JPC SYSTEMIC PATHOLOGY
Signalment ( #87-650): Rhesus monkey
HISTORY: This monkey was found dead in its cage.
HISTOPATHOLOGIC DESCRIPTION: SLIDE A: Lung: Up to 75% percent of the parenchyma is replaced by multifocal to coalescing granulomas composed of necrotic centers with occasional mineralization surrounded by numerous epithelioid macrophages, multinucleated giant cells (Langhans and foreign body type), and more peripherally by lymphocytes and plasma cells. Some granulomas are circumscribed by a thin fibrous connective tissue capsule. Multifocally, remaining alveolar septa are lined by hyperplastic type II pneumocytes. Alveolar spaces contain eosinophilic proteinaceous material (edema) admixed with numerous foamy alveolar macrophages, fewer lymphocytes, and scattered hemorrhage and fibrin. Multifocally, aggregates of lymphocytes and plasma cells surround blood vessels, which occasionally contain fibrin thrombi. Diffusely, the pleura is thickened to up to 2 mm by fibrosis, lymphocytes, plasma cells, distended lymphatics (edema), and hemorrhage. Multifocally, there is mild anthracosilicosis.
SLIDE B: Acid-fast stain: There are rare, intrahistiocytic, 0.5 um wide, acid-fast bacilli.
MORPHOLOGIC DIAGNOSIS: Lung: Granulomas, chronic, multifocal to coalescing, severe, with diffuse pleural fibrosis and rare intrahistiocytic acid-fast bacilli, Rhesus monkey (Macaca mulatta), nonhuman primate.
ETIOLOGIC DIAGNOSIS: Mycobacterial pneumonia
CAUSE: Mycobacterium tuberculosis
Signalment (#48.863-ML): 11 month-old, male Sannen goat (Capra aegagrus hircus)
HISTORY: This animal was part of a herd that had previously tested positive for bovine tuberculosis. It presented with fever, dyspnea, and claudication and tested positive for tuberculin cervical skin test.
SLIDE C: Lung: Affecting approximately 40% of this section, there are multifocal to coalescing granulomas that efface the pulmonary parenchyma, compress adjacent alveolar septa, collapsing the alveolar spaces, and elevate the pleural surface. Granulomas are centered on large areas of lytic necrosis with abundant eosinophilic karryorhectic and cellular debris with aggregates of mineral, surrounded by a layer of viable and degenerate neutrophils, surrounded by epithelioid macrophages with occasional multi-nucleated giant cells (Langhann’s and foreign-body type), further surrounded by lymphocytes and plasma cells with a rim of fibrous connective tissue. Adjacent alveolar septa are congested and thickened by macrophages, neutrophils, lymphocytes, and plasma cells. Alveoli occasionally contain pale eosinophilic fluid (edema) with increased numbers of alveolar macrophages. Blood vessels are occasionally surrounded by aggregates of lymphocytes and plasma cells. There is perivascular edema surrounding larger vessels. The pleural surface is moderately thickened by edema and increased fibrous connective tissue with scattered macrophages.
MORPHOLOGIC DIAGNOSIS: Lung: Granulomas, chronic, multifocal to coalescing, marked, Sannen goat (Capra aegagrus hircus), caprine.
