JPC SYSTEMIC PATHOLOGY
CARDIOVASCULAR SYSTEM
April 2022
C-P06

 

SIGNALMENT (JPC #2105205):  Dog; breed, age and gender not specified

 

HISTORY:  This dog had heart failure.

 

HISTOPATHOLOGIC DESCRIPTION:  Heart:  Diffusely and transmurally, cardiac myocytes are separated, surrounded, and lost with replacement by high numbers of lymphocytes, plasma cells, macrophages, fewer neutrophils, and fibroblasts with multifocal areas that contain eosinophilic beaded to finely fibrillar material (fibrin), increased clear space (edema), and ectatic lymphatics.  80 percent of remaining cardiomyocytes are either swollen with pale, vacuolated sarcoplasm (degeneration); shrunken with angular hypereosinophilic or fragmented sarcoplasm with pyknosis or karyolysis and loss of cross striations (necrosis); or shrunken with variation in size and variable separation by fibrous connective tissue (atrophy).  Multifocally, individual cardiomyocytes contain variably sized, up to 60 x 125 um, intrasarcoplasmic, oval pseudocysts that contain numerous 2-4 um, round to oval, protozoal amastigotes with a central distinct basophilic nucleus and a rod-shaped kinetoplast adjacent to the nucleus.

 

MORPHOLOGIC DIAGNOSIS:  Heart:  Pancarditis, lymphoplasmacytic and histiocytic, chronic-active, diffuse, severe, with cardiomyocyte degeneration and necrosis, and abundant intramyocytic protozoal amastigotes, breed not specified, canine.

 

ETIOLOGIC DIAGNOSIS:  Trypanosomal myocarditis

 

CAUSE:  Trypanosoma cruzi

 

SYNONYMS:  Chagas disease; American trypanosomiasis

 

GENERAL DISCUSSION:

• Trypanosoma cruzi is a hemoflagellate protozoan (Class Zoomastigophorea, Family Trypanosomatidae) that causes fatal chronic myocarditis in both dogs and humans
• Dogs are one of the main reservoirs for human infection, with young animals more susceptible to acute disease; opposums, armadillos, rats, guinea pigs, cats, pigs, raccoons, and monkeys serve as wild reservoirs of infection
• Trypanosomes are generally nonpathogenic in mammalian reservoir hosts
• Transmitted in the feces of “kissing” or “assassin” bugs (triatomin bugs) of the genera Triatoma, Rhodinius, and Panstrongylus in South and Central America, Texas, Arizona, New Mexico, California, and Oklahoma
• T. cruzi undergoes intracellular multiplication, in contrast to other trypanosomes
• Two major forms of trypanosomiasis:
  • American trypanosomiasis: Trypanosoma cruzi
  • African trypanosomiasis: Caused by other pathogenic members of the genus ( T. congolense, T. vivax, T. brucei brucei); these protozoal agents are transmitted through saliva of the tsetse fly, but have been transmitted mechanically by other biting and sucking insects, and vampire bats; as a rule, domestic animals and trypanosomes cannot coexist; prevents domestication of livestock in ¼ total African land surface

 

PATHOGENESIS:

Trypanosomiasis in general:

• Components of trypanosome pathogenicity still mostly unknown
• Infection of mammalian hosts occurs via several mechanisms:
  • Bite of the infected arthropod (salivarian trypanosomes)
  • Contamination of mucous membranes or abraded skin via feces (stercorarian trypanosomes)
  • Less common routes of transmission: Blood transfusion, transplacental, or transmammary
    • Amastigotes present in uterine muscle, decidual and endothelial placental cells, giant cells, spongioblasts, and endothelial cells of the labyrinthine layer in mice
  • Most salivarians are pathogenic and most stercorarian are non-pathogenic, but the pathogenic stercorarian cruzi is the exception to this generalization

Trypanosoma cruzi:

• Cytotoxic CD-8+ T cells are implicated in cardiac myocyte damage
• Two proteins on the surface of cruzi are involved in its entry into macrophages and other host cells
  • Trans-sialidase: Removes host cell sialic residues and transfers them to a parasite surface protein (Ssp-3), which binds to host cells
  • Penetrin: Binds extracellular matrix proteins, heparin, heparin sulfate, and collagen and mediates parasite invasion into host cells
• Intramacrophage survival due to rapid movement from lysosome to the cytosol
  • Neuraminidase: Removes sialic acids from host proteins lining the lysosomes and destabilizes this organelle
  • Hemolysins: Lysosomal acid pH stimulates parasite release of hemolysins, which form pores in and disrupt lysosomal membranes
• T. cruzi infection in mice results in pancreatic inflammation and parasitism within pancreatic β-cells with sparing of α cells; β-cell dysfunction, hyperglucagonemia, hypoinsulinemia, and hypoglycemia; due to defective hepatic gluconeogenesis
• Suppressor of cytokine signaling 2 (SOCS2) is increased in cruzi infection; SOCS2 -/- mice have decreased parasitemia, IFN-γ, TNF-α, SOCS1, and SOCS3 in the heart and spleen, increased T_reg cells and lipoxinA4
• Galectin-3 (gal-3), a soluble β-galactoside binding lectin involved in the pathogenesis of several types of cardiac dysfunction, regulates in vitro survival, proliferation, and type I collagen synthesis in cardiac fibroblasts; an in vivo study with cruzi-infected mice involving blockade of Gal-3 led to significant reduction of cardiac fibrosis and inflammation (Souza BSdF, et al., Am J Pathol.; 2017)

 

LIFE CYCLE:

• Four morphologic forms:
  • Amastigotes (intracellular form): Only form which lacks flagellum; multiplies within mammalian cells
  • Trypomastigotes (blood form): Infective form which does not multiply, extracellular; flagellated with characteristic undulating membrane
  • Epimastigotes (intermediate form); found in vectors and multiplies in the midgut
  • Promastigotes: Rapidly dividing stage
• (Vector): Kissing bug (triatomine bug) is infected by feeding on blood that contains T. cruzi trypomastigotes > trypomastigotes are ingested and move to the midgut > change into dividing form (epimastigotes) in the insect gut lumen > epimastigotes pass from midgut to hindgut > epimastigotes reproduce asexually (binary fission) and migrate / attach to the cell wall of the hindgut and rectum via their flagellum > epimastigotes transform into infective trypomastigotes > trypomastigotes remain in the rectal lumen until the vector takes another blood meal
• (Host):  Dog / human (inoculation of the parasite):  kissing bug (vector) takes a blood meal and ingest trypomastigotes from infected host  > vector passes the infective metacyclic trypomastigotes in the feces on skin surface > trypomastigotes enter wound or mucous membrane, such as conjunctiva > (cell penetration and transformation):  penetration of various phagocytic (macrophages / monocytes) and non-phagocytic cells (myocytes), typically around the site of entry >  lose flagella and transform into amastigotes > (asexual reproduction):  amastigotes multiply via binary fission in cells of infected tissue and multiply to form a pseudocyst > (transformation and dispersal):  intracellular amastigotes transform into “C-shaped”  trypomastigotes, rupturing the pseudocyst (within cell), and releasing trypomastigotes into the blood stream > (re-establishment of infection cycle):  some trypomastigotes circulate in the blood to infect more cells while others may be taken up via a blood meal by the vector     

 

TYPICAL CLINICAL FINDINGS:

• "Chagoma": Erythematous nodule at skin entry site
• Disease has 3 distinct phases:
  • Acute: Dogs <1-year-old; right-sided heart failure; cardiac arrhythmias; pale mucus membranes; increased capillary refill time; lymphadenitis; ascites; hepatomegaly; splenomegaly; pleural effusion; and meningoencephalitis; trypomastigotes in blood smears during acute phase; amastigotes are not found in blood samples
  • Intermediate (latent): Prolonged; lack of clinical signs, no detectable parasitemia
  • Chronic: Chronic myocarditis with bilateral cardiac dilatation; right then subsequent left sided heart failure; ascites; pleural effusion; cachexia; rough hair coat
    • Increased AST, CK (muscle damage), ALT (anoxia), lymphocytosis

 

TYPICAL GROSS FINDINGS:

• Acute: Pale myocardium with multiple yellowish-white myocardial spots and streaks, subendocardial and subepicardial hemorrhages (usually more severe in right atrium and ventricle); pulmonary edema; liver, spleen, and kidney congestion
• Chronic: Enlarged, flaccid heart with thin walls and fibrous plaques

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Myocarditis; amastigotes within cardiomyocytes
• T. cruzi morphology:
  • Trypomastigotes: In host blood and insect hindgut; undulating membrane running the entire length of the organism and a free flagellum
  • Amastigote: Intracellular; within pseudocysts primarily in muscle, especially heart muscle; can be found within macrophages of lymph nodes; round to oval, 1.5-4 um diameter, contain a nucleus, with a parallel, rod-like kinetoplast; no free flagellum or undulating membrane

