1-year-old male giant elephant shrew (Rhynchocyon peters)A 1-year-old male captive-bred giant elephant shrew (Rhynchocyon peters) presented with lameness of the right hind limb. The shrew had been pair housed with a male littermate in a 75 sq. ft. indoor enclosure since arriving 3 months earlier from the Smithsonian National Zoological Park. Empirical daily therapy with oral meloxicam (0.1 mg/kg) and a ten-day course of cefdinir (10 mg/kg) resulted in minimal improvement. Physical exam and radiographs revealed no remarkable findings. Three weeks later, the fifth digit of the left forelimb exhibited marked swelling. Further, a mass measuring 2 x 2 x 0.5 cm was palpated at the medial and lateral aspect of the right stifle. Subsequent, repeat radiographs of the affected digit (5th phalanges) and right stifle (distal femur and proximal tibia) revealed bone lysis and soft tissue swelling. Two weeks after limited success with oral antimycobacterial therapy using rifabutin (20 mg/kg) and azithromycin (15 mg/kg), the shrew became ataxic, lethargic and anorexic. Shortly after transport to an intensive care unit for supportive care, the shrew was found tachypneic in right lateral recumbency, and due to its deteriorating condition and poor prognosis, the elephant shrew was humanely euthanized and submitted for necropsy.
On gross examination, there was enlargement of the right femorotibial (stifle) joint with multiple, coalescing foci of purulent material (abscesses) within a 2 cm x 2 cm x 1.5 cm area of the quadriceps and a 3 cm x 2 cm area of the hamstring muscles.Â Crepitus suggestive of a fracture was present on palpation of the stifle joint.Â The fifth digit on the left front lateral toe was swollen.Â Numerous pinpoint to 0.2 cm white foci were found disseminated throughout all lung lobes and diffuse, pinpoint, white foci were frequently observed on liver surfaces.Â Approximately 2 ml of serous sanguineous fluid was observed in the abdominal cavity.
Lung: Within ~25% of the lung lobes, there are multiple individual to coalescing irregular granulomas composed centrally of necrosis with a peripheral rim of degenerative neutrophils, which in turn is surrounded by numerous macrophages, scattered multinucleated giant cells and occasional lymphocytes and plasma cells.Â Some granulomas encompass airways and vasculature with extension of inflammatory cells into the surrounding tissue.Â The pulmonary interstitium is also multifocally mildly to severely expanded by macrophages and neutrophils spatially distinct from granulomas.Â There are also multifocal areas within the airways that contain macrophages with multifocal loss of airway epithelium.Â Review of acid fast bacteria (AFB)-stained sections of lung and stifle joint revealed numerous AF-positive bacteria.
Lung: Pneumonia, pyogranulomatous, severe, chronic active, multifocal.
Right stifle joint and lung: Mycobacterium spp.
A 100% identity for Mycobacterium intracellular
The giant elephant-shrew (Rhynchocyon peters) is a small insectivorous mammal of the family Macroscelididae, widely distributed across central and southern Africa.Â Their traditional common English name comes from a resemblance between their long noses and trunk of an elephant, and an assumed relationship with the true shrews (family Soricidae) in the order Insectivora.Â Phylogentically, elephant shrews are closely related to aardvarks, golden moles and tenrecs.Â Currently, there are 15 known species in this strictly African mammal group, three of which are referred to as giant elephant shrews belonging to the genus Rhynchocyon.Â All three Rhynchocyon species are considered threatened due to habitat destruction and fragmentation.Â
Mycobacterium avium complexes (MAC) are a group of nontuberculous mycobacteria characterized as gram-positive, aerobic, non-motile, acid-fast rods.Â M.Â avium and M.Â intracellulare are the most notable species within the group.(30) Because M.Â avium ssp.Â avium and M.Â intracellulare are difficult to distinguish on the basis of phenotypic characteristics, the term M.Â avium complex is used when referred to these organisms.Â The mycobacterium now designated as M.Â intracellulare was first cultured in 1969 from the sputum of tuberculosis patients in the Battey State Hospital of Rome, Georgia and was originally referred to as Battey bacillus.(25) In 1971, the nontuberculosis mycobacteria were divided into three groups; based on their association with human disease, production of yellow or orange pigment, and their rate of growth.Â The photochromogens contain 3 species that develop yellow or orange pigment when exposed to light.Â Examples include M.Â kansasii, M.Â marinu, and M.Â simiae. The scotochromogens, including M.Â gordonae, M.Â szulgai and M.Â scrofulaceum, form orange-yellow pigment in the dark.Â The unpigmented M.Â avium complex (MAC), M.Â xenopi, and M.Â malmoense have been classified as nonphotochromogens.(25) Based on glycolipid typing MAC has been further subdivided into 28 serotypes.(28) Serotypes 1 to 6 and 8 belong to M.Â avium and serotypes 7, 12, 14, 16, and 18 to M.Â intracellulare.Â Rodents, insectivores, domestic animals and humans can be a reservoir of mycobacteria.Â The occurrence of mycobacteria in rodents was first reported by Wells and Oxon5, with a prevalence of 9 to 31% of Mycobacterium microti in rodents.Â Mycobacteriosis in shrews was also demonstrated by the isolation of the organism from tuberculous pathomorphological changes in the lungs, spleen, liver, kidneys and lymph nodes in 8 of 500 common shrews (Sorex araneus) caught in 1946 in Great Britain.