JPC SYSTEMIC PATHOLOGY

CARDIOVASCULAR SYSTEM

February 2025

C-B03 (NP)

 

SIGNALMENT (JPC #3103237): 6-year-old multiparous Holstein cow (Bos taurus)

 

HISTORY: Four days after calving the cow developed watery stool that continued for 2 weeks, accompanied by weight loss and decrease in body condition. 20 days after calving it was unable to rise from sternal recumbency and was euthanized.

 

HISTOPATHOLOGIC DESCRIPTION: Heart: The endocardium is diffusely expanded up to 1mm by collagen and fibroblasts (fibrosis) with multifocal accumulation of basophilic, granular material (mineral) and mineralized collagen fibers, which multifocally extend into the subendocardial myocardium, separating and surrounding bundles of cardiac myocytes. Subendocardial myocytes are occasionally swollen with sarcoplasmic vacuolation and enlarged, rectangular nuclei (degeneration), or are rarely shrunken and hypereosinophilic with fragmented sarcoplasm, loss of cross striations and occasional mineralization (necrosis). Multifocally, myocytes are expanded by an intracytoplasmic, round to oval, up to 40µm diameter, protozoal cyst with a 4µm thick, eosinophilic capsule, containing numerous, up to 10µm, basophilic, crescent-shaped bradyzoites.

 

MORPHOLOGIC DIAGNOSIS: 1. Heart: Endocardial mineralization and fibrosis, chronic, diffuse, marked, with myocardial degeneration, necrosis and mineralization, Holstein, bovine (Bos taurus).

2. Heart, myocardium: Sarcocysts, multifocal.

 

DISEASE NAME: Paratuberculosis or Johne’s disease

 

ETIOLOGIC DIAGNOSIS: Mycobacterial associated endocardial mineralization

 

CAUSE: Mycobacterium avium subspecies paratuberculosis (Map)

 

GENERAL DISCUSSION:

• MAP is an acid-fast, weakly gram-positive, non-motile, facultative intracellular bacillus
• 99% DNA homology with M. avium subsp. avium; MAP differs by dependence on mycobactin 
• IS900 insertion sequence (phenotype) element unique to MAP
• 2 strains known to cause paratuberculosis in various hosts, referred to as type I (S strain) isolated from sheep, and type II (C strain) first isolated from cattle; type II most common and have broad host range 
• Resistant to drying; can survive for months in water, soil, feces
• Worldwide distribution; primarily affects domestic ruminants (cattle, sheep, goats, camelids); also domestic and wild mammals, and birds
• Causes chronic enteritis leading to diarrhea, progressive emaciation, and death
• Significantly decreases milk production and longevity in cattle
• MAP requires a high concentration of iron in the tissue macrophages for growth, which is highest in the tissue macrophages of the ileocecal intestine; therefore, primary lesions are present in the ileum and large intestine
• Two main pathological forms of Johne’s disease are described: 
  • Paucibacillary form, inflammatory infiltrate composed of lymphocytes with some macrophages but few mycobacteria
  • Multibacillary form, mostly macrophages filled with numerous mycobacteria
• In sheep or goats with no clinical signs, there are focal granulomatous lesions in the intestinal lymphoid tissue
• There are no tests with high specificity and high sensitivity available for subclinically infected animals

 

PATHOGENESIS:

• Pathogenesis of mineralization is not well understood, but thought to be from macrophage production of a vitamin D analogue
• Infection of newborn and young animals can be followed by a latent period that may last for years, with intermittent bacterial shedding
• Transmitted via feces, milk, semen, urine, and transplacentally
• Transmitted (via fecal-oral route) in the first months of life, but clinical disease only appears in animals older than one year (usually 2 to 5 years)
• Bacteria invade via tonsils, Peyer’s patches M cells, and enterocytes, mainly in the jejunum and ileocecal valve > disseminate to mucosal lamina propria and local lymph nodes
• After entering the intestine through Peyer’s patches the bacteria reaches the lymph nodes, escaping the initial local immune defenses in the gut, before inducing lesions in the intestine (in sheep and goat)
• Goat immune systems may control the bacterial multiplication resulting in regression and healing of lesions, or an uncontrolled bacterial multiplication leading to clinical disease
• Multibacillary lesions correspond to borderline lepromatous forms, associated with marked humoral peripheral responses
  • M2 macrophages predominate
• Paucibacillary lesions, show strong cellular immune responses, correspond to borderline tuberculoid forms
  • M1 macrophages predominate (high iNOS; low TNF-a)
• Focal intestinal granulomatous lesions have a high cellular immune response (tuberculoid)
• Cell-mediated immunity is thought to be essential in controlling the progression of infection

