Comparative study of IFNγ and antibody tests for feline tuberculosis

Development of an enzyme-linked immunosorbent assay for the diagnosis of feline tuberculosis

Cases of feline tuberculosis (TB) can be challenging to diagnose. Currently, this is achieved through a combination of mycobacterial culture, polymerase chain reaction (PCR), or interferon-gamma release assay (IGRA); however, these each have limitations. There is limited data regarding the use of humoral immunodiagnostics for TB in cats. Therefore, we sought to develop an enzyme-linked immunosorbent assay (ELISA) to further facilitate the diagnosis of feline TB. A comparative PPD (purified protein derivative) antibody ELISA was optimised for use on serum and plasma, and was tested against samples from 14 cats with culture-confirmed TB and 24 uninfected controls. Selection of an appropriate positive cut-off value based on receiver-operator characteristic curve analysis gave test sensitivity of 64.3 % and specificity of 100 %. When tested on further samples from cats with strongly suspected mycobacteriosis, 32.9 % (23/70) were antibody positive. Notably, positive results were recorded in cats that failed to respond to the IGRA, and in one PCR and IGRA negative cat. No positive responses were identified in cats with non-tuberculous mycobacterial infections, or with non-mycobacterial diseases (n = 12). Therefore, antibody-based diagnostics may be useful adjunctive tests for cases of TB missed by the IGRA, helping protect both feline and, in turn, human health.

Ocular mycobacterial lesions in cats

Ocular mycobacterial infections are an under-recognized cause of morbidity in the domestic cat. This study aimed to explore the distribution, histopathological appearance, and severity of feline ocular mycobacterial lesions, and to characterize the immune cell population with immunohistochemistry. Routine histological staining with hematoxylin and eosin, and Masson’s trichrome, was performed to identify ocular lesions and assign an inflammation score based on the number of cells present. Acid-fast bacilli were detected with Ziehl-Neelsen, and immunohistochemistry for ionized calcium-binding adaptor protein-1 (Iba1), calprotectin, cluster of differentiation 3 (CD3), and Pax5 was undertaken on formalin-fixed paraffin-embedded tissue samples from 24 cases of ocular mycobacteriosis. Posterior or panuveitis with concurrent retinitis was identified in 20/24 cases (83%), with retinal detachment in 16/20 (80%) of these cases. Choroidal lesions had the highest median inflammation score. Ziehl-Neelsen-positive organisms were detected in 20/24 cases (83%), with the highest prevalence of acid-fast bacilli detected in choroidal lesions (16/20, 80%). Lesions were typically granulomatous to pyogranulomatous, characterized by abundant numbers of Iba1-positive macrophages, followed by calprotectin-positive granulocytes and monocytes, fewer T cells, and rarer B cells. However, where iritis was identified, inflammation was typically lymphoplasmacytic (11/16 cases, 69%). Where diagnostic testing was performed, tuberculosis (ie, infection with Mycobacterium bovis, Mycobacterium microti, or a nonspeciated Mycobacterium tuberculosis-complex pathogen) was diagnosed in 20/22 cats (91%), with Mycobacterium lepraemurium infection identified in the other 2/22 cats (9%). These results suggest the choroid is the primary site of lesion development in most cases of feline ocular mycobacteriosis, and inflammatory changes are associated with the presence of mycobacteria localized to ocular tissues.

Diagnostic accuracy of the interferon-gamma release assay (IGRA) for cases of feline mycobacteriosis

