History and Clinical Findings
A 5.5-year-old 6.5-kg (14.3-lb) neutered male domestic longhair cat was submitted to the Indiana Animal Disease Diagnostic Laboratory for postmortem examination. The cat had been evaluated at the Purdue University Veterinary Teaching Hospital because of a 2-year history of hind limb ataxia that had progressively worsened to hind limb paraparesis during the preceding 2 weeks. The cat had a history of asthma that had been previously treated with corticosteroids by the referring veterinarian, but the cat was not currently receiving any medications for asthma. Thoracic radiography revealed a soft-tissue nodule in the left caudal lung lobe. Magnetic resonance imaging of the spinal cord revealed multifocal spinal cord lesions that were hyperintense, compared with the adjacent portions of the spinal cord. Owing to worsening neurologic signs and poor prognosis, the cat was euthanized by IV injection of pentobarbital solution.
Necropsy Findings
At necropsy, the lungs were mottled pink to dark red. In the caudal aspect of the left caudal lung lobe, there was a 2.5 × 2.5 × 2-cm, fi m, irregularly shaped cyst with a 2- to 3-mm-thick, white to tan fib ous wall and multiple fi m irregular yellow-white foci (Figure 1).
Photograph of the thoracic cavity and lungs of a domestic longhair cat that had asthma and a 2-year history of hind limb ataxia that had progressively worsened to hind limb paraparesis during the preceding 2 weeks. Diagnostic imaging revealed a soft-tissue nodule in the left caudal lung lobe and multifocal spinal cord lesions. The cat was euthanized after evaluation. A firm irregularly shaped cyst (arrow) is evident in the left caudal lung lobe. The adjacent parenchyma is yellow and firm Cranial to the mass is a 3-mm-diameter translucent, subpleural air-filled cyst (a rowhead). Bar = 1 cm.
Citation: Journal of the American Veterinary Medical Association 248, 11; 10.2460/javma.248.11.1253
Photograph of the thoracic cavity and lungs of a domestic longhair cat that had asthma and a 2-year history of hind limb ataxia that had progressively worsened to hind limb paraparesis during the preceding 2 weeks. Diagnostic imaging revealed a soft-tissue nodule in the left caudal lung lobe and multifocal spinal cord lesions. The cat was euthanized after evaluation. A firm irregularly shaped cyst (arrow) is evident in the left caudal lung lobe. The adjacent parenchyma is yellow and firm Cranial to the mass is a 3-mm-diameter translucent, subpleural air-filled cyst (a rowhead). Bar = 1 cm.
Citation: Journal of the American Veterinary Medical Association 248, 11; 10.2460/javma.248.11.1253
Photograph of the thoracic cavity and lungs of a domestic longhair cat that had asthma and a 2-year history of hind limb ataxia that had progressively worsened to hind limb paraparesis during the preceding 2 weeks. Diagnostic imaging revealed a soft-tissue nodule in the left caudal lung lobe and multifocal spinal cord lesions. The cat was euthanized after evaluation. A firm irregularly shaped cyst (arrow) is evident in the left caudal lung lobe. The adjacent parenchyma is yellow and firm Cranial to the mass is a 3-mm-diameter translucent, subpleural air-filled cyst (a rowhead). Bar = 1 cm.
Citation: Journal of the American Veterinary Medical Association 248, 11; 10.2460/javma.248.11.1253
Formulate differential diagnoses from the history, clinical findings, and Figure 1—then turn the page →
Gross and Histopathologic Findings
Inside the lung lobe cyst, there were 2 ovoid (10-mm-long and 5-mm-diameter) red brown trematodes (Figure 2) and scanty cloudy brown fluid The cyst communicated with a smaller (3-mm-diameter) translucent, subpleural air-filled cyst
Photographs of the cut left caudal lung lobe (A) of the cat in Figure 1 and a formalin-fi ed trematode (B) removed from the cyst during necropsy. In panel A, the cyst has an irregular cavitation with a thick fib ous wall (asterisk), in which one of two 10-mm-long organisms was located (arrow). Bar = 5 mm.
Citation: Journal of the American Veterinary Medical Association 248, 11; 10.2460/javma.248.11.1253
Photographs of the cut left caudal lung lobe (A) of the cat in Figure 1 and a formalin-fi ed trematode (B) removed from the cyst during necropsy. In panel A, the cyst has an irregular cavitation with a thick fib ous wall (asterisk), in which one of two 10-mm-long organisms was located (arrow). Bar = 5 mm.
