JPC SYSTEMIC PATHOLOGY
DIGESTIVE SYSTEM
August 2021
D-B10

SIGNALMENT (JPC #1575721):  Adult coturnix quail

HISTORY:  The animal was on display in a zoo.

HISTOPATHOLOGIC DESCRIPTION:  

Slide A: Liver:  Effacing and replacing over 90% of normal hepatic architecture and multifocally elevating the capsule are numerous variably sized, up to 1 mm diameter, coalescing granulomas.  Granulomas are composed of a necrotic central core of brightly eosinophilic cellular and karyorrhectic debris surrounded by numerous epithelioid macrophages and multinucleate giant cells of both Langhans and foreign body type, admixed with fibrin and further surrounded by hypertrophied, reactive fibroblasts and concentric fibrous connective tissue admixed with numerous lymphocytes and plasma cells.  Moderate numbers of 1x2 um amphophilic bacilli are present extracellularly within the central necrotic cores as well as within the cytoplasm of multinucleate giant cells.  Diffusely between granulomas, hepatocytes are often surrounded and individualized by, or lost and replaced by, abundant fibrous connective tissue (fibrosis) and increased numbers of small bile ducts (biliary ductular reaction).  Diffusely, the small amount of remaining hepatic plate/cord architecture is disorganized.

Slide B: (Acid-fast):  Liver:  Multifocally within areas of lytic necrosis and within the cytoplasm of macrophages and multinucleated giant cells are low to moderate numbers of acid-fast 1x2 um bacilli.

MORPHOLOGIC DIAGNOSIS:  Liver:  Granulomas, multifocal to coalescing, marked, with marked fibrosis, bile ductular reaction, and moderate numbers of intrahistiocytic and extracellular acid-fast bacilli, etiology consistent with Mycobacterium spp., Coturnix quail (Coturnix coturnix), avian.

ETIOLOGIC DIAGNOSIS:  Hepatic mycobacteriosis

CAUSE:  Mycobacterium avium ssp. avium

CONDITION:  Avian mycobacteriosis

SYNONYMS:  Avian tuberculosis, Mycobacterium avium complex (MAC); Mycobacterium avium-intracellulare complex (MAIC)

GENERAL DISCUSSION:

• Small, aerobic, nonspore-forming, nonmotile, weakly gram-positive, acid-fast (specifically Ziehl-Neelsen) bacilli (acid-fast due to mycolic acid in cell wall)
• Mycobacteria are widely distributed saprophytes and may survive in the soil for years and have high resistance to heat, cold, water, dryness, pH changes, and many disinfections
• Mycobacterium are divided into two or three groups depending on the classification system used:
• Two groups:
  • Tuberculous mycobacteria: cause tuberculosis ( bovis, M. tuberculosis)
  • Nontuberculous or atypical mycobacteria: cause mycobacteriosis ( M. fortuitum, M. smegmatis, some members of M. avium, etc.); typically cause disease in immunocompromised hosts)
• Three groups:
  • Tuberculosis group: obligate pathogens tuberculosis, M. bovis, M. microti
  • Leprosy group: obligate pathogens lepraemurium
  • Opportunistic group, further subdivided by growth rate; mycobacteriosis is more commonly caused by the rapidly growing opportunistic mycobacteria (also known as atypical mycobacteria)
    • Rapid-growing opportunistic fortuitum, M. smegmatis, M. chelonae, M. abscessus, M. thermoresistibile;
    • Slow-growing opportunistic avium-intracellulaire complex, M. kansasii, M. ulcerans
• Avian mycobacteriosis:
  • A slow-spreading, usually chronic, granulomatous infection of semimature or mature birds of many species characterized by progressive weight loss and ultimately emaciation and death
  • Avian tuberculosis occurs in many kinds of birds but can also affect many mammals (swine are most frequently infected, but also cattle, horses, sheep, and nonhuman primates)

 

PATHOGENESIS:

• Fecal-oral transmission primarily via ingestion (contaminated soil +/- fomites, wild bird contact) à bacteria bind to enterocytes, form round to oval nodules (tubercles) that develop into diverticuli along the intestine à intermittent bacteremia with hematogenous spread to most other organs, bacterial shedding into feces
• Important concepts in the pathogenesis of tuberculosis (and mycobacteriosis) include the ability of mycobacteria to survive within macrophages and the role of cellular immune responses in inciting granulomatous inflammation and enhancing the ability of macrophages to kill bacilli
• Mycobacterial cell walls contain, in addition to the components found in other bacteria, a large hydrophobic layer of mycolic acids which bestows hydrophobicity, conferring environmental and antimicrobial resistance, and are important inducers of the initial macrophages response and, together with peptidoglycan (muramyl dipeptide), are responsible for most of the adjuvant activity that facilitates recruitment of antigen-presenting cells; other adjuvant activity is due to tuberculoproteins including purified protein derivative (PPD) capable of eliciting delayed-type hypersensitivity reactions used as the basis for intradermal skin testing (see I-M01)
• Increased virulence is associated with increased cell wall content of glycolipid, trehalose dimycolate (cord factor), and increased acid-fastness
• Intracellular survival due to cell wall glycolipids (mycosides) that protect against lysosomal digestion via inhibition of phagosome-lysosome fusion
• Mycobacterial resistance is partly related to allelic variation in the natural resistance-associated macrophage protein (Nramp) genes 1 and 2 which affect intracellular survival of pathogens by modifying lysosomal transport of divalent cations (e.g. iron and manganese)

 

TYPICAL CLINICAL FINDINGS:

• Chickens: Progressive wasting leading to uniquely extreme emaciation (although the appetite is usually maintained), diarrhea, occasional lameness, pale skin of face, wattles, and comb
• Prolonged disease course with high morbidity and mortality

 

TYPICAL GROSS FINDINGS:

• Firm, grayish-yellow granulomas (tubercles) often attached to and scattered along the periphery (i.e. antimesenteric surface) of the intestine
• Smaller, discrete granulomas are usually present in parenchymous organs (especially liver, spleen)
• In advanced cases, few organs are spared, and tubercles can be identified in the bone marrow of the femur
• The lung often has few/no lesions

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Tubercular form: Granulomas with central caseous core rimmed by multinucleated giant cells, epithelioid macrophages, lymphocytes, and plasma cells, sometimes with a rim of fibroblasts/connective tissue; typically with large numbers of acid-fast bacilli in the necrotic core and cytoplasm of macrophages (multibacillary); associated with more chronic disease; mineralization is rare in birds
• Atypical form (seen in psittacine birds, mammals): Diffuse infiltration of large numbers of histiocytes with many intracellular acid-fast bacteria; more often in acute disease

 

ADDITIONAL DIAGNOSTIC TESTS:

• PCR, IHC
• Cytology: impression smears from centers of tubercles readily reveal acid-fast bacilli
• Culture/bacterial identification – very slow-growing
• Special stains:
  • Acid fast stain (e.g. Fite-Faraco, Ziehl-Neelson): carbol-fuschin followed by decoloration with inorganic acids; acid-fastness depends on the amount and spatial arrangement of mycolic acids and their esters in the bacterial wall
  • Fluorescent dyes (e.g. auramine)
• Tuberculin test (wattle in birds) is available but has fallen into disuse
• ELISA to detect antibodies in serum

 

DIFFERENTIAL DIAGNOSIS:

For nodular lesions in birds:

• Neoplasia
• Fowl cholera (Pasteurella multocida): Gram negative bacilli; not acid-fast
• Salmonellosis (Gram negative bacilli; not acid fast):
  • Fowl typhoid (Salmonella gallinarum): Enlarged liver with greenish tint
  • Pullorum Disease (Salmonella pullorum): Tibiotarsal joint edema; grey miliary necrosis in lungs, liver, gizzard walls & intestines
• Escherichia coli (Hjarre’s Disease): Coligranulomas – granulomas in liver and intestinal tract; gram negative; not acid-fast

 

COMPARATIVE PATHOLOGY:

Selected mycobacterial disease in other species:

• Non-human primates: susceptible to avium-intracellulare complex (MAIC) and many atypical mycobacteria, causing thickened, corrugated small intestine and abdominal lymphadenopathy without tubercle formation, calcification, or fibrosis; also susceptible to M. tuberculosis complex (MTC) infection (see P-B10)
• Ruminants:
  • Johne’s Disease: avium subsp. paratuberculosis (MAP, see D-B09), most common in domestic ruminants but spontaneous disease can occur in free-ranging and captive nondomestic ruminants, camelids, and rabbits, equids, swine, and captive primates;
  • Tuberculosis: most commonly bovis in cattle, M. caprae and M. bovis in sheep and goats (See P-B10)
  • Bovine cutaneous opportunistic mycobacteriosis (formerly known as skin tuberculosis): In cattle, single to multiple 1-8cm diameter, pyograulomatous and fibrotic nodules of the dermis and subcutis often of the lower legs, occasionally affecting lymphatics (i.e. lymphangitis) are thought to be caused by atypical mycobacteria ( kansasii has been identified in some cases) and may cause false positives to bovine tuberculin tests
  • Dairy Cattle: avium ssp. paratuberculosis is associated with raised somatic cell count in dairy cattle
• Swine: avium complex (MAC) causes mycobacteriosis, often from ingestion of infected chicken or contaminated litter; mesenteric and mandibular lymph nodes and tonsils often affected, less commonly spleen, intestine, liver, and rarely lung
• Horses: Typically very resistant; sporadically infected with bovis, M. tuberculosis, or M. avium complex; typically via ingestion with GIT and associated lymph nodes affected and hematogenous dissemination to lungs; tubercules typically lack mineralization and resemble sarcoma-like nodules
• Dogs: Very resistant to mycobacteriosis
  • Rare atypical mycobacteriosis caused by Mycobacterium avium complex or other saprophytic mycobacteria is the result of contamination of a skin wound (canine leproid granuloma syndrome); 2017 report of generalized clinical signs associated with avium subsp. hominissuis and M. fortuitum
  • Mycobacterium avium-intracellulaire complex (MAIC) can occur in dogs especially in the southern United States, resulting in randomly distributed (hematogenous) hepatic granulomas;
  • Tuberculosis ( bovis or M. tuberculosis) transmitted via inhalation or ingestion resulting in pulmonary or GI granulomas, less often via skin inoculation resulting in cutaneous granulomas
• Cats:
  • Atypical mycobacterial infection is rare but more common in cats; recurrent pyogranulomatous skin nodules often in the inguinal dermis/subcutis often with draining sinuses; microscopically, organisms are more often extracellular in vacuoles sometimes lined by neutrophils; skin lesions may cause “pseudotumor” with unique proliferation of spindle-shaped histiocytes and intracellular bacteria; infections with slow-growing opportunistic mycobacteria tend to be disseminated resembling tuberculosis; recent reports of non-tuberculous Mycobacterium causing disseminated mycobacteriosis in cats
  • Feline leprosy caused by lepraemurium and probably other mycobacteria develops in cats living in cold, wet areas of the world (see I-B04)
• Rabbits:
  • Paratuberculosis: wild European rabbits are commonly infected with avium subsp. paratuberculosis that causes enteric disease similar to ruminants; serve as a significant reservoir for livestock infection and zoonotic potential should be considered between pet rabbits and their owners
  • Tuberculosis: Rabbits are fairly susceptible to tuberculosis and M. bovis but natural infections are rare; serve as a good lab model for human tuberculosis
• Rodents:
  • Mice: Laboratory mice are susceptible to experimental infections, but natural infections are rare; there are rare documented outbreaks of MAIC causing granulomas in lung, liver, and mesenteric lymph nodes; there are rare reports of tail infections with chelonae causing granulomas and osteomyelitis in several types of immunocompromised mice
  • Hamsters: Mycobacteriosis has been reported but is rare; reports include inadvertent inoculation with tuberculosis causing disseminated tuberculosis, and M. chelonai causing enlarged feet and lymph nodes with granulomatous inflammation in a pet hamster
  • Guinea pigs: Highly susceptible to tuberculosis ( tuberculosis, M. bovis) experimentally, but natural disease is rare and acquired presumably through human contact
• Wallabies: 2015 report of disseminated mycobacteriosis caused by avium subsp. avium causing flaccid paraplegia and osteomyelitis in 2 wallabies
• Banded Mongoose: Mycobacterium mungi (Mycobacterium tuberculosis complex) causes multifocal irregular granulomatous infiltrates in multiple organs, and or non-caseating granulomas with variable acid fast bacilli presence (prototyical granuloma formation uncommon)
  • Most commonly affected tissues included lymph nodes, liver, spleen, anal glands/sacs; other affected tissues included nasal mucosa and nasal planum;
  • Pathogenesis associated with scent marking behavior – unique exposure route
• Amphibians and fish: Most commonly associated with atypical mycobacterial species (i.e. such as M. marinum, M. chelonei, M. fortuitum); may be systemic.visceral (kidney, liver, spleen, etc.) and/or cutaneous; often associated with pigmented macrophages
• White-tailed Deer: characteristicls of subclinical paratuberculosis in white-tailed deer resemble those of cattle and red deer; no reported necrotizing granulomas in white tailed deer

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