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
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
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