Signalment:  

Age-unspecified female Yorkshire pig, (Sus scrofa).This Yorkshire pig was one of several animals belonging to a hemorrhagic shock study. This pig (animal number 30962), age unknown, was hemorrhaged over a 15-minute period until 55% of its estimated blood volume (EBV) was lost via the femoral artery catheter. At time 15 minutes, the pig received initial resuscitation therapy. Oxycyte (5 mL/kg) was given as a continuous infusion over 10 minutes via the external jugular vein. There was no reported history of clinical illness.

Gross Description:  

There were no reported gross findings at necropsy.

Histopathologic Description:

Lung: Diffusely, filling bronchi and bronchioles is an exudate composed of moderate numbers of viable and non-viable neutrophils, macrophages, fewer lymphocytes and plasma cells, admixed with edema, and rare fibrin. Multifocally, both bronchial and bronchiolar epithelium are mildly hyperplastic. A similar infiltrate extends into interlobular septa, expands and obscures alveolar septa, and fills alveolar spaces. Rarely, there is mild type II pneumocyte hyperplasia. Multifocally surrounding bronchi, bronchioles, and blood vessels (often lined by hyperplastic endothelium) are variably sized lymphoid follicles with vague germinal centers (BALT hyperplasia), with mild lymphocytolysis. Multifocally, the pleura is separated from the subjacent lung parenchyma by clear space (suspected artifact).

Morphologic Diagnosis:  

Lung: Pneumonia, bronchointerstitial, suppurative and histiocytic, chronic, diffuse, severe, with lymphoid (BALT) hyperplasia, mild lymphocytolysis, type II pneumocyte hyperplasia, bronchiolar and bronchial epithelial hyperplasia, and edema, Yorkshire pig, porcine.

Lab Results:  

-�-� Mycoplasma hyopneumoniae PCR: NEGATIVE
-�-� Mycoplasma hyopneumoniae IHC: NEGATIVE

Condition:  

Enzootic pneumonia

Contributor Comment:  

This is a case of suspected Mycoplasma hyopneumoniae, which is a common cause of non-fatal pneumonia in young pigs. The disease is prevalent in grower-finisher pigs; however, animals as young as 5-weeks may be affected.(1) Also known as porcine enzootic pneumonia, disease progression is often insidious in endemic areas where subclinical carriers serve as key sources of infection for na+�-�ve herds.(1)

Gross lesions associated with mycoplasmal pneumonia are discolored, collapsed, firm lungs affecting the cranioventral lung lobes.(1) Acute histologic lesions are characterized by alveoli containing macrophages and neutrophils along with edema.(1) Chronic infections in swine are similar to other species (e.g., rats, mice) where peribronchial/peribronchiolar (BALT), and perivascular lymphoid hyperplasia is a dominant histologic feature.

Although the exact pathogenesis is not completely understood, Mycoplasma hyopneumoniae firmly adheres to the cilia of the respiratory tree resulting in ciliostasis. Attachment to the respiratory epithelium invokes the following:
(1) Influx of neutrophils into the tracheobronchial mucosa
(2) Extensive loss of cilia (deciliation)
(3) Broncho-alveolar lymphoid tissue (BALT) hyperplasia
(4) Influx of mononuclear cells into the peribronchiolar, bronchiolar, and alveolar interstitium(3)

Diagnosis of Mycoplasma hyopneumoniae infection in the porcine lung is based on results of three methods: isolation of the organism by culture, immunofluorescence (IF) testing, or immunohistochemistry using polyclonal antibodies.(3)

Despite our inability to definitively diagnose Mycoplasma hyopneumoniae as a causative agent for the lung lesions in this case, the histologic lesions are highly suggestive of this entity.

JPC Diagnosis:  

Lung: Bronchopneumonia, pyogranulomatous, diffuse, chronic, severe, with BALT hyperplasia.