The aim of this study was to evaluate the sensitivity and specificity of the interferon-gamma release assay (IGRA) for diagnosing infections with members of the Mycobacterium (M.) tuberculosis-complex (MTBC) and non-tuberculous mycobacteria (NTM) in domestic cats, and to generate defined feline-specific cut-off values using receiver operating characteristic (ROC) curve analysis to improve test performance. Records of 594 cats that had been tested by IGRA were explored to identify individuals that had a culture and/or polymerase chain reaction (PCR)-confirmed case of mycobacterial disease, and those that had a final diagnosis of non-mycobacterial disease. A total of 117 cats - 80 with mycobacterial disease and 37 diagnosed with a condition other than mycobacteriosis - were identified for further detailed analysis. This population was used to estimate test sensitivity and specificity, as well as likelihood ratios for the IGRA to correctly identify a cat with or without mycobacterial disease. Agreement between IGRA results and culture/PCR using current and proposed new cut-off values was also determined. ROC analysis of defined confirmed infected and non-mycobacterial disease control cats allowed an adjustment of current test cut-offs that increased the overall test sensitivity for MTBC infections from 83.1 % (95 % confidence interval [CI]: 71.5-90.5 %) to 90.2 % (95 % CI: 80.2-95.4%), and M. bovis infection from 43 % (95 % CI: 28.2-60.7%) to 68 % (95 % CI: 51.4-82.1%) while maintaining high test specificity (100 % in both cases). Overall agreement between IGRA results and culture/PCR, while recognising that neither culture nor PCR tests have perfect sensitivity, improved from weak (κ = 0.57) to moderate (κ = 0.71) using new proposed IGRA test cut-off values. Application of these results, based upon the statistical analysis of accumulated test data, can improve the diagnostic performance of the feline IGRA, particularly for identifying infections with M. bovis, without compromising specificity.

Histological and immunohistochemical features suggesting aetiological differences in lymph node and (muco)cutaneous feline tuberculosis lesions

OBJECTIVES

To identify and describe histological and immunohistochemical criteria that may differentiate between skin and lymph node lesions associated with Mycobacterium (M.) bovis and M. microti in a diagnostic pathology setting.

MATERIALS AND METHODS

Archived skin and lymph node biopsies of tuberculous lesions were stained with haematoxylin and eosin, Ziehl-Neelsen and Masson's Trichrome. Immunohistochemistry was performed to detect the expression of calprotectin, CD3 and Pax5. Samples were scored for histological parameters (i.e. granulomas with central necrosis versus small granulomas without central necrosis, percentage necrosis and/or multinucleated giant cells), number of acid-fast bacilli (bacterial index) and lesion percentage of fibrosis and positive immunohistochemical staining.

RESULTS

Twenty-two samples were examined (M. bovis n=11, M. microti n=11). When controlling for age, gender and tissue, feline M. bovis-associated lesions more often featured large multi-layered granulomas with central necrosis. Conversely, this presentation was infrequent in feline M. microti-associated lesions, where small granulomas without central necrosis predominated. The presence of an outer fibrous capsule was variable in both groups, as was the bacterial index. There were no differences in intralesional expression of immunohistochemical markers.

CLINICAL SIGNIFICANCE

Differences in the histological appearance of skin and lymph node lesions may help to infer feline infection with either M. bovis or M. microti at an earlier stage when investigating these cases, informing clinicians of the potential zoonotic risk. Importantly, cases of tuberculosis can present with numerous acid-fast bacilli. This implies that a high bacterial index does not infer infection with non-zoonotic non-tuberculous mycobacteria.

Serial Interferon-Gamma Release Assay (IGRA) Testing to Monitor Treatment Responses in Cases of Feline Mycobacteriosis

The interferon-gamma release assay (IGRA) is used to diagnose cases of feline mycobacteriosis, but the use of serial testing to monitor treatment responses has not been evaluated in this species. From a population of cats that underwent IGRA testing for diagnostic investigation, individuals were identified with a pre- and end-of-treatment IGRA that passed control thresholds. The number of cats which reverted to negative at the end-of-treatment IGRA, changes in paired antigen-specific optical density (OD) values and differences in the pre-treatment antigen-specific OD values for those which underwent reversion were compared. Factors to explain reversion or recurrence of disease post-treatment were explored. Four of 18 cats (22%) reverted to negativity at the point of clinical resolution (p = 0.33), there was no difference in paired antigen-specific OD values (p ≥ 0.12), and cats that reverted did not have a lower baseline OD value (p = 0.63). No statistically significant factors were identified to predict reversion (p ≥ 0.08). Remaining positive at the end of treatment IGRA was not associated with recurrence of disease post-treatment (p = 0.34). Overall, these data suggest there is limited value in the use of the IGRA to monitor treatment responses in cats.

