JPC SYSTEMIC PATHOLOGY

URINARY SYSTEM

January 2024

U-T15 (NP)

 

Signalment (JPC #ML24078): 3-year old Hampshire ewe.

 

HISTORY: This ewe was found dead, along with several others, on a pasture in South Dakota in June. Depression and emesis as well as photosensitization were noted in surviving sheep. Clinical pathology results were:

            BUN               366 mg/dl       (10-20 mg/dl)

            SGOT             260 SF           (0-150 IU/ml)

            CPK                170 IU/l          (<200 IU/l)

 

HISTOPATHOLOGIC DESCRIPTION: Kidney, cortex: Multifocally, up to 70% of tubules are ectatic, dilated up to 100 µm in diameter, lined by attenuated epithelium, and contain variable amounts of proteinaceous material, few sloughed epithelial cells, eosinophilic cellular and karyorrhectic debris (necrosis), and, rarely, basophilic, anisotropic crystals (oxalate). Few tubules are lined by epithelial cells that are swollen with pale vacuolated cytoplasm (degeneration) or shrunken with hypereosinophilic cytoplasm and pyknotic nuclei (necrosis). Few glomeruli have hypertrophic parietal epithelium, and mild thickening of the basement membrane of Bowman’s capsule. There are multifocal aggregates of low numbers of lymphocytes and plasma cells scattered throughout the interstitium.

 

Liver: Diffusely, centrilobular hepatocytes are swollen and rounded with pale vacuolated cytoplasm (degeneration), which compress and distort sinusoids. Multifocally there is individual cell necrosis. Within the portal areas there are low numbers of lymphocytes and plasma cells.

 

MORPHOLOGIC DIAGNOSIS: 1. Kidney, cortex: Ectasia, tubular, multifocal, acute, moderate, with tubular degeneration and necrosis, Hampshire, ovine.

2. Liver, hepatocytes: Degeneration and necrosis, centrilobular, acute, moderate.

 

ETIOLOGIC DIAGNOSIS: Algal hepatic and renal toxicosis

 

CAUSE: Blue-green algae toxin of Anabaena sp.

 

GENERAL DISCUSSION: 

• Cyanobacteria (blue-green algae) are common in still fresh water or brackish water 
• Several genera are toxic and can have neurotoxins and/or hepatotoxins; the most common are Microcystis, Anabaena, and Aphanozomenon; most well-documented cases have involved Microcystis aeruginosa. Toxicosis is likewise generally from microcystin hepatotoxin. Peracute death is usually from neuromuscular injury. 
• Algal blooms occur predominantly in water with high nutrient content such as those with high concentrations of nitrogen and phosphate from fertilizer runoff and under conditions of hot, dry weather

 

PATHOGENESIS:

• Toxins are liberated when the algae cells die or are damaged; this may occur spontaneously in water, after application of copper sulfate for algae control, or in the rumen or stomach after ingestion
• Some deaths are too sudden to be due to liver damage and are thought to be the result of a “fast-death factor”
• There are two main categories of toxins: neurotoxin and hepatotoxin
  1. The neurotoxins include: Anatoxin-a, an alkaloid and potent post-synaptic depolarizing neuromuscular blocking agent; anatoxin-A(s), an organophosphorus compound and potent cholinesterase inhibitor; and saxitoxin and related paralytic shellfish toxins (sodium channel blockers)
  2. The hepatotoxins include: Microcystin-LR, a potent cyclic heptapeptide protein phosphatase inhibitor, and cylindrospermopsin, an alkaloid 
• Intoxication with microcystin-LR leads to disorganization of hepatocytic and endothelial cytoskeletal actin filaments, and disruption of their shape and integrity, leading to necrosis, apoptosis, and perisinusoidal hemorrhage; cytoskeletal changes are caused by inhibition of cytoplasmic protein phosphatase 1 and 2A and resultant rapid hyperphosphorylation of cytoskeletal proteins
• The distribution of necrosis is usually periacinar to massive, but varies within the individual liver and from case to case
• Dermatotoxic lyngbyatoxins are also occasionally synthesized by several species of cyanobacteria

 

TYPICAL CLINICAL FINDINGS:

• Peracute: Sudden death within one to two hours after drinking contaminated water
• Acute: Rapidly progressing paralysis, acute prostration, and convulsions
• Chronic: Cutaneous lesions characteristic of photosensitization may occur

 

TYPICAL GROSS FINDINGS:

• There may be no gross findings with sudden death or acute neurological disease
• Hepatotoxicosis results in icterus and a swollen, hemorrhagic and friable liver
• Cirrhotic livers are reported in chronic cases
• There is generalized petechiation and congestion
• There may be severe hemorrhagic gastroenteritis with bloody diarrhea

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Renal:
  1. Glomeruli with thickened basement membranes
  2. Tubular degeneration, necrosis, and ectasia
• Hepatic:
  1. Centrilobular to massive hepatic necrosis
  2. Hepatomegaly and karyomegaly with biliary proliferation and fibrosis
  3. Hemorrhage
  4. Eosinophilic cytoplasmic condensations around the outer nuclear membrane

 

Additional Diagnostic TESTS: 

 

DIFFERENTIAL DIAGNOSIS:

Hepatotoxins:

• Pyrrolizidine alkaloids induce nuclear and cytoplasmic gigantism (megalocytosis) due to an anti-mitotic effect with continued nucleoprotein synthesis
• Phomopsin blocks the polymerization of tubulin (the major component of microtubules), resulting in defective microtubule formation; mitotic cells arrest in metaphase
• Aflatoxin B1 binds mitochondrial and nuclear DNA, inhibiting biosynthetic processes and respiration, m-RNA synthesis, and ribosomal protein synthesis leading to hepatocellular necrosis with a distribution dependent on animal species

 

COMPARATIVE PATHOLOGY:

• Ruminants are the primary species affected, but can affect most vertebrates and some invertebrates
• Poisoning has been reported in horses, swine, dogs, and domestic poultry
• Fish: Rare cause of channel catfish mortality in ponds. Cyanobacterial die-offs cause hypoxia and off-flavored fillets from muscular uptake of cyanobacterial compounds 
• Cetaceans: Hepatic necrosis
• Shorebirds and waterbirds: Especially piscivorous species, through bioaccumulation in prey species or drinking/filtering contaminated water; gross and histologic lesions are unspecific; intestinal hemorrhage, catarrhal enteritis, hemorrhage, and striated muscle necrosis +/- massive hepatic necrosis.
• Avian vacuolar myelinopathy: Primarily affects American coots and bald eagles; Caused by cyanobacterium Aetokthonos hydrillicola, which is associated with the invasive aquatic plant Hydrilla verticillate (waterthyme); site specific, affects birds in good body condition, and reproducibly causes bilaterally symmetrical vacuolation, demyelination, spheroid formation, and mild gliosis in the brain and spinal cord; myelin splitting on EM is characteristic
• Bats: Suspected; multiple reports include acute death, death with cyanobacterial stomach contents, and hepatocellular microcystin accumulation without lesions
• Invertebrates: Captive Horseshoe crabs are susceptible to cyanobacterial gill disease, caused by Oscillatoria spp.; algae colonize gill lamellae; gross lesions include rupture of gill leaflets and extensive tissue necrosis; gill leaflets are expanded by increased numbers of hemocytes that form large aggregates obstructing the lumen of the leaflet admixed with regional necrosis and thick mats of algal cells that coat gill leaflets (LaDouceur, Vet Pathol 2019)

 

REFERENCES:

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2. Cullen JM, Stalker MJ.  Liver and biliary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. 6th ed., Vol. 2. St. Louis, MO: Elsevier Limited;2016:330.
3. Farina LL, Lankton JS. Chiroptera. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. London, UK: Academic Press; 2018:626.e2. 
4. Fenton H, McManamon R, Howerth EW. Anseriformes, Ciconiiformes, Charadriiformes, and Gruiformes. In: Terio, KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Academic Press Elsevier; 2018:701.
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6. Khan SA, Wickstrom ML, Haschek WM, Schaeffer DJ, Ghosh S, Beasley VR.  Microcystin-LR and kinetics of cytoskeletal reorganization in hepatocytes, kidney cells, and fibroblasts. Nat Toxins 1996;4:206-14.
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