Paragonimiasis acquired in the United States: native and nonnative species

Abstract

Paragonimiasis is a parasitic lung infection caused by lung flukes of the genus Paragonimus, with most cases reported from Asia and caused by P. westermani following consumption of raw or undercooked crustaceans. With the exception of imported P. westermani cases in immigrants, in travelers returning from areas of disease endemicity, and in clusters of acquired cases following consumption of imported Asian crabs, human paragonimiasis caused by native lung flukes is rarely described in the United States, which has only one indigenous species of lung fluke, Paragonimus kellicotti. Clinicians should inquire about the consumption of raw or undercooked freshwater crabs by immigrants, expatriates, and returning travelers, and the consumption of raw or undercooked crayfish in U.S. freshwater river systems where P. kellicotti is endemic when evaluating patients presenting with unexplained fever, cough, rales, hemoptysis, pleural effusions, and peripheral eosinophilia. Diagnostic evaluation by specific parasitological, radiological, serological, and molecular methods will be required in order to differentiate paragonimiasis from tuberculosis, which is not uncommon in recent Asian immigrants. All cases of imported and locally acquired paragonimiasis will require treatment with oral praziquantel to avoid any potential pulmonary and cerebral complications of paragonimiasis, some of which may require surgical interventions.

Fig 1

Regional U.S. distribution of cases of paragonimiasis caused by Paragonimus kellicotti, the American lung fluke, with all cases reported from the Mississippi River Drainage Basin.

Fig 2

P. westermani adult taken from a lung biopsy specimen, stained with hematoxylin and eosin (H&E). (Reprinted from an image from DPDx/CDC.)

Fig 3

Unembryonated P. kellicotti egg in bronchial alveolar lavage (BAL) fluid specimen. Magnification, ×1,000; oil immersion. (Reprinted from an image from DPDx/CDC [courtesy of Gary Procop].)

Fig 4

Unembryonated P. westermani egg in fecal wet mount. Note the operculum at the larger end. (Reprinted from an image from CDC/Mae Melvin.)

Fig 5

The life cycle of the lung fluke, Paragonimus kellicotti, the causative agent of North American paragonimiasis, is similar to the life cycle of Paragonimus westermani, the causative agent of Asian paragonimiasis. All Paragonimus species exhibit the same complex life cycle, which requires 2 sequential intermediate transport hosts, a freshwater snail and a crustacean, to deliver infective metacercariae to mammalian reservoir hosts, including humans. (Adapted from an image from DPDx/CDC.)

Fig 6

Semisulcospira kurodai freshwater snail. Semisulcospira freshwater species snails are the preferred first intermediate hosts for Paragonimus westermani throughout Asia, Africa, and South America. (Reprinted from an image from KENPEI, under a Creative Commons license.)

Fig 7

Asian freshwater crab species, a preferred second intermediate crustacean host for Paragonimus westermani throughout Asia. (Reprinted from an image from DPDx/CDC.)

Fig 8

The slender walker snail, Pomatiopsis lapidaria, is the preferred first intermediate host for Paragonimus kellicotti throughout the Mississippi River Drainage Basin of the U.S. Midwest. (Photo by Steve Cringan, reprinted from reference with permission. © 2005, Friends of the Great Plains Nature Center.)

Fig 9

Crayfish of the Oronectes species are the preferred second intermediate crustacean hosts for Paragonimus kellicotti throughout the Mississippi River Drainage Basin. (Reprinted from an image from Andreas R. Thomsen, from Wikimedia Commons.)