Citation: Journal of the American Veterinary Medical Association 248, 11; 10.2460/javma.248.11.1253
Photographs of the cut left caudal lung lobe (A) of the cat in Figure 1 and a formalin-fi ed trematode (B) removed from the cyst during necropsy. In panel A, the cyst has an irregular cavitation with a thick fib ous wall (asterisk), in which one of two 10-mm-long organisms was located (arrow). Bar = 5 mm.
Citation: Journal of the American Veterinary Medical Association 248, 11; 10.2460/javma.248.11.1253
Histologically, the cyst was surrounded by fib ous tissue and was lined by immature granulation tissue with heavy infilt ation by lymphocytes, plasma cells, eosinophils, and macrophages (Figure 3). Ectatic bronchi (up to approx 1 mm in diameter) adjacent to the cyst were lined by multifocally disrupted, transitional to nonkeratinizing stratified squamous epithelium and were fille with sloughed epithelial cells and a mixture of leukocytes. Lymphoid cells were numerous in the peribronchial tissue. Alveolar spaces around the cyst contained scattered yellow-brown, thin-shelled trematode eggs (approx 100 × 70 μm), most of which were ruptured and filled with macrophages, lymphoid cells, neutrophils, and fewer eosinophils. Inflammation extended into the visceral pleura, which was thickened by fib ous tissue and extensive new capillary formation. A few microscopic aggregates of lymphocytes, plasma cells, macrophages with vacuolated cytoplasm, and rare neutrophils were observed around intrapulmonary airways. Fragments of 1 trematode were removed from the cyst during necropsy for examination; it had a thick eosinophilic tegument and parenchymatous body with a reproductive tract consisting of a uterus containing ovoid eggs with thin yellow-brown refractile shells and testes with basophilic elongated sperm. The gross and histologic features of the organism and eggs were consistent with Paragonimus kellicotti.
Photomicrographs of sections of the pulmonary cyst and surrounding lung parenchyma from the cat in Figure 1. A—Notice the thick fib ous cyst wall lined by immature granulation tissue with heavy infiltration by lymphocytes, plasma cells, eosinophils, and macrophages. H&E stain; bar = 1 mm. B—An alveolar space adjacent to the cyst contains a ruptured trematode egg with a yellow-brown refractile shell that is infiltrated and su rounded by neutrophils and macrophages. H&E stain; bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 248, 11; 10.2460/javma.248.11.1253
Photomicrographs of sections of the pulmonary cyst and surrounding lung parenchyma from the cat in Figure 1. A—Notice the thick fib ous cyst wall lined by immature granulation tissue with heavy infiltration by lymphocytes, plasma cells, eosinophils, and macrophages. H&E stain; bar = 1 mm. B—An alveolar space adjacent to the cyst contains a ruptured trematode egg with a yellow-brown refractile shell that is infiltrated and su rounded by neutrophils and macrophages. H&E stain; bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 248, 11; 10.2460/javma.248.11.1253
Photomicrographs of sections of the pulmonary cyst and surrounding lung parenchyma from the cat in Figure 1. A—Notice the thick fib ous cyst wall lined by immature granulation tissue with heavy infiltration by lymphocytes, plasma cells, eosinophils, and macrophages. H&E stain; bar = 1 mm. B—An alveolar space adjacent to the cyst contains a ruptured trematode egg with a yellow-brown refractile shell that is infiltrated and su rounded by neutrophils and macrophages. H&E stain; bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 248, 11; 10.2460/javma.248.11.1253
Morphologic Diagnosis and Case Summary
Morphologic diagnosis: pulmonary trematodiasis (caused by Paragonimus kellicotti) and unrelated spinal cord lesions consistent with spinal oligodendroglioma and gliomatosis.
Case summary: pulmonary paragonimiasis in a cat.