 

ULTRASTRUCTURAL FINDINGS:

• Amastigotes in cardiomyocytes between myofibrils
• T. cruzi amastigotes: Striated periplast, kinetoplast adjacent and parallel to the nucleus, flagellum (not free), basal body, basal plaque, nucleus, nucleolus, endoplasmic reticulum, ribosomes, and mitochondria
• Trypomastigotes: Kinetoplast lies posterior to the nucleus
• Epimastigotes (intermediate form): Kinetoplast lies anterior to the nucleus 
• Promastigotes: Kinetoplast is located near the anterior end of the cell
• Myofibrils separated and disrupted; enlarged mitochondria; fragmented, vesicular sarcolemmal and nuclear membranes

 

ADDITIONAL DIAGNOSTIC TESTS:

• Giemsa stain: Nucleus red, kinetoplast purple
• PCR, cytology, culture, serology

 

DIFFERENTIAL DIAGNOSIS:

• Toxoplasma / Neospora: No kinetoplast
• Leishmania: Larger, kinetoplast perpendicular and adjacent to the nucleus; restricted to macrophages (not myocytes); no trypomastigote form
• Sarcocystis: No kinetoplast
• Histoplasma capsulatum: Intracellular yeast; no kinetoplast
• Other Trypanosoma (i.e. African trypanosomiasis): No tissue amastigote form
  • Acute: Generalized lymphadenomegaly, splenomegaly, petechiae on serosal membranes
  • Chronic: Signs of anemia, emaciation, subcutaneous and pulmonary edema, serous fat atrophy, lymphadenopathy (atrophied or enlarged)

 

COMPARATIVE PATHOLOGY: 

1. T. cruzi in other species:

• Nonhuman Primates: T. cruzi; occurs in captive NHPs housed outdoors; predominantly New World primate-species, but also reported in some Old World monkeys; in Central and South America, and southern United States; pathogenesis similar to humans and dogs; most common presentation is heart failure; transplacental transmission possible in marmosets and baboons
• Red-Necked Wallaby: Recent report of T. cruzi in a captive animal from Texas, United States co-infected with Toxoplasma gondii; asymptomatic prior to sudden death; lesions, among others, included lymphohistiocytic and necrotizing pancarditis with intrasarcoplasmic protozoal pseudocyts containing amastigotes, centrilobular to panlobular necrotizing hepatitis, necrotizing splenitis, pulmonary edema, and acute renal tubular degeneration (Díaz-Delgado, et al, J Comp Path 2020).
• Red panda: Recent report of T. cruzi in a captive animal from Kansa, United States; presented with one-week history of lethargy and progressive inappetance; trypomastigote organisms present with concurrent anemia; amastigotes present in heart, skeletal muscles, brain, peripheral nerves, liver, tongue, and testes (Huckins, et al, J Vet Diag Invest 2019)

Other Trypanosoma spp.:

• African trypanosomaiasis: Unlike T. cruzi, African trypanosomes undergo continual antigenic variation of outer glycoprotein coat to evade immunity; clinical and / or gross lesions include hemolytic anemia, pericarditis, myocarditis, meningoencephalitis, and uveal edema (“blue eye”) due to immune complex formation
• Bovine trypanosomiasis: T. theileri most common in the U.S.
  • Clinical findings: Often see numerous flagellated trypomastigotes in blood smears but usually non-pathogenic/incidental; anemia is the predominant finding with concurrent moderate thrombocytopenia and hypocomplementemia; competition among precursor erythrocytes and granulocytes is possible, potentially explaining why anemic animals are more susceptible to secondary viral / bacterial infections
  • Gross findings:
    • No pathognomonic gross lesions
    • Acute: Hemorrhagic syndrome may occur; lesions consistent with severe anemia (pale mucous membranes) with widespread mucosal or visceral hemorrhages
    • Chronic: Bilaterally enlarged, flaccid heart with serous pericardial fat atrophy, thinning of ventricular walls; fibrous plaques, pleural and abdominal effusion; lungs heavy with increased density +/- cranioventral bronchopneumonia; kidneys and liver symmetrically enlarged; liver with fine lobular pattern; gastrointestinal largely unremarkable; uniform splenomegaly with grossly visible Malpighian corpuscles; lymph nodes with generalized medullary pigmentation; bone marrow with increase in hematopoietic areas which may occupy all the cancellous and diaphyseal fatty areas; thymic atrophy
  • Histologic findings:
    • Heart
      • Acute disease: Diffuse granulomatous myocarditis with numerous pseudocysts containing amastigotes; most severe in right atrium and ventricle; degeneration and necrosis of myofibrils
      • Chronic disease: Lymphoplasmacytic myocarditis; mild necrosis; extensive loss of myocardial fibers and marked fibrosis (less inflammation); few organisms; most likely found at apex of the heart
    • Smooth muscle of the stomach, intestine, urinary bladder, and skeletal muscle: Mild multifocal granulomatous myositis with amastigotes
    • Liver: Centrilobular hepatic congestion and fibrosis; periportal lymphoplasmacytic proliferation; atrophy of hepatocellular cords; generalized Kupffer cell hyperplasia
    • Lungs: Pulmonary edema
    • Lymph nodes: Changes consistent with continuing stimulation with initial competent response followed by hyperplasia > atrophy > sclerosis; medullary histiocytosis, parafollicular lymphoid hyperplasia, plasmacytosis, rarely giant cells containing amastigotes
    • Thymus: Marked atrophy
    • Testicle: Germinal cells laden with amastigotes and an intense lymphocytic infiltration of the interstitium
    • Kidneys: Changes compatible with membranoproliferative glomerulonephritis
  • Horses: T. equiperdum (known as dourine) demonstrates some predilection for genital mucosae and is transmitted via coitus; differs from other trypanosomes because organisms reside within blood only intermittently or during virulent infections; clinical infection categories include genital (healed ulcers typically result in depigmented scars in males and females), cutaneous (more often occurs with virulent infections; edematous urticaria-like plaques in the skin), nervous (develop late in disease and often leads to death; paresis involving facial nerves and hindlimb motor nerves) and / or general (often continued or recurring fever, emaciation, severe anemia)
  • Suids: maintain parasitemia for a long time and are important reservoirs for trypanosomes pathogenic to domestic animals and humans; congolense, T. suis, T. brucei, T. evansi, T. simiae; generally do not develop severe disease, but can vary depending on species- T. suis and T. simiae typically cause more significant disease; symptoms also vary depending on species- severe anemia, immunossupression, disseminated intravascular coagulation, encephalitis, and myocarditis
  • Camels: T. evansii (known as nagana or surra); severe disease of old-world camels in South-east, East, and Central Asia, as well as North Africa; tsetse fly intermediate host; acute form- anemia, fever, edema, weakness to paralysis, pneumonia, abortion, mastitis, death, numerous parasites in blood smears; chronic form- anemia, edema, intermittent fever, progressive loss of condition, parasites found in blood smears only during periods of fever

 

Species	Disease	Definitive Host	Intermediate Host	Geographic Distribution
T. cruzi	Chagas disease; American Trypanosomiasis	Man; dogs, cats, monkeys, opossums, armadillos, raccoons, lemurs	Kissing bug	Central and South America and southern U.S.
T. evansi	Surra	Equidae (horses), camels,  ruminants, dogs, cats, elephants	Horse, tsetse flies	Africa, Asia, S. America, Far East
T. equiperdum	Dourine	Equidae	Transmitted by coitus	Cosmopolitan; rare in the United States
T. vivax	Souma, RBC parasitemia, myocarditis in cattle	Cattle, sheep, horses, goats, camels	Tsetse fly	Central and South America
T. brucei brucei	Nagana; myocarditis in dogs	Man; domestic and wild mammals (not goats)	Tsetse fly	Tropical Africa
T. congolense	Trypanosomiasis, localization within cerebral and skeletal muscle vasculature; orchitis with inflammation of vaginal tunics; myocarditis in cattle	Equidae, ruminants, pigs, dogs, camels, rabbits, rats, mice	Tsetse fly	Tropical Africa
T. rhodesiense, T. gambiense	African Sleeping Sickness	Man, antelopes	Tsetse fly	East and Tropical Africa
T. equinum	Mal de Caderas	Equidae		Tropical and Subtropical South America
T. hippicum	Murrina de Caderas	Horses and mules		Central America
T. carassii, T. cobitis, T. murmanensis	Anemia, hematopoietic damage, death	Fish	Leeches
T. lewisi	Non-pathogenic	Rats	Fleas	Research, wild rats in developing countries
T. nabiasi	Non-pathogenic	Rabbits	Rabbit flea	Europe, North America, Australia
T. rangeli	Non-pathogenic to vertebrate hosts	Man; cats, dogs	Uniquely, can be transmitted by inoculation or contamination	South America
T. melophagium	Non-pathogenic	Sheep	Ked
T. theodori	Non-pathogenic	Goats	Hippoboscid fly	Middle East
T. irwini, T. copemani, T. gilletti	Anemia and loss of body condition with concurrent disease	Koalas		Australia
T. vegrandis, T. copemani, T. sp. H25	Inflammation and degeneration of skeletal muscle, heart, tongue, and esophagus	Brush tail bettong		Australia

