Paragonimiasis
Paragonimus is a lung fluke (flatworm) that infects the lungs of humans after eating an infected raw or undercooked crab or crayfish. Less frequent, but more serious cases of paragonimiasis occur when the parasite travels to the central nervous system. Most commonly Paragonimus westermani. It infects an estimated 22 million people yearly worldwide. It is particularly common in East Asia. More than 30 species of trematodes (flukes) of the genus Paragonimus have been reported; among the more than 10 species reported to infect humans, the most common is P. westermani, the oriental lung fluke.
1.Causative agent
2. Characteristic & Epidemiology
Several species of Paragonimus cause most infections; the most important is P. westermani, which occurs primarily in Asia including China, the Philippines, Japan, Vietnam, South Korea, Taiwan, and Thailand. P. africanus causes infection in Africa, and P. mexicanus in Central and South America. Specialty dishes in which shellfish are consumed raw or prepared only in vinegar, brine, or wine without cooking play a key role in the transmission of paragonimiasis. Raw crabs or crayfish are also used in traditional medicine practices in Korea, Japan, and some parts of Africa.
Although rare, human paragonimiasis from P. kellicotti has been acquired in the United States, with multiple cases from the Midwest. Several cases have been associated with ingestion of uncooked crawfish during river raft float trips in Missouri.
3. Diagnosis
The clinical picture of chronic paragonimiasis resembles chronic bronchitis or tuberculosis. Persons may cough up coffee-colored or blood-tinged sputum, often accompanied by chest pain and/or shortness of breath. The sputum may be peppered consisting of clumps of eggs produced by the adult fluke living in the lung.
Peripheral eosinophilia is common and can be intense, especially during the early larval migration stages. Many patients have a spectrum of abnormalities on chest radiographs: lobar infiltrates, coin lesions, cavities, calcified nodules, hilar enlargement, pleural thickening and effusions. Ring-shaped opacities of contiguous cavities giving the characteristic appearance of a bunch of grapes are highly suggestive of pulmonary paragonimiasis. Central nervous system disease may provide similar "grapebunch" findings, characteristically seen in the temporal and occipital lobes on computed tomography of the brain. CNS involvement occurs in up to 25% of hospitalized patients and may be associated with Paragonimus-induced meningitis. CNS symptoms may include headaches, seizures, and visual disturbances. Paragonimus flukes may also invade the liver, spleen, intestinal wall, peritoneum, and abdominal lymph nodes.
Sputum examined microscopically may reveal Paragonimus eggs released by the flukes in the lungs. Keep in mind that the acid-fast stain that is used for TB testing of sputum destroys eggs. The eggs may also be found by multiple stool exams on different days as a result of coughed-up eggs that are swallowed. The microscopic eggs are yellowish brown, 80-120 µm long by 45-70 µm wide, thick-shelled, and with an obvious operculum. Serologic tests can be especially useful for early infections (prior to maturation of flukes) or for ectopic infections where eggs are not passed in stool.
Ectopic lesions from aberrant migration of flukes can involve any organ, including abdominal viscera, the heart, and the mediastinum. The infection can also affect the liver, spleen, abdomen, and skin. The most clinically recognizable ectopic lesions arise from cerebral paragonimiasis, which, in highly endemic countries, more commonly affects children. These children present with eosinophilic meningoencephalitis, seizures, or signs of space-occupying lesions. Many patients with central nervous system disease also have pulmonary infections. P. skrjabini often produces skin nodules, subcutaneous abscesses, or a type of creeping eruption known as "trematode larva migrans."
4. Transmission
Human paragonimiasis is acquired through ingestion of raw or undercooked crabs or crayfish, and is usually a lung infection. After ingestion, metacercariae excyst in the small intestine and release larvae that penetrate the duodenal wall and enter the peritoneal cavity. The larvae migrate for approximately 1 week, then penetrate the diaphragm, enter the pleural cavity, and migrate directly through lung tissue to reach the bronchi. There they form cystic cavities and develop into adult worms in 5-6 weeks. The adult parasites are reddish brown and ovoid, measuring 7.5-12 mm by 4-6 mm. Adult worms induce an inflammatory response in the lungs, generating a fibrous cyst that contains a purulent, bloody effusion and eggs released by the flukes which are passed into the environment via expectoration, or may be swallowed and passed with feces. When deposited in fresh water, eggs hatch to release miracidiae, which then invade specific snail hosts. Thousands of cercariae are later released from the infected snail, which encyst (as metacercariae) in the gills, muscles, legs, and viscera of freshwater crustaceans (crabs or crayfish).
5. Signs and Symptoms
Symptoms and signs mimic those of tuberculosis, and paragonimiasis should always be suspected in patients with tuberculosis who are non-responsive to treatment. Ectopic paragonimiasis may result from erratic migration of the juvenile worms: the most frequent locations include the abdominal cavity and subcutaneous tissues and, most frequently, the brain: cerebral paragonimiasis is a severe condition that may be associated with headache, visual impairment and epileptic seizures.
The acute phase (invasion and migration) may be marked by diarrhea, abdominal pain, fever, cough, urticaria, hepatosplenomegaly, pulmonary abnormalities, and eosinophilia. During the chronic phase, pulmonary manifestations include cough, expectoration of discolored sputum, hemoptysis, and chest radiographic abnormalities. Extrapulmonary locations of the adult worms result in more severe manifestations, especially when the brain is involved."[3] "Diagnosis is based on microscopic demonstration of eggs in stool or sputum, but these are not present until 2 to 3 months after infection. (Eggs are also occasionally encountered in effusion fluid or biopsy material.) Concentration techniques may be necessary in patients with light infections. Biopsy may allow diagnostic confirmation and species identification when an adult or developing fluke is recovered."[3]
Paragonimiasis can commonly be misdiagnosed as tuberculosis
6. Treatment
Praziquantel is the drug of choice: adult or pediatric dosage, 25 mg/kg given orally three times per day for 2 consecutive days.
Alternative: Triclabendazole, adult or pediatric dosage, 10 mg/kg orally once or twice. For cerebral disease, a short course of corticosteroids may be given with the praziquantel to help reduce the inflammatory response around dying flukes.
7. References
23 March 2012 | Geneva
Global burden of human foodborne trematodiasis: a systematic review and meta-analysis
The Lancet Infectious Diseases. Volume 12, Issue 3, March 2012, Pages 210–221
Centers for Disease Control and Prevention
Page last reviewed: January 10, 2013
Page last updated: January 10, 2013
Content source: Global Health - Division of Parasitic Diseases and Malaria