Repeated bouts of pulmonary tuberculosis in a hunting cat: reinfection or recrudescence?

CASE SUMMARY

A 7-year-old neutered male Siamese cat was referred for investigation of weight loss and hypercalcaemia (3.3 mmol/l; reference interval 2-3 mmol/l). Haematology, serum biochemistry, thoracic imaging, bronchoalveolar lavage (BAL), Ziehl-Neelsen staining of the BAL fluid and interferon gamma release assay (IGRA) were compatible with pneumonia caused by the less pathogenic member of the Mycobacterium tuberculosis complex, that is, M microti (the 'vole bacillus'), which is common in cats in the UK. Treatment with azithromycin, rifampicin and marbofloxacin was given for 2 months, followed by 4 months of azithromycin and marbofloxacin. Treatment recommendations for tuberculous pneumonia have since changed. The cat remained asymptomatic for 1 year but went on to develop M microti pneumonia on five other occasions, and was treated for 6-12 months on each occasion. The patient's clinical signs, hypercalcaemia and radiographic/CT pulmonary pathology always resolved completely, and the IGRA became negative, before antimycobacterial treatment was stopped. This suggests cure followed by reinfection owing to avid hunting behaviour. Alternatively, this could represent recrudescence of dormant disease. This case has previously been included in a study that described a series of cases of feline tuberculosis.

RELEVANCE AND NOVEL INFORMATION

This case shows that M microti infection in cats can present as recurrent episodes of pneumonia, even after prolonged treatment courses.

Mycobacterium microti: Not Just a Coincidental Pathogen for Cats

Public interest in animal tuberculosis is mainly focused on prevention and eradication of bovine tuberculosis in cattle and wildlife. In cattle, immunodiagnostic tests such as the tuberculin skin test or the interferon gamma (IFN-γ) assay have been established and are commercially available. Feline tuberculosis is rather unknown, and the available diagnostic tools are limited. However, infections with Mycobacterium tuberculosis complex members need to be considered an aetiological differential diagnosis in cats with granulomatous lymphadenopathy or skin nodules and, due to the zoonotic potential, a time-efficient and accurate diagnostic approach is required. The present study describes 11 independent cases of Mycobacterium microti infection in domestic cats in Switzerland. For three cases, clinical presentation, diagnostic imaging, bacteriological results, immunodiagnostic testing, and pathological features are reported. An adapted feline IFN-γ release assay was successfully applied in two cases and appears to be a promising tool for the ante mortem diagnosis of tuberculosis in cats. Direct contact with M. microti reservoir hosts was suspected to be the origin of infection in all three cases. However, there was no evidence of M. microti infection in 346 trapped wild mice from a presumptive endemic region. Therefore, the source and modalities of infection in cats in Switzerland remain to be further elucidated.

Mitchell J, Lodzinska J, Cazzini P, Varjonen K, Gunn-Moore DA. Systemic Mycobacterium kansasii Infection in Two Related Cats

Mycobacterial infections are a major concern in veterinary medicine because of the difficulty achieving an etiological diagnosis, the challenges and concerns of treatment, and the potential zoonotic risk. Mycobacterium kansasii, a slow-growing non-tuberculous mycobacteria, causes disease in both humans and animals. While infections have been well described in humans, where it may be misdiagnosed as tuberculosis, there are fewer reports in animals. Only four cases have been reported in the domestic cat. This case report describes systemic M. kansasii infection in two sibling indoor-only cats that presented two and half years apart with cutaneous disease that was found to be associated with osteolytic and pulmonary pathology. Infection with M. kansasii was confirmed in both cats by polymerase chain reaction on fine-needle aspirate of a lumbosacral soft tissue mass in one cat and on a tissue punch biopsy of a skin lesion in the other; interferon-gamma release assay inferred M. avium-complex and M. tuberculosis-complex infection in the two cats, respectively. Both patients made a full recovery following antimicrobial therapy with rifampicin, azithromycin, and pradofloxacin (plus N-acetyl cysteine in cat 2). This report highlights successful treatment of systemic M. kansasii mycobacteriosis in the cat and the challenge of accurately diagnosing this infection.

