the interferon-gamma (IFN-γ) release assay, both of which measure cell-mediated immune responses to Mycobacterium bovis infection. However, limitations in the performance of these tests results in a failure to identify all infected animals. In attempting to increase the range of diagnostic tests for tuberculosis, measurement of the cytokine IP-10 in antigen-stimulated blood has previously been shown to improve the detection of M. tuberculosis and M. bovis infection, in humans and African buffaloes (Syncerus caffer), respectively. In the present study, 60 cattle were identified by the single intradermal comparative tuberculin test as tuberculosis reactors (n = 24) or non-reactors (n = 36) and the release of IFN-γ and IP-10 in antigen-stimulated whole blood from these animals was measured using bovine specific ELISAs. There was a strong correlation between IP-10 and IFN-γ production in these samples. Moreover, measurement of the differential release of IP-10 in response to stimulation with M. bovis purified protein derivative (PPD) and M. avium PPD distinguished between reactor and non-reactor cattle with a sensitivity of 100% (95% CI, 86%–100%) and a specificity of 97% (95% CI, 85%–100%). These results suggest that IP-10 might prove valuable as a diagnostic biomarker of M. bovis infection in cattle.

The stability of plasma IP-10 enhances its utility for the diagnosis of Mycobacterium bovis infection in African buffaloes (Syncerus caffer)

The measurement of interferon gamma-induced protein 10 (IP-10) in antigen-stimulated whole blood is a sensitive biomarker of Mycobacterium bovis infection in African buffaloes (Syncerus caffer). However, this species often occurs in remote locations and diagnostic samples must be transported to centralised laboratories for processing. In humans, plasma IP-10 is highly stable and this feature contributes to its diagnostic utility; for this reason we aimed to characterize the stability of this molecule in buffaloes. Blood from M. bovis-infected and -uninfected animals was incubated with pathogen-specific peptides, saline and phytohaemagglutinin, respectively. Plasma fractions were harvested and aliquots of selected samples were: (i) stored at different temperatures for various times; (ii) heat treated before storage at RT, and (iii) stored on Protein Saver Cards (PSCs) at RT for either 2 or 8 weeks before measurement of IP-10. Incubation of plasma at 65°C for 20 min caused no loss of IP-10 and this protein could be quantified in plasma stored on PSCs for 2 and 8 weeks. Moreover, for all storage conditions, IP-10 retained its excellent diagnostic characteristics. These features of IP-10 might allow for the heat inactivation of potentially infectious plasma which would facilitate the safe and simple transport of samples.

The evaluation of candidate biomarkers of cell-mediated immunity for the diagnosis of Mycobacterium bovis infection in African buffaloes (Syncerus caffer)

We evaluated commercially available bovine enzyme linked immunosorbent assays (ELISA) and a human IP-10 ELISA to measure IP-10, MIG, MCP-1, MCP-2, MCP-3 and IL1-RA in buffalo plasma in order to identify sensitive markers of the immune response to Mycobacterium bovis-specific peptides. Additionally, we found that all coding mRNA sequences of these cytokines showed very high homology with their homologues in domestic cattle (97-99%) as did the derived amino acid sequences (97-99%). This high sequence homology between cattle and buffaloes supports the use of bovine ELISAs for the detection these cytokines in buffaloes. MCP-1 concentration showed a positive correlation with that of IFN-γ (p=0.0077) and appears to occur in far greater abundance in buffaloes when compared to humans. Using a bovine IP-10 ELISA, levels of this cytokine were found to be significantly increased in antigen-stimulated blood samples from M. bovis test positive buffaloes (p<0.0001) and IP-10 was detected in far greater abundance than IFN-γ. Measurement of IP-10 with this ELISA may prove to be a sensitive marker of M. bovis infection in African buffaloes.

Novel cause of tuberculosis in meerkats, South Africa

The organism that causes tuberculosis in meerkats (Suricata suricatta) has been poorly characterized. Our genetic analysis showed it to be a novel member of the Mycobacterium tuberculosis complex and closely related to the dassie bacillus. We have named this epidemiologically and genetically unique strain M. suricattae.

