JPC SYSTEMIC PATHOLOGY
Signalment (JPC #1879041): Cow
HISTORY: This cow was one of many from a herd with respiratory distress.
HISTOPATHOLOGIC DESCRIPTION: Lung: Diffusely, interlobular septa are markedly expanded up to 20 times normal by abundant edema, eosinophilic beaded fibrillar material (fibrin), and necrotic debris and are infiltrated by large numbers of degenerate neutrophils, with fewer macrophages and viable neutrophils. The interlobular septa, small caliber vessels, and bronchioles are outlined and surrounded by numerous lymphocytes and plasma cells (lymphoid hyperplasia). The surrounding alveolar spaces contain eosinophilic edema fluid, viable and degenerate neutrophils, plasma cells, histiocytes, lymphocytes, fibrin, and abundant necrotic debris. Multiple contiguous alveoli coalesce and are expanded by clear space (emphysema). Multifocally, alveolar septa are discontinuous with replacement by fibrin and necrotic debris (septal necrosis) or are expanded by lymphocytes, histiocytes, and edema. Vessel wall architecture is multifocally replaced by abundant necrotic debris, fibrin, and similar inflammatory cells (necrotizing vasculitis). Bronchi and bronchioles are multifocally filled with edema, fibrin, neutrophils, lymphocytes, and histiocytes.
MORPHOLOGIC DIAGNOSIS: Lung: Pleuropneumonia, fibrinonecrotic and suppurative, diffuse, severe, with interlobular, alveolar and interstitial edema, lymphoid hyperplasia, and necrotizing vasculitis, breed unspecified, bovine.
ETIOLOGIC DIAGNOSIS: Mycoplasmal pneumonia
CAUSE: Mycoplasma mycoides subsp. mycoides (small colony type) (MmmSC)
CONDITION: Contagious bovine pleuropneumonia (CBPP)
- Mycoplasma: Smallest self-replicating organisms, gram-negative, lack a true cell wall, pleomorphic, nonmotile
- Affects domestic cattle (Bos taurus and Bos indicus); also reported in bison, yak, and domestic buffalo
- The disease is endemic in Africa, India, China, and Southern Europe and is considered eradicated in the Western hemisphere and Australia; OIE-notifiable disease
- Pathogenic mechanisms are poorly understood; vasculitis is central to the development of the necrotic lesions and sequestration of lung tissue
- No toxins or invasins are produced by Mycoplasma species
- The pathogenicity seems to be determined by intrinsic metabolic or catabolic pathway functions or by the mycoplasmal outer surface
- Transmission is direct via inhalation of droplets from an infected animal (respiratory or urine); transplacental infection has been known to occur
- Organisms penetrate the mucus layer, attach to ciliated epithelium via surface neuraminic acid receptors, and immobilize the cilia
- The capsular polysaccharide galactan has a direct cytopathic effect and seems to lead to the contraction of blood vessels resulting in thrombosis, pulmonary edema, and immunosuppression
- A massive inflammatory reaction mainly restricted to the lungs is the principal pathologic consequence of infection
- The excessive inflammatory response is likely due to inappropriate activation of alveolar macrophages leading to excessive TNF-α production and excessive neutrophil recruitment with subsequent release of inflammatory mediators
- Vasculitis plays a central role in the necrosis and sequestration of lung tissue
- Mycoplasmas adhere intimately to lymphocytes, inducing lymphoplasmacytic proliferation and inactivation, which makes this a superantigen
- Chronic carrier state may develop due to harboring of live organisms in sequestered areas of necrotic tissue in the lung
TYPICAL CLINICAL FINDINGS:
- High morbidity and high mortality in naïve herds
- Acute death in less than one week following clinical signs of fever, mucoid nasal discharge, severe cough, rapid labored open-mouth respiration and grunting
- Usually there is prolonged incubation (2-8 months) with cough and a classic stance with elbows out, head extended, and back arched
- Morbidity approaches 90% with mortality ranging from 10-70%
- Calves less than six months old often develop polyarthritis (carpus and tarsus), and pregnant cows may abort
TYPICAL GROSS FINDINGS:
- Lesions are usually unilateral with extensive fibrin deposition and abundant straw colored fluid in the thoracic cavity
- Majority of infections are restricted to the caudal lung lobes
- The parenchyma does not collapse, and the cut surface is marbled with prominent interlobular septa
- Sequestra may be present; these are masses of necrotic lung parenchyma separated from viable lung tissue by purulent exudate and usually encased in a fibrous capsule
- Fibrinonecrotic pneumonia with severe serofibrinous pleuritis and pleural adhesions
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Marked thickening of interlobular septa by fibrin, edema, areas of coagulative necrosis and inflammation