Feline tuberculosis caused by Mycobacterium bovis infection of domestic UK cats associated with feeding a commercial raw food diet

Mycobacterium (M.) bovis can infect cats and is a demonstrated zoonosis. We describe an outbreak of M. bovis in pet cats across England and Scotland associated with feeding a commercial raw food diet. Forty-seven cats presented with (pyo)granulomatous lesions, lymphadenopathy, pulmonary and/or alimentary disease over a one-year period where M. bovis infection was suspected or definitively diagnosed, and the cats all consumed the same specific brand of commercial raw venison pet food. Infection with M. bovis genotype 10:a was confirmed by culture and DNA typing of isolates in a small number of cases (n = 5); PCR was used in combination with or as an alternative to culture (n = 12) and/or infection with a Mycobacterium tuberculosis complex group organism was strongly suggested by positive responses to an interferon-gamma release assay (IGRA; n = 34). Asymptomatic at-risk cats were screened by IGRA, identifying a further 83 infected cats. The five culture-positive cases were distributed across areas of England and Scotland at low risk of endemic bovine tuberculosis. Investigations revealed affected cats were mainly indoor-only, and had been fed the same commercial raw food as at least part of their diet. This diet was recalled by the manufacturer due to failure of statutory meat inspection of the component venison. As far as possible, other sources of infection were explored and excluded, including wildlife contact, access to raw milk and living with people with active M. bovis infection. Four owners and one veterinary surgeon were found to have high likelihood of latent tuberculosis infection. One owner required treatment. Although it was not possible to conclusively demonstrate a zoonotic origin for these infections, neither was it possible to eliminate the possibility. Our results provide compelling evidence that the commercial raw diet of these cats was the likely route of M. bovis infection in this outbreak of cases.

Feline Ocular Mycobacteriosis: Clinical Presentation, Histopathological Features, and Outcome

This study describes clinical and histopathological features, treatment, and outcome of cats diagnosed with ocular mycobacteriosis. Cases diagnosed from 2012 to 2017 were reviewed for (a) histopathological evidence of ocular (pyo)granulomatous inflammation containing acid-fast bacilli with mycobacterial morphology, (b) positive mycobacterial culture and/or mycobacterial DNA identified by polymerase chain reaction of ocular tissue, or (c) presumed mycobacteriosis based on ophthalmic examination and positive interferon-gamma release assay. Twenty-five cats (31 eyes) were included; 14 cats (17/31 eyes, 55%) were blind at presentation (unilateral: n = 12 cats; bilateral: n = 2 cats); one unilaterally affected cat later became bilaterally blind. Another 5 cats (7/31 eyes, 23%) became blind after initially being bilaterally visual (unilateral: n = 3 cats; bilateral: n = 2 cats). The commonest ocular finding was uveitis (87%). The main histopathological features were granulomatous to pyogranulomatous chorioretinitis with retinal detachment, anterior uveitis, optic neuritis, episcleritis, scleritis, and/or retrobulbar cellulitis. Nineteen cats (76%) had systemic signs, with disseminated disease being diagnosed in 9, defined by interstitial pulmonary disease, generalized lymphadenopathy, and/or nonocular infection. Nine cats were diagnosed with Mycobacterium bovis, 2 with Mycobacterium microti, 1 with Mycobacterium tuberculosis complex, and 1 with Mycobacterium avium-intracellulare complex. The infecting species was unknown in the remaining cats. Combined surgery (enucleation: n = 5 cats; biopsy: n = 3 cats) and systemic treatment with 2 or 3 appropriate antibiotics for 2 to 7 months resulted in remission in 8 of the 10 cats treated; however, the cat treated with dual therapy relapsed after 8 months. A total of 16 cats (64%) were euthanized; 2 were lost to follow-up.

