Resources for Health ProfessionalsDiseaseHuman paragonimiasis is acquired through ingestion of raw or undercooked crabs or crayfish, andis usually a lung infection. After ingestion, metacercariae excyst in the small intestine and releaselarvae that penetrate the duodenal wall and enter the peritoneal cavity. The larvae migrate forapproximately 1 week, then penetrate the diaphragm, enter the pleural cavity, and migrate directlythrough lung tissue to reach the bronchi. There they form cystic cavities and develop into adultworms 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 thatcontains a purulent, bloody effusion and eggs released by the flukes which are passed into theenvironment via expectoration, or may be swallowed and passed with feces. When deposited infresh water, eggs hatch to release miracidiae, which then invade specific snail hosts. Thousands ofcercariae are later released from the infected snail, which encyst (as metacercariae) in the gills,muscles, legs, and viscera of freshwater crustaceans (crabs or crayfish).

DiagnosisThe clinical picture of chronic paragonimiasis resembles chronic bronchitis or tuberculosis.Persons may cough up coffee-colored or blood-tinged sputum, often accompanied by chest painand/or shortness of breath. The sputum may be peppered consisting of clumps of eggs producedby the adult fluke living in the lung.

Peripheral eosinophilia is common and can be intense, especially during the early larval migrationstages. 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 grapesare highly suggestive of pulmonary paragonimiasis. Central nervous system disease may providesimilar "grapebunch" findings, characteristically seen in the temporal and occipital lobes oncomputed tomography of the brain. CNS involvement occurs in up to 25% of hospitalized patientsand may be associated with Paragonimus-induced meningitis. CNS symptoms may includeheadaches, 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 thelungs. 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-upeggs that are swallowed. The microscopic eggs are yellowish brown, 80-120 m long by 45-70 mwide, thick-shelled, and with an obvious operculum. Serologic tests can be especially useful forearly infections (prior to maturation of flukes) or for ectopic infections where eggs are not passedin stool.

Ectopic lesions from aberrant migration of flukes can involve any organ, including abdominalviscera, 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 patientswith central nervous system disease also have pulmonary infections. P.skrjabini often producesskin nodules, subcutaneous abscesses, or a type of creeping eruption known as "trematode larvamigrans."

TreatmentPraziquantel is the drug of choice: adult or pediatric dosage, 25 mg/kg given orally three timesper day for 2 consecutive days.

Alternative: Triclabendazole, adult or pediatric dosage, 10 mg/kg orally once or twice. Forcerebral disease, a short course of corticosteroids may be given with the praziquantel to helpreduce the inflammatory response around dying flukes.

Triclabendazole is not commercially available in the United States, it is not approved by the Foodand Drug Administration. However, it is available through CDC, under an investigational protocol.

PraziquantelOral praziquantel is available for human use in the United States.

Note on Treatment in PregnancyPraziquantel is pregnancy category B. There are no adequate and well-controlled studies inpregnant women. However, the available evidence suggests no difference in adverse birthoutcomes in the children of women who were accidentally treated with praziquantel during massprevention campaigns compared with those who were not. In mass prevention campaigns forwhich the World Health Organization (WHO) has determined that the benefit of treatmentoutweighs the risk, WHO encourages the use of praziquantel in any stage of pregnancy. Forindividual patients in clinical settings, the risk of treatment in pregnant women who are known tohave an infection needs to be balanced with the risk of disease progression in the absence oftreatment.

PregnancyCategoryB: Either animal-reproduction studies have not demonstrated a fetal riskbut there are no controlled studies in pregnant women or animal-reproduction studies have shownan adverse effect (other than a decrease in fertility) that was not confirmed in controlled studies inwomen in the first trimester (and there is no evidence of a risk in later trimesters).

Note on Treatment During LactationPraziquantel is excreted in low concentrations in human milk. According to WHO guidelines formass prevention campaigns, the use of praziquantel during lactation is encouraged. For individualpatients in clinical settings, praziquantel should be used in breast-feeding women only when therisk to the infant is outweighed by the risk of disease progress in the mother in the absence oftreatment.

Note on Treatment in Pediatric PatientsThe safety of praziquantel in children aged less than 4 years has not been established. Manychildren younger than 4 years old have been treated without reported adverse effects in massprevention campaigns and in studies of schistosomiasis. For individual patients in clinicalsettings, the risk of treatment of children younger than 4 years old who are known to have aninfection needs to be balanced with the risk of disease progression in the absence of treatment.

Page last reviewed: January 10, 2013Page last updated: January 10, 2013Content source: Global Health - Division of Parasitic Diseases and MalariaNotice: Linking to a non-federal site does not constitute an endorsement by HHS, CDC or any of its employees of the sponsors or theinformation and products presented on the site.

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TriclabendazoleTriclabendazole is not commercially available for human use in the United States.

Note on Treatment in PregnancyTriclabendazole has not been assigned a pregnancy category by the FDA. Data on the use oftriclabendazole in pregnant women are limited, although the available evidence suggests low riskof congenital anomalies. In large-scale interventions for which the World Health Organization(WHO) has determined that the benefit of treatment outweighs the risk, WHO allows use oftriclabendazole to pregnant women only in clinical settings where medical staff can monitor forcomplications.

Note on Treatment During LactationIt is not known whether triclabendazole is excreted in breast milk. Triclabendazole should be usedwith caution in breastfeeding women.

Note on Treatment in Pediatric PatientsThe safety of triclabendazole in children has not been established. In mass treatment programs forwhich the WHO has determined that the benefit of treatment outweighs the risk, WHO allows useof triclabendazole to school-age children, though use in children age 4 years and younger islimited to clinical settings where medical staff can monitor for complications.