JPC SYSTEMIC PATHOLOGY
Signalment (JPC #1822362): 3-year-old, Yorkshire sow
HISTORY: This sow presented with a history of recent loss of condition, posterior weakness, and neuromuscular tics.
HISTOPATHOLOGIC DESCRIPTION: Cerebrum at the level of the hippocampus and mesencephalon with subcommisural organ: Multifocally infiltrating the tunica adventitia and tunica media of small arteries and arterioles within the leptomeninges, cerebrum, and mesencephalon as well as filling Virchow-Robin spaces are moderate numbers of lymphocytes and plasma cells admixed with a small amount of proteinaceous fluid (edema) and scant fibrin. Diffusely the leptomeninges are expanded by edema and contain ectatic lymphatics, congested blood vessels, and few hemosiderin laden macrophages. Multifocally, typically centered on vessels within the hippocampus and mesencephalon, there are small foci of rarefaction characterized by edema and vacuolation of the neuropil.
MORPHOLOGIC DIAGNOSIS: Meningoencephalitis, lymphoplasmacytic, perivascular, multifocal, moderate, with perivascular and meningeal edema and multifocal neuropil rarefaction, Yorkshire, porcine.
Signalment (JPC #M0 4932): 3-week-old pig
HISTORY: This pig presented with clinical signs of a CNS disturbance.
cerebral cortex with lateral ventricle: Within the gray matter there are
multiple foci of rarefaction up to 2 mm in diameter characterized by increased
pallor, increased clear space (edema), and vacuolated neuropil (spongiosis).
Within these foci are few shrunken, angular, hypereosinophilic necrotic neurons
and mild gliosis. Capillaries and small blood vessels are often lined by hypertrophied
endothelial cells. Blood vessels are often surrounded by edema and few
lymphocytes and plasma cells that occasionally infiltrate the vessel walls and
fill Virchow-Robin space. Rarely, the vessel walls of small arteries and
arterioles are expanded by proteinaceous fluid, fibrin, and scant cellular debris
(necrotizing vasculitis). The leptomeninges are minimally expanded by low
numbers of lymphocytes and plasma cells and mild edema.
MORPHOLOGIC DIAGNOSIS: Cerebrum: Vasculitis, necrotizing, fibrinoid, and lymphoplasmacytic, multifocal, mild, with multifocal mild neuropil rarefaction, gliosis, rare neuronal necrosis, and perivascular and meningeal edema, Yorkshire, porcine.
ETIOLOGIC DIAGNOSIS: Verotoxic meningitis
CAUSE: Shiga-like toxin type IIe (verotoxin)-producing Escherichia coli (VTEC)
CONDITION: Edema disease
SYNONYM: Enterotoxemic colibacillosis; cerebrospinal angiopathy
· Generally occurs after weaning (feeder piglets 6-14 weeks of age) or after a change in diet
· Disorder of rapidly growing, healthy feeder pigs being fed high energy ration
· Morbidity around 30%, with mortality approaching 100% of affected animals
· Results in sudden death or nervous signs
· Enterohemorrhagic (ETEC) E. coli (specific O serotypes with Shiga-like toxin type IIe toxin production) colonization of the small intestine > Shiga-like toxin enters blood stream > toxin has affinity for endothelium expressing the receptors globotriaosylceramide and globotetraosylceramide > affinity for vessels in CNS, facial subcutis, colonic mesentery, and gastric cardia > damages endothelium and tunica muscularis (angiotoxin) > vasogenic edema and encephalomalacia
· Bacteria is spread via aerosols, direct contact, feed, and other vehicles
· Colonization of the small intestine by specific O serotypes of E. coli (O138, O139, O140, O141):
· E. coli epithelial colonization (jejunum / ileum) is mediated by F18ab fimbriae
· Genetic susceptibility depends on the ability of E. coli to adhere to the intestine; receptors for E. coli (ie. F18) are not present in all pigs
· Diarrhea is not a common feature of edema disease, although some strains produce a secretory enterotoxin that causes diarrhea