An outbreak of tuberculosis due to Mycobacterium bovis infection in a pack of English Foxhounds (2016-2017)

Mycobacterium bovis can cause tuberculosis (TB) in social mammals including lions, cattle and man, but canine infections are considered rare. In 2016/17 we investigated a M. bovis TB outbreak in a pack of approximately 180 Foxhounds within the bovine TB Edge Area of England. We employed a combination of immunological tests including an interferon gamma release assay (IGRA) and a serological assay (DPP VetTB, Chembio). Test‐positive hounds were euthanased and subjected to post‐mortem examination (PME). Overall 164 hounds were tested; 97 (59%) responded positively to at least one test. Eighty‐five (52%) dogs responded to M. bovis antigens by IGRA while only 21 (12.9%) had detectable serological responses. At PME three hounds (3.1%) had visible lesions (VL) due to M. bovis infection, later confirmed by culture. Samples from 24 non‐VL hounds were cultured and M. bovis infection was confirmed in a further three hounds (11%). This study is the first investigation and report of an outbreak of M. bovis TB in a canine species. We establish that, in principle, diagnostic tests used for identifying infected individuals of other species can effectively be used in the dog. Further work is urgently needed to establish the sensitivity and specificity of the testing approach used in this study for future clinical application.

Use of computed tomography imaging during long-term follow-up of nine feline tuberculosis cases

Case series summary Feline tuberculosis is an increasingly recognised potential zoonosis of cats. Treatment is challenging and prognosis can vary greatly between cases. Pulmonary infection requires extended courses of antibiotics, but methodologies for sensitively monitoring response to treatment are currently lacking. In this case series, we retrospectively examined the serial computed tomography (CT) findings in nine cats that had been diagnosed with tuberculosis. Changes in pathology (where applicable to tuberculosis) were correlated with the clinical presentation of each of the cats, the treatment protocol, and previous and contemporary diagnostic investigations. This study found that changes in CT findings during the medium- to long-term management of feline tuberculosis were highly variable between cats. The majority of cats had reduced pathology at re-examination during anti-tuberculous therapy, but pathology only resolved in a minority of cases. In some cases recurrence of pathology detected by CT imaging preceded clinical deterioration, allowing for rapid therapeutic intervention. Relevance and novel information When considered in combination with clinical findings, CT studies can aid in decision making regarding tapering of antibiotic protocols, or reintroduction of therapy in cases of recurrence or reinfection. This series also highlights that, in some cases, persistent abnormalities can be detected by CT, so complete resolution of CT pathology should not always be a goal in the management of feline tuberculosis.

Point of Care Tuberculosis Sero-Diagnosis Kit for Wild Animals: Combination of Proteins for Improving the Diagnostic Sensitivity and Specificity

Tuberculosis is a significant problem globally for domestic animals as well as captive and free ranging wild life. Rapid point of care (POC) serology kits are well suited for the diagnosis of TB in wild animals. However, wild animals are invariably exposed to environmental non-pathogenic mycobacterium species with the development of cross reacting antibodies. In the present study, POC TB diagnosis kit was developed using a combination of pathogenic Mycobacteria specific recombinant antigens and purified protein derivatives of pathogenic and non-pathogenic Mycobacteria. To benchmark the TB antibody detection kit, particularly in respect to specificity which could not be determined in wildlife due to the lack of samples from confirmed uninfected animals, we first tested well-characterized sera from 100 M. bovis infected and 100 uninfected cattle. Then we investigated the kit's performance using sera samples from wildlife, namely Sloth Bears (n = 74), Elephants (n = 9), Cervidae (n = 14), Felidae (n = 21), Cape buffalo (n = 2), Wild bear (n = 1) and Wild dog (n = 1).In cattle, a sensitivity of 81% and a specificity of 90% were obtained. The diagnostic sensitivity of the kit was 94% when the kit was tested using known TB positive sloth bear sera samples. 47.4% of the in-contact sloth bears turned seropositive using the rapid POC TB diagnostic kit. Seropositivity in other wild animals was 25% when the sera samples were tested using the kit. A point of care TB sero-diagnostic kit with the combination of proteins was developed and the kit was validated using the sera samples of wild animals.

