JPC SYSTEMIC PATHOLOGY
Signalment (JPC #1642875): Cat
HISTOPATHOLOGIC DESCRIPTION: Lung: Effacing and replacing up to 30% of the section are multifocal to coalescing nodular aggregates of numerous macrophages and fewer lymphocytes, plasma cells, neutrophils, eosinophils with abundant fibrous connective tissue and minimal hemorrhage that surround an adult trematode and eggs. The adult trematode is 2x3 mm, has a 40 um thick spiny tegument, and a spongy parenchyma that contains numerous subtegumental vitellaria with eosinophilic globular yolk material. Trematode eggs are 80 x 100um, and have a 1‑3um thick, yellow, anisotropic shell. In less affected areas there are pigment laden macrophages, lymphoid aggregates and hemorrhage. Multifocally, bronchial and bronchiolar lumena are filled with sloughed epithelial cells, low numbers of macrophages, neutrophils, lymphocytes and plasma cells. There is multifocal bronchiolar and alveolar smooth muscle hypertrophy, as well as hyperplasia of peribronchial mucous glands. Multifocally the tunica media of small and medium blood vessels is thickened by smooth muscle hypertrophy, and there is endothelial hypertrophy and vacuolation. The pleura is thickened 2-3 times normal by lymphocytes, plasma cells, macrophages, fibrous connective tissue, and hypertrophic (reactive) cuboidal mesothelial cells.
MORPHOLOGIC DIAGNOSIS: Lung: Pneumonia, granulomatous, nodular, chronic, multifocal, moderate, with fibrosis, pleuritis and adult trematodes and eggs, etiology consistent with Paragonimus sp., breed unspecified, feline.
ETIOLOGIC DIAGNOSIS: Pulmonary paragonimiasis
CAUSE: Paragonimus kellicotti
- Paragonimus spp. are flukes, belonging to the Troglotrematidae family, which cause pulmonary cysts in crayfish-eating mammals and man
- Two important species: P. westermanii (Asia) and P. kellicotti (North America)
- Of the trematodes, Paragonimus is the only genus that has its final habitat in the lungs
- Most commonly found in cats; occasionally found in dogs, pigs, and goats
- Widely distributed in the U.S.; frequently found in the Great Lakes and Mississippi Valley regions Life Cycle:
- 1st intermediate host: small aquatic snails; cercariae stage
- 2nd intermediate host: freshwater crabs or crayfish; metacercariae stage
- Ingestion of crayfish containing metacercariae>liberation of the metacercariae
- into the intestines>migration across the peritoneal and pleural cavities into the lungs > stimulate pyogranulomatous inflammation > fibrosis>cyst formation (in pairs within fibrous cysts connected to bronchioles by fistula into which eggs are released) > eggs are coughed up the tracheobronchial tree, swallowed and passed in feces> ciliated miracidium released from eggs in fresh water > miracidium infect snail species > after asexual reproduction within the snail, cercariae are released and penetrate the crayfish > develops to metacercariae in the crayfish
TYPICAL CLINICAL FINDINGS:
- Generally asymptomatic
- Occasionally chronic, deep, intermittent cough, weakness and lethargy
- Rupture of cysts may rarely cause pneumothorax
TYPICAL GROSS FINDINGS:
- Adult flukes are oval, red-brown, and 5‑10 mm long and 4‑7 mm in diameter; present in pairs in cavitations (raised, soft, dark brown, 1-3 cm in diameter) and occasionally bronchi; lesions are most common in the caudal lobes especially the right lobe
- Pleural adhesions, focal areas of emphysema
- Migrating metacercariae produce pleural hemorrhages and foci of eosinophilic and fibrinous pleuritis, which heal as small umbilicated scars
- Rupture of cysts may result in pneumothorax
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Granulomatous and eosinophilic pneumonia or granulomas that surround adults and eggs; hemosiderin laden macrophages
- Adults have a spiny tegument, ventral sucker, loose parenchyma (lack a body cavity), paired ceca with dark pigment, vitellaria containing eosinophilic globular yolk material, gonads of both sexes
- Caviations are surrounded by a fibrous capsule; mature cavitations establish connections with bronchioles and become partially lined by bronchiolar epithelium to form true cysts
- Eggs are gold-brown, operculate, 80‑110 um long by 40‑60 um wide; within eosinophilic granulomas or in subpleural and mediastinal lymphatics leading to pleuritis and lymphangitis
- Catarrhal and eosinophilic bronchitis with hyperplasia of peribronchiolar glands and smooth muscle
- Aelurostrongylus abstrusus is the most common lung nematode of cats; eggs form nodular lesions within alveoli
- Paragonimus westermanii (oriental lung fluke) is found in dogs, pigs, goats, cattle, foxes, and small mammals, principally in Asia
- Syrian hamsters: experimentally infected with P. kellicotti and may serve as small animal models of the disease
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