· Enterotoxin (Shiga-like toxin type IIe [Stx2e], AKA verotoxin 2e)
· Causes necrosis, not apoptosis, of endothelial and smooth muscle cells in blood vessels (disrupts protein synthesis leading to vascular permeability changes and cell lysis)
· Endothelial cell sensitivity to Shiga-like toxin depends on the amount of Shiga-like toxin receptor (globotriaosylceramide and globotetraosylceramide)
· Exposure of endothelial cells to lipopolysaccharides or cytokines (TNF-alpha, IL-1) increases sensitivity of some endothelial cells to the cytotoxic effects of Stx2e
· Shiga-like toxin/verotoxin induces production of IL-8 > attracts neutrophils
TYPICAL CLINICAL FINDINGS:
· Subcutaneous edema, primarily of the eyelids, forehead, nose, throat (jowls), and lips
· Nervous signs: Ataxia, convulsions, paralysis, aimless wandering and muscle tremors progressing to coma and death usually within 24 hours
TYPICAL GROSS FINDINGS:
· CNS: Characteristic bilaterally symmetrical areas of malacia (tan-grayish discoloration) of the caudal medulla, may extend rostralloy to the basal nuclei
· Alimentary: Edema of the stomach (especially the gastric cardia), mesentery of the spiral colon, and gallbladder
· Respiratory: Pulmonary edema with multifocal sublobular congestion; pleural effusions with white strands of fibrin; laryngeal edema
· Cardiac: Epicardial and endocardial petechiae; pericardial effusion
TYPICAL LIGHT MICROSCOPIC FINDINGS:
· Degenerative/fibrinoid angiopathy/vasculitis affecting small arteries and arterioles (not a prominent feature in this case)
· Early: Perivascular edema with protein-rich, eosinophillic droplets
· Late: Fibrinoid vascular necrosis is accompanied by infiltration of the tunica adventitia with neutrophils, lymphocytes, plasma cells and macrophages; endothelial hypertrophy; focal encephalomalacia in brainstem; necrotic foci eventually infiltrated by macrophages
· Thrombosis is usually not a feature (endothelium usually remains intact)
· Lesions are most frequent and most severe in the brainstem (caudal medulla to diencephalon) and cerebral and cerebellar meninges; spinal blood vessels also affected
ADDITIONAL DIAGNOSTIC TESTS:
For ataxia and recumbency in swine
· Pseudorabies/Aujeszky's Disease (porcine herpesvirus-1, N-V07): Nonsuppurative meningoencephalomyelitis with ganglioneuritis, neuronal degeneration, necrosis, and eosinophilic or basophilic intranuclear inclusion bodies
· Bacterial meningoencephalitis (Streptococcus suis, Haemophilus parasuis. Salmonella spp.)
· Water deprivation/salt toxicity (N-T08): Laminar cerebrocortical neuronal necrosis, with swollen astrocytes and perivascular eosinophilic cuffs in the leptomeninges
· Teschen's disease (Porcine enterovirus, N-V04): Nonsuppurative polioencephalomyelitis
· Arsenic Toxicity: Cerebral edema and hemorrhage from vascular necrosis, but primarily degeneration of the peripheral and optic nerves, and the spinal cord, and a hemorrhagic gastroenteritis
· Dietary microangiopathy of swine (Vitamin E-selenium deficiency, N-M22): Fibrinoid necrosis of small arteries and arterioles with fibrin thrombi; primary lesions include hydropericardium and cardiac hemorrhage (Mulberry heart disease) and massive hepatic necrosis (hepatosis dietetica)
· Porcine hemagglutinating encephalomyelitis virus (coronavirus): This disease affects pigs less than a week old; nonsuppurative meningoencephalomyelitis and neuronal degeneration primarily within the gray matter of the caudal brain stem and spinal cord
· Rabies (rhabdovirus, N-V06): Nonsuppurative encephalomyelitis with perivascular lymphocytic cuffing, gliosis and Negri bodies
· In humans, shiga-like toxin producing O157:H7 E. coli causes hemorrhagic colitis and hemolytic uremic syndrome characterized by acute renal failure, thrombocytopenia, and microangiopathic hemolytic anemia
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