Mycobacterium bovis infection in humans and cats in same household, Texas, USA, 2012

Mycobacterium bovis infection of cats is exceedingly rare in regions where bovine tuberculosis is not endemic. We describe the diagnosis and clinical management of pulmonary M. bovis infection in 2 indoor-housed cats and their association with at least 1 M. bovis-infected human in Texas, USA, in September 2012.

Mycobacterium bovis infection in the lion (Panthera leo): Current knowledge, conundrums and research challenges

Mycobacterium bovis has global public-health and socio-economic significance and can infect a wide range of species including the lion (Panthera leo) resulting in tuberculosis. Lions are classified as vulnerable under the IUCN Red List of Threatened Species and have experienced a 30% population decline in the past two decades. However, no attempt has been made to collate and critically evaluate the available knowledge of M. bovis infections in lions and potential effects on population. In this review we set out to redress this. Arguments suggesting that ingestion of infected prey animals are the main route of infection for lions have not been scientifically proven and research is needed into other possible sources and routes of infection. The paucity of knowledge on host susceptibility, transmission directions and therefore host status, manifestation of pathology, and epidemiology of the disease in lions also needs to be addressed. Advances have been made in diagnosing the presence of M. bovis in lions. However, these diagnostic tests are unable to differentiate between exposure, presence of infection, or stage of disease. Furthermore, there are contradictory reports on the effects of M. bovis on lion populations with more data needed on disease dynamics versus the lion population's reproductive dynamics. Knowledge on disease effects on the lion reproduction and how additional stressors such as drought or co-morbidities may interact with tuberculosis is also lacking. Filling these knowledge gaps will contribute to the understanding of mycobacterial infections and disease in captive and wild lions and assist in lion conservation endeavours.

Nosocomial spread of Mycobacterium bovis in domestic cats

Five domestic cats were euthanased owing to confirmed or suspected Mycobacterium bovis infection. The initial source of infection remains unclear. Cat A was presented to a veterinary clinic in County Kildare, Ireland, with a discharging submandibular lesion. The infection appears to have been transmitted to four other cats through direct (cats B and C living in the same household as cat A) and non-direct (nosocomial spread during routine operations; cats D and E) contact over a 13.5-week period. Of the five cases, two (B and D) had post-mortem examinations in which gross changes consistent with tuberculosis were seen, moderate numbers of acid-fast bacteria (AFB) were seen on microscopy and M bovis (spoligotype SB0978) was confirmed on culture. Of the remaining three cats, one had a swab taken from its draining ovariohysterectomy wound, which revealed large numbers of AFB with morphology consistent with M bovis (cat E). Two cases were euthanased without diagnostic tests; however, their history and clinical presentations were highly suggestive of tuberculosis (cats A and C). To our knowledge, this is the first documented case of nosocomial spread of M bovis in cats.

TB Summit 2014: prevention, diagnosis, and treatment of tuberculosis-a meeting report of a Euroscicon conference

World TB Day commemorates Dr Robert Koch’s first announcement on March 24, 1882, that the bacterium Mycobacterium tuberculosis is the causative agent of tuberculosis. Currently, the event comprises of several conferences, meetings and activities held all over the world with the singular intention of raising public awareness about the global health emergency.

In spite of having discovered the etiological agent of tuberculosis more than a century ago, a sizeable population still contract the disease every year and fall prey to it. In 2012, an estimated 8.6 million people developed the disease with 1.3 million succumbing to it. The number of TB deaths in children is unacceptably large, given that most are preventable. However, the challenge appears to be shifting toward attempts to control the rise and spread of the drug resistant variants of the microbe. To achieve this, a concerted effort from academia, clinical practice, and industry has been put forth.

The TB Summit 2014 attempted to raise awareness as well as bring together experts involved in different aspects of tuberculosis research to help establish a more collective approach to battle this age-old disease.