Conference Comment:  

In conference, the moderator led a brief review of the morphologic patterns of pneumonia. Bronchopneumonia is the most common type of pnuemonia in domestic animals. It is characterized by inflammatory lesions arising primarily within the airways (with occasional spread into the surrounding interstitium), and there is usually cranioventral consolidation of the lungs. Bronchopneumonias are typically caused by many types of inhaled bacteria, including Mycoplasma spp. Fibrinous bronchopneumonia in particular has a propensity for depositing on pleural surfaces, thus some pathologists refer to it as pleuropneumonia. In contrast, inflammatory lesions develop within alveolar walls and the bronchiolar interstitium in cases of interstitial pneumonia. The portal of entry can by hematogenous or aerogenous. Interstitial pneumonia tends to be diffuse and is generally associated with viruses, toxins, sepsis, or protozoa such as Toxoplasma spp. The term bronchointerstitial pneumonia describes pulmonary lesions with features of both interstitial and bronchopneumonia and is specifically associated with viruses that cause necrosis in both bronchiolar and alveolar epithelial cells (e.g. small ruminant respiratory syncytial virus, canine distemper and porcine/equine influenza). With embolic pneumonia, sterile or septic (e.g. from vegetative valvular endocarditis), thromboemboli are delivered hematogenously to the lung; inflammation is random and multifocal and it centers upon pulmonary arterioles and alveolar capillaries. Verminous pneumonia typically exhibits a caudodorsal distribution.(3) Based on this broad classification scheme, the microscopic lesions in this case are most consistent with bronchopneumonia secondary to Mycoplasma hyopneumoniae.

The contributor provides an excellent summary of M. hyopneumoniae. See WSC 2013-2014, conference 7, case 1 for further discussion of Mycoplasma spp., and table 1 for an abbreviated list of Mycoplasma species important in veterinary medicine.

Table 1. Select Mycoplasma species of veterinary importance.⁴

Mycoplasma species	Hosts	Disease
M. mycoides subsp. mycoides (small colony type)	Bovine	Contagious bovine pleuropneumonia
M. bovis	Bovine	Mastitis, pneumonia, arthritis, otitis
M. agalactiae	Ovine, Caprine	Contagious agalactia (mastitis)
M. capricolum subsp. capripneumoniae	Caprine	Contagious caprine pleuropneumonia
M. capricolum subsp. capricolum	Ovine, Caprine	Septicemia, mastitis, polyarthritis, pneumonia
M. mycoides subsp. capri (includes strains previously classified as M. mycoides mycoides large colony type)	Ovine, Caprine	Septicemia, pleuropneumonia, mastitis, arthritis
M. ovipneumoniae	Ovine, Caprine	Pneumonia
M. pulmonis	Rodents--rat and mouse	Colonize nasopharynx and middle ear; affect respiratory and reproductive tracts and joints
M. hyopneumoniae	Swine	Enzootic pneumonia
M. hyosynoviae	Swine (10-30 weeks of age)	Polyarthritis
M. hyorhinis	Swine (3-10 weeks of age)	Polyserositis
M. suis	Swine	Mild anemia, poor growth rates
M. ovipneumoniae		mild pneumonia
M. haemofelis	Feline	Feline infectious anemia
M. cynos	Canine	Implicated in kennel cough complex
M. haemocanis	Canine	Mild or subclinical anemia; more severe signs in splenectomized animals
M. gallisepticum	Turkeys and Chickens	Chronic respiratory disease; infectious sinusitis
M. synoviae	Turkeys and Chickens	Infectious synovitis
M. meleagridis	Feline, Equine	Conjunctivitis in cats, pleuritis in horses
M. equigenitalium	Equine	Abortion

References:

1. Caswell JL, Williams KJ. Respiratory system. In: Maxie MG, ed. Jubb, Kennedy, and Palmers Pathology of Domestic Animals. Vol 2. 5th ed. Vol. 2. Philadelphia, PA: Elsevier Saunders; 2007;591-592.

2. Kwon D, Chae C. Detection and localization of Mycoplasma hyopneumoniae DNA in lungs from naturally infected pigs by in situ hybridization using a digoxigenin-labeled probe. Vet Pathol. 1999;36:308-313.

3. Lopez A. Respiratory system, mediastinum, and pleurae. In: Zachary JF, McGavin MD, eds. Pathologic Basis of Veterinary Disease. 5th ed. St. Louis, MO: Elsevier Mosby; 2012:494-504, 520-521.

4. Quinn PJ, Markey BK, Leonard FC, FitzPatrick ES, Fanning S, Hartigan PJ. Mycoplasmas. In: Veterinary Microbiology and Microbial Disease. 2nd ed. Ames, Iowa: Wiley-Blackwell; 2011; Kindle edition.

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4-1. Lung

4-2. Lung

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