- Fibrinous pleural effusion, fibrinous pleuritis
- Fibrin thrombi, vasculitis, infarction, non-suppurative arteritis, thrombosis of pulmonary arteries, veins and lymphatics
- Fibrinous pericarditis, peritonitis, polysynovitis
- Lymphoid hyperplasia
- Mycoplasmas are pleomorphic bacteria that lack cell walls, membrane bound organelles, fimbria, and flagella
- Large numbers of mycoplasma attach to and destroy cilia
- Cilia are distorted, broken and lost with basal body degeneration
- Ballooning and blebbing of epithelial cell plasma membranes is typical
ADDITIONAL DIAGNOSTIC TESTS:
- Culture of organism on specialized media
- Immunohistochemistry and PCR for rapid diagnosis
- Serologic assays: Complement fixation test and competitive ELISA for screening an entire herd; hampered for individual animal diagnostics by limited sensitivity; frozen samples of lesional lung, pleural fluids and lymph nodes are optimal for isolation of the agent
- Mannheimia haemolytica: Most important respiratory pathogen in cattle, rapid spread, lungs typically bilaterally affected
- Mycoplasma bovis:
- An animal with bovis may be concurrently affected in one or more of the anatomic locations listed below; for example in cows, mastitis is often accompanied by pneumonia, and in calves otitis media is often accompanied by arthritis or pneumonia
- The bacterium induces apoptosis of bovine lymphocytes, suppresses the proliferative response of lymphocytes to mitogens, and impairs neutrophil activation
- Lungs: MmmSC and bovis result in similar gross lesions; the gross lesions of M. bovis are characterized by caseonecrotic bronchopneumonia with multiple well delineated necrotic foci filled with caseous material, linear necrotic lesions in interlobular septa, extensive fibrosis, necrotic sequestra, and acute fibrinous to chronic fibrosing pleuritis; lesions of M. bovis lack the extensive fibrinous exudates in interlobular septa and on the pleural surface seen with MmmSC
- Ears: Predominant pathogen isolated from the middle ear of calves with otitis media; characterized by suppurative to caseous exudate with frequent extensive osteolysis
- Mammary glands: An important cause of infectious mastitis in cows; readily transmitted to uninfected animals once it has entered a herd; mild to severe fibrinosuppurative to caseonecrotic inflammation
- Joints: Arthritis and tenosynovitis characterized by fibrinous to caseous exudate accompanied by fibrosis; periarticular involvement foci of caseous necrosis, linear necrotic lesions and extensive fibrosis; pneumonia is found in nearly all calves with bovis arthritis
- Other associated lesions include subcutaneous decubital abscesses, meningitis (complication of otitis media-interna), cardiac disease (isolated reports of myocarditis and endocarditis)
- bovis causes particularly severe disease in farmed bison, with high morbidity and mortality
- Histophilus somni: Suppurative and fibrinous bronchopneumonia; coagulative necrosis with streaming necrotic leukocytes
- Acute bovine pulmonary emphysema and edema (ABPE): Also known as atypical interstitial pneumonia (AIP), “fog fever” or acute respiratory distress syndrome (ARDS)
- AIP is caused by ingestion of plants containing L-tryptophan or other pneumotoxins that are converted to 3-methylindole
- Histologic lesions include alveolar and interstitial edema and emphysema with formation of hyaline membranes
- Goats: Three mycoplasmas are associated with respiratory infections in goats:
- M. mycoides ssp. capri (Mmc):
- Ubiquitous pathogen in small ruminants causing mastitis, arthritis, keratitis, pneumonia and septicemia and also found as a saprophyte in the ear canal
- The designation mycoides ssp. mycoides large colony type has been discarded and bacteria of this type are now considered a serovar of Mmc
- M. capricolum ssp. capripneumoniae
- Considered the only etiologic agent of typical contagious caprine pleuropneumonia (CCP)
- Gross lesions are similar to those of bovine disease
- Histologically: Severe fibrinous pleuropneumonia but distention of the interlobular septa and formation of pulmonary sequestra less obvious than in bovine disease
- M. capricolum capricolum: Fibrinopurulent polyarthritis in kids
- M. mycoides ssp. capri (Mmc):
- Sheep: M. ovipneumoniae isolated with P. multocida in enzootic ovine pneumonia
- M. hyopneumoniae: Enzootic pneumonia
- M. hyorhinis: Arthritis and polyserositis
- Deer: M. bovis: Pneumonia
- Bison: M. bovis: Pneumonia, polyarthritis, fibrinosuppurative pleuritis, and disseminated microabscesses
- Chickens and turkeys:
- M. synoviae: Tenosynovitis, arthritis, and sinusitis
- M. gallisepticum: Sinusitis
- Rats and mice:
- M. pulmonis: Pneumonia
- M. arthritidis: Arthritis
- Humans: pneumonia: Primary atypical pneumonia
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