Agreement between assays of cell-mediated immunity utilizing Mycobacterium bovis-specific antigens for the diagnosis of tuberculosis in African buffaloes (Syncerus caffer)

We assessed the use of Mycobacterium bovis-specific peptides for the diagnosis of tuberculosis in African buffaloes (Syncerus caffer) by evaluating the agreement between the single intradermal comparative tuberculin test (SICTT), the Bovigam(®) EC (BEC) assay, the Bovigam(®) HP (BHP) assay and two assays utilizing the QuantiFERON(®) TB-Gold (in tube) system employing 20 h (mQFT20 assay) and 30 h (mQFT30 assay) whole blood incubation periods. Of 84 buffaloes, 45% were SICTT-positive, 48% were BEC-positive, 50% were BHP-positive, 37% were mQFT20-positive and 43% were mQFT30-positive. Agreement between the BEC and BHP Bovigam(®) assays was high (κ=0.86, 95% CI 0.75-0.97) and these detected the most test-positive animals suggesting that they were the most sensitive assays. Interferon-gamma release was significantly greater in buffaloes that were test-positive for all tests than in animals with discordant but positive Bovigam(®) results. Agreement between the mQFT assays was equally high (κ=0.88, 95% CI 0.77-0.98); however, all buffaloes with discordant mQFT results (n=6) were mQFT30-positive/mQFT20-negative, including three confirmed M. bovis-infected animals, suggesting that the mQFT30 assay is the more sensitive of the two. Agreements between the two Bovigam(®) and two mQFT assays were moderate, suggesting that in its current format the mQFT assay is less sensitive than either the BEC or the BHP assays.

Zoonotic Mycobacterium bovis-induced tuberculosis in humans

We aimed to estimate the global occurrence of zoonotic tuberculosis (TB) caused by Mycobacterium bovis or M. caprae infections in humans by performing a multilingual, systematic review and analysis of relevant scientific literature of the last 2 decades. Although information from many parts of the world was not available, data from 61 countries suggested a low global disease incidence. In regions outside Africa included in this study, overall median proportions of zoonotic TB of ≤1.4% in connection with overall TB incidence rates ≤71/100,000 population/year suggested low incidence rates. For countries of Africa included in the study, we multiplied the observed median proportion of zoonotic TB cases of 2.8% with the continental average overall TB incidence rate of 264/100,000 population/year, which resulted in a crude estimate of 7 zoonotic TB cases/100,000 population/year. These generally low incidence rates notwithstanding, available data indicated substantial consequences of this disease for some population groups and settings.

Development of a diagnostic gene expression assay for tuberculosis and its use under field conditions in African buffaloes (Syncerus caffer)

The development of diagnostic tests for tuberculosis (TB) in exotic species is constrained by host biology and the limited availability of suitable assay reagents. As such, we evaluated a gene expression assay (GEA) which is easily modified for novel species and allows for initial sample processing under field conditions. African buffaloes (Syncerus caffer) were categorized using the single comparative intradermal tuberculin test, and blood from test-positive and test-negative animals was incubated for 20 h in "Nil" tubes (containing saline) and "TB Antigen" tubes (containing Mycobacterium tuberculosis complex (MTC)-specific antigens) of a commercial human TB test, the QuantiFERON(®)-TB Gold (In-Tube) (QFT) assay. Blood samples were then stabilized in RNAlater(®) and transported to the laboratory for RNA extraction. A Custom TaqMan GEA was used to calculate the relative abundance of interferon-gamma (IFN-γ) mRNA in the TB Antigen tube compared to that in the Nil tube as a marker of immune activation in response to MTC antigen recognition. The GEA results from the two buffalo groups were compared and a cutoff value of 2.85 was calculated to differentiate between animals from these groups with a sensitivity of 80% (95% C.I.: 56-94%) and a specificity of 95% (95% C.I.: 75-100%). Further optimization of this assay could provide a highly useful tool for the diagnosis of MTC infection in exotic species.

Modification of the QuantiFERON-TB Gold (In-Tube) assay for the diagnosis of Mycobacterium bovis infection in African buffaloes (Syncerus caffer)

African buffaloes (Syncerus caffer) are the most significant wildlife maintenance hosts of Mycobacterium bovis, the causative organism of bovine tuberculosis (BTB). Current diagnostic tests for the detection of M. bovis infection in free-ranging buffaloes have numerous limitations and we wished to evaluate a modification to a human TB assay, the QuantiFERON-TB Gold (In-Tube) assay (QFT), as a practical diagnostic test for BTB in buffaloes. One hundred and seventy-five buffaloes were tested using the single intradermal comparative tuberculin test (SICTT) and a modified QFT (mQFT). An appropriate cut-off point for the mQFT was derived from SICTT results using receiver operator characteristic curve analysis. Twenty-six SICTT-positive buffaloes were killed and subjected to necropsy, and selected tissues were processed for mycobacterial culture and speciation. An optimal cut-off point for the mQFT was calculated as 66pg/ml. The assay correctly detected 39/40 SICTT-positive buffaloes and 129/134 TST-negative buffaloes and M. bovis was cultured from 21/26 slaughtered SICTT/mQFT-positive animals. The mQFT shows promise as a practical test for M. bovis infection in buffaloes and shows a sensitivity and specificity at least similar to that of the TST.