ETIOLOGIC DIAGNOSIS: Mycobacterial pneumonia
CAUSE: Mycobacterium bovis
- Mycobacterium are small, facultative intracellular, aerobic, gram positive (but poorly staining), non-motile and non-spore-forming bacilli
- Mycobacteria are acid-fast because of the mycolic acid and high lipid content of their cell walls; also very resistant to heat, pH changes and many disinfectants
- Mycobacteria are generally divided into three large groups
- Tuberculosis group (referred to as tuberculosis complex or MTBC): M. tuberculosis, M. bovis, M. microti
- Leprosy group: lepraemurium, M. leprae, M. visibilis
- Opportunistic group:
- Rapid-growing: e.g. fortuitum, M. chelonae, M. abscessus
- Slow-growing: e.g. ulcerans, M. avium-intracellulare complex (MAIC) including M. avium spp. paratuberculosis
- Of the MTBC, tuberculosis and M. bovis are most common and the term “tuberculosis” is used to refer to either organism and the term “mycobacteriosis” used to refer to other nontuberculous mycobacteria
- Humans serve as reservoir for tuberculosis which most commonly infects non-human primates; M. bovis most commonly infects ruminants with many wildlife reservoirs (predominantly deer in the US)
- MTBC usually causes a rapidly progressive, fatal respiratory syndrome with early, widespread dissemination of lesions
- MTBC affects old and new world primates
- Natural resistance-associated macrophage protein (Nramp 1 & 2) is a membrane protein involved in innate immunity to bovis (in humans and mice) that is primarily expressed in macrophages and tissues of the reticuloendothelial system
- Important concepts include ability of mycobacteria to survive within macrophages and the cellular immune response to incite granulomatous inflammation and enhancing ability of macrophages to kill bacilli
- Route of infection is usually via inhalation of infected aerosol droplets and less commonly via gastrointestinal tract, cutaneous exposure, transplacental, and genital transmission
- Bacilli are ingested by alveolar macrophages which may destroy the organism; alternatively bacterium inhibits phagosome-lysosome fusion, allowing it to survive and replicate; macrophage triggers an innate immune response, recruiting additional inflammatory cells
- Phagocytized through interaction with pathogen pattern recognition receptors (PRRs) including complement receptors 1, 3, and 4, mannose, surfactant proteins, LAM, and CD14
- Macrophages cause a delayed type IV hypersensitivity reaction by acting as an antigen-presenting cell and secreting IL-12 which causes CD4+ TH1 lymphocytes to secrete IFN-gamma (which activates additional macrophages) and IL-2 (which induces proliferation and survival of T lymphocytes) leading to a cell-mediated immunityàtuberculoid granuloma
- Heavily infected macrophages die off forming the necrotic center
- Large numbers of organisms lead to extensive cell necrosis and tissue destruction; bacilli replicate extracellularly in the liquefied material
- Bacilli are released when tubercles rupture and enter the airways, spreading to other parts of the lung or may be coughed up and swallowed, entering the GI tract
- Mycobacterial virulence factors include proteins and cell wall components:
- Hydrophobic layer of mycolic acids: Bestows hydrophobicity to cell wallàenvironmental and antimicrobial resistance
- Cord factor (trehalose dimycolyl): Surface glycolipid that inhibits chemotaxis, acts as adjuvant and is leukotoxic; also main component of complete Freund’s adjuvant (CFA)
- Mycosides form a barrier against lysosomal digestion and allow organism to survive within macrophage
- Tuberculoproteins and purified protein derivatives are necessary for development of humoral and cell-mediated immune responses
- Sulfatides: Surface glycolipid containing sulfur which prevents fusion of phagosome with lysosome and interferes with reactive oxygen species
- Lipoarabinomannan (LAM): Heteropolysaccharide; inhibits macrophage activation by IFN-gamma, induces macrophages to secrete TNF-alpha (causes fever, tissue damage) and IL-10 (suppresses T cell proliferation), and can scavenge oxygen radicals
- ESAT-6: Implicated in lysis of phagosomal membrane, induction of apoptosis, expansion of granuloma, activation of inflammasome, induction of TNF-alpha secretion by T lymphocytesàmacrophage death
- MTBC: Known to divert host cellular metabolism to promote lipid body formation; MTBC prefers to catabolize host-cell cholesterol for carbonàshift to anaerobic functioningàdormant-like state
- Phthiocerol dimycocerosate (PDIM): Present on outermost surface of cell wall; influences TLR binding and activation of macrophages
