JPC SYSTEMIC PATHOLOGY
Signalment (JPC # 1619887): Three-week-old pig, breed and gender unspecified
HISTORY: This pig died after developing upper respiratory distress. At necropsy, there was a fibrinonecrotic membrane lining the nasal sinuses
HISTOPATHOLOGIC DESCRIPTION: Nasal turbinate: Diffusely, the subepithelial connective tissue is thickened up to 1 mm by many infiltrating lymphocytes, plasma cells, and fewer macrophages which infiltrate to the level of the turbinate bones multifocally. Diffusely, the respiratory epithelium is ulcerated or attenuated, and multifocally undergoes squamous metaplasia and there are small amounts of fibrin and hemorrhage adhered to the mucosa. Nasal mucous gland epithelial cells are often enlarged up to 50 um in diameter (cytomegaly) with abundant, often vesiculate cytoplasm and a single 20-30um, basophilic, irregular, smudgy to granular intranuclear viral inclusions that fills and distends the karyomegalic nucleus. Multifocally, the mucous glands are ectatic, lined by attenuated, degenerate and/or necrotic epithelium, and gland lumina contain viable and degenerate neutrophils admixed with variable amounts of amphophilic mucus and necrotic cellular debris. The nasal cavity is partially filled with an exudate composed of hemorrhage and sloughed and necrotic epithelial cells. Multifocally, the vascular endothelium is hypertrophic (reactive), and perivascular connective tissue is edematous with dilated lymphatics. There are multifocal areas of mild turbinate bone resorption and remodeling.
MORPHOLOGIC DIAGNOSIS: Nasal turbinate: Rhinitis, lymphoplasmacytic and necrotizing, subacute, diffuse, marked, with mucosal ulceration, glandular epithelial karyomegaly, cytomegaly, and intranuclear viral inclusions, breed unspecified, porcine
ETIOLOGIC DIAGNOSIS: Cytomegaloviral Rhinitis
CAUSE: Suid Herpesvirus 2 (Cytomegalovirus)
CONDITION: Inclusion Body Rhinitis
- Betaherpesvirus that causes an acute to subacute, mild rhinitis with high morbidity and low mortality 3-5-week-old suckling piglets
- Characteristic slow replication of betaherpesviruses leads to formation of greatly enlarged cells (cytomegaly)
- Transplacental transmission causes fetal death or weak neonates that succumb to generalized infection, but no placental injury
- Horizontal transmission occurs via close contact with nasal, ocular or vaginal secretions or with urine – predominant mode of transmission in enzootically infected herds, and infection is usually subclinical
- The virus replicates slowly in nasal submucosal and lacrimal glands producing cytomegaly, followed by viremia, and dissemination to additional epithelial sites, including renal tubules, liver and duodenum; replication may also occur in pulmonary and splenic macrophages (typical small “herpesviral-like” viral inclusions), and pulmonary macrophages may become persistently infected
- The mild rhinitis can progress to a mucopurulent discharge with subsequent blockage of nasal passages and interference with suckling, resulting in rapid weight loss and death
TYPICAL CLINICAL FINDINGS:
- Suckling piglets have a mild rhinitis with sneezing, coughing, and serous oculonasal discharge
- Pregnant sows have mild lethargy and anorexia with delivery of stillborn or weak piglets that die shortly after birth, often without clinical signs; piglets less than 3 weeks-old (neonates) that show clinical signs will exhibit sneezing, lethargy, anorexia, respiratory distress and subcutaneous edema of the jaw and tarsal joints
- Neonatal or suckling piglets that survive infections are often stunted
TYPICAL GROSS FINDINGS:
- Uncomplicated cases in suckling piglets (3-5 weeks): Nasal mucosal hyperemia, congestion; mucopurulent nasal discharge that occurs with secondary bacterial infections
- Generalized disease in neonates (<3 weeks): Catarrhal rhinitis, hydrothorax, hydropericardium, pulmonary and subcutaneous edema and renal petechiae
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- In suckling piglets, necrotizing, nonsuppurative rhinitis with large, 8-12 um, basophilic, intranuclear viral inclusion bodies in epithelial cells of nasal mucosa and cytomegaly of the nasal epithelium and glands, Harderian and lacrimal glands
- Inclusions are most numerous in epithelium, but also occur in macrophages and endothelial cells
- Inclusion bodies, cytomegaly, and karyomegaly are pathognomonic when present
- Immunosuppressed piglets develop systemic infection with necrosis of the liver, lungs, adrenal glands, and brain; Intranuclear viral inclusions occur in epithelial cells of renal tubules and glomeruli; lacrimal, Harderian and salivary glands; less commonly in hepatocytes, adrenal gland, esophageal submucosal glands, lymph nodes, spleen and lung
- Double-stranded, DNA virus with an enveloped virion approximately 150-200 nm in diameter and an 80-120 nm diameter, icosahedral nucleocapsid
- Atrophic rhinitis, a mixed bacterial (Pasteurella multocida and Bordetella bronchiseptica) infection that results in inflammation and atrophy of the nasal turbinates with septal deviation
- Penetrating wounds or removal of needle teeth can introduce Fusobacterium necrophorum, causing a paranasal abscess in young pigs (bull nose)
- Beta herpesviruses are species specific viruses that have been described in mice (murid herpesvirus 1), rats (murid herpesvirus 2), guinea pigs (cavid herpesvirus 2), elephants (elephantid herpesvirus), horses (equid herpesvirus 2), cattle (bovine herpesvirus 4), and various primates (cercopithecine herpes virus 5 & 8, aotine herpesvirus 1 & 3, etc.)
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