JPC SYSTEMIC PATHOLOGY

CARDIOVASCULAR SYSTEM

March 2025

C-P04 (NP)

 

SIGNALMENT (JPC #2019036): Cow

 

HISTORY: None

 

HISTOPATHOLOGIC DESCRIPTION: Heart: Focally expanding the myocardium of one section is a 3 x 3 mm larval cestode bladder containing a cross section of a 600µm diameter invaginated scolex (cysticercus). The bladder is surrounded by a 4 mm thick fibrous capsule admixed with abundant eosinophilic cellular and karyorrhectic debris (necrosis), numerous epithelioid macrophages, and fewer lymphocytes, plasma cells, and eosinophils. The cestode bladder wall is characterized by a peripheral 6µm thick, eosinophilic tegument surrounding an up to 60µm thick layer of spongy parenchyma with embedded 5 µm diameter, basophilic, round, calcareous corpuscles. The scolex has a 4 µm thick, eosinophilic tegument, spongy parenchyma, numerous calcareous corpuscles, and two muscular suckers. Replacing 50% of the second section of heart is a focally extensive area of dense fibrous connective tissue admixed with numerous lymphocytes, plasma cells, and macrophages, fewer eosinophils and neutrophils, and scattered foreign body-type multinucleate giant cells and mineralized debris. The small and medium caliber arteries located within the fibrous connective tissue have walls that are thickened up to 2x normal by medial smooth muscle hypertrophy. Multifocally the tunica media of arterioles are swollen, pale, and vacuolated (degeneration) and the tunica adventitia is thickened by concentric layers of pale, fibrillated fibrous connective tissue. Cardiomyocytes adjacent to areas of fibrosis are either hypereosinophilic and fragmented with pyknosis or karyolysis (necrotic) or vacuolated and swollen (degenerate), and myofibers are often separated by eosinophilic beaded to fibrillar material (fibrin) and increased clear space (edema). Multifocally, cardiac myocytes contain thin-walled, 100 X 200 µm protozoal cysts, which separate myofibrils and contain numerous 3 X 5 µm, basophilic, crescent-shaped bradyzoites (sarcocysts).

 

MORPHOLOGIC DIAGNOSIS:

1. Heart: Myocarditis, granulomatous and eosinophilic, chronic, multifocal, severe, with cardiomyocyte degeneration and necrosis, fibrosis and focal cestode larva (cysticercus), breed unspecified, bovine.

2. Heart, cardiomyocytes: Sarcocysts, intracellular, few.

 

ETIOLOGY: Cysticercus bovis

 

ETIOLOGIC DIAGNOSIS: Myocardial cysticercosis (and sarcocystosis)

 

GENERAL DISCUSSION:

• Sarcocystis spp. are discussed in M-P04
• Cysticercus bovis is a larval cestode (metacestode) that occurs in cattle and occasionally other herbivores worldwide; it preferentially infects heart and masticatory muscles (M-P03), although cysts may also occur in liver, lungs, CNS and lymph nodes
• The adult stage, Taenia saginata, is the most common and longest tapeworm in humans; it has 4 suckers and lacks a rostellum and hooks
• A cysticercus is a fluid-filled, thin-walled, muscular cyst, with an invaginated scolex and neck of a single tapeworm

 

PATHOGENESIS:

• Likely similar to the pig tapeworm, Cysticercus cellulosae (adult stage T. solium)
• Cysticerci are enclosed in a fibrous capsule derived from endomysium
• Induce a crescentic zone of degenerative lysis (presumably enzymatically) to allow growth of the cysticercus within the inelastic fibrous capsule
• Evade immune destruction by inactivating elements of the complement system
• Lymphocytes and variable number of eosinophils surround capsule
• Larvae are eventually destroyed by the immune system, mineralized, and removed

 

LIFE CYCLE: 

• Humans with adult intestinal tapeworm pass gravid proglottids in feces > proglottids rupture releasing eggs > eggs eaten by intermediate host > egg hatches in the duodenum > released hexacanth or oncosphere penetrates the mucosa and enters intestinal vasculature > circulates to muscle and other tissues > develops into encysted cysticercus form 
• Human infected by eating insufficiently cooked beef or veal containing cysticerci
• Bile salts cause evagination of the scolex and neck, and subsequent budding; the larva attaches to the intestinal mucosa and develops into an adult