 

REFERENCES:

1. Agnew D. Camelidae. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier, 2018:201-202.
2. Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents & Rabbits. 4th ed. Ames, IA: Blackwell Publishing Ltd; 2016:152,300.
3. Cheville NF. Pathogenic protozoa. In: Ultrastructural pathology: The Comparative cellular basis of disease. 2nd ed. Wiley-Blackwell, 2009:529-34.
4. Church ME, Terio KA, Keel MK. Procyonidae, Viverridae, Hyenidae, Herpestidae, Eupleridae, and Prionodontidae. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier, 2018:315.
5. Díaz-Delgado J, Kellerman TE, Auckland L, et al. Trypanosoma cruzi Genotype I and Toxoplasma gondii Co-infection in a Red-Necked Wallaby. J Comp Pathol. 2020;179:52-58.
6. Durham AC, Boes KM. Bone marrow, blood cells, and the lymphoid/lymphatic system. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:834.
7. Esper L, et al. Role of SOCS2 in modulating heart damage and function in a murine model of acute Chagas disease. Am J Pathol. 2012;181(1):130-40.
8. Gal A, Castillo-Alcala F. Cardiovascular System, Pericardial Cavity, and Lymphatic Vessels. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:692.
9. Greene CE. African trypanosomiasis. In: Greene CE, ed. Infectious Diseases of Cats and Dogs. 4th ed. St. Louis, MO: Elsevier-Saunders; 2012:730-34.
10. Higgins D, Rose K, Spratt D. Monotremes and Marsupials. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier, 2018:475.
11. Huckins GL, Eshar D, Schwartz D, et al. Trypanosoma cruzi infection in a zoo-housed red panda in Kansas. J Vet Diag Invest. 2019;31(5):752-755.
12. Lowenstine LJ, McManamon R, Terio KA. Apes. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier, 2018:402.
13. Martínez MAJ, Gasper DJ, Muciño MCC, Terio KA. Suidae and Tayassuidae. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier, 2018:221.
14. McAloose D, Stalis IH. Prosimians. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier, 2018:338.
15. Nagajyothi F, Kuliawat R, Kusminski CM, et. al. Alterations in glucose homeostasis in a murine model of Chagas disease. Am J Pathol. 2013;182(3):886-94.
16. Noga EJ. Fish Disease Diagnosis and Treatment. 2^nd Ames, IA: Wiley-Blackwell; 2010:179.
17. Schlafer DH, Foster RA. Female genital system. In: Maxie MG, ed. Jubb, Kennedy, Palmer’s Pathology of Domestic Animals. Vol 3. Philadelphia, PA: Elsevier Saunders; 2016:445-447.
18. Snowden KF, Kjos SA. American trypanosomiasis. In: Greene CE, ed. Infectious Diseases of Cats and Dogs. 4th ed. St. Louis, MO: Elsevier-Saunders; 2012:722-30.
19. Souza BSdF, Silva DN, Carvalho RH, et al. Association of cardiac galectin-3 expression, myocarditis, and fibrosis in chronic Chagas disease cardiomyopathy. Am J Pathol. 2017;187(5):1134-1146.
20. Stockham SL, Scott MA. Fundamentals of Veterinary Clinical Pathology. 2^nd Ames, IA: Blackwell Publishing; 2008:98,185.
21. Straight K, Else JG, Eberhard ML. Parasitic Diseases of Nonhuman Primates. In: Abee CR, Mansfield K, Tardif S, et al, eds. Nonhuman Primates in Biomedical Research. 2^nd Vol 2. San Diego, CA: Elsevier; 2012:204-205.
22. Valli VEO, Kiupel M, Bienzle D. Hematopoietic system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 3. 6th ed. Philadelphia, PA: Saunders Elsevier; 2016:121-124.

Click the slide to view.

---