Exposure of wild boar to Mycobacterium tuberculosis complex in France since 2000 is consistent with the distribution of bovine tuberculosis outbreaks in cattle

The Eurasian wild boar (Sus scrofa) is increasingly considered as a relevant actor in the epidemiology of animal tuberculosis (TB). Therefore, monitoring TB in wild boar becomes a key tool for establishing comprehensive control schemes for this disease. To estimate the exposure of free living wild boar to Mycobacterium tuberculosis complex (MTC) in France, a bovine-purified protein derivative based ELISA was used to test 2,080 archived serum samples of hunter-harvested animals in 58 French “départements”. Two cut-off values were used for diagnostic interpretation: 0.2, recommended by the manufacturer (specificity: 96.43%; sensitivity: 72.6%), and 0.5 (specificity: 100%; sensitivity: 64%). During the same period, at the 0.2 cut-off, global true seroprevalence was 5.9% (IC_95%: 4.3%-7.7%) and 76% of the sampled “départements” had seropositive wild boar, including seven cattle TB-free “départements. At the 0.5 cut-off, global true seroprevalence was 2.2% (IC_95%: 1.5-3.2) and positive wild boar belonged to 21% of the “départements”. All but one of these positive “départements” had reported at least one cattle TB outbreak since 2000. A good consistence between seropositive wild boar and TB outbreaks in cattle was found, especially at the 0.5 cut-off value (the mean distance to the nearest cattle TB outbreak was 13km and 27km for seropositive and seronegative wild boar, respectively; P<0.05). The use of an ELISA to detect MTC antibodies in wild boar has permitted the description of the geographic distribution of MTC contact in wild boar in France. Our results suggest that the ELISA could be used as a first screening tool to conduct TB surveillance in wild boar at a population level. High-risk wild boar populations (e.g. overabundant) could be tested and if identified positive by ELISA they should be surveyed in detail by combining pathology and culture.

Mycobacterioses in cats: ABCD guidelines on prevention and management

OVERVIEW

Mycobacterial infections are important in humans and animals. Cats can be infected by several Mycobacterium species, which may cause different syndromes, mainly tuberculosis, atypical or non-tuberculous mycobacteriosis and leprosy. In recent years, awareness has increased about how to recognise and confirm these infections. More cases are diagnosed today, which probably means that the disease has escaped detection in the past.

INFECTION

Most cases in cats are cutaneous, presenting as nodules in the skin and draining tracts, ulceration and local lymphadenopathy; however, systemic dissemination may also occur.

DIAGNOSIS

Definitive diagnosis is difficult when the bacterium cannot be detected by histology or culture. However, species confirmation is essential for treatment and prognosis, so material for culture and polymerase chain reaction should be submitted in every suspected case.

TREATMENT

Treatment is challenging. A combination of two or three antibiotics is needed, and treatment must be continued for some months, which makes owner compliance especially difficult in cats. ZOONOTIC RISK: There is a zoonotic risk associated with some mycobacterial species. Concerns should be communicated in every case of an immunocompromised owner in contact with an infected cat.

Rapid detection of serum antibody by dual-path platform VetTB assay in white-tailed deer infected with Mycobacterium bovis

Bovine tuberculosis (TB) in cervids remains a significant problem affecting farmed herds and wild populations. Traditional skin testing has serious limitations in certain species, whereas emerging serological assays showed promising diagnostic performance. The recently developed immunochromatographic dual-path platform (DPP) VetTB assay has two antigen bands, T1 (MPB83 protein) and T2 (CFP10/ESAT-6 fusion protein), for antibody detection. We evaluated the diagnostic accuracy of this test by using serum samples collected from groups of white-tailed deer experimentally inoculated with Mycobacterium bovis, M. avium subsp. paratuberculosis, or M. bovis BCG Pasteur. In addition, we used serum samples from farmed white-tailed deer in herds with no history of TB, as well as from free-ranging white-tailed deer culled during field surveillance studies performed in Michigan known to have bovine TB in the wild deer population. The DPP VetTB assay detected antibody responses in 58.1% of experimentally infected animals within 8 to 16 weeks postinoculation and in 71.9% of naturally infected deer, resulting in an estimated test sensitivity of 65.1% and a specificity of 97.8%. The higher seroreactivity found in deer with naturally acquired M. bovis infection was associated with an increased frequency of antibody responses to the ESAT-6 and CFP10 proteins, resulting in a greater contribution of these antigens, in addition to MPB83, to the detection of seropositive animals, compared with experimental M. bovis infection. Deer experimentally inoculated with either M. avium subsp. paratuberculosis or M. bovis BCG Pasteur did not produce cross-reactive antibodies that could be detected by the DPP VetTB assay. The present findings demonstrate the relatively high diagnostic accuracy of the DPP VetTB test for white-tailed deer, especially in the detection of naturally infected animals.

