Trichinosis - Acute

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TRICHINELLOSIS

Evolution
Larvae
Cysts
Inflammation
Muscle fibers
Infection
Myopathy
Necrosis
Chronic

Trichinellosis: Active

Trichinella Myopathy: Evolution

Initial stages
- Ingestion of foodbourne cysts
- Systemic spread of larvae
Small larvae
- Emerge from vessels
- Invade muscle fibers
  - Produce delta shaped lesions in fibers
  - May be present within, or at edge of, delta lesions
Larval growth
- Larvae: Progressive increased size within muscle fibers
- Muscle fibers
  - Develop difusely abnormal internal architecture
  - Some fibers become necrotic
- Eventually surrounded by capsule and move to extracellular space
Histiocytic inflammation
- Replaces muscle fiber cytoplasm in fibers with larvae
- Surround larvae that become extracellular
- Muscle has multifocal cellularity
Cysts
- Extracellular larvae become surrounded by cysts composed of collagen
- Cysts contain larvae, nurse cells and fluid
- Cysts often have little associated inflammation
- Cysts containing larvae are infectious if ingested and wall is degraded
Chronic
- Cyst walls can persist without organisms
- Some cysts develop calcification inside

Trichinellosis: Active Myopathy

Multifocal
Fiber size: Varied
Necrosis
Replacement of muscle fibers by histiocytic cells
Regeneration
Focal invasion: Scattered

Myopathy: Multifocal, Ongoing

H&E stain

H&E stain

Muscle containing Cysts, Unencysted larvae, Giant cells & Muscle fiber necrosis

Muscle fibers: Necrosis & Replacement by large histiocytic cells

H&E stain

Gomori trichrome stain

Muscle fibers
Ongoing myopathy: Necrosis & Replacement by large histiocytic cells
Chronic changes: Internal nuclei in some muscle fibers

VvG stain

Muscle Fiber Damage: Stages

Muscle Fiber Necrosis
Pale muscle fiber cytoplasm (Arrow)

H&E stain

Muscle Fiber Necrosis: Cell invasion
Cells in muscle fiber cytoplasm

H&E stain

Muscle Fiber Necrosis: Cell replacement
Cells (Large, Histiocytic) replace muscle fiber

H&E stain

Trichinellosis: Muscle Fiber Invasion

VvG stain

VvG stain

Δ (Delta) lesions (White arrow)
Focal, Subsarcolemmal (Early) changes in muscle fibers after larval invasion

H&E stain

NADH stain

H&E stain

Inclusions in Muscle fibers

VvG stain

VvG stain

Inclusions in muscle fibers: Possible trichina larva within muscle fibers

VvG stain

NADH stain

Muscle fibers: Other pathology

VvG stain

VvG stain

Muscle Fibers
Necrosis
Vacuolation
Invasion by larvae

VvG stain

VvG stain

Trichinellosis: Larvae

Extracellular, in endomysium, indenting muscle fibers

H&E stain

PAS stain

Trichinellosis: Unencysted extracellular larvae

H&E stain

H&E stain

Unencysted larva (White arrows)
Inflammatory foci: Surround extracellular, unencysted larva
- Many cells in the infiltrates are histiocytes (macrophages) that
  - Contain nuclei that are larger and paler than those in T-cells
  - Stain with acid phosphatase and esterase (Below)
- May include multinucleated giant cells (Above, Right; Below)

Acid phosphatase stain

Esterase stain

Multinucleated Giant Cell containing a Larva

H&E stain

Larva, extracellular: Surrounded by cells

VvG stain

Trichinellosis: Cysts Contain larvae & Nurse cells
Congo red stain	Gomori trichrome stain
Larvae: Encased in cysts within muscle Each cyst contains one coiled larva (Strongly stained by PAS (Below)) Cysts also contain "nurse" cells with large nuclei The outer edge of the cyst is a well-defined wall "Fluid" in cysts stains with NADH & Alkaline phosphatase(Below) There is little inflammation around well-formed cysts