The Mycobacterium avium complex - an underestimated threat to humans and animals.

INTRODUCTION AND OBJECTIVE: The Mycobacterium avium complex (MAC) is a group of acid-resistant bacteria within the Mycobacteriaceae. Their cell walls have a specific structure impervious to many disinfectants. Mycobacteria are widespread in the environment and can also be found in food. This aim of the article is to review the current state of knowledge about the sources of infection, symptoms and treatment of MAC diseases in humans and animals, and summarizes the available methods for identifying the bacteria. It pays a special attention to the zoonotic potential of MAC bacteria and possible routes of transmission between humans and animals, including possible food-borne routes. BRIEF DESCRIPTION OF THE STATE OF KNOWLEDGE.: MAC bacterial infections occur both in immunocompetent people and those with functional predispositions and compromised immunity, particularly during HIV infection or immunosuppressive treatment. The incidence of MAC infections in humans is growing, with the most common form of infection being pulmonary disease (MTC-PD); however, there are conflicting reports on the role of Mycobacterium avium paratuberculosis (MAP) in the development of Crohn's disease. MAC bacteria can also attack livestock, household pets, and wild animals. Unfortunately, treatment is lengthy and often fails due to microbiological relapse; there is also increasing evidence of MAC bacteria are developing multi-drug resistance. CONCLUSIONS: Although new antibiotics are being created to inhibit the growth and division of Mycobacterium avium, there is clearly a need for further research into the virulence factors associated with MAC bacteria. Further studies should also examine the role of MAP in the etiopathogenesis of Crohn's disease.

Oesophageal Obstruction in a Donkey Due to Mediastinal Lymphadenitis Caused by Mycobacterium avium Complex.

Mycobacterial infections are rare in horses, donkeys and mules. Although there are a few reports in horses, mycobacterial disease is poorly documented in the donkey. Mycobacterial infection of equine species typically affects the alimentary tract, causing granulomatous enterocolitis resulting in diarrhoea and chronic weight loss, while lymph nodes and liver may also be affected. We now document recurrent oesophageal obstruction, secondary to cranial mediastinal lymphadenitis caused by Mycobacterium avium complex (MAC). To the best of our knowledge, this is the first report of MAC infection in a donkey in the UK.

Intestinal Mycobacterium avium Infection in Pet Dwarf Rabbits (Oryctolagus cuniculus).

Mycobacteriosis has been rarely described in pet rabbits (Oryctolagus cuniculus). Here we present two cases of intestinal mycobacteriosis from north-eastern Germany. The first adult rabbit was euthanized due to severe cardiovascular failure, hypothermia and chronic weight loss. Necropsy revealed cachexia and a focal, fibrinonecrotic lesion in the caecum. Histologically, severe granulomatous inflammation, with numerous multinucleated giant cells and abundant acid-fast bacilli, was detected under the fibrinonecrotic material in the abdominal wall adjacent to the caecal lesion, caecal lymph nodes, spleen, liver and lungs. Microbiological culture detected Mycobacterium avium subspecies hominissuis, Escherichia coli, Clostridium disporicum and Bacteroides ovatus. A retrospective assessment of 2,013 other pet rabbit necropsies, performed between 1995 and 2019, revealed one additional case of intestinal mycobacteriosis. This animal had been euthanized due to persistent hindlimb lameness and necropsy revealed comminuted fractures of the pelvic bones and multiple large liquefied abscess-like lesions in the caecal and colonic walls. Histology revealed granulomatous inflammation with acid-fast bacilli. Polymerase chain reaction on formalin-fixed, paraffin-embedded tissue identified the presence of M. avium spp. In contrast to European wild rabbits (Oryctolagus cuniculus) from Scotland, these findings indicate that intestinal mycobacteriosis is rare in pet rabbits from north-eastern Germany. Zoonotic potential should be considered due to the close contact between pets and their owners and the chronic course of the disease with an initial lack of clinical signs.

DIAGNOSIS AND MANAGEMENT OF MYCOBACTERIOSIS IN A COLONY OF LITTLE PENGUINS (EUDYPTULA MINOR).

A group of zoo-housed little penguins (Eudyptula minor) was diagnosed with mycobacteriosis. While undergoing multidetector computed tomography (MDCT) imaging for an unrelated research project, pulmonary lesions were detected in multiple individuals. In general, birds appeared healthy and free of outward signs of disease. After the loss of three individuals, polyclonal mycobacterial disease due to Mycobacterium avium-intracellulare complex was confirmed. Surviving birds were treated with rifampin (45 mg/kg), ethambutol (30 mg/kg), clarithromycin (10 mg/kg), and enrofloxacin (30 mg/kg) compounded into a single capsule administered once a day in food. After 3 mo of therapy, MDCT imaging documented a decrease in nodule size and number in all remaining birds, with further improvement documented after 13 mo of treatment. MDCT imaging was invaluable for diagnosing disease, documenting disease progression over time, and assessing response to therapy. Early initiation of therapy before the development of outward signs of disease led to resolution of mycobacterial pulmonary lesions in multiple penguins. Mycobacterial disease in this group of little penguins, as well as previously published reports, suggests that the species is at increased risk for developing mycobacteriosis.