Facts and dilemmas in diagnosis of tuberculosis in wildlife

Mycobacterium bovis, causing bovine tuberculosis (BTB), has been recognized as a global threat at the wildlife-livestock-human interface, a clear "One Health" issue. Several wildlife species have been identified as maintenance hosts. Spillover of infection from these species to livestock or other wildlife species may have economic and conservation implications and infection of humans causes public health concerns, especially in developing countries. Most BTB management strategies rely on BTB testing, which can be performed for a range of purposes, from disease surveillance to diagnosing individual infected animals. New diagnostic assays are being developed for selected wildlife species. This review investigates the most frequent objectives and associated requirements for testing wildlife for tuberculosis at the level of individual animals as well as small and large populations. By aligning those with the available (immunological) ante mortem diagnostic assays, the practical challenges and limitations wildlife managers and researchers are currently faced with are highlighted.

Evaluation of gamma interferon and antibody tuberculosis tests in alpacas

We describe the performance of cell-based and antibody blood tests for the antemortem diagnosis of tuberculosis (TB) in South American camelids (SAC). The sensitivity and specificity of the gamma interferon (IFN-γ) release assay, two lateral flow rapid antibody tests (Stat-Pak and Dual Path Platform [DPP]), and two enzyme-linked immunosorbent assay (ELISA)-based antibody tests (Idexx and Enferplex) were determined using diseased alpacas from Mycobacterium bovis culture-confirmed breakdown herds and TB-free alpacas from geographical areas with no history of bovine TB, respectively. Our results show that while the sensitivities of the IFN-γ and antibody tests were similar (range of 57.7% to 66.7%), the specificity of the IFN-γ test (89.1%) was lower than those of any of the antibody tests (range of 96.4% to 97.4%). This lower specificity of the IFN-γ test was at least in part due to undisclosed Mycobacterium microti infection in the TB-free cohort, which stimulates a positive purified protein derivative (PPD) response. The sensitivity of infection detection could be increased by combining two antibody tests, but even the use of all four antibody tests failed to detect all diseased alpacas. These antibody-negative alpacas were IFN-γ positive. We found that the maximum sensitivity could be achieved only by the combination of the IFN-γ test with two antibody tests in a "test package," although this resulted in decreased specificity. The data from this evaluation of tests with defined sensitivity and specificity provide potential options for antemortem screening of SAC for TB in herd breakdown situations and could also find application in movement testing and tracing investigations.

Field application of serodiagnostics to identify elephants with tuberculosis prior to case confirmation by culture

Three serologic methods for antibody detection in elephant tuberculosis (TB), the multiantigen print immunoassay (MAPIA), ElephantTB STAT-PAK kit, and DPP VetTB test, were evaluated using serial serum samples from 14 captive elephants infected with Mycobacterium tuberculosis in 5 countries. In all cases, serological testing was performed prior to the diagnosis of TB by mycobacterial culture of trunk wash or tissue samples collected at necropsy. All elephants produced antibody responses to M. tuberculosis antigens, with 13/14 recognizing ESAT-6 and/or CFP10 proteins. The findings supported the high serodiagnostic test accuracy in detecting infections months to years before M. tuberculosis could be isolated from elephants. The MAPIA and/or DPP VetTB assay demonstrated the potential for monitoring antimycobacterial therapy and predicting TB relapse in treated elephants when continuously used in the posttreatment period. History of exposure to TB and past treatment information should be taken into consideration for proper interpretation of the antibody test results. Data suggest that the more frequent trunk wash culture testing of seropositive elephants may enhance the efficiency of the TB diagnostic algorithm, leading to earlier treatment with improved outcomes.