 

TYPICAL CLINICAL FINDINGS:

• Usually asymptomatic in cattle
• Rare cases of massive infection result in pyrexia, weakness, anorexia, and death

 

TYPICAL GROSS FINDINGS:

• One or more white to gray cysts, <1 cm in diameter, projecting from the surface of the heart, skeletal muscle, or other tissue
• Cysticercus bovis larvae prefer the heart and masticatory muscles but may be found in many different muscles or other organs

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Myofibers displaced by cyst; surrounded by a fibrous capsule and minimal lymphohistiocytic and eosinophilic inflammation
• Cysticerci: The invaginated scolex and neck are composed of an eosinophilic tegument, parenchyma containing calcareous corpuscles, and a web-like, lightly eosinophilic matrix, suckers, scolex with no hooklets, surrounded by a thin-walled cyst
• Glycoprotein-rich cyst wall provokes little host reaction when intact; rupture evokes granulomatous inflammation, fibrosis, and mineralization

 

ADDITIONAL DIAGNOSTIC TESTS:

• Identification of eggs/proglottids
• PCR

 

DIFFERENTIAL DIAGNOSIS:

• Echinococcosis granulosus (D-P28B): Hydatid disease
  • Definitive host (host of the adult tapeworm): Dogs and wild carnivores
  • Intermediate host (host of the metacestode): Sheep, cattle, horses, cervids, swine, apes, and humans
  • Larval stages form unilocular hydatid cysts that localize in the lung, liver, and other organs
  • Thick outer membrane, encasing a germinal membrane that contains brood capsules connected to the membrane by a stalk; brood capsules containing many ovoid, hooklet-laden scolices
  • Hydatid cysts are usually surrounded by mononuclear cells, eosinophils, giant cells, and fibrosis; in humans most cysts are located in the liver
  • Cysts may calcify or rupture, resulting in a severe inflammatory reaction or death

 

COMPARATIVE PATHOLOGY:

 

• Swine: 
  • T. solium is the pork tapeworm; metacestode is C. cellulosae; majority of larvae (Cysticercus cellulosae) are found in the heart, masseter, tongue, and shoulder muscle
  • Humans can be definitive and intermediate hosts for T. solium (the cause of neurocysticercosis in humans, the leading cause of seizures and epilepsy in the developing world); cysticerci often develop in cerebral or ocular locations and can be fatal
  • Adults have a rostellum with hooks, and the metacestode has hooks
• Rats: Cysticercus fasciolaris (D-P22) associated hepatic fibrosis and granulomatous inflammation may progress to fibrosarcoma; additional lesions include gastric and intestinal hyperplasia
• Sheep: Infection of Coenurus cerebralis (N-P12B) in sheep is known as “gid”
• Birds: Cestodes are common in poultry, wild birds, and wild-caught pet bird; typically do not cause significant disease, except with high parasite loads

 

REFERENCES:

1. Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents and Rabbits. 4th ed. Ames, IA: Blackwell Publishing; 2016:153.
2. Bowman DD. In: Bowman DD, ed. Georgis’ Parasitology for Veterinarians. 10th ed. St. Louis, MO: Saunders Elsevier; 2013:145-147.
3. Cooper BJ, Valentine BA. Muscle and tendon. In: Maxie MG, ed. Jubb, Kennedy and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. St. Louis, MO: Elsevier; 2016:239-240.
4. Fitz-Coy SH. Parasitic Diseases. In: Boulianne M, ed. Avian Disease Manual. 8th ed. Jacksonville, FL: American Association of Avian Pathologists, Inc; 2019:103-132, 145.
5. Gardiner CH, Poyton SL. An Atlas of Metazoan Parasites in Animal Tissues. Washington, DC: American Registry of Pathology; 2006:50-55.
6. Lowenstine LJ, McManamon R, Terio KA. Apes. In: Terio K, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals, San Diego, CA: Elsevier 2018: 400.
7. Schmidt RE, Struthers JD, Phalen DN. Pathology of Pet and Aviary Birds. 3rd ed. Hoboken, NJ: John Wiley & Sons, Inc.; 2024:180-182,495,537,585.
8. Valentine BA. Skeletal muscle. In: McGavin MD, Zachary JF, eds. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022: 1011.

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