Detection of Mycobacterium tuberculosis infection in dogs in a high-risk setting

Dogs infected with Mycobacterium tuberculosis can develop clinical tuberculosis (TB) but there are currently no validated immunological assays for diagnosing this infection in this species. Using a post mortem survey we investigated the prevalence of non-clinical M. tuberculosis infection and clinical TB disease in a high-risk population of dogs and developed and utilised a novel interferon-gamma release assay to determine the risk of transmission of M. tuberculosis from TB patients to contact dogs. The prevalence of clinical TB in dogs from a high-risk setting was 1% (95% CI: 0-5%) while the prevalence of immunological sensitization to M. tuberculosis antigens in dogs living in contact with sputum smear-positive TB patients was 50%. The IGRA proved a useful test of M. tuberculosis infection in dogs and the high levels of transmission of this pathogen from humans to companion dogs should be considered when assessing the zoonotic risks associated with such animals.

'Emerging' mycobacteria in South Africa

Disease can be caused by various species of the genus Mycobacterium. A number of reports, both published and unpublished, of rarely reported mycobacteria have surfaced in South Africa in the last few years. Some unusual hosts have also been involved, causing concern in some quarters.These include reports on Mycobacterium goodii in a spotted hyaena (Crocuta crocuta), M. xenopi in a ruffed lemur (Varecia variegata), M. intracellulare in wild-caught chacma baboons (Papio ursinus), the 'dassie bacillus' in free ranging rock hyrax (dassies; Procavia capensis) the 'oryx bacillus' from free-ranging buffalo (Syncerus caffer) and M. tuberculosis in suricates (Suricata suricatta), a domestic dog and in baboons. In this article it has been attempted to put these in context and show how improved surveillance and technologies have allowed mycobacteria to be identified to species level more easily. Most of the unusual mycobacterial species have most likely been present in the region for many years and have probably caused disease episodes before, but have been misdiagnosed. Each case must be evaluated carefully with respect to the animal species involved, the environment in which the host is found and the mycobacterial species, and operational decisions made accordingly.

Detection of Mycobacterium tuberculosis infection in chacma baboons (Papio ursinus) using the QuantiFERON-TB gold (in-tube) assay

BACKGROUND

Early diagnosis of simian tuberculosis (TB) is vital to prevent transmission of this disease. We evaluated the ability of the QuantiFERON-TB Gold (In-Tube Method) assay (QFG-IT) to detect TB in chacma baboons (Papio ursinus).

METHODS

Fifty-one baboons were tested using the Tuberculin Skin Test (TST) and the QFG-IT. Baboons testing positive, and animals exposed to infected individuals, were euthanised and subjected to necropsy. Selected tissues were processed for histopathology, mycobacterial culture and genetic speciation.

RESULTS

Tuberculosis was confirmed in one TST positive/QFG-IT positive animal and one TST negative/QFG-IT positive animal. One TST positive/QFG-IT negative animal and five TST negative/QFG-IT negative animals were confirmed uninfected following necropsy.

CONCLUSION

The QFG-IT correctly detected TB in two baboons, including one TST negative individual and correctly identified six baboons as uninfected, including one TST positive individual. The QFG-IT shows promise as a sensitive, specific test for TB in chacma baboons.

Erythrocyte Morphology and Haemoglobin Types of Neonatal Roan Antelopes (Hippotragus equinus) with Hypochromic Poikilocytic Anaemia

Neonatal, poikilocytic anaemia in some members of the Hippotragini has previously been documented but not fully investigated. This study was undertaken to describe the erythrocyte morphology of roan antelopes (Hippotragus equinus) during the first 4 weeks after birth and to identify aspects of haemoglobin (Hb) production that might be implicated in this syndrome. Twenty-nine roan antelope calves were sampled on, or close to, 1, 7, 14 and 28 days after birth. Erythrocyte morphology was characterized, and microhaematocrit values and Hb parameters determined, for each sampling occasion. Findings indicated a significant change in erythrocyte morphology during the neonatal period and two haemoglobin types, fetal and adult, were identified. The perinatal onset of adult Hb synthesis was delayed relative to the termination of fetal Hb production, resulting in the observed anaemia. Haemoglobin concentration and erythrocyte morphology were significantly correlated. These findings suggest an intimate relationship between Hb synthesis and the observed poikilocytosis. An imbalance in the synthesis of the alpha- and beta-globin chains of Hb (a thalassaemia) may prove to be the underlying pathophysiology of this syndrome.