JPC SYSTEMIC PATHOLOGY

CENTRAL NERVOUS SYSTEM

January 2023

N-B06

Signalment (JPC #1492918): A monkey

HISTORY: This monkey developed seizures

HISTOPATHOLOGIC DESCRIPTION: Slide A: Cerebrum: Multifocally effacing 50% of the section, elevating the pia mater, and affecting both gray and white matter are multiple, well-circumscribed, coalescing granulomas up to 5 mm in diameter centered on a dense aggregate of cellular and karyorrhectic debris with loss of cellular architecture (lytic necrosis) admixed with basophilic, finely granular mineral and degenerate neutrophils. Necrotic areas are bordered by a rim of abundant epithelioid macrophages admixed with fewer scattered multinucleated giant cells (Langhans and foreign-body type) and are further bounded by a rim of lymphocytes and plasma cells. These inflammatory cells infiltrate the adjacent, less affected tissue. At the periphery of the granulomas are increased numbers of small caliber vessels lined by hypertrophied (reactive) endothelium. The neuropil between granulomas contains multifocal areas of rarefaction characterized by increased pallor with loss of neuropil (necrosis), moderate numbers of foamy macrophages (gitter cells), reactive astrocytes with abundant eosinophilic cytoplasm and eccentric nuclei (gemistocytic astrocytes), increased numbers of glial cells (gliosis), and edema (spongiosis). The scant remaining leptomeninges present in this section are mildly expanded by lymphocytes, plasma cells, and macrophages.

Slide B: Acid fast stain: Cerebrum: Rarely, within necrotic cellular debris and within the cytoplasm of multinucleate giant cells, there are few 5-6µm in length acid-fast bacilli.

MORPHOLOGIC DIAGNOSIS: Cerebrum: Granulomas, multifocal to coalescing, severe, with gemistocytosis, gliosis, and rare extracellular and intrahistiocytic acid-fast bacilli, monkey, non-human primate.

CAUSE: Mycobacterium tuberculosis

ETIOLOGIC DIAGNOSIS: Cerebral mycobacteriosis

GENERAL DISCUSSION:

Mycobacterium Tuberculosis Complex (MTC) encompasses mycobacterial spp. that are capable of generating a tuberculoid granuloma, to include: Mycobacterium tuberculosis, Mycobacterium africanum, Mycobacterium bovis, Mycobacterium microti, Mycobacterium canettii, Mycobacterium caprae, Mycobacterium pinnipedii, Mycobacterium suricattae, Mycobacterium mungi, Mycobacterium dassie, and Mycobacterium oryx

Mycobacterium sp. are non-motile, gram-positive (but almost unstainable), acid-fast, non-spore forming, facultative intracellular, aerobic bacilli
M. tuberculosis and M. bovis are the most common etiologies producing mediastinal lymphadenopathy in NHPs

There is no apparent difference in distribution and character of the lesions produced by these two species

Tuberculosis in NHP is most commonly acquired from humans via aerosol
M. tuberculosis affects Old World primates more often than New World primates; cynomolgus macaques are best model of human disease
Mycobacterium sp. most frequently cause granulomatous pneumonia (P-B10) and enteritis (D-B09, D-B10) in various species; CNS manifestations are rare
In humans and mice, resistance to M. bovis is related to allelic variation in the natural resistance-associated macrophage protein (Nramp) genes 1 and 2

PATHOGENESIS:

Transmission primarily by aerosol droplet inhalation (although ingestion of infected materials can occur)
Virulence factors:

Proteins – immunomodulation and protection against reactive oxygen species and reactive nitrogen intermediates
Cell wall components

Lipoarabinomannan (LAM) – prevent phagosomal maturation through transient inhibition of cytoplasmic Ca²⁺
Cord factor (dimycolyl trehalose) - surface glycolipid that inhibits chemotaxis, acts as adjuvant and is leukotoxic
Sulfatides - surface glycolipid containing sulfur which prevents fusion of phagosome with lysosome and interferes with reactive oxygen species
Mycobacteria secrete urease - inhibits acidification of phagosomes
Cell wall lipid lipomannan induces fusion of epitheliod macrophages, creating Langhans-type multinucleated giant cells

Mycobacterial components [LAM, lipomannan, phosphatidylinositol mannosides (PIMs), 19-kDa lipoprotein, trehalose dimycolate (TDM)] are recognized by pattern recognition receptors (PRR), bind and initiate proinflammatory cascades
M. tuberculosis enter macrophages by binding DC-SIGN via cell wall component ManLAM, with a lesser role played by CR3 and MR
Initial pulmonary infection:

M. tuberculosis enters macrophages by endocytosis mediated by several macrophage receptors: Mannose receptors bind lipoarabinomannan, a glycolipid in the bacterial cell wall, and complement receptors bind opsonized mycobacteria
Once inside the macrophage, M. tuberculosis organisms replicate within the phagosome by blocking fusion of the phagosome and lysosome; M. tuberculosis blocks phagolysosome formation by inhibiting Ca²⁺ signals and the recruitment and assembly of the proteins that mediate phagosome-lysosome fusion