Comments
In North America, paragonimiasis in humans, dogs, cats, and multiple species of wild carnivores is caused by the trematode P kellicotti.1–3 Paragonimus kellicotti is endemic to much of eastern North America, and most infections are reported in the north central and southeastern United States.2
The life cycle of P kellicotti requires 2 intermediate hosts. Eggs that are shed via the feces of infected mammals into water develop and hatch into ciliated miracidia, which invade the fi st intermediate hosts, aquatic snails of the genus Pomatiopsis.2,3 Cercariae develop within the snails and encyst as metacercariae in the second intermediate hosts, crayfish2–4 Infection of a definiti e host results from ingestion of crayfish containing metacercarial cysts or from ingestion of animals that have recently eaten crayfish4,5
Metacercariae migrate from the gastrointestinal tract into the peritoneal cavity then enter the pleural cavity through the diaphragm and migrate into the lungs.4 The flu es establish pulmonary cysts within 4 to 5 weeks after infection.4 Cysts communicate with the bronchial tree to facilitate expulsion of operculated eggs (characteristic of P kellicotti) into the airways.4 Eggs are coughed up, swallowed, and expelled in the feces.4
In cats and dogs, clinical signs of P kellicotti infection are usually mild and may include coughing, sneezing, exercise intolerance, hemoptysis, and dyspnea.2 Pneumothorax and sudden death resulting from cyst rupture have been reported.6 Cysts may be evident radiographically 4 to 5 weeks after infection and appear as nodular, multiloculated, well-defined densities2,4,5
Grossly, P kellicotti cysts are usually found in the caudal lung lobes and more often in the right caudal lobe.5 Gross necropsy findings may include lung distension and consolidation and fib ous pleural adhesions.5 On cut surface, cysts are well demarcated with a thick fib ous wall containing necrotic debris surrounding adult flu es, which usually are present in pairs.2,5 Cysts may communicate with the bronchial tree to facilitate deposition and expulsion of eggs from the lungs.4,5
Microscopically, cysts have a thick wall of granulomatous inflammation or granulation tissue, which may be lined by squamous epithelium.5 Characteristic ova with ovoid yellow-brown shells and a distinct operculum surrounded by granulomatous inflammation may be present in the lung parenchyma.5 In chronic stages of infection, inflammation may regress resulting in local interstitial fib osis. Microscopic features of Paragonimus flat orms include oral and ventral suckers, a thick eosinophilic tegument with spines, a solid parenchymatous body with no cavity, vitelline glands, and a bifurcated intestinal tract ending in a blind cecum.3 Paragonimus spp, like other trematodes except those of the family Schistosomatidae, are monoecious hermaphrodites; on microscopic examination, a uterus containing characteristic eggs and testes with basophilic elongated sperm may be seen.7 Other microscopic findings in and around the lungs may include bronchial submucosal gland hyperplasia, smooth muscle hyperplasia, reactive hyperplasia of the pleural mesothelium, and fib inous pleural adhesions.5
Definiti e diagnosis of pulmonary paragonimiasis in live animals is provided by identification of characteristic yellow-brown operculated eggs in the feces or bronchial mucus and identification of adult flu es in thick-walled pulmonary cysts at necropsy.2 Treatment for cats and dogs may include administration of albendazole, fenbendazole, or praziquantel.2
In the cat of the present report, histopathologic features of the spinal cord lesions were consistent with spinal oligodendroglioma and gliomatosis. The reported neurologic signs were attributed to the spinal neoplasia and were unrelated to Paragonimus infection.
References
1. Lane MABarnsanti MCSantos CA, et al. Human paragonimiasis in North America following ingestion of raw crayfish Clin Infect Dis 2009;49:e55–e61.
2. Conboy G. Helminth parasites of the canine and feline respiratory tract. Vet Clin Small Anim Pract 2009;39:1109–1126.
3. Bowman DD. Helminths. In: Georgis’ parasitology for veterinarians. 9th ed. St Louis: Elsevier, 2009;124–125.
4. Sherding R. Parasites of the lung. In: Textbook of respiratory disease in dogs and cats. St Louis: Elsevier, 2004;555–556.
5. Weina PJEngland DM. The American lung flu e, Paragonimus kellicotti, in a cat model. J Parasitol 1990;76:568–572.
6. Harrus SNyska AColorni A, et al. Sudden death due to Paragonimus kellicoti infection in a dog. Vet Parasitol 1997;71:59–63.
7. Gardiner CHPoynton SL. An atlas of metazoan parasites in animal tissues. Washington, DC: Armed Forces Institute of Pathology, 2006;46–49.
