JPC SYSTEMIC PATHOLOGY
Signalment: (JPC# 1782647): Two-day-old piglet
HISTORY: This piglet had profuse, watery feces and vomited milk curd.
HISTOPATHOLOGIC DESCRIPTION: Small intestine with attached mesentery: Diffusely and circumferentially there is a loss of normal intestinal villar architecture with a dilated lumen and thinned intestinal wall characterized by villi that are severely blunted, shortened, and fused with marked crypt loss, reducing the ratio of villus height to crypt depth to less than 1:1. The mucosal lining is reduced to a single layer of attenuated basophilic enterocytes, and remaining crypts are lined by either flattened, attenuated epithelium, or hypertrophic epithelial cells that occasionally pile up and contain a moderate amount of foamy basophilic cytoplasm, a large irregularly ovoid nucleus with finely stippled chromatin, one prominent nucleolus and few mitotic figures (regeneration). Multifocally crypt lumina contain small amounts of eosinophilic cellular and karyorrhectic debris (necrosis) and few macrophages, lymphocytes and plasma cells (crypt abscess). Diffusely, the lamina propria is moderately expanded by lymphocytes and plasma cells.
MORPHOLOGIC DIAGNOSIS: Small intestine: Villous necrosis and loss, diffuse, acute, severe with multifocal crypt regeneration and crypt abscesses, breed unspecified, porcine.
ETIOLOGY: Porcine coronavirus (alphacoronavirus 1)
ETIOLOGIC DIAGNOSIS: Coronaviral enteritis
CONDITION: Transmissible gastroenteritis (TGE)
- Highly contagious disease in piglets <10-14 days of age, characterized by near 100% morbidity, vomiting and profuse diarrhea; may cause diarrhea and villous blunting in susceptible pigs regardless of age, although the youngest are most severely affected (i.e. neonates/nursing/suckling)
- May affect pigs of all ages in susceptible herd
- Enveloped, single-stranded RNA virus
- Seasonal, usually winter and spring; virus sensitive to sunlight, resistant to freezing
- A cause of porcine periweaning failure-to-thrive syndrome (PFTS)
- Severity of clinical signs decreases with age, mild or in apparent signs in sows
- Similar disease presentation and pathologic changes as porcine epidemic diarrhea virus (PEDV) (most commonly reported in Asia and Europe but caused recent U.S. epidemic), also caused by a Coronavirus, but is antigenically distinct and can be distinguished with diagnostic testing (i.e. PCR etc.)
- Virus ingestion > infection of mature differentiated columnar epithelial cells of intestinal villi > loss of disaccharidase activity (enterocytes are source of these enzymes) > undigested lactose (from milk) within lumen > osmotic diarrhea
- Virus destroys villi > loss of intestinal surface area > malabsorption diarrhea
- Virus does not infect undifferentiated cells of the crypts > as infected villus cells are shed, crypt epithelium proliferates > migrates up and lines shortened villi > altered sodium transport across undifferentiated epithelium lining shortened villi > accumulation of electrolytes and water in the lumen
- Several mechanisms account for the age-dependent susceptibility to TGE:
- Neonates have tall villi (villus height:crypt depth is 7-9:1) with mature differentiated enterocytes and short inactive crypts of undifferentiated epithelium
- Results in large population of susceptible cell, and crypts that are slow to repair
- Neonates are inherently susceptible to dehydration, electrolyte imbalances, and hypoglycemia
- Gastric secretions of neonates are not as acidic as in older animals (virus is acid labile), and milk buffers gastric acid, protecting the virus
- Piglets older than 3 weeks are more resistant:
- Virus production in enterocytes of older pigs is less efficient, possibly due to the onset of the immune response or the inability of these regenerating cells to support virus growth