Granulomatous Rhinitis in a Horse due to Mycobacterium intracellulare Infection.

Mycobacterial infections in horses are uncommon, but are caused most frequently by Mycobacterium bovis of the Mycobacterium tuberculosis complex or Mycobacterium avium of the M. avium complex. Disease caused by Mycobacterium intracellulare, the second most common species within the M. avium complex, has not been reported in horses to date. Mycobacteriosis in horses most often presents as enteric, pulmonary or, rarely, systemic disease. Here we report a case of M. intracellulare infection in a horse presenting as a granulomatous nasal mass.

Resolution of a Localized Granuloma Caused by Mycobacterium avium-intracellulare Complex on the Cere of a Bruce's Green Pigeon (Treron waalia).

A 3-year-old female Bruce's green pigeon (Treron waalia) was presented with granulomatous inflammation of the cere and underlying tissues with osteomyelitis and bone proliferation of the dorsal premaxilla. Biopsy and culture revealed the presence of Mycobacterium avium-intracellulare complex, and multi-antimicrobial treatment was initiated with clarithromycin, ethambutol, rifabutin, and enrofloxacin. The cere lesion improved and no evidence of systemic granulomas was observed over 4 months of treatment, although leukocytosis and monocytosis persisted. Five months after discontinuation of antibiotic therapy, the white blood cell count had normalized, but distal beak irregularities and partial recurrence of the mass were present. The bird died 15 months after discontinuation of antibiotic therapy and necropsy revealed no evidence of active mycobacteriosis of the beak or cere. This report documents an unusual clinical presentation of mycobacteriosis, in addition to its successful resolution.

Systemic infection of Mycobacterium avium subspecies hominissuis and fungus in a pet dog.

A 3-year-old neutered female poodle with a long history of dermatophytic skin disease was presented with lethargy, anorexia and progressive weight loss. Abdominal ultrasonography revealed markedly enlarged mesenteric lymph nodes and multiple hypoechoic foci in the spleen. Cytology of the mesenteric lymph nodes and spleen showed granulomatous inflammation with fungal organisms and negatively stained intracytoplasmic bacterial rods consistent with Mycobacteria spp. Based on culture, multiplex polymerase chain reaction and sequence analysis, the bacterium was identified as Mycobacterium avium subspecies hominissuis. Despite treatment with antibiotics, the dog's condition deteriorated, and it died approximately 3 weeks after first presentation.

Pulmonary mycobacteriosis caused by Mycobacterium intracellulare in a Tasmanian devil (Sarcophilus harrisii).

The health of captive Tasmanian devils (Sarcophilus harrisii) is currently of increased interest because wild populations are being decimated by the spread of devil facial tumour disease. This report describes the pathology of an aged captive Tasmanian devil that had a pulmonary mycobacterial infection caused by Mycobacterium intracellulare in addition to multiple neoplastic processes.

Rapid mycobacterial liquid culture-screening method for Mycobacterium avium complex based on secreted antigen-capture enzyme-linked immunosorbent assay.