Without prior sensitization bacteria proliferate in the pulmonary alveolar macrophages and airspaces during the earliest stage of primary tuberculosis (< 3-weeks), which leads to bacteremia and seeding of multiple sites

Development of delayed (Type IV) hypersensitivity:

At approximately 3-weeks after infection, a T-helper 1 (T_H1) response activates macrophages to become bactericidal due to mycobacterial antigens that enter draining lymph nodes and are displayed to T cells
Differentiation of T_H1 cells depends on IL-12, which is produced by antigen-presenting cells that have encountered the mycobacteria; M. tuberculosis makes several molecules that are ligands for TLR2, and stimulation of TLR2 by these ligands promotes production of IL-12 by dendritic cells
Maturation of T_H1 cells, both in lymph nodes and in the lung, produce IFN-γ that ultimately aids in mycobacterial killing and the paucibacillary character of M. tuberculosis granulomas;

INF-γ is the critical mediator that enables macrophages to contain the M. tuberculosis infection through four key mechanisms;

(1) Stimulates formation of the phagolysosome in infected macrophages, exposing the bacteria to an inhospitable acidic environment
(2) Stimulates expression of inducible nitric oxide synthase (iNOS), which produces nitric oxide, capable of destroying several mycobacterial constituents, from cell wall to DNA
(3) Mobilization of antimicrobial peptides (defensins)
(4) Stimulates autophagy to remove damaged organelles and M. tuberculosis

T_H1 response also orchestrates the formation of granulomas and caseous necrosis; macrophages activated by IFN-γ differentiate into the “epithelioid histiocytes” that characterize the granulomatous response, and may fuse to form giant cells; this response halts the infection before significant tissue destruction or illness; in other cases the infection progresses due to advanced age or immunosuppression, and the ongoing immune response results in tissue destruction due to caseation and cavitation; activated macrophages also secrete TNF, which promotes recruitment of more monocytes
NK-T cells that recognize mycobacterial lipid antigens bound to CD1 on antigen-presenting cells, or T cells that express a γδ T-cell receptor, also make IFN-γ
TLR4, TLR9, and TLR adaptor molecule, MyD88 play important protective rolls during M. tuberculosis infection

TYPICAL CLINICAL FINDINGS:

Non-specific initially; followed by depression, vomition, behavioral changes, cachexia
Seizures
Occasional sudden death
In Old World monkeys, commonly results in a rapidly progressive, debilitating disease

TYPICAL GROSS FINDINGS:

Pulmonary: Caseous (tuberculous) nodules in the hilar lymph nodes and lung that extend into the thoracic pleura; lesions may be cavitary; hallmark of disease is typical tubercle
Widely disseminated, multifocal, pinpoint to large, nodular foci of confluent, caseous granulomas to most major organs (especially spleen, kidney, liver, and various lymph nodes); cerebral mycobacteriosis may manifest as meningitis or as an intraparenchymal tuberculoma
Meningitis: Granular roughening or gelatinous appearance of the meninges; rare in non-human primates
Granulomas may involve adjacent bone and dura

TYPICAL LIGHT MICROSCOPIC FINDINGS:

Focal, typical granulomas may surround a necrotic, occasionally mineralized, core
Lymphocytes, plasma cells and epithelioid macrophages surround the core
Multinucleated giant cells common at the periphery of the granuloma
Involved vessels exhibit obliterative endarteritis
In chronic lesions, fibrous, adhesive arachnoiditis develops
Acid fast bacilli are rarely detectable due to macrophage activation in killing M. tuberculosis as a process of granuloma formation

ULTRASTRUCTURAL FINDINGS:

Mycobacterial features: Twisted bacillus shape; fibrillar, electron-opaque nuclear area; periphery is densely filled with ribosomes; capsule in close contact with cell wall

ADDITIONAL DIAGNOSTIC TESTS:

Acid fast (depends on the amount and spatial arrangement of mycolic acids and their esters within the bacterial cell wall)
Intradermal tuberculin skin test (eyelid or abdominal skin; I-M01)
Culture and PCR necessary for speciation

DIFFERENTIAL DIAGNOSIS:

Meningitis in nonhuman primates:

Streptococcus pneumoniae: the most common cause of fibrinopurulent meningitis/meningoencephalitis in non-human primates; dull, thickened and opaque leptomeninges; fibrinopurulent meningoencephalitis; necrotizing vasculitis, possibly with thrombosis
Cytomegalovirus (CMV): Betaherpesvirus; suppurative to nonsuppurative meningoencephalitis with necrosis and fibrinous exudates and characteristic intranuclear inclusion bodies; usually observed with SIV
Cryptococcus neoformans: Common opportunistic infection
Neisseria meningitides
Haemophilus influenzae
Pseudomonas aeruginosa
Pasteurella multocida
Klebsiella pneumoniae
Listeria monocytogenes

COMPARATIVE PATHOLOGY:

Nontuberculous mycobacterial infections in nonhuman primates:

M. avium associated with SIV and chronic diarrhea

M. avium ss. paratuberculosis - Johne’s disease
M. avium-intracellulare
Atypical mycobacteria: M. marinum, M. kansasii, M. lepraemurium

Cattle:

M. bovis – zoonotic, pneumonia, case report of penile tuberculosis in a bull (J Comp Pathol. 2020)
M. avium ss. paratuberculosis - Johne’s disease
M. caprae - Report of natural infection causing GI granulomas in multiple animals (J Comp Pathol. 2020)

Cervids

M. bovis reservoir for cattle
Case report of M. kansasii disseminated infection in a white-tailed deer (J Vet Diagn Invest. 2020)

Horses: Often alimentary with lesions in retropharyngeal and mesenteric lymph nodes and intestine

M. bovis most common in the horse
M. avium, proliferative tuberculoid granulation tissue resembling lardaceous or sarcomatous lesions described in equine tuberculosis
Case report of equine rhinitis from M. intracellulare (M. avium complex pathogen) (J Comp Pathol. 2019)

Sheep and goats: Rare pneumonia
Swine: Often systemic; M. bovis, similar lesions as in cattle;
Dog & Cat: Discrete tuberculoid granulomas are uncommon; lesions usually appear as granulation tissue with random scattered macrophages and giant cells

20 cases of feline ocular granulomas from MTC pathogens M. bovis, M. microti, or non-speciated MTC (Vet Pathol. 2022)
M. avium ss. hominissuis reported in 8 mini schnauzers (J Vet Diagn Invest. 2017)
Case report of dog with M. tuberculosis (J Vet Diagn Invest. 2022)
M. lepraemurium in cats

African clawed frogs: M. marinum; sarcoma-like inflammatory response
Birds: M. avium complex; CNS infection very rare; most often GI portal of entry
Fish: “fish tank granuloma” M. marinum, M. fortuitum; zoonotic. Also M. chelonae.
Guinea pigs: M. bovis and M. tuberculosis; highly susceptible to tuberculosis experimentally, natural disease is rare; disseminated caseating tubercles in lung, spleen, liver, lymph nodes (cervical, portal, inguinal, prescapular)
Hamster: rare.

M. tuberculosis - laboratory inoculation.
M. chelonae - Single report: pet hamster with granulomatous swelling of feet and lymph nodes

Mice:

Laboratory mice are susceptible to experimental infections with Mycobacteria, naturally occurring infections are rare
Rise in interest using mice (B6 strain preferred strain) as a model for nontuberculous mycobacterial infections b/c of their importance in AIDS patients
B6 and BALB/c mice carry a susceptibility (Bcg s) allele, and DBA/2 and C3H/He carry a resistance (Bcg r) allele – determinant of phagocytic host defense mechanisms that control intracellular pathogen infections
M. chelonae - tail lesions reported in immunocompromised mice (RAG1, T-cell receptor, Fas ^1pr null, and thymectomized mice)

Rabbits:

Highly susceptible to M. bovis and M. tuberculosis - extrapulmonary lesions typical of tuberculosis with granulomas, giant cell formation, multibacillary
Wild European rabbits are reservoir of M. avium ss. paratuberculosis (Johne’s)

Laboratory rabbits are valued models of TB due to cavitary pulmonary lesions

Lemurs (ring-tailed, ruffed, black, and mongoose):

M. tuberculosis infection results in formation of granulomatous inflammation or granulomas, few intralesional acid-fast positive bacilli; pulmonary infection is most common
62 cases of MTC pathogen M. mungi in wild banded mongooses (Mungos mungo) causing lymphogranulomatous infiltrate in nasal planum, anal sacs, LN, liver, spleen, lung (Vet Pathol. 2018)

Elephants: Infection most often result in pulmonary disease with spread to thoracic lymph nodes. Indian elephant more susceptible than African
Free ranging rhinos: M. bovis or M. tuberculosis have been reported to cause granulomas in lungs and lymph nodes
Hyrax:

Mycobacterium widely reported
MTC species known as “dassie bacillis”, M. microti, M. africanum, M. microti-like bacteria reported in some cases
Weight loss, lameness, pneumonia, reproductive failure
Granulomas found in the lungs, liver, spleen, and kidneys with acid-fast bacilli

Cetaceans (whales):

Atypical mycobacteriosis; ulcerative dermatitis, panniculitis, pneumonia, lymphadenitis due to M. marinum, M. chelonae, M. abscessus

Pinnipeds (seal/sea lions):

MTC member M. pinipedii generally respiratory disease either:

1.) Granulomatous pleuropneumonia and thoracic lymphadenitis or
2.) Caseating granulomas within the lungs and thoracic LNs

Sirenia (manatees etc.)

Granulomas in lung, pleura, LN, testicle, skin
M. marinum, M. fortuitum, M. kansaii, M. chelonae

Reptiles, bony fish, and amphibians: most commonly non-tuberculoid granulomatous dz. In skin/systemic, multiple species but M. marinum, M. fortuitum, M. chelonae most common.

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