 

TYPICAL CLINICAL FINDINGS:

• Weight loss and cachexia
• Decreased milk production 
• Diarrhea
• Infertility

 

TYPICAL GROSS LESIONS:

• Thickening of the intestinal wall, granulomatous enteritis, lymphangitis, and lymphadenitis of regional lymph nodes
• Intestinal ulcers and strictures
• Focal lesions are more common in lymph nodes in initial/latent forms of the disease
• Aortic and endocardial subintimal fibrosis and mineralization

 

TYPICAL LIGHT MICROSCOPIC LESIONS:

• Intestine:
  • Diffuse granulomatous infiltrates; may be in jejunal Peyer’s patches and the patch at the ileocecal valve or severe diffuse lesions throughout the intestine
  • Granulomas or giant cells in intestinal villi and lymph nodes; multinucleated Langhans giant cells are common in cattle (not sheep/goat)
  • Peyer’s patches lymphoid depletion
  • Dilation of intestinal glands associated with infiltrates in the lamina propria, causing occlusion
  • Intestinal mucosal ulceration with transmural inflammation and serositis > may heal or perforate 
  • Granulomatous arteritis in small to medium-sized vessels in the submucosa (may require IHC to be observed)
  • Acid fast bacilli within macrophages and dilated intestinal lymphatics
  • Lymphocytic inflammation of submucosal nervous plexuses rarely observed
  • Loss of CD4+ T cells and an increased frequency of gamma–delta T cells in the ileum of cattle has been observed in multibacillary lesions
  • Lymphangiectasis is most common/severe in small ruminants
• Lymph nodes/Lymphatics: 
  • Foci of necrosis and calcification in mesenteric lymph nodes
  • Granulomas in the ileal and jejunal lymph nodes
  • Granulomatous lymphangitis
• Liver: Microscopic granulomas; liver biopsy is a useful diagnostic tool in sheep
• Lung: Minimal lesions
• Vessels: Mineralization and fibrosis of the aortic wall 
• Heart: Endocardial subintimal fibrosis and mineralization

 

ADDITIONAL DIAGNOSTIC TESTS:

• Bacterial culture and PCR (from blood, feces, milk, semen, urine, and tissues)
  • MAP has 15-20 copies of the insertion sequence IS900 which differentiates it from M. avium subspecies avium
• Bacterial demonstration in tissue: IHC, acid-fast, and in situ hybridization (ISH); IHC and acid-fast demonstrate low numbers of bacteria in lesions
  • Labelling by MAP antibody is more efficient than Ziehl–Neelsen (ZN) staining for organism detection
  • Wall-deficient bacterial forms (like mycobacteria) are usually negative to ZN and difficult to culture, but can be demonstrated by in situ hybridization
• IHC: Antibody to lysozyme is useful in immunolabelling macrophages or giant cells 

• Others: Complement fixation test (CFT), AGID, ELISA (ELISA superior to CF or AGID)

 

DIFFERENTIAL DIAGNOSIS:

• Systemic bacterial infection 
• Salmonellosis: Generally acute; gram-negative bacteria; not acid-fast
• M. bovis: Usually fewer organisms; nodule formation; fibrosis; necrosis; calcification; classic granulomas
• Vitamin E/Selenium imbalance
• Vitamin D toxicity
• Calcinogenic plant toxicosis (Cestrum diurnum, Trisetum flavescens, Solanum malacoxylon, and Solanum torvum)
• Traumatic reticulopericarditis

 

COMPARATIVE PATHOLOGY: 

• See D-B09 for a more in-depth Comp path regarding the gastrointestinal lesions
• Spontaneous disease occurs in ruminants, camelids, equids, and primates
• Natural infection occurs in lagomorphs, rodents, carnivores, and birds
• Experimentally induced in mice, rabbits, guinea pigs, hamsters, and macaques 

 

REFERENCES:

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