JPC SYSTEMIC PATHOLOGY
SIGNALMENT (JPC #2133912): A pig
HISTOPATHOLOGIC description: Heart, ventricle: Multifocally disrupting the epicardium, myocardium, and endocardium and surrounding, separating, isolating, and replacing cardiac myocytes are high numbers of lymphocytes, plasma cells, and macrophages, moderate amounts of clear space (edema), eosinophilic fibrillar material (fibrin), and basophilic granular material (mineral). Within affected areas, cardiac myocytes are swollen with vacuolated sarcoplasm (degeneration) or shrunken with hypereosinophilic sarcoplasm, loss of cross striations, and pyknosis (necrosis).
Morphologic diagnosis: Heart: Pancarditis, lymphoplasmacytic and histiocytic, multifocal, severe, with myocardial necrosis, breed unspecified, porcine.
cause: Encephalomyocarditis virus (EMCV)
Etiologic diagnosis: Picornaviral myocarditis
- Family Picornaviridae; genus Cardiovirus, a group of 3 closely related viruses all referred to as EMCV
- Viral strains may produce either myocarditis or reproductive failure (sows)
- Rodents may act as a reservoir host with shedding of virus in urine and feces
- Pigs are the most often affected species
- Transmission to swine is oral (ingestion of rodent carcasses, or fecal or urine contamination of food or water), and horizontal transmission has been reported in swine
- Clinical disease due to viral effect and immune response to virus within the myocardium, including myocytes and endothelium
typical Clinical findings:
- Any age of pig can be affected
- Peracute disease: Sudden death or brief excitation, collapse, then death due to myocardial failure (usually preweaning pigs)
- Milder cases: Fever, anorexia, listlessness, trembling, staggering, progressive paralysis, or dyspnea
- Infection has been associated with reproductive failure in sows: mummified fetuses, still birth, early embryonic death, failure of conception
- In a recent large-scale retrospective study assessing aborted swine fetuses (Salogni 2016), an infectious etiologic agent was identified in 58.8% of fetuses, of which EMCV was identified in 3/323 with an identified infectious etiologic agent, the most common causes were PCV-2 > PRRSV > coli and Streptococcus sp.
typical Gross findings:
- Hydrothorax, hydropericardium, ascities, pulmonary congestion, edema
- Severe cases: extreme pallor of the ventricles, yellow-white 2-10mm diameter foci throughout myocardium
- Less severe cases: minimal to no findings
typical light MICROSCOPIC findings:
- Focal to diffuse myocardial necrosis with patchy mineralization and variable amounts of lymphocyte and macrophage infiltrates, progression to fibrosis with chronicity
- Late-term aborted fetuses: multifocal myocardial necrosis
- Scant evidence of encephalomyelitis (typically rodents only)
- Viral particles may be found within myocytes and endothelium of the heart
ADDITIONAL DIAGNOSTIC TESTS:
- Virus detection by culture, PCR (a new reliable RT-rtPCR reported by Qin 2018), or immunohistochemistry (not commercially available)
Myocarditis in pigs:
- Foot and mouth disease (picorna/aphthovirus): Gross and microscopic cardiac lesions may be indistinguishable from EMCV
- Porcine parvovirus in pigs can induce a nonsuppurative myocarditis
- Porcine circovirus-2 associated with post-weaning multisystemic wasting syndrome
- Vitamin E/Se deficiency (Mulberry heart disease)
- Edema disease ( coli): Mesenteric edema similar to that seen with EMCV; vascular endothelial damage by shiga-like II variant (SLT IIv) verotoxin attaching to its receptor (globotetrasylceramide) on endothelial cells
- Porcine reproductive and respiratory syndrome virus (PRRSV, arterivirus) - Epidemic disease is characterized by an acute phase of slowly spreading inappetence, fever, and dyspnea lasting 2 weeks (rolling inappetence) followed by a second phase lasting 1-4 months and consisting of late-term reproductive failure
- Porcine circovirus-2
- Aujeszky"s disease (psuedorabies virus): Transplacental infections occur in pigs causing abortion in about 50% of sows pregnant in the first month, and the delivery of macerated, mummified, and normal fetuses when infection occurs at later stages of gestation
- Porcine Parvovirus (PPV): classically considered the cause of SMEDI
- Bacterial infection: coli, Streptococcus sp., Staphylococcus sp., Pasteurella sp., Shigella sp., Yersinia sp.
- The type B strain of EMCV can affect multiple species including primates (including humans), swine, mice, raccoons, and other mammals
- Nonhuman primates:
- Many species can affected, both wild and captive, with outbreaks reported
- In addition to the normal exposure from rodents, horizontal transmission is suspected, and placentitis with increased fetal loss has been reported in baboons
- The heart is the most significantly affected organ; neurologic lesions are rare, and best described in squirrel monkeys, including cerebral perivascular lymphohistiocytic infiltrates, neuronal necrosis, satellitosis, and meningeal hemorrhage
- Baboons: There have been several recorded epizootics, suggesting increased susceptibility
- Differential diagnosis for myocarditis in NHP: coxsackie virus (enterovirus), toxoplasmosis, trypanosomiasis, experimental SIV infection
- May act as a reservoir host, spreading disease to animals via contaminated food, water, or surface from shedding of virus in urine and feces;
- Infection is usually clinically inapparent;
- Virus is not reported to naturally infect laboratory rodents, although fatal encephalitis and/or myocarditis is common with experimental infection
- Mice: Natural reservoir host, experimental inoculation routinely results in both encephalitis and myocarditis
- Rats: Often also implicated in viral transmission
- Outbreaks cause sudden death (fatal myocarditis) and tend to occur across mammalian taxa; infection has been reported in carnivores, tapirs, rhinoceros, pygmy hippopotamuses, Thomson’s gazelle, elephants, an oryx-addax cross, and other exotic hoofstock
- Elephants: infection occurs in captive and free-ranging African and Asian elephants; primary differential diagnosis is elephant endotheliotropic herpesvirus (see C-V05)
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