Sensors in automated liquid culture systems for mycobacteria, such as MGIT, BacT/Alert 3D, and Trek ESP II, flag growth of any type of bacteria; a positive signal does not mean that the target mycobacteria are present. All signal-positive cultures thus require additional and often laborious testing. An immunoassay was developed to screen liquid mycobacterial cultures for evidence of Mycobacterium avium complex (MAC). The method, called the MAC-enzyme-linked immunosorbent assay (ELISA), relies on detection of MAC-specific secreted antigens in liquid culture. Secreted MAC antigens were captured by the MAC-ELISA with polyclonal anti- Mycobacterium avium subsp. paratuberculosis chicken immunoglobulin Y (IgY), detected using rabbit anti-MAC IgG, and then revealed using horseradish peroxidase-conjugated goat anti-rabbit IgG. When the MAC-ELISA was evaluated using pure cultures of known mycobacterial (n = 75) and nonmycobacterial (n = 17) organisms, no false-positive or false-negative MAC-ELISA results were found. By receiver operator characteristic (ROC) analysis of 1,275 previously identified clinical isolates, at the assay optimal cutoff the diagnostic sensitivity and specificity of the MAC-ELISA were 92.6% (95% confidence interval [95% CI], 90.3 to 94.5) and 99.9% (95% CI, 99.2 to 100), respectively, with an area under the ROC curve of 0.992. Prospective evaluation of the MAC-ELISA with an additional 652 clinical samples inoculated into MGIT ParaTB medium and signaling positive per the manufacturer's instructions found that the MAC-ELISA was effective in determining those cultures that actually contained MAC species and warranting the resources required to identify the organism by PCR. Of these 652 MGIT-positive cultures, the MAC-ELISA correctly identified 96.8% (of 219 MAC-ELISA-positive cultures) as truly containing MAC mycobacteria, based on PCR or high-performance liquid chromatography (HPLC) as reference tests. Only 6 of 433 MGIT signal-positive cultures (1.4%) were MAC-ELISA false negative, and only 7 of 219 MGIT signal-negative cultures (3.2%) were false positive. The MAC-ELISA is a low-cost, rapid, sensitive, and specific test for MAC in liquid cultures. It could be used in conjunction with or independent of automated culture reading instrumentation. For maximal accuracy and subspecies-specific identification, use of a confirmatory multiplex MAC PCR is recommended.

Histopathological classification of systemic Mycobacterium avium complex infections in slaughtered domestic pigs.

The aim of this study was to classify the histopathological features of pigs infected with Mycobacterium avium complex (MAC). We used slaughtered pig organs systemically infected with MAC. The results showed granulomatous lesions which were observed predominantly in the digestive organs and regional lymph nodes rather than respiratory organs. The histological picture showed a wide range of granulomatous stages from exudative to fibrotic reactions to the MAC infection. Eosinophils and giant cells were characteristically observed in the exudative reactions. The histopathological type in primary focus tended to be maintained in the respective organs. Most strains with the same genotype showed pathogenicity for guinea pigs irrespective of the type of granuloma. Although these findings suggest that different stages of a granulomatous lesion originating from the same causative agent might influence histological patterns, other possibilities such as the hereditary background of the host, or the effects of viral infections should be considered.

Disseminated Mycobacterium avium infection in young cats: overrepresentation of Abyssinian cats.

Disseminated Mycobacterium avium-intracellulare complex (MAC) infection was diagnosed in 10 young cats (1-5 years of age) from Australia or North America between 1995 and 2004. A further two cats with disseminated mycobacteriosis (precise agent not identified) were recognised during this period. Of the 12, 10 were Abyssinian cats, one was a Somali cat and one was a domestic shorthair cat. None of the cats tested positive for either FeLV antigen or FIV antibody. The clinical course of these infections was indolent, with cats typically presenting for weight loss, initially in the face of polyphagia, with a chronicity of up to several months. Additional clinical features included lower respiratory tract signs and peripheral lymphadenomegaly. A marked diffuse interstitial pattern was evident in thoracic radiographs, even in cats without overt respiratory involvement. Hair clipped to perform diagnostic procedures tended to regrow slowly, if at all. Diagnosis was generally made by obtaining representative tissue specimens from mesenteric lymph nodes, liver or kidney at laparotomy, or from a popliteal lymph node. The primary antecedent event was most likely colonisation of either the alimentary or respiratory tract, followed by local invasion and eventual lymphatic and haematogenous dissemination. Nine cases were treated using combination therapy with agents effective for MAC infection in human patients. Two cats are still undergoing initial therapy and have responded. Of the remaining seven, all responded during long courses (5-14 months) of clarithromycin combined with either clofazimine or rifampicin, and a fluoroquinolone or doxycycline. Of these, three cats remain well (with durations between 2 months and 2 years following therapy); two developed recurrent disease (at 3 months and 2 years, respectively, following therapy) and have restarted therapy. The remaining two cats improved 1 year and 5 months, respectively, after diagnosis but ultimately succumbed. The two cats in which therapy was restarted have improved dramatically. Certain lines of Abyssinian and Somali cats likely suffer from a familial immunodeficiency that predisposes them to infection with slow-growing mycobacteria such as MAC.

Septic arthritis and granulomatous synovitis caused by infection with Mycobacterium avium complex in a horse.

A 12-year-old American Saddlebred gelding was referred to a veterinary teaching hospital for evaluation of a chronic lameness problem in the right radiocarpal joint. The horse had been treated for osteoarthritis of the right radiocarpal joint with multiple injections of cortisone during the past 3 years. The horse was severely lame on the right forelimb at a trot. Radiography and computed tomography revealed a 3 x 2-cm lytic defect in the distal portion of the radius and periarticular bone proliferation around the right radiocarpal joint. Ultrasonography of the distal portion of the radius revealed a soft tissue mass in the palmarolateral aspect of the joint. Proliferative synovium with a large amount of fibrin was observed in the dorsal and palmar aspects of the joint via arthroscopic examination of the right radiocarpal joint. Histologic examination of synovial biopsy specimens revealed proliferative granulomatous synovitis with giant cells. Mycobacterium avium complex was cultured from the synovial fluid. Infection with M avium complex should be considered in horses with chronic recurring arthritis associated with granulomatous synovitis.