- Crypt epithelium is actively proliferative so it can regenerate faster
TYPICAL CLINICAL FINDINGS:
- < 2 weeks of age
- Vomiting and profuse yellow watery diarrhea, rapid weight loss
- Pronounced dehydration, hypoglycemia, metabolic acidosis
- Near 100% mortality within 2 - 5 days
- > 2 weeks of age
- Transient vomiting and diarrhea
- Dehydration, unthrifty condition
- Likely to recover
- Feeder pigs and sows
- Inapparent or mild fever, inappetance, diarrhea
- Agalactia in affected sows
TYPICAL GROSS FINDINGS:
- External: Dehydration, perineum stained with fluid feces
- Stomach: May contain milk curd
- Small intestine: Flaccid, walls thin and transparent, distended with gas and yellow frothy fluid with flecks of mucus
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Small intestinal villous atrophy and epithelial cell necrosis (but not pathognomonic for TGE); decrease in villus height:crypt depth [7 or 9:1 à 1:1]
- Hypertrophy of crypts (prominent regeneration)
- Mixed submucosal inflammatory cell infiltrate if secondary invaders are present
ADDITIONAL DIAGNOSTIC TESTS:
- Immunofluorescence (IFA) or immunoperoxidase staining
- Virus isolation
DIFFERENTIAL DIAGNOSIS: (For diarrhea in piglets)
- coli (enteric colibacillosis) (D-B13)
- Profuse diarrhea in piglets < 10 days of age (peak incidence at 3 days of age)
- No vomiting, may have mild villous atrophy
- Presence of bacilli adherent to brush border of enterocytes
- Rotavirus enteritis (D-V07, V08)
- Disease in suckling and weaned pigs (1 - 5 weeks of age)
- High morbidity and low mortality
- Villous atrophy less severe than in TGE
- Clostridium perfringens type C (clostridial enterotoxemia) (D-B02)
- Affects newborn piglets less than one week of age
- Bloody diarrhea, mucosal hemorrhage and necrosis, rapid death
- Porcine epidemic diarrhea (Alphacoronavirus)
- Type I causes diarrhea in pigs up to 4-5 weeks of age
- Type II causes diarrhea in pigs of all ages
- Similar signs as TGE but less severe
- Even though the disease is less severe, animals are productively infected, and can continue to shed the virus long term
- Hemagglutinating encephalomyelitis virus (Betacoronavirus): Vomiting and wasting disease
- Affects piglets under 10 days of age
- Vomiting is characteristic; acute encephalomyelitis may also occur.
- Diarrhea may occur but is not severe.
- Coccidiosis (Isospora suis) (D-P01)
- Diarrhea without blood in piglets 5-15 days of age (peak incidence 7 -10 days of age)
- Clinical signs precede production of oocysts.
- Porcine Deltacoronavirus
- Similar condition to PEDV and TGE but distinguishable
- Diarrhea and vomiting in all age groups, mortality in young piglets
- In a recent JVDI article, mesenteric lymph node and small intestine were the main sites of virus detection via IHC
- Antigenically related coronaviruses:
- Porcine respiratory coronavirus (PRCV): A deletion mutant of TGE with tropism for the respiratory system; causes mild respiratory disease
- Canine coronavirus (D-V03): Enteritis
- Feline infectious peritonitis virus (S-V03, U-V06, P-V15): Peritonitis, pneumonia, meningoencephalitis, panophthalmitis
- Feline enteric coronavirus: Diarrhea in kittens
- Other coronaviruses not antigenically related to TGE:
- Porcine hemagglutinating encephalomyelitis virus: Vomiting, wasting, encephalomyelitis
- Porcine epidemic diarrhea virus: Gastroenteritis
- Mouse hepatitis virus [lethal intestinal virus of infant mice (LIVIM)] (D-V04): Hepatitis, enteritis, encephalomyelitis
- Sialodacryoadenitis virus in rats (D-V05, S-V02): Necrosis of salivary and nasolacrimal glands
- Bovine coronavirus: Winter dysentery
- Bluecomb virus of turkeys: Enteritis, cyanosis of skin of head and neck
- Severe acute respiratory syndrome (SARS): Coronavirus
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