FINAL   DIAGNOSIS - Pulmonary paragonimiasis        

 History:  The right middle lung lobe from a 3-year-old domestic shorthair cat was submitted for histopathology.  The cat had presented to the referring veterinarian with the primary complaint of a persistent cough.  The cat was wheezing, but no other abnormalities were noted.  A heartworm test was negative.  No parasitic ova were detected on fecal flotation.  No abnormalities were noted on a CBC and chemistry panel.  Thoracic radiographs were sent to a radiologist for interpretation.  Approximately one week after the first visit, the cat presented in respiratory distress.  Interpretation of the radiographs from the first visit revealed collapse of the right middle lung lobe with prominent bronchial markings in the remainder of the lung.  The right middle lung lobe was excised and submitted for histopathology.

Gross Findings: A few, 1.0-2.0 cm in diameter, red-brown, poorly delineated, firm nodules bulged from the right middle and right caudal lung lobes.

Histopathology: Alterations in sections of the right middle lung lobe included atelectasis, mild multifocalgranulomatous pneumonia with intralesionaltrematode eggs, and hyperplasia of the bronchiolar epithelium and peribronchiolar glands.  The trematode eggs were oval, yellow-brown, and approximately 100 microns in length by 55 microns in diameter with a single, flattened operculum, morphologically typical of Paragonimuskellicotti.  Adult flukes were not observed.

Discussion:  Paragonimuskellicotti is a trematode parasite of cats, dogs, mink, muskrats, raccoons, skunks, coyotes, foxes, goats, pigs and opossums in North America.  It is found in the North Central, Midwest, and Southeast regions of the United States.

  The distribution of Paragonimuskellicotti is restricted to the area inhabited by its first intermediate host, Pomatiopsislapidaria, an aquatic snail.  The second intermediate hosts are crayfish of the genera Cambarus, Procambarus, orOrconectes.  Definitive hosts become infected when they ingest crayfish with encysted metacercariae.  Metacercariae exist in the small intestine of the definitive host, and the immature flukes penetrate the intestinal wall, migrate in the peritoneal cavity, penetrate the diaphragm, migrate in the pleural cavity, and penetrate the lung where they mature into adult flukes.  Adult flukes live in pairs within cystic cavities connected to bronchioles.  Eggs from adult flukes are carried up the mucociliary escalator, swallowed, and excreted with the feces.

  The severity of clinical signs caused by Paragonimuskellicotti   relates to the number of infecting flukes.  Migration of immature flukes can cause lethargy, pyrexia, anorexia, and weight loss.  Adult flukes and their eggs can cause chronic coughing, dyspnea, salivation and hemoptysis.

  Lesions caused by migration of the immature flukes include multifocaleosinophilic peritonitis, hepatitis, and diaphragmatic myositis.  Mediastinal and pulmonary pleural adhesions to the diaphragm and costal pleura can also occur.  Cysts containing adult flukes can be observed as 1.0-2.0 cm in diameter, red-brown, firm, spherical pulmonary nodules.  Adult flukes are red brown and approximately 1.1 x 0.6 x 0.5 cm.  Microscopic lesions include multifocaleosinophilic and granulomatous pneumonia with intralesionaltrematode ova, hyperplasia of bronchiolar epithelium and peribronchiolar glands, and peribronchiolar infiltration of lymphocytes and plasma cells.  Extrapulmonarygranulomatous lesions have been reported.

  Diagnosis of paragonimiasis can be made with detection of eggs on fecal sedimentation or transtracheal wash.  Pulmonary cysts can be observed on radiographs.  Treatment of paragonimiasis with an appropriate anthelmintic is usually rewarding.  The anthelmintic kills adult flukes, and the cystic lesions resolve.  Surgery is typically not necessary.

  The incidence of paragonimiasis is reportedly increasing around the Great Lakes due to increased numbers of a second intermediate host, Orconectesrusticus,the rusty crayfish, which is thought to have been inadvertently introduced to the Great Lakes by fishermen.  Paragonimiasis should be considered in outdoor pets that present with a chronic cough.

-by Matt Renninger, DVM, ADDL Graduate Student