(5) Mycobacteria are found in the feed and bedding, as well as the droppings of livestock.(9).Â Insectivores and small rodents commonly come into contact with mycobacteria via plants, animal foods, watery environments or contact with birds or humans infected with MAC.Â At the same time, shrews can easily get inside human or livestock housing and contaminate the environment with their droppings.Â Mycobacterium avium-intracellulare is a common cause of disseminated disease among patients with human immunodeficiency virus (HIV) infection.(3) In a recent study, Voles (Microtus pennsylvanicus) infected with M.Â bovis were capable of disseminating the organism via their feces.Â Both M.Â intracellulare and M.Â avium are capable of gastric transit in animals without destruction due to their resistance to acid.Â In this way they can be spread over long distances with the migration of the animal.(6) Also, there are several other possible routes of mycobacterial transmission: a) through direct contact with rodent excreta, b) ingestion of food or water contaminated with rodent excreta, c) ingestion of the animal itself, d) inhaling aerosolized rodent excreta, or e) rodent bites, or through ectoparasites.(9)
Depending on the route of infection, affected mammals can present with local cutaneous disease or systemic signs related to the alimentary, and/or respiratory tracts.Â Typically, disseminated MAC disease begins as a localized process that progress rapidly to include numerous organ systems (i.e.Â pulmonary, central nervous system, lymphatic, gastrointestinal, and musculoskeletal system).(2-4,7,9-12,14,16-19,21-22,24) The common clinical signs of a MAC infection in immune compromised humans are respiratory distress(19,26), anemia, chronic diarrhea, weight-loss(14), lymphadenitis(19,23), lethargy, hepatosplenomegaly, and arthritis.(29,31) MAC infections must be differentiated from M.Â tuberculosis or M.Â bovis, and other nontuberculous mycobacterial infections, as well as histoplasmosis, cryptococcosis, coccidioidomycosis, and blastomycosis.Â The rapid speciation and prevalence estimation of these infecting organisms is desirable because of the public health concerns associated with M.Â avium intracellulare, M.Â bovis, and M.Â tuberculosis infections.(27) Thus, laboratory diagnoses by culture, PCR, and /or histopathology are the traditional methods of testing.Â A positive culture of MAC from normally sterile sites (blood, bone marrow, lymph node, or liver biopsies), should be considered diagnostic of disseminated disease.(21)
In this case, one of three possible mechanisms probably explains the occurrence of disseminated MAC.Â The first possibility is that MAC was introduced directly into the tissue via direct inoculation, then disseminating to various organs over a period of time.Â Secondly, MAC is ubiquitous in the environment, including water sources, and can contaminate drinking water.(18) Water distribution systems have been reported as a possible source of infection in hospitals, homes, and commercial buildings.(1) Because MAC grows slowly, a six month lag between inoculation and clinical presentation, as seen in humans, is biologically plausible.(13) The third possibility is that the shrew had undiagnosed disseminated MAC at the time of arrival, and underwent a period of stress, which suppressed the immune system.Â Stress of any kind can tip the scale in the direction of the mycobacteria and produce fulminant infection.Â Systemic mycobacterial infection is an important differential diagnosis for an acute on-set of lameness in insectivores.
Lung: Pneumonia, granulomatous and caseating, multifocal to coalescing, moderate, with numerous intracellular bacilli.
This case does not have discrete granulomas, but manifests rather as nodular aggregates of granulomatous inflammation that appear to spread from alveolus to alveolus.Â Caseous necrosis is not typical in granulomatous disease without the formation of discrete granulomas; however, conference participants felt that the morphology of the lesions in this case of MAC-induced nontuberculous mycobacteriosis supported granulomatous as a more descriptive and appropriate term.
In contrast to nontuberculous mycobacterial infections such as MAC, Mycobacterium tuberculosis is the prototypical etiologic agent resulting in granulomas and subsequent tubercle formation.Â Tubercles form when granulomas develop and coalesce.Â The center of a tubercle typically consist of white, friable material (caseous necrotic debris) derived from lysed cells and bound by epithelioid macrophages, multinucleated giant macrophages, lymphocytes, plasma cells, fibroblasts and collagen.Â With time, tubercles may become calcified.Â
Generally speaking, granulomas form as the result of cell-mediated immunity to a poorly degradable entity such as Mycobacteria.Â Initially, antigen presenting cells (APC), such as alveolar macrophages, present phagocytized mycobacterial antigen and MHC class II proteins to na+ï¿½-ï¿½ve T-cells.Â Binding of the T-cell receptor with mycobacterial antigen and exposure to the cytokine IL-12 released by the APC promotes differentiation from na+ï¿½-ï¿½ve CD4+ TH1 lymphocytes to activated T-helper 1 lymphocytes producing IL-2, which, in turn, activates additional T cells, tumor necrosis factor, and interferon-Î³.Â Interferon-Î³ is an important factor in the differentiation of monocytes to epithelioid macrophages and multinucleated giant cells.(17)
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