Latent infection as a source of disseminated disease caused by organisms of the Mycobacterium avium complex in simian immunodeficiency virus-infected rhesus macaques.

Whether infection with Mycobacterium avium complex (MAC) among patients with acquired immune deficiency syndrome results from recent exposure to virulent strains or reactivation of latent infection acquired years earlier is unknown. To address this question, tissue samples from 47 simian immunodeficiency virus (SIV)-infected and 63 SIV-uninfected rhesus macaques were cultured. MAC was cultured from 14 SIV-uninfected macaques (22.2%) and 32 SIV-infected macaques (68.1%); median bacterial burdens were 33.3 and 998.7 cfu/g, respectively. Genetically distinct strains of MAC were identified for 13 SIV-uninfected macaques (20.6%) and 15 SIV-infected macaques (31.9%). A genetically identical MAC strain (K128A) was identified for 25 SIV-infected macaques (53.2%) and 1 SIV-uninfected macaque (1.6%). Multivariate analysis identified infection with SIV/Delta(B670), diagnosis of an SIV-related tumor or opportunistic infection, and birth on site as risks for MAC infection. SIV-uninfected and SIV-infected macaques yielding unique strains of MAC were considered to have latent and reactivation infection, respectively, whereas animals infected with strain K128A were considered to have recent infection, demonstrating that both mechanisms occur among rhesus macaques.

Disseminated Mycobacterium avium complex infection following renal transplantation in a cat.

An 11-year-old cat with a history of renal transplantation and treatment with cyclosporine and prednisolone was examined because of vomiting, diarrhea, inappetence, lethargy, and weight loss. Abdominal ultrasonography revealed 2 large heteroechoic masses thought to be mesenteric lymph nodes. Ultrasound-guided biopsy was performed, and histologic examination of biopsy specimens revealed granulomatous inflammation of presumptive lymph node tissue. Examination of sections stained with acid-fast stains revealed innumerable acid-fast bacilli within histiocytes, and a presumptive diagnosis of mycobacteriosis was made. The cat's clinical condition deteriorated, and euthanasia was elected. At necropsy, granulomatous inflammation was present within the mesenteric lymph nodes, spleen, liver, small and large intestines, lungs, and bone marrow. Bacterial culture yielded Mycobacterium avium, a slow-growing, opportunistic, saprophytic mycobacterium that can cause tuberculous lesions that are clinically indistinguishable from those associated with classic tuberculosis. It is a rare cause of disseminated mycobacteriosis in human transplant recipients. To our knowledge, this is the first report of disseminated M avium complex infection in a feline transplant recipient.

Duplex PCR for differential identification of Mycobacterium bovis, M. avium, and M. avium subsp. paratuberculosis in formalin- fixed paraffin-embedded tissues from cattle.

We previously isolated and sequenced two genomic segments of Mycobacterium avium subsp. paratuberculosis, namely, f57, a species-specific sequence, and the p34 gene, coding for a 34-kDa antigenic protein. Comparison of sequences upstream of the p34 open reading frame (us-p34) from M. avium subsp. paratuberculosis and M. tuberculosis showed a 79-base deletion in M. tuberculosis. Sequence analysis of the p34 genes in another two species, M. bovis (strain BCG) and M. avium (strain D4), confirmed the differences observed between tuberculous and nontuberculous species. A duplex diagnostic PCR strategy based on coamplification of nonhomologous us-p34 and species-specific f57 sequences was therefore developed. Duplex PCR yielded three different patterns, specific either for tuberculous bacilli (M. tuberculosis, M. bovis, and M. africanum), for both nontuberculous mycobacteria M. avium and M. intracellulare, or for M. avium subsp. paratuberculosis. The specificity of this single-step DNA-based assay was assessed on DNA from cultured mycobacterial strains, as well as on a panel of formalin-fixed and paraffin-embedded tissues from cattle. Molecular assay results from tissular DNA were compared to conventional bacteriological and histological test results, including those obtained by Ziehl-Neelsen staining on tissue biopsy specimens. Molecular discrimination was successful and confirmed the value of duplex us-p34 and f57 sequence amplification for differential diagnosis of tuberculosis, paratuberculosis, or infections caused by other members of the M. avium complex.