- Mycobacteria secrete urease: Inhibits acidification of phagosomes
- Cell wall lipid lipomannan: Induces fusion of epitheliod macrophages, creating Langhans-type multinucleated giant cells
TYPICAL CLINICAL FINDINGS:
- Anorexia with listlessness, weakness, depression
- Progressive emaciation
- Cutaneous abscesses and peripheral lymphadenopathy
- Hepatomegaly, splenomegaly
- Coughing, exercise intolerance, progressive dyspnea
TYPICAL GROSS FINDINGS:
- Tubercles are circumscribed, often encapsulated, tan to yellow foci of granulomatous inflammation with a central core of caseous necrosis and/or mineralization and are the classic gross lesion
- Larger lesions may have a liquid or suppurative core
- In infections of tuberculosis in NHPs, caseous nodules in lungs, tracheobronchial lymph nodes, spleen, kidney, liver, intestine, and mesenteric lymph nodes
- In infections of bovis in cattle, respiratory infections most commonly have lesions in retropharyngeal, tracheobronchial, and mediastinal lymph nodes
- Other organs affected depend on the route of exposure and stage of disease and include regional lymph nodes, spleen, liver, kidney, intestine, mesenteric lymph nodes, vertebra, and spinal cord
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Tubercles are the classic lesion; central core of caseous necrosis with nuclear debris +/- mineral, surrounded by epithelioid macrophages and multi-nucleated giant cells, encapsulated by collagenous connective tissue with lymphocytes, plasma cells +/- neutrophils; acid-fast bacilli can be located within macrophages or extracellularly
- In elk and deer with bovis, suppurative inflammation may be prominent with less fibrosis and giant cells
- Fibrillar, electron-opaque nuclear area
- Periphery is densely filled with ribosomes
- Capsule in close contact with cell wall
ADDITIONAL DIAGNOSTIC TESTS:
- Intradermal tuberculin skin test (eyelid or abdominal skin)
- PCR, ELISA
- Special stains: Acid-fast (Fite-Faraco, Ziehl-Nielson) and the recently developed technique: Auramine O and Rhodamine B fluorescent stains
- Culture: Lowenstein-Jensen media, takes 4-8 weeks to culture ( tuberculosis prefers glycerol and is niacin-positive; M. bovis is inhibited by glycerol and is niacin-negative)
- Foreign body granuloma
- Cestode cysts
- Pneumonyssus simicola (lung mite): Important differential in macaques
- Bacterial diseases: Nocardiosis, actinomycosis, actinobacillosis, Fusobacterium necrophorum, Mycoplasma bovis
- Fungal diseases: Blastomycosis, aspergillosis, histoplasmosis, coccidiodomycosis
- Non-human primates are also susceptible to avium-intracellulare complex (MAIC) and many atypical mycobacteria
- Respiratory and enteric syndromes
- Most commonly bovis
- Extensive caseation and calcification of tubercles
- May spread to pleura (hard, white nodules=”pearl disease”)
- Usually enteric with lesions in retropharyngeal and mesenteric lymph nodes and intestine
- Most commonly MAIC
- caprae is most common with M. bovis and MAIC also occurring
- Usually respiratory syndrome, similar to cattle
- Very susceptible to MAIC; usually enteric with lesions in retropharyngeal and mesenteric lymph nodes and spreads hematogenously to lungs
- bovis, similar lesions as in cattle
- Guinea pigs
- Highly susceptible but natural disease is rare; tuberculosis and M. bovis
- Relatively resistant; MAIC most reported
- B6 and BALB/c carry Bcgs susceptibility allele
- DBA/2 and C3H/He carry Bcgr resistance allele
- bovis and M. tuberculosis; prone to develop cavitary pulmonary lesions and disseminated to other organs
- Uncommon; when it occurs, cats usually get bovis (very resistant to M. tuberculosis), while dogs more susceptible (to both species) than cats; M. microti also reported in dogs and cats
- Tuberculosis in dogs and cats often appears as granulation tissue; discrete tubercles are uncommon
- Usually enteric disease for cats, respiratory disease for dogs
- Dogs and cats are fairly resistant to MAIC (usually enteric)
- Rule out lepraemurium (feline leprosy); M. ulcerans is a rare cause of atypical mycobacteriosis in cats (ulcerative and nodular skin lesions)
- Most common chronic disease of aquarium fish; infects kidney, spleen, other viscera, skin, bones; not specific to respiratory system (gills)
- Most commonly marinum, M. fortuitum, M. chelonae, and others
- Only psittacines contract tuberculosis and M. bovis
- MAIC is common in other species; usually alimentary disease
- Koalas and opossums in Australia are naturally infected with ulcerans
- Most commonly tuberculosis with many cases of M. bovis.
- bovis and MAIC
- Spleen, liver, intestines
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